GB2507255A

GB2507255A - A Heat Transfer Assembly

Info

Publication number: GB2507255A
Application number: GB1216942.1A
Authority: GB
Inventors: Richard James Boyle; Christophe Williams; Norman Cottington
Original assignee: Naked Energy Ltd
Current assignee: Naked Energy Ltd
Priority date: 2012-09-21
Filing date: 2012-09-21
Publication date: 2014-04-30
Also published as: EP2898270A1; GB201216942D0; US20150247653A1; WO2014045054A1

Abstract

A heat transfer assembly (102, fig 1) comprising an elongate envelope, an elongate heat transfer device having an elongate heat transfer chamber 111 and an elongate heat exchanger 107 passing longitudinally through at least part of the chamber. The elongate chamber is transparent or translucent and preferably glass. The heat transfer chamber 111 may extend the whole length of the device, the heat exchanger 107 may extend the whole length of the heat transfer chamber. The heat exchanger 107 enters at a first end extends substantially the whole length of the chamber and may turn back and exit the chamber at the first end. Also disclosed is an arrangement where there are plural fluid flow chambers and a common heat transfer chamber serving the fluid flow chambers, a heat exchanger passing through at least a portion of the heat transfer chamber. Also disclosed is an arrangement where there is a working fluid pathway, a heat transfer chamber located on the working fluid pathway and a heat exchanger passing at least partially through the heat transfer chamber.

Description

I

Heat Transfer Device

Field of the Invention

This invention relates to heat transfer devices and in particular heat transfer devices for use in solar energy convertcr devices which convert incident solar energy into heat and electricity.

Devices converting solar energy into electricity are known. One means of converting solar energy into electricity is the use of photovoltaic arrays. Photovoltaic arrays generally consist of semi-conductor materials appropriately encapsulated, and arranged to generate electricity when exposed to solar radiation.

Separately, devices converting solar energy into useable heat are known. A variety of thermal collection devices are known which absorb heat energy when exposed to solar radiation.

These thermal solar collectors heat up as they absorb heat energy from solar radiation and this heat energy may then he extracted for use, for example by pumping a liquid flow, such as water, through the thermal collector in order to heat the liquid.

Tt has heen proposed to combine Ihese Iwo Lechnologies Lo provide a hyhrid solar energy collector converting solar energy simultaneously into both electricity and heat. Such hybrid devices have heen lound Lo sulTer from Lhe problem LhaL the elements oF ihe phoLovolLaic array become hot when the device is operating. In general, the efficiency of photovoltaie elemenis drops as iheir Lemperature increases. Also, in general, pholovollaic elemenis subject to high Lemperatures may sufFer degradation resulLing in a permanent decrease in efliciency.

As a result, in use, ihe electricily generaLing efficiency oF Ihe phoLovollaic arrays of such hybrid devices Lends to he low, and Lends Lo reduce over Lime.

Accordingly, a heat transfer device suitable to transfer heat away from a solar collector is desirable.

Summary of the Invention

A first aspect provides a heat transfer assembly comprising: an elongate envelope; an elongate heal transfer device located within Ihe envelope, ihe heat transfer device having an elongate heat transfer chamber: and an clongatc hcat cxchangcr passing longitudinally through at least a portion of thc clongatc heal transfer chamber.

Preferably, thc elongate cnvelopc is transparcnt or translucent.

Preferably,thc elongatc envelope is glass.

Preferahly,lhe elongate heal Iransfer chamber exiends along subslantially Ihe whole length of the elongate heal transfer device.

Preferably,the elongate heat exchanger extends along substantially the whole length of the elongale heal transfer chamber.

Preferably,the elongate heat exchanger comprises a tube which passes through a first end of the elongale heal transfer chamber, exlends along subslanlially ihe whole kngih of ihe elongate heat transfer chamber, and turns back to pass for a second time through the first end of the elongale heal transfer chamber.

Preferably,the elongate heat exchanger comprises a tube which passes twice through a first end of the elongate envelope.

Preferably, the elongate heat exchanger comprises a tube which passes through a first end of Ihe elongale heal transfer chamber, exlends along subslanlially ihe whole kngih of ihe elongale heat transfer chamber, and passes through a second end of the elongate heal transfer chamber opposite the first end.

Preferably, the tube and/or the elongate heat transfer device comprise means to accommodate differential thermal expansion between the tube and elongate heat transfer device.

Preferably, the means lo accommodate differenlial thermal expansion comprise a beflows structure of the tubc.

Preferably, the elongate heat exchanger comprises a tube which passes through a first cnd of the elongate cnvelopc, extends along substantially the whole length of the elongate envelope, and passes through a second end of the elongate envelope opposile the first end.

Preferably, the tube and/or the elongate envelope comprise mcans to accommodate differential thermal cxpansion between the tube and elongate heat transfer device, and the elongate envelope.

Preferably, thc means to accommodate differential thermal cxpansion comprise bends in the tube.

Preferably, ihe elongate heal exchanger comprises a Lube which passes Lhrough a lirsl end of the elongate envelope, passes through the elongate heat transfer chamber, and turns back to pass for a second time through the firsl end of the elongale envelope.

Preferably, Ihe elongale heal exchanger comprises inner and ouler concentric luhes which pass through a first cnd of the elongate hcat transfer chamber and extend along substantially the whole length of the elongate heat transfer chamber, wherein the outer concentric tube is closed at an end remote from the first end of the elongate heat transfer chamber.

Preferably, the elongate envelope is at least partially evacuated.

Preferably, the heat transfer assembly further comprises at leasL one pholovollaic element mounled on the elongale heal transfer device.

Preferably, the elongate heat transfer chamber is a vapor chamber.

Preferably, the vapor chambcr is at least partially evacuated.

Preferably, the heal transfer assembly is arranged for rotation about a rotation axis.

Preferably, the elongate envdope is cylindrical and has an axis of symmetry, and Ihe axis of rotation is paralici to thc axis of symmetry.

Preferably, the axis ol rotation and the axis ol symmetry are coaxial.

Preferably, the axis of rolation coincides with the location of a tube passing through an end of the elongate envelope.

Preferably, the tube passes twice through the first end of the elongate envelope and the axis of rotation passes between the locations at which the tubes passing through the end of the elongate envelope.

Preferably, the axis of rotation passes centrally between the locations at which the tubes passing through the end of thc elongatc cnvelope.

A sccond aspcct provides a solar collector array comprising a plurality of heat transfer assemblies according to the first aspect mounted in parallel on a common supporting structure.

Preferably, the solar collector array further comprises means for synchronously rotating all of the plurality of heat transfer assemblies relative to the supporting structure about their respective axes of rotation.

Preferably, the solar collector array further comprises means for rotating thc supporting structure about an axis perpendicular to thc axes of rotation of the heat transfer assemblies.

A third aspect provides a heat transfer device comprising: a plurality of fluid flow chambers; a common heat transfer chamber serving all of the fluid flow chambers: a heat exchanger passing through at least a portion of the heat transfer chamber.

Preferably, the heat transfer device comprises more than two fluid flow chambers.

A third aspect provides a heat transfer device comprising: a working fluid pathway; a heat Iransfer chamber localed on ihe working fluid palhway; a hcat cxchanger passing through at lcast a portion of thc hcat transfcr chambcr.

Preferably, thc hcat transfer dcvicc compriscs a plurality of working fluid pathways.

Preferably, the heat transfer chamber extends along substantially thc whole lcngth of the hcat transfcr device.

Preferably, the heal exchanger exlends along subslanhially the whole length of the heal transfer chamber.

Preferably, the heal exchanger comprises a lube which passes ihrough a firsh end of the heat transfcr chamber, extends along substantially thc whole lcngth of the heat transfer chamber, and turns back to pass for a second time ihrough Ihe lirst end of the heal Iransfer chamber.

Preferably, the heal exchanger comprises a lube which passes ihrough a firsh end of the heat transfer chamber, extends along substantially the whole length of the heat transfer chamber, and passes hhrough a second end of Ihe heal iransfer chamber opposile Ihe firsi end.

Preferably, the tube and/or the heat transfer device comprise means to accommodate differential thermal expansion between the tube and heat transfer device.

Preferably, the means to accommodate differential thermal expansion comprise a bellows structure of the tube.

Preferably, the heat exchanger comprises inner and outer concentric tubes which pass through a first end of the heat transfer chamber and extend along substantially the whole length of the heat transfer chamber, wherein the outer concentric tube is closed at an end remote from the first end of the heat transfer chamber.

Preferably, the heat transfer device further comprises at least one photovoltaic element mounted on thc hcat transfer device.

Preferably, the heat transfer chambcr is a vapor chamber.

Preferably, the vapor chamber is at leasi partially evacuated. I 0

Preferably, the heat transfer assembly further comprises an envelope, the heat transfer device being located within the envelope.

Preferably, the envclope is transparcnt or translucent.

Preferably, the envelope is glass.

Preferably, the heat exchanger comprises a tube which passes through a first end of the heat transfer chamber, exiends along subslanlially the whok length of the heal transfer chamber, and turns hack to pass for a second time through the first end of the heat transfer chamber, and furlher comprises a lube which passes Iwice lhrough a firsi end of Ihe envelope.

Preferably, the heal exchanger comprises a lube which passes ihrough a firsl end of the heat transfer chamber, exiends along subslanlially the whok length of the heal transfer chamber, and passes through a second end of Ihe heal transfer chamber opposile Ihe lirsi end, and ftirther comprises a lube which passes ihrough a lirsi end of the envelope, exiends along substantially thc whole lcngth of thc envelope, and passcs through a second end of the envelope opposite the first end.

Preferably, Ihe luhe and/or the envelope comprise means lo accommodate differential thermal expansion helween the lube and heal Iransfer device, and ihe envelope.

Preferably, the means to accommodate differential thermal expansion comprise bends in the tube.

Preferably, the heal exchanger comprises a lube which passes lhrough a first end of the heat transfer chamber, extends along substantially the whole length of the heat transfer chamber, and passes through a second end of the heal transfer chamber opposite the lirsi end, and further comprises a tuhe which passes through a lirsi end of the envelope, passes through the heal transfer chamber, and turns back to pass for a second lime through the lirsi end of the envelope. I 0

Preferably, the heat transfer assembly is arranged for rotation about a rotation axis.

Prefcrably, the elongate cnvclopc is cylindrical and has an axis of symmetry, and thc axis of rotation is parallel to thc axis of symmetry.

Preferably, the axis ol rotation and the axis ol symmetry are coaxial.

Preferably, the axis of rolation coincides with the location of a tube passing through an end of the envclope.

Preferably, the tube passes twice through the first end of the envelope and the axis of rotation passes between the locations at which the tubes pass through the first end of the envdope.

Preferably, the axis of rotation passes centrally between thc locations at which thc tubes pass through the first end of the elongate envelope.

A fourth aspect provides a solar collector array comprising a plurality of heat transfer assemblies according to any the second or third aspects mounted in parallel on a common supporting structure.

Preferably, the solar collector array further comprises means for rotating thc supporting struclure about an axis perpendicular lo the axes of rolalion of the heal transfer assemblies.

A!ilth aspecl provides a heal Iransfer assembly compnsing a p'urality of connected heat transfer devices each according lo the second or Ihird aspecls, wherein each heal transfer device has a separate heal iransier chamber: and an envelope; the pluralily 0! heal transfer devices being located within the envelope.

Preferably, the heal iransier assembly further comprises a heal exchange neiwork, the heat exchange neiwork connecting the respeclive heat exchangers of the pluralily of heat transfer devices.

Preferably, the envelope is an elongatc envelope.

Preferably, the envelope is transparent or translucent.

Preferably, the envclope is glass.

Preferably, the heat exchange network comprises a plurality of tubes which pass through an end of the envelope.

Preferably, the envelope is at least partially evacuated.

Preferably, the heal iransfer assembly is arranged for rolalion ahoul a rolalion axis.

Preferably, the envelope is cylindrical and has an axis of symmetry, and the axis of rotation is parallel to the axis of symmetry.

Preferably, the axis of rotation and the axis of symmetry are coaxial.

Preferably, the axis of rotation coincides with the location of a tubc passing through an cnd of the envelope.

A sixlh aspect provides a solar collecior array comprising a plurality 0! heat transfer assemblies according lo the fifth aspeci mounted in parallel on a common supporling siruclure.

Preferably, Ihe solar colleclor array Further comprises means br synchronously rolaling all of the plurafily of heal transfer assemblies relative lo Ihe supporting structure ahoul their respeclive axes 0! roLalion.

Preferably, the solar collector array further comprises means for rotating the supporting structure about an axis perpendicular to the axes of rotation of the heat transfer assemblies.

A sevenLh aspecL provides a heat transfer device comprising: a fluid flow means parLially lilled with a liquid and arranged so that a first surface is in thermal contact with thc liquid in a part of the fluid flow mcans inclined to thc horizontal and conlaining (be liquid; the first part of the fluid flow means being divided into a plurality of first fluid flow channels each having an upper end and a low-er end and al leasl one second!luid how channel having an upper end and a lower end aTanged so that the liquid in the first fluid flow channels is in better thermal contact with the first surface than thc liquid in the second fluid flow channel; and the upper ends of the first and second fluid flow channels bcing connected together by a vapor manifold, and a second surface being located in the vapor manifold; wherein the vapor manifold is at least partially evacuated; whereby, when the first surface is hotter than the second surface, heat energy from the first surface causes the liquid in the first fluid flow channel to vaporize, and the vapor travels through the liquid in the first fluid flow channel to the surface of the liquid, such that the liquid circulates around the first fluid flow channel and the second fluid flow channel; vapor travels from the surface of the liquid through the vapor manifold to the second surface and condenses at the second surface; and condensed liquid relurns from the second surface to ihe Firsi pan oF Ihe fluid how means; whereby hcat cncrgy is transported from the first surface to the second surface.

Preferably, the second surface is a surface of a heat exchanger containing a fluid, whereby, when the first surface is hotter than the fluid, heat energy is transported from the first surface to the fluid.

Preferably, the second surface is an external surface of a tube containing the fluid.

Preferably, the fluid is arranged to flow through the tube.

Preferably, the vapor manifold extends between first and second opposed surfaces, and the tube passes through the first surface, extends through the vapor manifold between the first and second surfaces, and passes through the second surface.

Preferably, the vapor manifold comprises a surface, and the tube passes through the surface, extends within the vapor manifold, and passes ihrough the surface For a second Lime.

Preferably, the vapor manilold comprises a surface, Ihe tuhe passes through Lhe first surface and extends within the vapor manilold: and an inner tube is arranged wiLhin the tube, whereby Lhe fluid is arranged Lo flow Lhrough the inner Lube, and to flow between the Lube and the inner tube.

Preferably, the first part of the fluid flow means is divided into a plurality of first fluid flow channels and a plurality of second fluid flow channels.

Preferably, the number of first fluid flow channels is the same as the number of second fluid flow channels.

Preferably, (lie first and second Iluid how channeh are located side by side wiih first hluid flow channels and second fluid flow channels interleaved.

Preferably, ihe cross seclional area of the first fluid how channel and Ihe cross sectional area of the second fluid flow channel are cqual.

Preferably, thc first fluid flow channel is in thermal contact with thc first surface across a greater area than thc second fluid flow channel.

Preferably, the lowcr ends of thc first and second fluid flow channels are connected togcther.

Preferably, the first part of the fluid flow means is inclined to the horizontal by an anglc of up to 90°.

Preferably, the liquid comprises water.

Preferably, the liquid comprises ethanol.

Preferably, the liquid comprises a mixture of water and ethanol.

Preferably, the mixture comprises up to 25% ethanol.

Preferably, the Iluid comprises waler.

Preferably, the part of the fluid flow means above the surface of the liquid is at a pressure of 40mbaror less.

Preferably, the part of the fluid flow means above the surface of the liquid is at a pressure of 2 mbar or less.

Preferably, the pan oF the fluid how means above the surFace oF Ihe liquid is at a pressure of 1 mbar or less.

Preferably, the part of Ihe Iluid how means above the surface oF the liquid is at a pressure of 1(12 mbar or lcss.

Preferably, the part of the fluid flow means above the surface of the liquid is at a pressure of to3 mbar or lcss.

Preferably, the part of the fluid flow means above the surface of the liquid is at a pressure of t(16 mbar or lcss.

Preferably, the first fluid flow channels are closer to the first surface than the second fluid flow channels.

Preferably, at east a part oF each first fluid flow channel is located between the hirsi surface and a second fluid flow channel.

Preferably, the first fluid flow channels lie between the first surface and the second fluid flow channels.

Preferably, each of the hirsi and second fluid flow channels has a section hounded hy a perimeter, and a proportion of Ihe perimeler oF Ihe firsi Iluid flow channel which is in Ihermal contact with the first surface is greater than a proportion of the perimcter of the sceond fluid flow channel which is in thcrmal contact with the first surface.

Preferably, at icast a portion of at least onc surface of each first fluid flow channcl in thermal contact with the first surfacc comprises features arranged to promotc vapor bubblc nucleation.

Preferably, at least a portion of at least one surface of each first fluid flow channel in thermal conlaci with the firsi surface has a surface Lexture adapted to promote vapor huhhle nucleaLion.

Preferably, said portion of at least one surface has a roughencd surface texturc.

Preferably, thc roughened surface tcxturc is providcd by a solder laycr.

Preferably, vapor traveling from thc surface of thc liquid to thc second surfacc passcs through thc manifold.

Preferably, condensed liquid rcturning from thc second surface to the first part of the fluid flow mcans passes through the manifold.

Preferably, the second surface is located above the first surface such that the condensed liquid returns from the second surface to the first part of the fluid flow means by gravity.

Preferably, al least a portion of a surface of each first fluid how channel in Lhermal conLacL with the first surface has a dimpled surface profile.

Preferably, the dimpled surface profile comprises a regular array of dimples.

Preferably, Lhe regular array of dimples comprises dimples arranged in rows separaled by hat strips withoul dimples.

Preferably, the first and sccond fluid flow channels are located between first and sceond spaced apart plates.

Preferably, thc first plate is in thermal contact with the first surfacc and forms a surfacc of the or each first fluid flow channel.

Preferably, there are a plurality of first fluid flow channels and a plurality of second fluid flow channels localed side by side with firsi fluid how channels and second Iluid flow channels arranged alternately, and each first fluid flow channel is separated from an adiacent second fluid flow channel by a partition cxtending bctwcen and attachcd to thc first platc and thc second plate.

Prefcrably, the first platc has a dimpled surfacc profile comprising a rcgular array of dimples arranged in rows separated by flat strips without dimples, and each partition is attached to the first platc at a position locatcd in onc of the flat strips.

Preferably, the part of cach partition extending between the first platc and thc second plate is substantially flat.

Preferably, a plurality of the partitions are formed by a third plate.

Preferably, all of the partitions are formed by a single third plate.

Preferably, the third plate is corrugated.

Preferably, each of the plates comprises a metal or a metal alloy material.

Preferably, each of the plates comprises mild steel.

Preferably, each of the plates comprises tin coated mild sled.

Preferably, thc plates arc bonded togethcr by a bonding techniquc including at least one of: soldering; spot welding; rollcr welding; and an adhesive.

Preferably, the plates are bonded together by soldcr joints and at least a part of the first plate forming a surface of each first fluid flow channel is coated with solder.

Preferably, the heal iransfer device comprises a substantially rigid heat conducting struclure.

An eighth aspect provides a hcat transfer dcvice comprising: a pluralily of firsl Iluid how channels each having an upper and a lower end, inclined lo ihe horizontal, and containing a liquid; a sccond fluid flow channel having an upper and a lower end, connected to the first fluid flow channels and containing the liquid; a vapor manifold connecting the upper ends of the first and second fluid flow channels; a first surface in thermal contact with the liquid in the first fluid flow channel; and a second surface in the vapor manifold; whemby, when the first surface is hotter than the second surface, heat energy from the first surface causes liquid in the first fluid flow channels to vaporize; the vapor travels upwardly along the first fluid flow channels; the vapor drives a flow of liquid from the second fluid flow channel to the first fluid flow channels and upwardly along the first fluid flow channels: and Ihe vapor Iravels From a surface o1 ihe Uquid to Ihe second surface and condenses al Ihe second surface; whereby heal energy is transported away from the lirsl surface to the second surface.

A ninth aspeel provides a heal transfer device comprising: a lirsl surface: a second surface; a liquid reservoir in thermal conlact with ihe hirsi surface and containing a liquid; wherein the liquid reservoir comprises a plurality of first fluid flow channels inclined to the horizontal and containing the liquid and a second fluid flow channel connected to the first fluid flow channel and containing the liquid; the device further comprising a vapor manifold connecting upper ends of the first and second fluid flow channels; the first surface is in thermal contact with the liquid in the first fluid flow channel, the second surface is in the vapor manifold; and the vapor marniold is al least partially evacualed; whereby, when the first surface is hotter than the second surface, heat energy from the first surface causes liquid in the first fluid flow channel to vaporize; Ihe vapor travels upwardly along ihe firsl fluid flow channel, into the vapor manillild, and condenses at the second surface; the vapor drives a flow of liquid from the second fluid flow channel to the first fluid flow channel and upwardly along the first fluid flow channel; and condensed liquid returns from the second surface to the liquid reservoir; whereby heat energy is transported away from the first surface to the second surface.

A tenth aspect provides a heat transfer device comprising: a first surface; a second surface; a liquid reservoir in thermal contact with the first surface and containing a liquid; and a vapor manifold containing the second surface: wherein al leasi a pan of Ihe vapor manillild is al leasi parlially evacuated: whereby, when the first surface is hotter than the second surface, heat energy from the first surFace causes liquid in ihe liquid reservoir to vaporhe; the vapor travels to the vapor manifold and condenses at the second surface; and condensed liquid returns From the second surface to Ihe liquid reservoir: whereby heal energy is transported from Ihe Iirst surface lo Ihe second surFace.

PreFerably, al easl a pan oF ihe heal iransfer device is located in an envelope under at least a partial vacuum.

Preferably, the envelope is one of: a cylindrical tube; an elliptical tube.

Preferably, the envelope is formed, at least in part, of glass.

Preferably, a plurality of tubes are mounted in a solar energy collecting array.

Preferably, at least one of the plurality of tubes is rotatable to track light incident on the solar energy collecting *ray.

Preferably, thc plurality of tubcs are rotatablc to track light incident on thc solar cnergy collccting array.

Preferably, the heat transfer devicc comprises a substantially rigid heat conducting structurc.

A sixth aspect provides an energy gcncrator comprising a hcat transfcr dcvice according to any preceding claim, and at lcast one photovoltaic element, thc encrgy gencrator having an clcctrical output and a heated fluid output.

The invention further provides systems, devices and articles of manufacture for implementing any of the aforementioned aspects of the invention.

Description of Figures

The invention will now he described in delail with reference to the lollowing figures in which: Figure I is a diagram of a Firsi embodiment oF a hybrid solar energy convener according Lo the invenlion; Figure 2 is a diagram of a tube useable in the hybrid solar energy converter of Figurc 1; Figure 3 is a cut away diagram of a solar cnergy collcctor asscmbly useabic in thc hybrid solar energy convertcr of Figure 1; Figure 4 is a transverse cross-section along the line A-A of the solar energy collector assembly of Figure 3; Figure 5 is a longitudinal cross-sectional diagram along the line B-B of the solar energy collcctor assembly of Figure 3; Figure 6 is a cut away vicw of the solar collector asscmbly of Figurc 3; Figure 7 is a diagram of a central sheet useable in the solar cnergy collector assembly of Figure 3; Figure 8 is an explanatory diagram illustrating the operation of the solar cncrgy collcctor assembly of Figure 3; Figure 9 is a transverse cross section along the line C-C of the solar energy collector assembly of Figure 3; Figure I OA is an explanalory diagram of Gie solar energy cofleclor assemhly of Figure 3: Figure I OB is an explanatory diagram o1 the so'ar energy collecior assembly of Figure 3: Figure [IA is a detailed phin view ola pan ol the solar energy collecior assembly ol Figure 3; Figure 1 lB is a cross seclion along ihe line D-D of a the part of Ihe solar energy collector assembly ol Figure 3; Figure 12 is a diagram showing a part of the solar cnergy collector asscmbly of Figure 3 with the photovoltaic elements rcmovcd; Figure 13 is a diagram of a part of a solar encrgy collcctor assembly according to a sceond embodiment according to the invention; Figure 14 is a diagram ol a part ol a solar energy collector assemhly according to a Ihird embodiment according to the invention; Figure 15 is a diagram oF a part of a solar energy collector assemhly according to a Ihird embodiment according to thc invention; Figure 16 is a diagram of a fourth cmbodiment of a hybrid solar cnergy convcrter according to the invention; Figure 17 is a cut away diagram of a part of a solar energy collector assembly useablc in the hybrid solar energy convcrtcr of Figure 16; Figure 18 is a diagram of a solar energy collector arranged for rotation about a single axis; Figure 19 is a diagram of a solar energy collector array arranged for rotation about two axes; Figure 20 is a disgram of a solar energy collector arranged for rotation about a single axis; and Figure 21 is a diagram of a solar energy cofleclor array arranged br rotation about Iwo axes.

Detailed Description of the Invention

First emhodiment Apparatus according to a first cmbodimcnt of the present invention is illustratcd in Figurc 1.

Figure 1 shows a gcneral exterior view of a first cmbodiment of a hybrid solar encrgy convcrter 101 according to the present invcntion.

Overview In the first embodiment, the hybrid solar energy converter 101 includes a solar energy collector assembly 102 housed within a sealed transparent tube 103. The solar energy collector assembly 102 includes an elongaLe heal Iransport elemenL 1 04 and an array of photovoltaic elements 105 mounted on an upper surface of the elongate heat transport element 104. The hybrid solar cncrgy convcrtcr 101 also includcs a support assembly 106 at onc cnd oF Ihe transparenL Lube 103. One end oF ihe solar energy colleelor assembly 102 is connecied to thc support assembly 106. In onc example thc photovoltaic clcmcnts 105 may bc formcd of silicon, in anothcr example thc photovoltaic elements 105 may bc formcd of gallium arsenide.

in other examples, photovoltaic elements of othcr suitable semiconductor matcrials may be used. in other cxamples organic photovoltaic elements may bc used. In other examples hybrid photovoltaic clemcnts may bc used.

Photovoltaic elemcnts may also be refcrred to as photovoltaic cells, solar cells or photoelectric cells. For the avoidance of doubt, in thc prescnt application the tcrm photovoltaic element is used to refer to any element which converts incident electromagnetic radiation into electrical energy.

in ihe lirsl embodimeni, the heat Iransport element 104 includes a heal exchanger 107 arranged to transfer heat energy from the heat transport element 104 to a first fluid. The heat exchanger 107 is localed wiihin the heal transport element 1 04 in ihe lirsL embodiment, and accordingly is not visible in figure 1.

in one possible example, in use the hybrid solar energy converler lOl maybe mounled on a rool. Accordingly, mounling brackets maybe provided.

An overview of thc opcration of the hybrid solar cncrgy convertcr 101 of the first cmbodiment is that solar encrgy, in other words sunlight, incidcnt on the hybrid solar cncrgy converter 101 passes through thc sealed transparcnt tube 103 and is incident on thc photovoltaic elcments 105 of the solar energy collector assembly 102. The photovoltaic elements 105 convcrt a part of thc energy of the incident solar encrgy into electrical energy, and convert a part of the energy of the incident solar energy into heat energy. A further part of the incident solar energy may be incident on any parts of the solar energy collector assembly 1 02 which are not covered by the pholovoltaic dements 1 05, and this further part of Ihe incident solar energy may also he converted into heat energy. In general, it is desirable to maximize the proportion of the surface of the solar encrgy collector asscmbly 102 exposed to incideni solar energy which is covered by the pholovollaic demenis 105, and to minimii,e the proportion which is not so covered. However, in some circumstances it may be preferred to leave some parts of this exposed surface uncovcred, for examplc to simplify manufacture and/or assembly of the solar energy collector assembly 102 and attachment of the photovoltaic elements 105 to the solar energy collector assembly 102. Usually, in the first embodiment the surface of the solar energy collector assembly exposed to incident solar energy will be the upper surface.

The electrical energy produced by the photovoltaie elements 105 is carried along the heat transport element 104 by electrical conductors and away from the solar energy converter 101 for use. The heat energy absorbed by the photovoltaic elements 105 is transferred into the heat transport element 104, cooling the photovoltaic elements 105, and is then transferred in the heal exchanger 107 to the lirsl fluid. The lirsi Iluid is suppfled to the heat transport element 104 and the heat exchanger 107 through the support assembly 106, and the heated first fluid travels out of the heal transport element 104 and through the support assembly 106, so that the heat energy in the heated first fluid can he removed from the solar energy converter 101 and is available br use.

Tn one typical arrangement, the hybrid solar energy converter I UI may he used in a domestic situation, such as on a household rool, to generate deetricity br househdd use and/or for export, and to generate hot water for a domestic hot water and/or heating system. in this arrangement the heat energy transferred to the first fluid in the heat exchanger 107 is used by a domestic or industrial hot water system, and the electrical energy produced by the photovoltaic elements 105 is supplied to an electrical supply system. in some arrangements the first fluid may be water.

Accordingly, the heat transport element 104 cools the photovoltaic elements 105. The eI'Iiciency ol semiconductor pholovohaic elements generally drops as the temperature of the semiconductor material rises. The temperature above which efficiency drops with increasing S temperaturc and the rate at which efficiency drops with increasing temperature will vary for dilierent semiconduclor materials and diFFerent designs oF photovoltaic element. For silicon photovoltaic elements the efficiency of electrical energy generation generally drops by about 0.35% to 0,5% for each degree centigrade of temperature increase above 25°C.

transparent tube in the first embodiment illustrated in Figure 1 the sealed transparent tube 103 is formed by a cylindrical glass tube having one open end 103a and one closed domed end 103b. The sealed transparent tube 103 is illustrated in more detail in Figure 2. The open end 103a of the cylindrical glass tube is sealed by a metal end cap 120 which is bonded to the glass tube with adhesive to form an air tight seal. [he interior of the tube 103 is at least partially evacuated.

That is, the interior of the tube is at a pressure below normal atmospheric pressure. The pressure of the vacuum within the tube 103 may he 1 o-mbar.

The open end iO3a of the cylindrical glass tube sealed by the cap 120 is attached to the support assembly 106 and the closed domed end I 03h is remote from the support assembly 106.

insulated electrical conductors (not shown) pass through the metal cap 1 20 to carry the electrical energy generated by the photovoltaic elements 105 away From the so'ar energy collector assembly 1 02.

As discussed above, the solar energy collector assembly 102 housed within the transparent tube 103 includes photovoltaic elements 105. l'ypically, photovoltaic devices are made from semiconductor materials which may suffer from oxidation and other environmental effects adversely affecting their performance and lifetime when exposed to the atmosphere. [he use of an evacuated tube 103 may protect the semi-conductor materials of the photovoltaic elements 105 from such environmental damage. This may allow the cost of encapsulating the pholovoltaic elements to he avoided.

The use of an cvacuated tubc may also incrcase thc efficicncy with which hcat can be collected Irom incideni solar energy by the solar energy coflecior assembly 102. Having the solar encrgy collector assembly 102 surrounded by an cvacuated tube 103 may reduce or effectively prcvent convcctive hcat loss from thc solar energy collector assembly 102 into the matcrial of thc transparent tube 103 and the air around the hybrid solar encrgy convcrter 101.

Othcr vacuum pressures may be used. In some examples thc vacuum prcssure may be in the range 10.2 mbar to i0 mbar. in gcneral, it is cxpected that lower vacuum pressure, or in other words a hardcr vacuum, will provide greater insulating benefits. Further, it is expected that lowcr vacuum pressure, or in other words a harder vacuum, will provide greater protection from environmental damage in examples where the photovoltaic elements are not encapsulated. In practice the benefits of using a lower vacuum pressure may need to he balanced against the increased cost of achieving a lower vacuum pressure. In some examples a vacuum pressure of I 02 mhar, or lower, may he used.

in an alternalive example Ihe sealed transpareni Luhe 103 may he filled wiLh an inert gas instead of being evacuated. In particular, the inert gas may he nitrogen.

In anoiher alternative example the sealed transparenl tuhe 103 may he lilled with an men gas at a reduced pressure. In some examples this may he achieved by lilling (lie lube 103 with the inert gas and then evacualing Ihe tube 103. In particular, Ihe men gas maybe nitrogen.

in the illustrated first embodimcnt thc tube 103 is cylindrical having a circular cross section.

in alternative examples the tube 103 may have other shapcs. in somc examples thc cross sectional size and/or shapc of the tube 103 may vary at different positions along its length. in an alternative example the tube 103 may have an elliptical cross section. in particular, the tube 103 may have an elliptical cross section with the long axis of the ellipse aligned with the plane of the solar energy collector assembly 102. The use of a tube 103 having an elliptical cross-section with the long axis of the ellipse aligned wiih ihe phine of Lhe sohir energy collector assembly may reduce the amount of glass required by the tube 103 and may reduce reflection losses duc to thc reflection of incident solar cnergy from thc tube 103.

In the illustrated first embodiment the tube 103 is formed of glass. The use of glass may allow the vacuum within the tube 103 to be maintained longer because the rate of migration of gas molecules from the atmosphere through glass is, in practice, effectively zero. in alternative examples suitable transparent plastics materials or laminated structures may be used to form the tube 103.

In the illustrated first embodiment the tube 103 is transparent. in alternative examples the tube may be only partially transparent.

In the illustrated first embodiment the metal end cap 120 may be bonded to the glass tube 103 by adhesive. In other embodiments alternative glass to metal bonding techniques may he used, br example welding, brazing or soldering.

Tn the illuslraLed first embodiment Lhe Lube 103 has a metal end cap 120 at one end iO3a. in alternative examples the end cap 120 may he made of other materials. In some examples the end cap 120 may he made of glass. This may reduce conduelive heal losses From Lhe coflecLor assembly 102.

Tn Ihe illuslrated lirsi embodiment the lube 103 has an end cap 120 al one end I 03a and one domed end lO3b. in alternative examples the tube 103 may have an open end sealed by an end cap at both ends.

Collector assembly in the first embodiment, the solar energy collector assembly 102 includes a heat transport element 104 and an array of photovoltaic elements 105 mounted on a surface of the heat transport element 104. In order to allow radiant solar energy to he incident on the photovoltaic elements 105 Ihe array of photovohaic elements 105 are mounted on the surface of Ihe heat transport element 104 which is exposed to the incident radiant solar energy in operation of the hybrid solar energy converter 101. this will usually bc thc upper surfacc of thc hcat transport element 1 04.

in some alTangements thc surfacc of the heat transport element 104 exposed to the incident radiant solar energy may not be the upper surface. in particular, this would be the ease if the solar energy collector assembly 102 was located in a vertical, or substantially vertical, plane, or if the incident solar radiant energy was incident horizontally or from below, for example after redirection by an optical system, such as a mirror. Accordingly, references to upper and lower surfaces, and similar directional terminology in this description, should be understood as referring to the situation illustrated in the figures where the solar energy collector assembly is in a plane at an angle to the horizontal and radiant solar energy is incident from above.

in the illustrated example of the first embodiment, the solar energy collector assembly 102 is supporLed by a cylindrical Lube 119 of Ihe heat transport elemenL 104. The cylindrical tube 119 passes through the end cap 120 and extends between the heat transport element 104 and Lhe supporL assembly 106. Although two seclions ol' cyfindrical Lube 119 can he seen extending between the heat transport element 104 and the support section 106 in figure 1, Lhese are hoLh secLions of the same cylindrical tube 119, as wifi he explained in more detail below.

Where the cylindrical Lube 119 passes through Lhe end cap 120 the cyfindrical tube 1 19 is soldered to the end cap 120 to retain the cylindrical tube 119 in place and support the solar energy collector assembly 102. h alternative examples the cylindrical tube 119 may be secured to the end cap 120 in other ways. In one example the cylindrical tube 119 may be welded to the end cap 120.

The supporting of the solar energy collector assembly 102 by a physical connection through the cylindrical tube 119 may increase the efficiency with which heat can he collected from incideni solar energy by the solar energy collecior assembly 102. Having the solar energy collector assembly 102 supported by a single physical connection through the cylindrical tube 119 may rcducc conductivc hcat loss from thc solar encrgy collector assembly 102 into the supporting structure outside ihe transparent lube.

in thc first embodiment the heat transport clement 104 has a substantially flat uppcr surface 104a. Each of thc photovoltaic elements 105 is square, and thc width of thc heat transport element 104 is the same as thc width of cach square photovoltaic clement 105. Five square photovoltaic elements 105 are mounted sidc by sidc to one anothcr along the length of the heat transport element 104. Substantially the entirc upper face of the heat transport clement 104 is covered by the photovoltaie elements 105. Covering a large proportion of the upper surface 104a of the heat transport element 104 with photovoltaie elements 105 may increase the efficiency of the hyhnd solar energy converter 101.

In one example the square photovoltaic elements 105 may each he a 125mm by 125mm square and 0.2mm thick. in anoiher example the square photovoltaic elements may each he a 156mm by 156 mm square. In other examples, photovoltaic elements having other sizes or shapes may he used.

The pholovollaic dements 105 are bonded 10 Ihe substantially flat upper surface 1 04a of ihe heat Iransporl dement 104 using a layer 149 of heat conducling adhesive in a similar manner to Ihe lirst emhodimenL. This thermafly conductive adhesive bonding layer 149 is shown in Figure 3. The adhesive bonding layer 149 is dectrieally insulating. The adhesive bonding layer 149 between the photovoltaic elements 105 and the heat transport element 104 is arranged to be thin, this may improve the degree of thermal conduction between the photovoltaie elements 105 and the heat transport element 104. this may increase the rate of heat transfer laterally across the photovoltaie elements 105. An adhesive material loaded with solid spheres of a predetermined size may be used to form the adhesive bonding layer 149.

This may allow a thin adhesive layer 149 to be consistently and reliably formed. The adhesive bonding layer 149 is formed of a flexible or "forgiving" adhesive material. This may relieve stresses in ihe assembled solar energy collector assembly 102 and reduce any siress applied Lo the photovoltaic elements 105.

The pholovolLaic elemenls 105 are semiconducLor phoiovolLaie elemenis Formed of silicon. In one examplc the photovoltaic elements are formed of single-crystal silicon, in one example the photovoltaic elements arc formed of amorphous silicon. In one example thc photovoltaie elements arc formed of polyerystallinc silicon, or polysilicon. h other examples alternative types of semiconductor photovoltaie elements may be used.

As discussed above, in operation of the hybrid solar encrgy converter 101 the photovoltaie elements 105 are cooled by the heat transport element 104. Ibis cooling may allow the temperature of the photovoltaie elements S to be maintained at a desired value.

This cooling may provide the advantage that the appearance of hot spots or regions in the photovoltaie elements 105 can he reduced or eliminated, and the temperature of the pholovoltaic elements 105 mainiained al a uniform desired value. Such hot spots or regions may for example he produced by heating by incident solar radiation, by inhomogeneities or Faults in (be pholovoltaic elements 105, or by a combination of, or interaction heLween, these causes.

Such hol spots or regions can reduce Ihe efficiency of (be photovollaic elemenLs 105. Tt is believed thai hot spoLs in (be phoLovollaic elemenls 1 05 may reduce (be eflicieney oF (be phoLovoltaic elements lOS in Lhe shori term, and may also degrade the perlbrmance of Lhe photovoltaie elements 105 in the longer term. As discussed above, the efficiency of photovoltaie elements reduces as the tcmperature increases. In the short term a hot spot in a photovoltaie element may reduce the output of the photovoltaie element because the material forming the hot spot is at a higher temperature than the rest of the photovoltaie element, and so has a reduced efficiency compared to the rest of the photovoltaie element. Further, in the longer term the degrading of the performance of the photovoltaic element may also take place more rapidly at a hot spot because the material forming the hot spot is at a higher temperature than the rest ol' the photovollaic element.

Accordingly, maintaining the photovoltaic elements 105 at a more uniform temperature value and reducing, or eliminaling, hot spots or regions may improve lhe efficiency of lhe photovoltaic elements 105 at a specific temperature, and may reduce the amount of degradation of the photovoltaie elements 105 caused by higher temperatures.

Ibis may allow the photovoltaie elements 105 to operate at a higher overall temperature than would otherwise be the ease. this may be understood by considering that where hot spots exist in the photovoltaie elements 105 it may be the temperature induced reduction in efficiency and temperature induced degradation in these hot spots that limits the maximum operating temperature of the photovoltaie element 105 as a whole. As a result, reducing, or eliminating, these hotspots may allow the maximum operating temperature of the photovoltaic element 105 as a whole to he raised.

The illusiraled example of the lirsi embodiment has a solar energy colleclor assembly 102 supported by a physical connection through the cylindrical tube 119. In other examples altemative supporting arrangements may he used. in some examples lhe solar energy eofleclor assembly 102 may he supported by physical connections at each end of the solar energy collector assembly 102. In some examples, the physical conneclion al one end of the solar energy collecior assemffly may be Ihe through Ihe cylindrical tube. In general, it is advantageous Lo minimize Ihe number of physical supports in order Lo minimize the escape of heal from ihe solar energy eollecLor assembly by conduction ihrough the physical supports.

In other examples the number of photovoltaic elements 105 mounted on the heat transport element 104 may be different. in other examples the relative sizes of the photovoltaie elements 105 and the heat transport element 104 may be different.

In some examples the adhesive layer 149 may comprise an epoxy resin which remains non-brittle after curing.

In other examples the adhesive layer 149 may be formed by a double sided adhesive tape.

Heat transporl elemenl The heat transport element 104 according to the first embodiment is shown in more detail in a cut away view in Figure 3, and in transverse and longitudinal cross-sectional views in Figures 4, and 5 respectively. The transverse cross section of Figure 4 is taken along the line A-A in Figure 3. The longitudinal cross section of Figure 5 is taken along the line B-B in Figure 3.

in the second embodiment, the elongate heat transport element 104 is generally rectangular.

The heat transport element 104 has a flat upper surface 104a and a lower surface 104b which is flat across most of its area, and has an outwardly projecting section 110 along one edge 104e of the heat transport element 104. The outwardly projecting section 110 contains and defines an elongate heat transfer chamber or vapor manifold 111 extending along substantially the entire length of the elongate heat transport element 104. In operation the heat Iransporl element 104 is arranged lo he transversely sloping, so that Ihe side edge I 04e of Ihe heat transport element 104 bearing the outwardly proleeting section 110 is higher than the opposile side edge I 04d of Ihe heat transport element I 04, For reasons which will he explained in detail below. The inclination angle of the heat transport element 104 to the horizonlal may he small. An inclination of about 50 is suffieieni. Larger angles of inclinalion may he used ii' desired. An angie ol' inelinalion up to and including 900 may he used, i.e. Ihe heal Iransport dement 104 may he arranged Lransversely vertically.

Figure 6 shows a cut away plan view from below of the heat transport element 104 of figure 3 with the outwardly projecting section 110 removed, so that the heat exchanger 107 is visible.

As can be best seen in Figure 6, the heat exchanger 107 is comprises a cylindrical tube 119 which extends within the elongate heat transfer chamber or vapor manifold 111 along substantially the entire length of the elongate heat transfer chamber or vapor manifold 111.

The cylindrical tube 119 comprises first and second parallel straight sections 1 19a and 1 19b, each parallel 10 the sides of the vapor manifold Iii, such as the upper surFace 1 (Na and ihe prolecting section 110, and extending along substantially the entire length of the vapor manifold 111. The two straight sections 1 19a and 1 19b arc connected togethcr by a curved seclion I I 9c.

in usc, the first fluid passes along thc cylindrical tube 119 as indicated by the arrows in figure 6, so that the first fluid passes through the first straight scction 1 19a, thc curved scction 1 19c and the second straight scction 1 19b, so that the first fluid passes through the cylindrical tube 119, and travels along substantially the entire length of thc vapor manifold twice.

In the illustrated example thc first and second scctions 1 19a and 1 19b of thc cylindrical tube 119 are arranged onc above the other and thc first fluid cntcrs through the first section ll9aa and leaves through the second section 1 19h. in other examples the direction of flow of the first fluid may be reversed. In other examples the first and second sections 1 19a and 1 19h may be differently arranged.

The heat transport element 104 has an upper surface 104a formed by an upper sheet 114 and a lower surface I (Nb formed by a lower sheet 115. A central shed 116 is located heiween ihe upper sheet 114 and the lower sheet 115, so that fluid flow passages 117 and 118 running Lransversely across ihe heat Iransporl element I 04 are defined between Ihe ceniral shed I 1 6 and each of the upper shed 114 and the lower shed Ii 5. The Iluid flow passages 117 and 118 are sloped along their lengths. in the illusirated example ihe heal Iransport element I 04 is Lransversely sloping, and as a result the fluid how passages Ii 7 and I IS running Lransversely across the heat transport clement 104 will be sloped along their lengths.

Figure 5 shows the profile of the central sheet 116 in morc detail. Figure 5 shows a longitudinal cross section along the line B-B in Figure 3. the central sheet 116 is formcd with a corrugated profile having ridgcs and troughs which run transversely across the hcat transport element 104. The cross-sectional profile of the corrugated central sheet 116 can he understood as a zig-zag profile with the points of the zig-zag forming the peaks and troughs being Ilaliened. Accordingly, the upper and lower fluid how passages 117 and 118 are interleaved. The upper and lower fluid flow passages 117 and 118 are arranged side by side in a planar array with upper fluid flow passages 117 and lower fluid flow passages 1 iS arranged alternatdy.

To be more specific, in thc illustratcd examplc of the first embodiment the central shcet 116 comprises a plurality of flat surfaces connectcd by folds running transversely across thc hcat transport element 104. As shown in Figure 7, thc central shcet 116 compriscs a first serics of first coplanar surfaces 11 Ôa spaced apart equidistantly in a first plane C and a sccond scries of second coplanar surfaces 1 16b spaced apart equidistantly in a second plane D, each of the first and second coplanar surfaccs 1 lôa and 1 lob having thc samc width, and the separation betwcen successive coplanar surfaces 1 16a or 1 16b of each of thc first and second series of first and second coplanar surfaces 1 16a and 1 lob being larger than the width of the coplanar surfaces 11 6a and 11 6h. The first and second planes C and D are parallel and spaced apart.

The first and second series of coplanar surfaces are arranged so that in plan view, i.e. when viewed perpendicularly lo the first and second planes C and D, each oF ihe lirsi coplanar surfaces 1 16a is located equidistantly between two of the second coplanar surfaces 1 16h, and vice-versa. The First and second coplanar surfaces I I 6a and Ii 6h are inierconnected by a First series of first parallel linking surfaces 116c and a second series of second parallel linking surFaces I I Gd.

As is shown parlicularly in Figure 5, the central sheet 116 is arranged with the lirsi surFaces 1 16a conlacling an inner face of the upper sheet I 14 and the second surfaces I lOb contacling an inner facc of the lower sheet 115. The first surfaccs 1 16a of the central sheet are bonded to the uppcr shect 114 and the second surfaces 1 Rib of the central sheet 116 are bonded to the lowcr sheet 115. Accordingly, the upper lower, and central shccts 114, 115, 116 dcfine a plurality of trapezoid cross-section upper fluid flow channcls 117 and lower fluid flow channels 115 betwcen them. The upper fluid flow channels 117 are defincd between thc upper sheet 114 and the central sheet 116. The lower fluid flow channels 118 are defined between the lower sheet 115 and the central sheet 116. The trapezoid upper fluid flow channels are arranged so Ihal the larger one of the Iwo parallel faces of Ihe trapezoid channel is lormed by the upper sheet 114.

The edges of the heat Iransporl elemeni I 04 are formed by upwardly bent parts of Ihe thwer sheet 115, which are bondcd to the upper shcet 114. the photovoltaic elcments 105 are bondcd to the upper sheet 114. At the edgcs of the heat transport clcment 104, thc upper shcct 114 is bonded directly to the lower sheet 115, the central sheet 116 is not located between the upper and lower sheets 114 and 115 at their edges.

In some examples the central sheet 116 may extend at least partially between the upper and lower sheets 114 and 115 at the end edges of the heat transport element 104 so that the upper and lower sheets 114 and 115 are both bonded to the central sheet 116. this may assist in locating and securing the central sheet 116 relative to the upper and lower sheets 114 and 115.

As discussed above, the heat transport element 104 has an outwardly projecting section 110 along Ihe upper side edge I 04c of Ihe heat Iransport elemeni 1 04. The outward'y projecling section 110 is substantially semi-cylindrical and is formed by an outwardly projecting part of the thwer sheet 115. The ouiwardly projecling section 110 defines a vapor manifold Ill. The fluid flow channels 117 and 118 connect to the vapor manifold 111. It should he noted that the central shed I 16 exlends across mosi of Ihe widLh of ihe vapor manifold Ill.

Accordingly, the upper fluid flow channds 117 defined between the upper shed 114 and the cenlral sheet I 16 conned lo the vapor manifold I Ii lowards the lop of the vapor manifold ii!, while the lower Iluid flow channels Ii 8 defined between the lower shed 115 and the central sheet 116 connect to the vapor manifold 111 towards the bottom of the vapor manifold 111. All of the upper and lower fluid flow channels 117 and 118 are interconnected by the vapor manifold 111.

At the lower side edge 104d of the heat transport element 104 opposite the outwardly prolecting section 110, there is a gap 123 between the edge of the central sheet 116 and the side edge 104c of the heat transport element 104 formed by an upwardly bent part of the lower sheet 115. This gap 123 allows waler to how between different ones of the hluid how channels 117 and 118. The gap 123 extends along the side edge 104d of the heat transport elcmcnt 104, and forms a fluid manifold 124 interconnccting all of thc upper and lower fluid flow channels 117 and 118.

At each end of thc heat transport clement 104 the substantially semi-cylindrical outwardly projccting scction 110 extending most of thc lcngth of thc heat transport element 104 is eloscd by an end wall 108. The uppcr and lower sheets 114 and 115 are sealcd by the cnd walls 108 so that the interior of thc heat transport elcment 104 is sealed. The cylindrical tube 119 passes through thc end wall 108 adjacent the opcn end of thc glass tube 103 and thc end cap 120, through the end cap 120 and into the support asscmbly 106. ihc cylindrical tube 119 within the heat transfer ehambcr or vapor manifold 111 forms thc heat cxchanger 107 and acts to carry heat energy from the heat transport element 104 away from the hyhnd solar energy converter 101, as will he explained below.

The cylindrical lube 119 physically supports the solar energy cofleclor assemffly 102 within the sealed transparent tube 103. There is no other physical support of the solar energy collector assembly 102. This may reduce conductive heat losses from the solar energy collector assembly 102, which may increase the amount of useful heat energy produced by the hybrid solar energy convener 1W.

The fluid Ilow channds 117 and 118 are al easl partially fflled with degassed distilled waler 12! as a working Iluid and the intenor of the heal transport element 104 including the hluid flow channels 117 and 118, and the vapor manifold 111 arc at least partially evacuated. that is, the interior of the hcat transport clemcnt 104 is at a pressure below normal atmospheric pressure. the interior of thc hcat transport element 104 may be undcr a vacuum at a pressure of io mbar. Thc heat transport element 104 is arranged to bc laterally inclined to the horizontal with the sidc 104a of the hcat transport elemcnt 104 wherc the vapor manifold 111 is located being arranged to he higher than the opposite side 104h of the heat transport element 104.

In the illustrated first embodiment the amount of water 121 in the fluid flow channels 117 and 118 is such that an upper surfacc 132 of the water 121 in the lower fluid flow channcls 1 IS is level wilh the ends oF the lower Iluid how channels 118 where the lower fluid flow channels 118 connect to thc vapor manifold 111. in thc illustratcd sccond embodimcnt the levcl of the surface 132 of the water 121 in the upper fluid flow channcls 117 and lower fluid flow channels 118 is substantially the same. Accordingly, in the illustratcd second cmbodiment the lowcr fluid flow channels arc fihlcd with liquid water, while the upper fluid flow channels 117 are only partially filled with liquid watcr.

In other examples thc level of the water 121 may be different. in somc examples the upper surface 132 of the water 121 in the lowcr fluid flow channels 1 IS may bc bclow the vapor manifold 111. in some examples the upper surface 132 of the water 121 in the lower fluid flow channels 118 may he above the bottom of the vapor manifold 111, with some water being present in the bottom of the vapor manifold 111.

It is expected that in practice the heat transport element 104 will operate most efficiently with Ihe upper surface 1 22 oF the waler being al, or close lo, Ihe poini where Ihe lower Iluid how channels 118 contact the vapor manifold 111. If the level of the water in the heat transport elemeni 1 04 is too high, so that the upper surface I 22 of Ihe waler is (no high wilhin the vapor marniold Ill, the efficiency of operation oF the heal transporl elemeni I 04 may he reduced, as will he discussed in more delail helow.

Thc upper surface 132 of the water 121 in thc upper fluid flow channels 117 may bc higher than in the lower fluid flow channels 118 as a result of capillary action. The extcnt of this capillary effect in any specific examplc will dcpend upon the dimensions of the upper fluid flow chaimels 117. in the illustrated first embodiment somc of the inncr surfacc of the upper sheet 114, that is, the surface forming a part of thc upper fluid flow channels 117, is above the surface of the water 121. In some examples the upper fluid flow channels 117 may have a small enough cross-sectional area that the upper surface 123 of the water 121 in the upper Iluid flow channels 117 is al Ihe ends of Ihe upper Iluid flow channds 117 due to capiflary action.

Tt should he noled ihal ii is nol necessary thai Ihe inner surface of the upper sheet 114, ihat is, thc surface forming a part of thc uppcr fluid flow channels 117, is below the upper surface 132 of thc water 121 at a position corresponding to the location of the uppermost parts of the photovoltaie clcmcnts 105. However, in some examples this may be the case.

In opcration of the first embodiment, when the solar cnergy collector assembly 102 is exposcd to incident solar radiative energy, the photovoltaic elements 105 absorb some of this energy, converting a part of the absorbed energy into electrical encrgy. ihe rcmainder of the absorbed energy is converted into heat energy, raising the temperature of the photovoltaic elements 105.

The absorbed heat energy flows from the photovoltaie elements 105 into the heat transport element 104, being transmitted through the upper sheet 114 and into the water 121 inside the upper fluid flow channels 117, which water is in contact with the inner surface of the upper metal sheet 114 across Ihe larger parallel Rices of the irapeioid upper Iluid flow channds 117.

The liquid waler 121 inside Ihe upper fluid flow channds 117 absorbs Ihe heal energy from the photovoltaic elements 105 passing through the upper sheet 114 and vaporizes, producing bubbks 122 of steam or water vapor, as shown in ligure S. The liquid waler may vaporiie and produce bubbles as a result of either or both of conveclion boiling and nuclealion. Al ihe vacuum pressure of I0 mhar inside the upper fluid flow channels I 17 waler boils 1mm around 0°C, so ihal the waler I 21 vaporizes readily at lhe normal operating lemperalures of the hybrid solar energy converter 101.

The bubbles 122 of water vapor are less dense than the liquid water 121. Further, as explained above the upper fluid flow channels 117 are sloping along their lengths. Accordingly, as a result of this density difference the water vapor bubbles 122 travel upwards along the upper fluid flow channels 117 towards the upper side edge 104c of the heat transport element 104 and the surface of the water 121. When a bubble 122 of water vapor reaches the surface of the water 121 Ihe vapor is rdeased mb the vacuum above Ihe waler 121 in ihe vapor manilold 111. Further, as a bubble 122 travels upwards along a fluid flow channel 117 the bubble 122 will act as a piston to drivc thc liquid watcr, and any othcr bubbles 122 abovc it, upwardly along Ihe upper fluid how channd I 17. This pistonic driving may lend bo accelerate Ihe speed with which thc vapor bubbles 122 move upward along thc uppcr fluid flow channcls 117.

Ibis pistonic driving may act to pump liquid water upwards along thc uppcr fluid flow channels 117 to thc cnds of thc uppcr fluid flow channels 117, where the liquid water will be ejected from the uppcr fluid flow channcls 117 into thc vapor manifold 111. In thc illustratcd first embodiment, wherc somc of thc inncr surface of thc upper sheet 114 is above the surface of the water 121, this pumping of liquid water upwards along the upper flow channels 117 ensures that the part of the inner surface of the upper sheet 114 above the surface of the water 121 is in contact with a flow of water so that it can be cooled.

The amount of the pistonic driving produced by the bubbles 122 will depend upon the relative sizes of the bubbles 122 compared to the cross-sectional areas of the upper fluid flow channels 117. The amount of pisbonic driving produced by the bubbles 122 may he increased where the size of the bubbles is relatively large compared to the cross-sectional areas of the upper fluid flow channels 117. The pistonic driving produced by the buhbks 122 may he particularly effective in examples where the size of the bubbles 122 of water vapor is equal to, or on'y a lilUe smaller Ihan, the cross seclional areas of the upper fluid flow channels I 17.

In practice Ihe sites of individual waler vapor bubbles will vary. However, Ihe likely average sites of ihe bubbles and the likely variability in their sites can he determined in any specific ease, based on the operating parameters to be used in the hybrid solar energy converter.

The bursting of the bubbles of water vapor at the water surface and any pistonic pumping of liquid water out of the ends of the upper fluid flow channels 117 may generate droplets of liquid water, and may project at least some of these water droplets into the vacuum within the vapor manifold 111 above the water surface. As a result, the heat transfer mechanism may he a multi-phase system comprising liquid water, water vapor and droplets of liquid water, and nol jusi a two-phase syslem comprising liquid waler and water vapor only. The presence of such droplets of water in the vacuum, and any pumping of liquid water out of the ends of the uppcr fluid flow channels 117, may enhancc the ratc of vaporization by increasing the surface area of Ihe water exposed to the vacuum.

Tie water vapor in the vacuum within the vapor manifold 111 travels at a very high speed through the vacuum within the vapor manifold 111 into contact with the exterior surface of the tube 119 forming the heat exchanger 107. The travel speed of the hot water vapor in the vacuum is very fast, approximating to the thermal speed of the water vapor molecules. The water vapor condenses on the external surface of the tube 119, which acts as a heat exchange surface. The condensed water falls off the tube 119 to the bottom of the vapor manifold 111, and is returned back into the water 121 within the lower fluid flow channels 1 18. Ibis generating of hot water vapor within the upper fluid flow channels 117 and the vapor manifold 111, and the condensing of the hot water vapor on the tube 119, followed by return of the condensed water into the fluid flow channels 117 and 118, transfers heat energy from Ihe heal iransfer dement 104 Lo ihe first fluid wiihin ihe Lube ii 9.

Thus, Lhe working Iluid is caused to circulate on a working Iluid pathway inside Ihe heat transfer device such that the heat of the working fluid is transferred to the heat exchanger in Lhe heal Lransl'er chamber. In ihe illustraled example the working fluid pathway is formed by Lhe Iluid how channels i17 and 118 and the heat oh ihe working hluid is absorbed from Lhe cooled surface I 04a of Ihe heal transporl element I 04.

the first fluid flows from the support element 106, through the heat transfer element 104, where it absorbs heat, and the heated fluid then returns to the support element 106. In the illustrated first embodiment the first fluid is water and a pumped water supply passes through the support element 106 and the cylindrical tube 119.

Any liquid water ejected from the upper fluid flow channels 117 into the vapor manifold 111 which does not vaporize will also fall to the bottom of the vapor manifold 111, and is returned hack mb the waler 121 wiihin the lower fluid flow channels 118.

Thc dcscription indicates that watcr dropicts and condenscd water falls into the bottom of the vapor marnlold 1 I I -Tn some examples, depending upon Ihe onenlalion o1 ihe collector assembly 102, some or all of this water may fall into the lower fluid flow channels 11 S without ncccssarily contacting thc surface of the vapor manifold 111.

Thc location of thc heat cxchanger 107 within the heat transfer chamber or vapor manifold 111 may improve the efficiency of thc hcat transfer element 104 by providing a short path for watcr vapor to travel bctween thc uppcr surface of the working fluid and the heat exchanger 107.

As is explained above, all of the upper and lower fluid flow channels 117 and 118 are interconnected by the fluid manifold 124 formed by the gap 123. Accordingly, it is not important which of the lower fluid flow channels 118 is entered by any liquid water returning 1mm the vapor manik)]d Ill.

As is clear from the descriplion ahove, the heal Iransier chamber or vapor manifold Ill generally includes liquid water in addition to water vapor when the hybrid solar energy convener 101 is operaling. How-ever, as is also discussed above, ii the level ol ihe waler in ihe heal transporb dement 104 is lou high, so thai the upper surFace 122 of ihe water is boo high wiihin the vapor manik)ld ill, bhe elliciency of operabion of Ihe heat bransport dement 104 may he reduced. This reducbion in elliciency 0! operation may occur because there is insufficient space within the vapor manifold 111 abovc the surface of thc water for the movement and cvaporation of thc droplets of liquid water. Ibis reduction in efficiency of operation may occur because the droplets of liquid water and waves and splashing upwardly of thc liquid watcr surfacc may rcduce thc open, or water frcc, cross sectional area of the vapor manifold 111 at some locations to a rclatively small amount, or even to zero, momentarily closing the vapor manifold 111. This reduction in the open, or water free, cross sectional area of the vapor manifold 111 may interfere with the movement of the water vapor in the vacuum within the vapor manilold Ill -TIc bubblcs 122 of watcr vapor will tcnd to movc upwardly through thc liquid watcr in thc upper fluid flow channel I 17 because oF the low-er densily of Ihe waler vapor compared lo ihe liquid watcr 121, which will rcsult in an upward buoyancy forcc on cach bubblc 122. Furthcr, thc movcmcnt of thc bubblcs 122 of watcr vapor will tcnd to drivc thc liquid watcr 121 in thc uppcr fluid flow channcl 117 upwardly, particularly in cxamplcs whcrc pistonic driving takcs placc. As a result, thc bubblcs 122 of watcr vapor causc thc watcr 121 in thc uppcr and lowcr fluid flow chaimcls 117 and 118 to circulate, with rclativcly hot liquid watcr and bubbles 122 of watcr vapor flowing upwards along thc uppcr fluid flow channcls 117, and rclativcly cool liquid watcr flowing downwards along the lowcr fluid flow channels 118. The uppcr and lower fluid flow channcls 117 and 118 arc intcrconncctcd by thc vapor manifold 111 and thc fluid manifold 124, as explained above. Accordingly, the relatively hot liquid water flowing upwards along the upper fluid flow channels is continuously replaced by relatively cool liquid water from the lower fluid flow channels 118. This circulation is driven primarily by the diFference in densily heiween ihe waler vapor and the liquid waler. However, this circualion may also be driven by convection as a result of the difference in density between the relatively hot liquid water in ihe upper Iluid flow channels 117 and the relatively cool liquid water in the lower fluid flow channels 118, in a similar manner to a thermosiphon.

Accordingly, the upper fluid how channels I 17 may be regarded as riser channels, while ihe lower hluid how channels I 18 may he regarded as sinker channels or return channds.

As the bubbles 122 o1 waler vapor travel upwardly along Ihe upper hluid how channels I 17 thc pressure head acting on the bubbles 122 decrcascs, so that thc bubblcs 122 tcnd to expand.

As a rcsult, thc tcndcncy of thc vapor bubblcs 122 to collapse and implode is rcduced by thc cffects of the cxpansion and deercasing pressure as thc bubblcs 122 move upwardly. When considcring this point, it should bc rcmembered that whcn thc heat transport clcmcnt 104 is opcrating thc bubbles 122 will bc fomiing within an established dcnsity driven circulation fluid flow and will move upwardly carried by this flow in addition to the hubbies movement due to their own buoyancy relative to the liquid water. Further, it is believed that expansion of the hubbies 122 as they move upwardly wifl further increase (lie speed of Ihe density driven circulation flow by increasing the buoyancy of the expanding hubbIes 122. In some examples cxpansion of thc bubblcs as thcy move upwardly may also incrcasc thc dcgrcc of pistonic driving.

Ibis dcnsity drivcn circulation may form a highly cffcctivc hcat transport mcchanism bccausc watcr has a rclatively high enthalpy of vaporization, so that thc movemcnt of thc bubblcs 122 of watcr vapor may carry a largc amount of hcat energy, in addition to thc hcat cncrgy carried by thc movcmcnt of rclativcly hot watcr out of thc uppcr fluid flow channels 117, and its rcplaccmcnt by cooler watcr. in arrangcments whcrc pistonic driving of thc flow of thc liquid watcr by thc water vapor bubbles takes place thc cffcctivcncss of thc hcat transport mcchanism may bc furthcr incrcascd by thc incrcasc in thc flow ratc of thc liquid watcr caused by the pistonic driving. Ibis pistonic driving is a component of the overall density driving producing the density driven circulation. The pistonic driving is caused by the density difference between the liquid water and the bubbles of water vapor.

In general, the speed of the density driven circulation increases and the effectiveness of the heal transport mechanism increases as the lemperalure ol' (lie upper sheet 1 14 of Ihe heat transport element 104 increases.

The density driven circulalion ol' the waler 121 within the Iluid how channds 117 and 118 is a vapor driven circuialing or rofling Ilow.

The density driven circulation of the water 121 within the fluid flow channels 117 and 118 becomes particularly vigorous, and becomes particularly effective as a heat transport mcchanism, when the temperature of the upper sheet 114 of the heat transport element 104 becomes sufficiently high that the water 121 within the fluid flow channels 117 and 118 enters a rolling boil state. The effectiveness of the heat transport mechanism significantly increases when rolling boiling of the water 121 commences. In general, when other parameters of the system remain constant, entry into the rolling boil state will take place when the lemperature of Ihe upper sheet 1 14 of the heal transporl elemenl 104 reaches a specific temperature.

Tn Ihe illuslraled example using water, the waler 121 wiihin fluid flow channds 117 and 118 may entcr a rolling boil state at a tempcraturc of about 40°C.

The arrangement of fluid flow channels 117 extending laterally across the hcat transport element 104 may allow the vertical height of the liquid water in the heat transport element 104 to be reduced compared to arrangements in which the density driven flow extends along the length of a heat transport element, and so reduce the pressure head acting on the liquid water at the bottom of the heat transport element 104. In general, increased pressure reduces the tendency of liquids to vaporize and so increases the boiling point of liquids. Accordingly, reducing the pressure head acting on the liquid water at the bottom of the heat transport element 104 may increase the tendency of the liquid water 121 towards the lower ends of the upper fluid flow channels 117 to vaporize and produce bubbles 122, and so may improve the efficiency and effeeliveness of Ihe heal transporl element 104.

in particuhir, the reduclion of the pressure head acting on ihe liquid water at the hollom of ihe upper fluid flow channels 117 may reduce any temperature differential along the lengths of the upper fluid flow channels between iheir Ihe lop and hollom ends by reducing any difference in ihe lendeney of Ihe liquid waler Lu vaporbe due lo differences in pressure. This may reduce temperature differenlials helween Ihe diliereni points on the heal Iransport elemeni 104 and may assist in reducing or avoiding the formalion of hot spots in ihe photovoltaie elements 105.

in general the forming of hot spots in the photovoltaie elements 105 is undesirable because these may lead to a reduction in the efficiency of electrical energy generation in the photovoltaie elements 105, which reduction in efficiency may be permanent.

The arrangement of the upper fluid flow channels 117 extending laterally across the heat transporl elemeni 104 and interconnected by a heat iransier chamber or vapor manifold I Ii containing a heat exchanger 107 extending longitudinally along the heat transport element 104 may allow a vcry rapid flow of heat encrgy along the hcat transport clement 104 away from any upper fluid flow channel 117 having a higher lemperalure. This may reduce temperature diffcrentials bctwccn the different points on the heat transport elcment 104 and may reduce, or avoid, thc formation of hot spots in the photovoltaic elcments 105.

Thc provision of thc two separate hcat transport mechanisms of the movemcnt of water vapor along the heat transfcr chamber or vapor manifold 111 and thc density driven flow of liquid watcr and water vapor along cach of the upper fluid flow channcls 117, respcctively acting longitudinally and transverse the lcngth of the hcat transport elemcnt 104, may tcnd to equalize the temperature across the entire upper surface of the heat transport element, and thus tend to equalize the temperature across the photovoltaic elements 105 and reduce, or avoid, the formation of hot spots.

The movement of waler vapor along the heal transfer chamber or vapor manifold Iii provides a very rapid heat transport mechanism that tends, by the vaporization and condensalion of waler, lo move heat energy from relativdy hol localions lo relalively cold locations. As a result, the movement of water vapor along the heat transfer chamber or vapor mamlold III may lend lo equalize Ihe temperalure of the liquid water surface at different positions along ihe heal transfer element 104, in addilion lo transporling heal energy from ihe heal Iransporl dement 104, and specifically from the upper surface 1 04a of the heal Iransport elemeni 1 04, lo ihe heat exchanger I 07 formed by the tube I 1 9. This temperalure equalizalion may have the effect of removing more heat energy from hotter parts of the upper surface 104a of the heat transport element 104, and so tending to equalize the temperature across the upper surface 104a. It is clear that such isothermal cooling will tend to reduce, or avoid, the formation of hot spots, for example in any photovoltaie element attached to the upper surface 104a.

The lower sheet 115 of the heat transport element 104 has a plurality of hollow ridges 125 exiending between the flat part of ihe lower surface I 04h and Ihe semi-cylindrical surface of the outwardly projecting section 110. Each hollow ridge 125 has a V' profile, and the hollow ridges 125 are located spaced apart at regular intervals along the length of the heat transport elemeni 104. Figure 9 shows a transverse cross seclion of Ihe heal Iransport elemenl 104 taken along the line C-C in Figure 3. The line C-C of Figure 9 is parallel to the line A-A of Figure 4, but passes through one of the hollow ridges 125. the hollow ridges 125 act as supports for the outwardly projecting section 110, acting as buttresses and helping to keep the curved part of the lower sheet 115 forming the outwardly projecting section 110 fixed relative to the flat part of the lower metal sheet 115 and the other parts of the heat transport element 104.

the hollow ridges 125 also act as drains to return liquid water from the vapor manifold 111 into the lower fluid flow chaimels 118, as will be explained in more detail below.

As explained above, the vapor manifold 111 is semi-cylindrical, being defined by the semi-cylindrical oulwardly projecting section 110 formed by a curved pan of Ihe lower sheet 115.

Further, as explained above, the heat transport element 104 is transversely sloping so that the side edge I 04c of Ihe heal Iransporl element 104 bearing Ihe oulwardly projecting section 110 is higher than the other side edge 104d of the heat transport element 104. As a result, depending upon the lransverse inelinalion angle of the heat transporl element 104 Ihere may, or may nol, he parts of Ihe vapor manifold 1 I I which are thcaied below-Ihe ends of Ihe low-er fluid how channels I I S where Ihe lower Iluid how channels 1 I 8 conned lo the vapor manilold iii.

Figures iDA and lOB are explanatory diagrams, each showing a transverse cross sectional view of the heat transport element 104 corresponding to the view shown in Figure 4. Figure IOA shows the heat transport element 104 inclined at a relatively large angle to the horizontal, while Figure lOB shows the heat transport element 104 inclined at a relatively small angle to the horizontal.

When Ihe heal Iransport element is inclined at a relalively small angk to ihe horiionial, as shown in Figure bA, the lower fluid flow channels 118 connect to the vapor manifold 111 at the lowest point of the semi-cylindrical outwardly projecting section 110 of the lower sheet deFining the vapor mamlold Iii -In Ihis posilion all liquid waler within ihe vapor manifold 111 will drain directly into thc lower fluid flow channels lift in contrast, when the heat transport clcmcnt 104 is inclined at a relatively largc anglc to the horizontal, as shown in Figure 1 OB, thc part of the semi-cylindrical outwardly projecting scction 110 of the lower sheet 115 dcfining thc vapor manifold 111 is located bclow the point at which the lower fluid flow channels 118 connect to the vapor manifold. h this position, in the abscnce of the hollow ridges 125, somc liquid water within the vapor manifold 111, spccifically liquid water below the horizontal line 126, could be retained within the vapor manifold 111 and not drain into thc lower fluid flow channels 118.

The hollow ridges 125 form a drain path for liquid water in the vapor manifold 111 to return to the lower fluid flow channels 118 and so prevent the retention of a reservoir of liquid water wiihin ihe vapor marniold Ill which mighL oLherwise occur.

As discussed above, ihe heat Iransport assembly 1 04 can operale wiih Uquid waler wiihin ihe vapor manifold 111. I lowever, in the absence of the hollow ridges 125 the existence and size olany reservoir oHiquid waler relained in the vapor manifold Ill wifi vary depending on Ihe angle oF inclinalion lo Ihe horizonlal of the heal Iransport element 104, and ihe resuhing changes in lhe liquid waler level in Ihe fluid how channels 117 and 118 aL different angles of inclinalion may adversdy ahièct Ihe operalion of Ihe heat Iransport dement 104 aL some angles of inclination and so limit thc range of angles of inclination at which thc heat transport elcmcnt 104 can be uscd.

Accordingly, thc hollow ridges 125 may extend the range of angles of inclination at which the heat transport clement 104 can be uscd.

Depending upon the geometry of the different parts of the heat transport element 104 in any specilic design, even when the hollow-ridges 125 are used there may slill he a minimum angle of inclination at which the heat transport element 104 can operate without the retention of liquid water in thc vapor manifold 111 having advcrsc effects on operation of the hcat Iransporl element 104.

in thc illustrated example of the first cmbodiment thc hollow ridges 125 act as supports for thc outwardly projecting scction 110 and also act as drains to return liquid water from the vapor manifold 111 into the lower fluid flow channels 11g. in some examples these functions may bc carricd out by separate dedicated structures.

The corrugated profile of the central shcet 116 and the bonding of the first and second surfaces 1 16a and 11 6b of the central sheet 116 to the upper sheet 114 and the lower sheet 115 so that the linking surfaces 11 6e and 11 6d of the central sheet 116 interconnect the upper and lower sheets 114 and 115 increases the strength and rigidity of the heat transport element 104. This may make the heat transport element 104 a more rigid structure. This may tend to reduce the amounl of Ilexing of the heat Iransporl element 104 in use. This may prevent damage to the photovoltaic elements 105 by reducing the amount of mechanical stress applied lo the photovollaic elemenls 105. This may allow the upper, lower, and/or central metal sheets 114, 115, 116, to he thinner, which may reduce weight and costs. This may allow the upper meLd sheet 114 to he thinner, which may improve the transfer of heal from Ihe pholovollaic elemenis lOS mb the liquid waler wilhin Ihe upper fluid how channels II?.

The heal Iransport element i 04 is a suhslanlially rigid slruclure. This may minimize changes in the level of the upper surfacc 132 of the water 121 due to flexing of the components of the heat transport element 104, such as the upper and lower sheets 114 and 115. Such changes in the level of the upper surface 132 of the water 121 may affect the efficiency of the cooling of the photovoltaic elemcnts 105.

As is explained above, the interior of the heat transport element 104 is evacuated, and the heat transport element 104 is located within an evacuated tube 103. Usually the heat transport elemeni 104 and ihe evacualed lube I 03 are evacualed to Ihe same pressure. Tn the illustraled example of the second embodiment described above this pressure maybe i03 mbar.

When Ihe waler within the heal Iransporl elemenl 1 04 is heated the proporlion of Ihe waler in a vapor phasc will incrcase and the proportion in a liquid phase will decrcase. As a result the pressure within the heat transport element 104 will incrcasc, producing a pressurc differential betwcen the intcrior and exterior of thc hcat transport element 104. this pressure differential may cause the uppcr and lower metal sheets 114 and 115 to balloon', or bend outwards. the interconnection of the upper and lower metal sheets 114 and 115 by thc linking surfaces 1 16c and 11 6d of the central metal sheet 116 may resist such ballooning of the upper and lower metal shcets 114 and 115 and reducc or prevent ballooning. Arranging for the linking surfaces 1 16c and 1 16d of thc central mctal shcct 116 to bc straight may incrcase the resistance to ballooning. Reducing or preventing ballooning may prevent damage to the photovoltaic elements 105 by reducing the amount of mechanical stress applied to the photovoltaic elements 105. This may allow the upper metal sheet 114 to he thinner, which may reduce weighi and eosls and/or may improve the transfer of heal from the pholovoltaic elemenls 105 into the liquid water within the upper fluid flow channels 117.

The above description of the operation of the heat transfer element 104 according to the second embodimenl describes ihe Iransfer of heal energy from Ihe photovollaic elemenls I 05 lhrough Ihe upper metal shed 114 and into the waler within Ihe upper fluid flow channels 117.

In addilion, in ihe regions of the upper melal sheet 114 bonded to the firsl surfaces I 16a, some heal energy will pass through the upper melal shed 114 and the cenlral metal shed 116 into the water within the lower fluid flow channels 118. Although this transfer of heat encrgy will cool the photovoltaic elements 105, thc heating of the water in the lower fluid flow channels 118 is generally undesirable because it will tend to counteract and slow thc density drivcn circulation of water produced by the heating of the water in the upper fluid flow channels 117 described above. Accordingly, it is preferred for thc sizes of thc first surfaces 1 16a of the central metal sheet 116 in contact with the upper metal sheet 114 to be as small as possible, subject to the contact area between the first surfaces 1 16a and the upper metal sheet 114 being sufficiently large Lu form a rdiahle bond of the required strength.

It is not nccessary for the heat transport clement 104 according to thc first embodiment to be inclined to the horiíonlal along its longiludinal axis. In other words, ii is nol necessary for the end of the heat transport elcmcnt 104 adjacent the support assembly 106 to be highcr than the end of the hcat transport clcment 104 remote from thc support assembly 106.

In thc illustrated first cmbodiment the heat transport element 104 is * ranged to be horizontal along its longitudinal axis. That is, the end of the heat transport clemcnt 104 adjaccnt the support assembly 106 should be at thc sainc height as the end of the heat transport element 104 remote from thc support asscmbly 106. However, in practice somc deviation from the horizontal may be tolerated without significant impact on the operation of the hcat transport element 104. Such deviation from the horizontal will result in differences in the level of the liquid water surface relative to the structure of the heat transport element 104 at different positions thong the length of the heat transport element 104. As is explained above, the level oF Ihe liquid waler surface may he varied. Accordingly, the minor diFFerences in level caused by small deviations from the horizontal may he accommodated.

In the illustrated example of the first embodiment, each of the upper and lower sheets 114 and has a dimpled prohle. This dimpled prolile is shown in more delail in Figures Ii A and 11 B. Figure ii A shows a plan view from above of a part of the upper shed 114. Figure II B shows a cross section through the upper shed 114 athng Ihe line D-D in ligure Ii A. As is shown in Figure 1 1A, a plurality of dimples 127 arc formed in the flat upper surface 104a of the heat transport clemcnt 104 in thc upper shcct 114. The dimples 127 are formcd in straight rows and columns to form a regular two dimcnsional square array, and are spaced apart lcaving a flat strip 12S between each row of dimplcs 127.

Each dimple 127 comprises a looped recess 127a having a circular inner perimeter 127h and a square outer perimeter 127c. The square outer perimeter 127c has rounded off corners 127d.

Within the circular inner perimeter 1 27h a circuhir region I 27e is raised relative to Ihe looped recess 127. The circular region 127e is at the same level as the surface 104a of the flat strips of the upper shcet 115 outsidc thc dimple 127.

Thc flat strips 12S run transversely across the upper sheet 114 and havc the samc width as the width of the first coplanar surfaces 1 16a of thc central sheet 116. the flat strips 128 provide flat arcas for bonding with the first surfaces 1 16a of thc central shcet 116. the flat strips 12R may allow rcliable and strong bonds to bc made between the first surfaces 1 lôa and thc upper sheet 114. Ic flat strips 12S may allow a good scal to be formed between adjacent upper fluid flow passages 117.

A plurality of dimples 129 are formcd in the lower shcct 115. the dimplcs 129 arc formcd in straight rows and columns to form a regular two dimensional square array, and are spaced apart leaving a flat strip 130 between each row of dimples 129. The dimples 129 in the lower sheet 115 are the same as the dimples 127 in the upper sheet 114. The flat strips 128 run transversely across the upper metal sheet 114 and have Ihe same widLh as the width of ihe First and second coplanar surfaces 11 6a and 11 6h. The flat strips 130 provide flat areas for bonding with the second surFaces 1 16h @1 the central sheet 116. The Ilal slrips 130 may allow reliable and strong bonds to be made between the second surfaces 11 6b and the lower sheet 115.

Tn the illustrated example oF the lirsi embodiment oF Ihe invention holh ihe dimples 127 in ihe upper sheet 114 and ihe dimples 130 in the lower shed 115 are lbrmed by downward recesses.

Accordingly, the dimples 127 in Ihe upper shed 114 have recesses exlending into the heal transport element 104, while thc dimples 130 in thc lower sheet 115 have recesses cxtending out of the heat transport clcment 104. In othcr examplcs thc dimplcs 127 and 130 may be formcd by recesses cxtending upwardly, or by recesses cxtcnding in opposite dircetions.

Thc array of dimples 130 on thc lowcr metal shcct 115 extends across the flat part of the lower sheet 115, but does not extend into the semi-cylindrical surface of the outwardly prolecting section 110. Further, the array of dimples 130 on the lower sheet 115 has dimples omitled Irom (be array al the locations ol' the hollow ridges 125.

Thc dimples 127 and 130 may incrcasc thc rigidity of thc uppcr and lower shccts 114 and 115.

This may lend lo reduce (be amouni of flexing of the heat transporl elemenl 104 in use. This may prcvcnt damagc to thc photovoltaic elcmcnts 105 by rcducing thc amount of mechanical strcss applied to thc photovoltaic clcmcnts 105. this may allow thc uppcr, lowcr, and/or central sheets 114, 115, 116, to bc thinner, which may reducc wcight and costs. This may allow the upper sheet 114 to be thinner, which may improve the transfer of hcat from the photovoltaic clcmcnts 105 into thc liquid watcr within the upper fluid flow channels 117.

Tic surfaces of the dimples 127 may providc additional nucleation sites for the formation of watcr vapor bubbles 122, which may improvc efficiency.

In examples where adhesive is used to attach the photovoltaic elements 105 to the heat transport element 104 the dimples 127 on the flat upper surface 104a of the heat transport elemeni 104 may provide reservoirs l'or Ihe adhesive. This may aflow more secure allachment of the photovoltaic elements 105. This may allow a thinner layer of adhesive to he used, which may improve the transfer of heat from (lie pholovollaic dements lOS into the liquid water within the upper fluid flow channels 117.

As discussed above the heal Iransporl elemenl 104 has a Ilal upper surface 1 04a formed by an upper sheet 114 wiLh a dimpled profile. In addition the upper shed 114 is has Iwo longiludinal recesses I 29 running across in its upper surface I 04a which lorm Iwo parallel iroughs running along the upper surface 104a of the hcat transport elcment 104. Figurc 12 shows onc of these recesses 129. Electrically conductivc ribbons or wires 130 run along thc longitudinal recesses 129 betwcen the heat transport element 104 and thc photovoltaic elements 105. the wircs 130 are electrically connected to the photovoltaic elemcnts 105 and to the conductors 21 which pass through the cap 12 to provide a conductive path to carry the clcetrical power generated by the photovoltaic elements 105 out of the sealed transparent tube 103. This electrical power may he supplied to an inverter for voltage conversion and/or for conversion to alternating curreni br supply lo a domestic or mains elecirical syslem.

In examples where adhcsivc is uscd to attach thc photovoltaic clcmcnts 105 to thc hcat Iransporl elemenl 104, an electrically insulating adhesive can he used Lo deciricafly insLilale thc clcctrically conductive ribbons or wires 130 from thc photovoltaic clcmcnts 105 and from thc uppcr surfacc l04a of thc hcat transport clcment 104. the clcctrically insulating adhcsivc can also bc uscd to electrically insulate the photovoltaic elemcnts 105 from thc upper surfacc 104a of thc hcat transport clcmcnt 104.

in thc first cmbodimcnt thc longitudinal rcccsscs 129 run pcrpendicularly to thc fluid flow channels 117 and 11K Accordingly, cach of the first surfaces 1 16a of thc central metal shcct 116 has two rcccsscs to rcceive the longitudinal rcccsses 129.

in the illustrated example of the first embodiment each dimple 127 comprises a looped recess with a circular inner perimeter 127b and a square outer perimeter l27c, with the circular region I 27e at Ihe same level as ihe surface I 04a of ihe flat strips of ihe upper metal sheet 115 outside the dimple 127. In some examples the circular region 127e may not be at the same level as the surface I 04a of ihe Hal strips of ihe upper melal shed 115 oulside ihe dimple 127.

in other examples different dimple shapes and/or profiles may be used. In some examples the perimeters may have difiereni shapes. In some examples Ihe circular region I27e may not he at Ihe same evel as the surface I 04a of Ihe Hal sirips of the upper melal shed 115 outside ihe dimple 1 27. in some examples the dimples may simply comprise a recessed region, raiher Ihan a recessed ouler region surrounding a relatively raised inner region.

in thc illustrated example of thc first embodiment 0.2 mm thick tin coatcd mild steel shccts are used to form the diffcrent sheets of thc heat transport element. In alternative examples other thicknesses may be used, in particular 0.1 mm thick tin coatcd mild steel shccts may be used. the use of a thinner upper metal sheet may improve thc ratc of heat energy transfcr from the photovoltaic elements to the water inside the upper fluid flow channels. In other examples the different sheets may have different thicknesses.

In the illustrated example of the first embodiment the spacing between the upper sheet 114 and thc parallel lower sheet 115 is 1.8mm at the locations of the longitudinal recesses 129.

Accordingly, ihe thickness of ihe Iluid flow channels 117 and 118 at the locations of the longitudinal recesscs 129 is 1.6mm, since the thickness of the central sheet is 0.2mm.

The use of mild steel may avoid or reduce problems produced by differential thermal expansion of the silicon semiconductor photovoltaic elements 105 and the heat transport element 104 because the coefficients of thermal expansion of silicon and mild steel are similar.

Tie sheets used to form the heat transport element may be shaped by pressing.

In other examples different materials may he used, in particular sheets of other metals or metal alloys, such as copper or brass may be used. In other examples the upper, lower and/or partition sheets may he formed from materials which are not metals. In other examples there may he openings in the upper sheet allowing the water inside the upper Iluid flow channels Lo directly contact the back surfaces of the photovoltaie elements to maximize heat transfer. In such examples Ihe Lhiclcness or malerial used Lu lorm the upper sheet could he selecled without having to take thermal conductivity into account.

In the illustrated example of Ihe lirst embodiment Ihe tube 119 is cyfindrical. In oLher examples different Lube shapes may he used. In some examples a tube 119 having an elliptical cross seclion may he used. The use of an elliptical tube may increase Ihe heal exchange area formed by the exterior of the tube 119 where the water vapor condenses, which may improve the heat transfer rate between the water vapor and the fluid within the tube 119.

In different examples the size of the tube 119 may be varied. However, the tube 119 should not entirely fill the vapor manifold 111. If there is insufficient free space within the vapor manifold 111 to allow the water vapor and liquid water to freely circulate this may adversely affect the operation of the heat transport element 104.

In the illustrated example of the first embodiment the tube 119 is made from copper. In other examples different materials may bc used. lie tube 119 is connectcd at only one end to the heal Iransporl element I 04, with the other end, (lie curved section I I 9e, being free lo move relative to the heat transport element 104. Accordingly, differential thcrmal expansion of the tube 119 and thc hcat transport element 104 is not gcnerally a problcm and will gcnerally not necd to be takcn into account when selceting matcrials.

in the first embodiment of the invention the roughening of the surfaces of the upper sheet 114 produced by the tin coating may providc nucleation sitcs, increasing thc tendency of the liquid watcr 121 to vaporize and form bubbles 122 of water vapor. In thc first embodiment of the invention thc roughening of the surfaccs of thc central sheet 116 produced by thc tin coating may provide nucleation sites, increasing the tendency of the liquid water 121 to vaporize and form hubbIes 122 of water vapor.

In some examples oLher coatings may he added lo the surFaces of the upper shed 114 in order to promote or increase nucleation and formation of bubbles of water vapor. In some examples Ihese coatings may he of metals, or pas1ics. In some exampks these coalings may he of PTFE.

In the illusiraled example of the lirsi embodimeni the diliereni sheds are soldered together. In allemative embodiments diftereni bonding techniques may he used. Tn some exampks the different sheds may he bonded by techniques including spot welding, roller welding or adhesive.

in thc illustratcd cxample of thc first embodiment inner faces of thc upper and lower shccts 114 and 115, and both faces of the ccntral metal sheet 116, are coated with a solder layer. in the illustratcd examplc the solder layers are 2 to 6 microns thick. Other examples may have different thicknesses.

The edges of Ihe upper and lower sheets I 14 and I 1 5 are then soldered logether to lorm a gas tight seal between them, and to form a gas tight seal between the upper and lower sheets 114 and 115 and the tube 119. As is explained above, the central metal sheet 116 is not located heiween Ihe upper and lower melal sheds 114 and 115 al their edges.

I'hc hcat transport elcment 104 is then heated in an oven to a sufficiently high tcmperaturc to reflow the solder layers on the upper, lower and ccntral sheets 114, 115, 116, and is simultaneously evacuated.

This manufacturing procedurc may cnsure good solder bonding betwcen the central sheet 116 and the upper and lower sheets 114 and 115. this manufacturing procedure may allow a bettcr levcl of vacuum to be achieved within the heat transport clemcnt 104 by cvacuating the heat transport element 104 at a high temperature when out-gassing by the metal sheets and solder is taking place.

The solder may microscopically roughen Ihe surfaces of the upper and central sheets I 14 and 116, This may provide nucleation sites, increasing the tendency of the liquid water 121 to vaporize and I'orm bubbles 122 of waler vapor.

Tn other examples, a solder layer is Formed on the ceniral shed 1 I 6 only on Ihe parts of the eenLral metal shed which conlaci Ihe upper or lower sheds 1 14 and I IS. As can he undersLood From a comparison of Figures 13 and 14 ibis will he the contaci laces of Ihe first and second surfaces i I 6a and 1 I 6h. Similarly, in some examples a so'der layer is formed on the surfaces of the upper sheet 114 and the lower shcet 115 only on the parts of the surfaces which will contact one of thc othcr sheets. Rcducing the amount of solder used may rcduce costs.

In one example the upper shcet 114 only is coatcd in solder across its entire surface, while the central sheet and lower sheet 116 and 115 are coated in solder only on the parts of the surfaces which will contact one of the other sheets. This may allow the solder layer to provide nucleaiion sites Ofl ihe surface of ihe upper sheet 114 forming paris of ihe upper fluid how channels, while reducing the total amount of solder used.

As explained above, in ihe illustrated example of the lirsi emhodimeni the flow ol waler vapor and liquid watcr through thc hcat transport clcmcnt 104 tends to kccp thc cooled upper surfacc of the hcat transport clement 104 at a uniform opcrating tcmpcraturc during opcration.

Tiat is, thc cooled upper surfacc of thc heat transport elcmcnt 104 tends to bc kept isothermal.

The isothermal naturc of the cooled upper surfacc of thc heat transport clement 104 tcnds to give rise to isothermal cooling of the photovoltaic elements 105, where hotter parts of the photovoltaic elements 105 tend to be preferentially cooled so that the photovoltaic elements themselves tend to become isothermal.

Such isothermal cooling provides further advantages in addition to those provided by cooling.

Isothermal cooling may provide the advantage that the appearance of hot spots or regions in the pholovoltaic elemenis 105 produced by healing by incideni solar radialion can he reduced or eliminated. Such hot spots or regions can reduce the efficiency of the photovoltaic elemenis 1 05.

Tsoihermal coohng may simplify the conlrol and wiring arrangemenis of ihe pholovollaic elemenis 105 by reducing or eliminaiing any requirement br compensation br differences in the perlbrmance of ihe dilTerent paris of the photovoltaic elemenis 105 Ihat are at dilTerent temperalures.

lsothcrmal cooling tends to reduce, or prevent, the formation of hot spots or regions in the photovoltaic elements 105. As is explained above, this may allow the efficiency of the photovoltaic elements 105 to be improved at a specific temperature. Further, this may reduce the amount of degradation of the photovoltaic elements 105 caused by higher temperatures.

Still further, this may allow the photovoltaic elements 105 to operate with a given degree of efficiency at a higher temperature than would otherwise he the ease. This may allow the solar energy collector assembly 102 including the photovoltaic elements 105 to he operated at a higher temperature without rcducing the efficiency with which the photovoltaic elements 105 produce electrical energy.

One example of this effect of isothcrmal cooling is that the gencral figure quoted abovc for silicon photovoltaic clcments that the cfficieney of clcctrical cnergy generation generally drops by about 0.35% to 0.5% for each degree ccntigradc of tempcrature incrcasc above 25°C may not apply to silicon photovoltaic elcmcnts that are isothermally cooled. Such isothcrmally coolcd silicon photovoltaic elcments having hotspots climinated or rcduced may havc a higher threshold temperature at which thc efficiency of electrical energy generation begins to drop and/or may have a reduced rate of reduction in efficiency for each degree centigrade of temperature increase above the threshold temperature. Further, the temperature at which there is a risk of permanent degradation of the silicon photovoltaic elements may also be increased for isothermally cooled silicon photovoltaic elements. Similar effects may he lound in photovoltaie elements formed of other semiconductor materials.

In some examples, one or more layers ol heat conductive material maybe located between the upper sheet 114 and the photovoltaic elements 105. Such layers of heat conductive material may increase the rate of heat transfer between the photovoltaic elements 1 05 and the upper sheet I 1 4, and thus the rate of heat transfer between the photovoltaic elements 1 05 and the liquid within the upper fluid how channels 117. Such layers oh heat conductive material may also increase the rate oh heat transfer laterafly across the photovoltaic elements lOS.

Accordingly, providing a layer of heat conductive material may increase the degree of isothermal cooling and further tend to reduce, or eliminate, thc formation of hot spots or regions in the photovoltaic elements 105.

The heat transport element may be used in other applications separately from the rest of the solar energy converter.

In some examples control methods can he used to control the temperature of the solar energy collcctor assembly 102. In some cxamples the tcmperature of the solar encrgy collector assembly 102 maybe controlled by changing the rate of remova' ol heal energy from Ihe solar cnergy collector assembly 102.

In some examples the rate of removal of heat energy from the solar encrgy collector assembly 102 can be controlled by altering the flow rate of the first operating fluid passing through the tube 119 forming thc heat exchangcr 107.

In some examples the rate of removal of heat energy from the solar encrgy collector assembly 102 can bc controlled by altering thc vacuum prcssure within the tube 103. This may change the rate of convective heat loss from the solar energy collector assembly 102 to the tube 103.

In general, heat transferred to the tube 103 will be rapidly lost to the outside environment by convection and/or conduction.

In some examples the rate of removal of heat energy from the solar energy collector assembly 102 can he conirolled by altering Ihe vacuum pressure wiihin ihe heal Iransport elemenl 104.

In general, the tendency of the liquid water within the upper fluid flow channel 117 to vaporize and Form bubbles of vapor I 22 will increase as the vacuum pressure is reduced, and Ihe Lendency of the liquid waler wiihin the upper fluid how channd 117 Lo vaporize and Ibrm hubhks of vapor I 22 will decrease as ihe vacuum pressure is increased. As is explained above, Ihe densily driven circulation of waler around ihe upper and lower Iluid flow channels I 17 and 1 IS and the transport of heat cnergy along the vapor manifold 111 and the tube 119 are both driven by watcr vapor. Accordingly, altering the tendency of the liquid water to vaporize by altering the vacuum pressurc may allow thc ratc of removal of heat energy from the solar cnergy collector assembly 102, and the rate of removal of heat energy from thc photovoltaic elements 105 to be controlled, and so allow the temperature of the solar energy collector assembly 102 and photovoltaic elements 105 to he controlled.

Furiher, the temperature al which rolling boiling of Ihe waler 121 wiihin Ihe upper fluid how channel 117 commences will tend to increase as the vacuum pressure is increased, and will tcnd to dccrease as thc vacuum pressure is dccrcased. Accordingly, in examples where the vacuum pressure wiihin the heal transporl elemeni I 04 is allered ihe temperalure al which Ihe watcr 121 within the upper fluid flow channel 117 commenccs rolling boiling can be changed.

As is explained above, the density driven circulation of water around the upper and lower fluid flow channels 117 and uS becomcs particularly vigorous, and becomes particularly effcctive as a heat transport mcchanism, when the water 121 within the uppcr fluid flow channel 117 enters a rolling boil statc. Accordingly, altcring thc temperature at which the watcr 121 within the upper fluid flow channel 117 commcnces rolling boiling by altering the vacuum pressure may allow the ratc of rcmoval of heat encrgy from thc solar cnergy collcctor assembly 102 and photovoltaic elements 105 to he controlled, and so allow the temperature of the solar energy collector assembly 102 and photovoltaic elements 105 to be controlled.

In some examples ihe temperalure o1 Ihe solar energy collector assembly 102 may he controlled by changing the amount of solar energy incident on the solar energy collector assembly 102, and so changing ihe rate of absorption of heal energy by the solar energy collector assembly 102.

Tn some examples the amouni of incideni solar energy may he controlled by changing ihe orientation of Ihe solar energy collecior assembly relalive to Ihe direclion o1 Ihe incident solar energy. This can he carried oul using a drive mechanism able Lo rotale the solar energy collcctor assembly about onc or more axcs.

In some examplcs the amount of incidcnt solar cnergy may be controllcd using adjustable light intcrcepting or blocking mechanisms in thc path of the incident solar encrgy. In some examples variablc filtcrs, shutters, stops, or thc likc may be uscd. In somc examples these adiustable light intercepting or blocking mechanisms may comprise physical devices. In some examples these adjustable light intercepting or blocking mechanisms may comprise devices having electronically controlled oplical characteristics, such as liquid crystals.

In examplcs where the temperature of the solar energy collector assembly and/or the pholovoltaic elements are to he controlled, a temperature sensor and a temperature controller may be provided, togcthcr with a tcmpcrature control mechanism arrangcd to carry out one, some, or all, of the methods of controlling temperature described above.

the temperature sensor is arranged to measure the temperature of the solar energy collector assembly and provide this temperature value to the temperature controller. The temperature controller can then operate the temperature control mechanism in a suitable manner to control the temperature of the solar energy collector assembly to the desired value.

Examples where the temperature of the photovoltaic elements is to he controlled a temperature sensor arranged to measure the temperature of a photovoltaic element or elements and provide this temperature value to the temperature controller may he provided. This may he additional to, or instead of, the Lemperature sensor arranged Lo measure the temperature of the solar energy collector assembly. The temperature controller can then operate the temperature control mechanism in a suitable manner Lo conLrol the temperature of the photovoltaic element or elements to the desired value.

In some examples the Lemperature sensor can he provided on Lhe upper surface of the solar energy collector assemffly. In some examples Lhe temperature sensor can he formed on the same semiconducLor wafer as a photovolLaic element.

Conveniently, the temperature controller may be a suitably programmed general purpose computer.

The illustrated first embodiment is a hybrid solar energy converter comprising photovoltaie elements and arranged to convert incident solar radiation into outputs of both electrical energy and hot water. In other examples the photovoltaic elements may be omitted to provide a solar energy converter arranged Lu converL incident solar radiation into an output @1 hot water.

Second Embodiment Tn a second embodiment a different arrangement of the tube lorming the first heat exchanger is used. Othcrwise, the sccond embodiment is substantially similar to the first embodiment.

Figure 13 shows a cut away plan view from below of a hcat transport element 104 according to the second embodiment with the outwardly projecting scction 110 removed, so that the heat exchanger 107 is visible.

As shown in Figure 13, in the second embodiment the heat cxchanger 107 comprises a cylindrical tube 133 which extends within the vapor manifold 111 along the entire length of the vapor manifold 111. the cylindrical tube 133 comprises a first straight section 133a forming the heat exchanger 107 which extends parallel to the sides of the vapor manifold 111, such as the upper surface 104a and the prolecting section 110, and extends through one end 108 of Lhe vapor mamlold ill, aiong the entire length of the vapor manifold lii, and through the other end 108 of the vapor manifold 111. A straight return section 1 33h extends behind the rear face of the heal transport dement 104 through the end cap 120 to the support element 106.

The lirst and second sections I 33a and I 33h are connected together by a curved secLion I 33c.

Tn use, the first fluid passes along the cylindrical tube 133 as indicated by the arrows in figure 13, so that the first fluid passes through thc first straight section 133a, the curved section 133c and the second straight section 133b, so that the first fluid passes through the cylindrical tube 119, and travels along substantially the entire length of the vapor manifold 111.

In the illustrated example the first and second sections 133a and 133b of the cylindrical tube 133 are arranged one above the other and the first fluid enters through the first section 133a and leaves through the second section 133h. In other examples the direction of flow of the lirsi Iluid may he reversed. In other examples Ihe lirsi and second seclions 133a and 133h may be differently arranged.

Similarly lo ihe lirsi embodiment, in other examples ihe lube I 33 may he shapes olher ihan cylindrical, in somc examples thc tubc 133 may havc an elliptical cross section. in some examples the cylindrical tube 133 may have a different cross sectional shape at different positions. For example, the first straight section 133a may have an elliptical cross section, while the second straight section 133b and the curved section 133e may have a circular cross section.

in different examples the size of the tube 133 may be varied. However, the tube section 133a should not entirely fill the vapor manifold 111. if there is insufficient free space within the vapor manifold 111 to allow the water vapor and liquid water to freely circulate this may adversely affect the operation of the heat transport element 104.

in the illustraled example ihe lube i 33 is made from mild steel. In some examples ihe tube 133 and the heat transport element 104 maybe formed of other materials.

in some examples, different materials may he used for the tube 133 and the heat transport elemeni 1 04. in such examples, since Ihe Lube section 1 33a is connected al hoih ends to ihe heal transporL elemenl 104, it may he necessary to lake diFFerential ihermal expansion of ihe lube 133 and the heal lransporL element i04 mb account when selecting maLerials. In such examples where diFFerent malerials are used, lhe lube 133 and/or one or both oF ihe end Faces 108 of the vapor manifold 111 could be formed with flexible elements to allow relative movement of the tube 133 and the heat transport element 104 in order to accommodate differential thermal expansion. Such flexible elements could be formed from the material of the tube 133 and/or the end faces 108, or could be separate components. This may allow a wider range of materials to be used. Such flexible elements could be formed at one or both ends of the heat transport element 104. In one example the flexible element could be provided by forming a bellows arrangement in the wall of the tube 133.

Third Embodiment In a third embodiment a different anangement of the tube forming the first heat exchanger is used. Otherwise, the Ihird embodiment is substantially similar to the first embodiment.

Figure 14 shows a cut away plan view from below of a heat transport element 104 according to the third embodiment with the outwardly projecting section 110 removed, so that the heat exchanger 107 is visible.

As can be best seen in Figure 14, the heat exchanger 107 is comprises a cylindrical tube assembly 134 which extends within the vapor manifold 111 along substantially the entire length of the vapor manifold 111. the cylindrical tube assembly 134 comprises an inner concentric tube 134a and an outer concentric tube 134h. fle tube assembly 134 is shown in cross section in Figure 14, to allow the both of the concentric tubes 134a and 134h to be seen.

The inner and outer concentric tubes 134a and 134h run parallel to the sides of the vapor mamlold iii, such as Ihe upper surface l04a and Ihe projecting section itO, and extend along substantially the entire length of the vapor manifold 111. The outer concentric tube 1 34h extends slightly further than the inner concentric Lube 1 34a, the outer concenlric Lube I 34h is sealed by an end cap 134c, and the inner concentric tube 134a is open ended, so that the inner and outer concentric tubes 1 34a and 1 34h form a sing'e Iluid flow path.

Tn use, the first fluid passes through the cylindrical Lube assembly 134 as indicaled by the arrow-s in figure 14, so that the first fluid passes through Lhe inner concentric tube I 34a along substantially the entire length of the vapor manifold 111, then moves outwardly into the outer concentric tube 134b, and travels through an annular channel 134d defined between the inner concentric tube 134a and the outer concentric tube 134b back along substantially the entire length of the vapor manifold 111.

The water vapor in the vacuum within the vapor manifold 111 condenses on the outer surface of the outer concentric tube 134h and transfers heat energy from the heat transfer element 104 to the First Iluid within the lube assembly 134.

In thc illustrated cxample the first fluid enters through the inner concentric tube 134a and leaves through Ihe annular channel 1 34d. In other examples the direction ol flow ol the first fluid may be reversed.

in the illustrated example of the first embodiment the tube 119 is cylindrical. In other examples different tube shapes may be used. In some examples a tube 119 having an elliptical cross section may be used. Tie use of an elliptical tube may increase the heat exchange area formed by the exterior of the tube 119 where the water vapor condenses, which may improve the heat transfer rate between the water vapor and the fluid within the tube 119.

in different examples the size of the tube assembly 134 may be varied. however, the tube assembly 134 should not entirely fill the vapor manifold lii.

in the illustrated example of the third embodiment the lube assembly 134 is made from copper. In other examples different materials may he used. The tube assembly 134 is connected at only one end to the heal transport element 104, with the other end being free to move relative to the heat transport element 104. Accordingly, differential thermal expansion oF the tube assembly 134 and the heat Iransport element i 04 is not generally a problem and will generally not need to he considered when selecting materials.

Fourth Embodiment in a fourth embodiment a different arrangement of the tube forming the first heat exchanger is used. Otherwise, the fourth embodiment is substantially similar to the first embodiment. [he fourth embodiment may be used in examples where the tube 103 has an end cap 120 at each end.

Figure 15 shows a cut away plan view from below of a heat transport element 104 according to the fourth embodiment with the outwardly projecting section 110 removed, so that the heat exchanger 107 is visible.

As shown in Figure 15, in thc fourth cmbodimcnt thc hcat cxchangcr 107 comprises a cylindrical tube i35 which exiends within (be vapor manilold ill along ihe entire lengih of thc vapor manifold 111. ihe cylindrical tubc 135 compriscs a straight scetion 135a forming thc hcat cxchangcr 107 which cxtcnds parallcl to thc sidcs of thc vapor manifold 111, such as thc uppcr surfacc 104a and thc projecting scction 110, and cxtcnds through onc cnd 108 of thc vapor manifold 111, along thc cntirc length of thc vapor manifold 111, and through thc othcr cnd 108 of thc vapor manifold 111.

At cach cnd of thc straight scction 135a a rcspcctivc connccting scction 135b of thc tubc 135 cxtcnds through thc cnd cap 120 at cach cnd of thc tubc 103 to a support structurc, such as thc support element 106.

In use, the first fluid passes along the cylindrical tube 135 as indicated by the arrows in figure 14, so thai the lirst Iluid passes through the lirst siraighi seclion I 35a and travels along substantially the entire length of the vapor manifold 111.

Similarly to the first embodiment, in other examples the tube 135 may be shapes other than cylindrical. In some examples the tube i35 may have an elfipiical cross section. In some examples ihe cylindrical tube 135 may have a diftereni cross seciional shape at dilTerent positions. For example, (be firsi siraight seclion 1 35a may have an elliptical cross seclion, while ihe connecling sections I 35h of ihe tube 135 have a circular cross section.

in diffcrcnt cxamplcs thc sizc of thc tubc 135 may bc varicd. Howcvcr, thc tubc scction 135a should not cntircly fill thc vapor manifold 111. If thcrc is insufficicnt free spacc within thc vapor manifold 111 to allow thc watcr vapor and liquid water to frccly circulate this may advcrscly affcct thc opcration of thc hcat transport clcmcnt 104.

In the illustrated example the tube 135 is made from mild steel. In some examples the tube and Ihe heat Iransporl e]emenL 104 maybe formed of other malerials.

In some examples, different materials may bc used for the tube 135 and thc heat transport elemeni 1 04. In such examples, since Ihe Lube section 1 35a is connected al both ends to the heat transport element 104, it may bc necessary to take differential thermal expansion of the tube 135 and the heat transport element 104 into account when selecting materials, in such examples where differcnt materials are used, the tube 135 and/or onc or both of the end faces 108 of the vapor manifold 111 could be formed with flexible elements to allow relative movement of the tubc 135 and the heat transport element 104 in order to accommodate differential thermal cxpansion. Such flexible elcments could bc formed from the material of the tubc 135 and/or thc cnd faces 108, or could be separate components. Ibis may allow a widcr range of materials to be used. Such flexible elements could bc formed at onc or both ends of the heat transport element 104. k one example the flexible element could be provided by forming a bellows arrangement in the wall of the tube 135.

As show-n in ligure 15, Lhe connecting sections I 35h of Lhe Lube 135 are bent Lhrough bends or elbows. These bends may provide flexibility or "give" in order to accommodate differential thermal expansion of Lhe heat transport elemenL I 04 and tube 135 and the Lube 1 03. In oLher examples different means to accommodate differential thermal expansion may be provided.

Filth EmhodimenL Apparalus according to a 111th embodiment ol' Lhe preseni invention is iflustraLed in Figure 16.

Figure 16 show-s a general exterior view of a I'ifih emhodimenL of a hybrid so'ar energy convcrter 201 according to the present invcntion.

Overview In the fifth embodimcnt, the hybrid solar cnergy convcrter 201 includes a solar cnergy collector assembly 202 housed within a scaled transparcnt tube 203. the solar encrgy collector assembly 202 includes a heat transport element 204 and an array of photovoltaic elements 205 mounted on an front surface of the heat transport element 204, the front surface being the surface exposed to incideni solar radiation in use. The hybrid solar energy converter 201 also includes a support assembly 206 at one end of the transparent tube 203. One end of the solar cncrgy collector assembly 202 is connccted to the support assembly 206. Similarly to the!irst embodimeni, in diftereni examples the pholovoltaic elemenls 205 may he lormed of silicon, or gallium arscnide, or other suitable semiconductor materials, in other examples organic photovoltaic elcments may be uscd. in other examples hybrid photovoltaic elements may bc used.

In thc fifth embodiment, the support assembly 206 supplies a first fluid to a heat exchanger 207 arrangcd to transfcr heat encrgy from the heat transport element 204 to the first fluid.

In onc possible example, in use the hybrid solar energy converter 201 may be mounted on a wall. Accordingly, suitable mounting brackets maybe provided.

In overview, the operation of the hybrid solar energy converter 201 of the fifth embodiment is similar Lo operalion ol' Lhe hybrid solar energy convener 101 of the Iirst emhodimenL. Solar energy incident on the hybrid solar energy converter 201 passes through the sealed transparenL tube 203 and is incident on Ihe photovollaie dements 205 oF Lhe solar energy collector assembly 202. The photovoltaic elements 205 convert a part of the energy of the ineideni solar energy into elecLrieal energy, and converi a pan ol' Lhe energy of Lhe incident solar energy into heat energy. A further pan of Ihe incident solar energy may he incident on any paris ol' the solar energy collecior assembly 202 which are nol covered by the phoLovoltaic elemenis 205, and this I'uriher part ol' the incident solar energy may also he converted into hcat energy.

In general, it is desirable to maximize the proportion of the surface of the solar encrgy collcctor assembly 202 exposed to incidcnt solar encrgy which is covcrcd by the photovoltaic elements 205, and to minimize the proportion which is not so covcred. However, in some circumstances it may be preferred to leave some parts of this exposed surface uncovered, for example to simplify manufacture and/or assembly of the solar energy collector assembly 202 and atiachmenl of ihe photovollaic elements 205 lo the solar energy collecior assembly 202.

Thc clcctrical cncrgy produccd by thc photovoltaic elcmcnts 205 is carried along thc hcat transporl element 204 by electrical conduciors and away from ihe solar energy convener 201 for use. the hcat cncrgy absorbed by the photovoltaic elcments 205 is transferred into thc hcat transport clement 204, cooling the photovoltaic elements 205, and then transferred into the first fluid by the heat exchanger 207.

In one typical arrangement, the hybrid solar energy convertcr 201 may be used to gencrate electricity, and to gcneratc hot water. Similarly to the first embodiment, in this alTangement the first fluid is water and thc hcat energy iransfcrrcd to the heat exchanger 207 is transferrcd into a pumped water supply flowing through the heat exchanger 207 to heat thc water. this heated water is then used by a domestic or industrial hot water system, and the electrical energy produced by the photovoltaie elements 205 is supplied to an electrical supply system.

Transpareni lube In the fifth embodiment illustrated in Figure 16 the sealed transparent tube 203 is similar to the sealed Iransparent Lube 103 of ihe first embodimeni, having one dosed domed end and one open end sealed by an end cap 220. The interior of the tube 203 is at least partially evacuated. Thai is, the interior of the lube 203 is below normal aimospheric pressure.

The pressure of the vacuum wiihin the tube 203 may he 1 ft3 mhar. Other pressures may he used, as discussed regarding the firsi emhodimenL Tn some examples ihe vacuum pressure may be in the range 1112 mbar to i0 mbar. in general, it is expected that lower vacuum pressure, or in other words a hardcr vacuum, will provide greater insulating benefits. Further, it is cxpected that lowcr vacuum pressurc, or in othcr words a harder vacuum, will provide greater proiection from cnvironmental damage in cxamples where thc photovoltaic elements are not encapsulated. In practice thc benefits of using a lower vacuum pressure may need to he balanced against the increased cost of achieving a lower vacuum pressure. In some examples a vacuum pressure of 102 mhar, or lower, may he used.

In an alternative example the sealed transparent tube 203 may he filled with an inert gas instcad of bcing cvacuatcd. in particular, thc incrt gas may bc nitrogen.

In another alternative example the sealcd transparent tubc 203 may be filled with an inert gas at a rcduced pressurc. in some examples this may be achieved by filling the tube 203 with the incrt gas and then evacuating the tubc 203. in particular, the inert gas may bc nitrogen.

In the illustratcd fifth embodiment thc tubc 203 is cylindrical having a circular cross section.

Similarly to the first and second embodimcnts, in alternative examples the tubc 203 may have other shapes. in some cxamples the cross sectional size and/or shapc of the tube 203 may vary at different positions along its length. in an alternative example the tube 203 may have an elliptical cross section. In particular, the tube 203 may have an elliptical cross section with the long axis of the ellipse aligned with the plane of the solar energy collector assembly 202.

In Ihe illusiraled fifth embodiment the Luhe 203 is formed of glass. in allernative examples suitable transparent plastics materials or laminated structures may he used to form the tube 203.

In the illusirated Iifih embodiment Ihe lube 203 is LransparenL in alternalive examples ihe tube maybe only parlially Iransparenl.

In the illusiraled filth emhodimenL the melal end cap 220 maybe bonded Lu ihe glass lube 203 by adhesive, in other embodiments alternative glass to metal bonding techniques may be used, for example welding, brazing or soldering.

Similarly to the first embodiment the tube 203 has a metal end cap 220 at one end. in alternative examples the end cap 220 may be made of other materials. In some examples the end cap 220 may he made of glass. This may reduce conductive heat losses from the collector assembly 202.

Collector assembly In thc fifth cmbodiment, thc solar cncrgy collector assembly 202 includes a hcat transport elemeni 204 and an array of phoLovoltaic elemenLs 205 mounted on one surface of the heat transport elcment 204. In ordcr to allow radiant solar cncrgy to be incidcnt on thc photovoltaic elements 205 thc array of photovoltaic elements 205 are mounted on the surface of the heat transport element 204 which is exposed to the incident radiant solar energy in operation of the hybrid solar energy converter 201. In the fifth embodiment the heat transport element 204 may be mounted vertically. h examples where the heat transport element 204 is not mounted vertically the surface which is exposed to the incident radiant solar energy in operation will usually be the upper surface of the heat transport element 204.

In some alTangements the surface of the heat transport element 204 exposed to the incident radiant solar energy may not be the upper surface. In particular, this would be the case if the incident solar radiant energy was incident horizontally or from below, for example after redirection by an opLical syslem such as a mirror.

Tn the illusiraLed example of Lhe!iith embodimenl, Lhe solar energy colleclor assembly 202 is supported by cylindrical tubes 234 of the heat transport element 204. The cylindrical tubes 234 pass ihrough the end cap 220 and mb the supporl assembly 206, as will be explained in more detail below. Where the cylindrical Lube 234 passes through the end cap 220 ihe cylindrical lube 234 is soldered 10 Lhe end cap 220 Lu reLain Lhe cylindrical lube 234 in place and supporl Lhe solar energy coflecLor assembly I 02.

The cylindrical tubes 234 are assemblies comprising inner and outer concentric tubes 234a and 234b, similarly to the heat exchanger arrangement according to the third embodiment. In alternative examples the heat exchanger arrangements according to the first, second or fourth embodiments may be used instead.

In alternative examples the cylindrical tubes 234 may he secured to the end cap 220 in other ways. In one example ihe cyfindrical luhes 234 maybe welled 10 ihe end cap 220.

ihc supporting of the solar encrgy collector assembly 202 by physical connections through Ihe cylindrical Luhes 234 may increase Ihe efficiency with which heal can he coflecled Irom incident solar energy by the solar energy collector assembly 202. Having the solar energy collector assembly 202 supportcd by physical connections only through the cylindrical tubes 234 may reduce conductive heat loss from the solar energy collector assembly 202 into the supporting structure outside the transparent tube.

in thc illustrated example of the fifth embodiment the heat transport element 204 has a substantially fiat front surface 204a. Each of the photovoltaic elements 205 is squarc, and the width of the hcat transport element 204 is the same as the width of each squarc photovoltaic element 205. Six square photovoltaie elements t05 are mounted side by side to one another along the length of the heat transport element 204. Substantially the entire front face of the heat transport element 204 is covered by the photovoltaic elements 205. Covering a large proporlion of ihe upper surface 204a of the heal Iransport element 204 wilh pholovollaic elements 205 may increase the efficiency of the hyhrid solar energy converter 201.

In one example the square photovoltaie elements 205 may each he a 125mm by 125mm square and 0.2mm Ihiek. in anoiher example the square photovoltaic elemenls may each he a 1 56mm by 1 56 mm square. In other examples, photovoltaic elemenls having other sizes or shapes maybe used.

The photovoltaic elements 205 are hondcd to the substantially flat upper surface 204a of the heat transport element 204 using a layer of heat conducting adhesivc in a similar manncr to the first embodiment. the adhesive bonding layer is electrically insulating. the adhesive bonding layer between the photovoltaie clements 205 and the heat transport element 204 is arranged to be thin, this may improve the degree of thermal conduction between the photovoltaic elements 205 and the heat transport element 204. This may increase the rate of heat transfer laterally across the photovoltaic elements 205. An adhesive material loaded with solid spheres of a predetermined site may he used In lorm the adhesive honding layer. This may allow a thin adhesive layer to be consistently and reliably formed. The adhesive bonding layer is formed of a flcxible or "forgiving" adhcsive material, this may relieve strcsses in the assembled solar energy colleelor assembly 202 and reduce any siress applied lo ihe photovoltaic clcmcnts 205.

Thc photovoltaic elements 205 are scmiconductor photovoltaic clcments formed of silicon, in one embodimcnt the photovoltaic elcments are formed of single-crystal silicon, in one cmbodiment the photovoltaic clemcnts are formed of amorphous silicon. In one embodiment the photovoltaic elemcnts are formed of polycrystalline silicon, or polysilicon. in other cmbodiments alternative typcs of semiconductor photovoltaic elcments may be used.

Similarly to the first embodiments, in operation of the hybrid solar energy converter 201 the photovoltaic elements 205 are cooled by the heat transport element 204, which may provide similar advantages to those discussed above. This cooling may allow the temperature of the pholovoltaic elements 205 lo he mainlained at a desired value.

This cooling may provide the advantage that Ihe appearance oF hol spols or regions in the photovoltaic elements 205 can he reduced or eliminated, and the temperature of the pholovoltaic elements 205 mainlained al a uniForm desired value. Such hot spots or regions may br exampk he produced by healing hy incident solar radiation, by inhomogeneilies or faults in the pholovoltaic elemenls 205, or by a eomhinaiion of, or interaction heiween, these causes.

As discussed above regarding the first cmbodiment, such hot spots or regions can reducc the cfficiency of the photovoltaic elements 205 in the short term, and may also degrade the performance of the photovoltaic elemcnts 205 in the longcr tcrm.

Accordingly, maintaining the photovoltaic elements 205 at a more uniform temperature value and reducing, or eliminating, hot spots or regions may improve the efficiency of the pholovoltaic elements 205 al a specilic temperalure, and may reduce ihe amouni of degradation of the photovoltaic elements 205 caused by higher temperatures.

This may allow the pholovohaic elements 205 Lo operale at a higher overall Lemperature than would otherwise bc thc case, for the samc reasons as discussed rcgarding the first embodiment.

Thc illustrated example of the fifth embodimcnt has a solar cnergy collector assembly 202 supported only by physical conncctions through thc cylindrical tubes 234. In other examples alternative supporting arrangements may be uscd. in some examples the solar cnergy collector assembly 202 may be supportcd by a physical connections both ends of the solar energy collcctor assembly 202. In some examples, thc physical connections at one cnd of thc solar energy collector assembly may he the through the cylindrical tubes 234. In general, it is advantageous to minimize the number of physical supports in order to minimize the escape of heat from the solar energy collector assembly by conduction through the physical supports.

In other examples the number of photovoltaic elements 205 mounted on the heat transport elemeni 204 may he dilTerent. in olher examples Ihe relalive sites of the phoLovollaic elements 205 and the heat transport element 204 may he different.

In some examples Ihe adhesive layer may comprise an epoxy resin which remains non-bnltle alter curing.

In other examples the adhesive laycr may be formcd by a double sided adhesive tapc.

Heat transport element Thc heat transport element 204 according to the fifth embodiment is shown in more detail in a cut away view in Figurc 17.

In the fifth embodiment, the heat transport element 204 is generally rectangular. The heat transport elemenl 204 has a hat front surface 204a and a rear surface 204h which is hIal across most of its area, and has three outwardly projecting sections 210 spaced out along its length, with a first outwardly projecting section 210 at an upper end of the hcat transport element 204, a second oulwardly projecting section 210 localed one Ihird of the way along the lengLh ol the heat transport element 204, and a third outwardly projecting section 210 located two thirds of the way along thc length of the heat transport element 204.

The hcat transport element 204 is divided into three sections, an upper section 204c, a central section 204d, and a lower section 204e. Each section 204c to 204e is cooled by a separate density driven circulation acting as a hcat transport mechanism similar to the mechanism of the sccond embodiment and comprising a respcctive one of the three outwardly projecting sections 210. Each of the three scctions 204c to 204e supports and cools two of the six photovoltaic elements 205.

Each outwardly projecting section 210 contains and defines an elongate heat transfer chamber or vapor marnlold 21 I exiending subsianlially Irom one side to Ihe olher of the heat Iransport element 204. In operation the heat transport element 204 is arranged to he longitudinally sloping, so thai the heal Iransport element 204 has an upper end and a low-er end. The heat transport element 204 may be arranged longitudinally vertically, or at an angle to the vertical.

The heal transport element 204 has a Ironl surface 204a Formed by a Ironi sheet 21 4 and a rear surface 204h lormed hy a rear shed 215. Three cenlral sheds 216 are localed heiween the Ironi shed 214 and Ihe rear shed 215, with one of Ihe central sheets 216 in each oh the sections 204a to 204e, so that fluid flow passages 217 and 21S runrnng longitudinally along the heat transport element 204 are defined between each central sheet 216 and each of the front sheet 214 and the rear sheet 215. Since the heat transport element 204 is longitudinally sloping the fluid flow passages 217 and 21S running longitudinally along the heat transport element 204 will be sloped along their lengths.

Each central sheet 216 has a similar profile to the central sheet 116 of the first embodiment, except that, compared to the second embodiment, the profile of the central sheets 2 16 of the third embodiment is rotated through 900 to define flow channels running longitudinally along the heat transport clcment 204. Ihe cross-sectional profilc of the corrugated ccntral shccts 216 can he understood as a fig-/ag prolde with the poinis of the fig-/ag lorming the peaks and troughs being flattened.

To bc morc spccific, in the illustrated cxample of thc fifth embodimcnt the central sheets 216 each comprise a plurality of flat surfaces connected by folds running longitudinally along the heat transport element 204. Accordingly, thc front, rear, and central shccts 214, 215, 216 define a plurality of trapezoid cross-section front fluid flow channels 217 and rear fluid flow channels 218 bctween thcm. the front fluid flow channels 217 are defined between the front sheet 214 and the central sheets 216. the rear fluid flow channels 218 arc defined betwcen the rear sheet 215 and the central sheets 216. the trapezoid front fluid flow channels 271 are arranged so that the larger one of the two parallel faces of each trapezoid channel 217 is formed by the upper sheet 214.

The front and rear fluid flow channels 217 and 218 of the fifth embodiment respectively correspond in lunction to the upper and thwer fluid flow channels I 17 and I I S of the second embodiment.

The edges of the heal transport element 204 are lormed by bent parts of the rear sheet 2 15, which are bonded to the front sheet 214. The photovoltaic elements 205 are bonded to the front sheet 214. Al the edges of the heat transport element 204, the front sheet 214 is bonded dircctly to the rear sheet 215, the central shcets 216 are not located between the front and rear sheets 214 and 215 at their edges.

In some examples thc central sheets 216 may cxtend at least partially bctwccn the front and rear sheets 214 and 215 at the side edges of thc hcat transport element 204 so that the front and rear sheets 214 and 215 are both bonded to the central sheets 216. This may assist in locating and securing the central sheets 216 relative to the front and rear sheets 214 and 215.

As discussed above, the heat transport element 204 has three outwardly prolecting sections 210 cach running transversely across thc rcar surfacc 2Mb of the heat transport clcmcnt 204.

Each outwardly projecting section 210 is subsianlially semi-cylindrical and is Formed by an outwardly projecting part of the rear shcet 215. Each outwardly projecting section 210 defines a vapor manifold 211. The fluid flow channels 217 and 218 connect to the vapor manifolds 211. it should be notcd that the central shccts 216 extend across most of thc width of the vapor manifolds 211. Accordingly, the front fluid flow channels 217 dcfincd between the front shcct 214 and thc central sheets 216 conncct to the vapor manifolds 211 towards the top of each vapor manifold 211, while the rear fluid flow channels 218 defined betwccn the rear sheet 215 and thc central sheets 216 connect to the vapor manifolds 211 towards the bottom of each vapor manifold 211.

The front and rear fluid flow channels 217 and 218 are formed into three groups with the front and rear fluid flow channels 217 and 218 of each group interconnected by one of the vapor manilolds 211. Each group of Iluid how channels 217 and 218 extends along one of Ihe sections 204c to 204e of the heat transport element 204 and, together with the vapor manifold with which Ihey are connected, lorms a separale heat Iransport mechanism coohng Ihe respective section 204c to 204e of the heat transport element 204.

Figure 17 is an explanatory diagram showing a thngitudinal cross seclion of a part of Ihe heat Iransport elemenl 204 along the line D-D in Figure 16. Figure 17 shows the section of the heat Iransport element 204 around the houndary hetween Ihe ceniral section 204d and the thwer section 204e. The boundary between thc central section 204d and the upper section 204c is identical.

At the top of the lower section 204e of the heat transport element 204, at the top of the outwardly projecting section 110, there is a wall 231 extending transversely across the interior of the heat transport element 204. The wall 231 contacts and is bonded to the front and rear sheets 214 and 215 and forms a fluid tight seal between the fluid flow channels 217 and 218 of the central section 204d of ihe heat Iransport elemeni 204 and ihe Vapor marnlold 211 of the lower section 204e of the heat transport element 204. The walls 131 divide the interior of thc hcat transport clcmcnt 204 into thrcc scparate fluid circulation rcgions corrcsponding to ihe sections 204c Lo 204e of the heal Iransport element 204.

Thcrc is a gap 223 bctwccn thc cdgc of thc ccntral shcct 216 of thc ccntral scction 204d of thc hcat transport clcmcnt 204 and thc wall 231. this gap 223 allows watcr to flow bctwccn diffcrcnt oncs of thc fluid flow channcls 217 and 218. Thc gap 223 extends along thc sidc wall 231, and forms a fluid manifold 224 intcrconnccting all of thc front and rcar fluid flow channcls 217 and 218 of thc ccntral section 204d.

in thc fourth cmbodimcnt thc hcat exchanger 207 compriscs a cylindrical tubc asscmbly 234 which extends within the elongate heat transfer chamber or vapor manifold 211 along substantially the entire length of the elongate heat transfer chamber or vapor manifold 211.

The cylindrical tube assembly 234 comprises an inner concentric tube 234a and an outer concentric lube 234h. The inner and ouler conceniric luhes 234a and 234h run parallel to the sides of the vapor manifold 211, such as the upper surface 204a and the projecting section 210, and exiend along subslanlially the entire lenglh of the vapor manilold 211. The outer concentric tube 234b extends slightly further than the inner concentric tube 234a, the outer concentric lube 234h is sealed by an end cap, and Ihe inner conceniric Lube 234a is open ended, so thai ihe inner and outer concentric luhes 234a and 234h form a singk fluid how path.

in usc, thc first fluid passcs through thc cylindrical tube assembly 234, so that thc first fluid passcs through thc inncr conccntric tubc 234a along substantially thc cntirc lcngth of the vapor manifold 211, then movcs outwardly into thc outcr conccntric tube 234b, and travcls through an annular channcl 234d defined between the inncr concentric tubc 234a and thc outer concentric tubc 234b back along substantially the cntire length of the vapor manifold 211.

At each edge oF ihe heat lransporl element 204 Ihe suhslanliafly semi-cylindrical outwardly prolecting section 210 extending most of the width of the heat transport element 204 is closed by an end wall 20S. The uppcr and lower sheets 214 and 215 are sealcd by the cnd walls 20R so that ihe inlerior of the heal transporl elemenl 204 is sealed. The cylindrical lube 234 passes through the end wall 20S and the end cap 220 and into thc support assembly 206. Each cylindrical tube 234 within the vapor manifold 211 forms a heat cxchanger 207 and acts to caiy heat energy from part of thc hcat transport element 204 away from thc hybrid solar cnergy converter 201, as will be explaincd bclow.

Thc cylindrical tubes 234 physically support the solar energy collector assembly 202 within the sealed transparent tube 203. Therc is no other physical support of the solar encrgy collcctor asscmbly 202. As in thc prcvious embodimcnts this may reduce conductivc hcat losses from the solar energy collector assembly 202, which may increase the amount of useful heat energy produced by the hybrid solar energy converter 201.

The fluid how channds 217 and 2! 8 are al easl partially hUed wiih degassed distilled waler 221 as a working fluid and the interior of the heat transport element 204 including the fluid how channels 217 and 218 and ihe vapor maniFolds 21! are al kast parliafly evacualed. That is the interior of the heat transport element 204 is below normal atmospheric pressure. The intenor of Ihe heal Iransporl elemenl 104 maybe under a vacuum at a pressure oil -3 mhar.

Tn the Filth emhodimenl Ihe amounl oF waler 221 in Ihe Iluid how channels 217 and 2!8 is similar lo ihe hirsl emhodimeni excepl that Ihe inlerior of each of Ihe seclions 204c to 204e is sealcd off from the others so that the level of the water 221 is independent in each of the sections 204c to 204e of thc heat transfer element 204.

In each of the three scctions 204c to 204e the level of the watcr 221 in the fluid flow channcls 217 and 218 is such that the upper surface of the water 221 in the rear fluid flow channcls 218 is level with the ends of the rear fluid flow channels 218 where they connect to the vapor manifold 211. In the illustrated fifth embodiment the level of the surface of the water 221 in the Ironi Iluid flow channels 217 and rear Iluid how channels 218 is the same. Accordingly, in the illustrated fifth embodiment the rear fluid flow channels 218 are filled with liquid water, while thc front fluid flow channcls 217 are only partially filled with liquid watcr.

Similarly to the first embodiment, in other examples the level of the water 221 may be diffcrent. in somc cxamplcs the upper surface of thc water 221 in the rcar fluid flow channcls 218 may be bclow thc vapor manifold 211. h some examples the upper surfacc of the water 221 in the rear fluid flow channels 218 may be above the bottom of thc vapor manifold 211, with somc watcr being prcsent in the bottom of the vapor manifold 211.

it is expected that in practice thc heat transport clemcnt 204 will operate most cfficiently with the upper surface of the water being at, or close to, the point wherc thc lower fluid flow channels 218 contact the vapor manifold 211. If the level of the water in the heat transport element 204 is too high, so that the upper surface of the water is too high within the vapor manifold 211, the efficiency of operation of the heat transport element 204 may he reduced, br the same reasons as are discussed regarding Ihe first embodiment.

The upper surface oh Ihe water 221 in the Ironi hluid flow channds 217 may he higher Ihan in the rear fluid flow channels 218 as a result of capillary action. The extent of this capillary cued in any specilic exampk will depend upon Ihe dimensions of Ihe Ironi hluid how channels 217. In the iflusiraled IiITh emhodimeni some olihe inner surface ol the upper shed 214, thaI is, Ihe surface lorming a part @1 the upper Iluid flow channels 217, is above the surFace oF Ihe water 221. In some examples Ihe Front Iluid flow channels 217 may have a small enough cross-sectional area that the uppcr surfacc of thc watcr 221 in the front fluid flow channels 217 is at the ends of thc front fluid flow channcls 217 duc to capillary action.

Similarly to the first cmbodiment, it is not ncccssary that the inner surface of thc front sheet 214, that is, the surface forming a part of the front fluid flow channels 217, is below the surface of the water 221 at a position corresponding to the location of the uppermost parts of the photovoltaic elements 205 for each of the sections 204c to 204e of the heat transport elemeni 204. How-ever, in some emhodimenls ibis may he the case.

In opcration of thc fifth cmbodimcnt, whcn thc solar cncrgy collector assembly 202 is exposed Lo incideni solar radialive energy, Ihe pholovoltaic elemenls 205 ahsorh some of Ihis cncrgy, convcrting a part of thc absorbcd energy into electrical energy. the remainder of thc absorbed cncrgy is converted into hcat cncrgy, raising thc temperature of thc photovoltaic elements 205. The absorbcd hcat cncrgy flows from thc photovoltaic elcments 205 into thc hcat transport clcmcnt 204, bcing transmitted through thc front shcct 214 and into thc watcr 221 insidc thc front fluid flow channels 217, which watcr is in contact with the inncr surface of the front metal shcct 214 across thc largcr parallel faces of the trapezoid front fluid flow channcls 217.

the liquid water 221 inside the front fluid flow channels 217 absorbs the heat energy from the photovoltaic elements 205 passing through the front sheet 214 and vaporizes, producing bubbles 222 of steam or water vapor. At the vacuum pressure of i03 mbar inside the front Iluid flow channels 217 waLer boils Irom around 0°C, so ihaL Lhe water 221 vaporizes readily at the normal operating temperatures of the hybrid solar energy converter 201.

As discussed above regarding the first embodiment, the bubbles 222 of water vapor are less dense Ihan the liquid waler 22!. Further, as explained above ihe I'ronL Iluid flow channels 117 are sloping along Lheir lengths. Accordingly, as a result of Lhis densily difference ihe water vapor bubbles 222 iravel upwards along Lhe fronL Iluid flow channels 217 towards ihe Lop of Lhe heal Lransporl dement 204 and the surface of the water 221. When a buhifie of water vapor 222 reaches the surface of the water 221 the vapor is released into the vacuum above thc water 221 in the respective vapor manifold 211. Further, the bubbles 222 will give rise to pistonic driving in a similar manner to the first embodiment. in the illustrated fifth embodiment, where some of the inncr surface of the upper sheet 214 is above the surface of thc water 221, this pumping of liquid water upwards along the upper flow channels 217 ensures that the part of the inner surface of the upper sheet 214 above the surface of the water 221 is in contact with a flow of water so that it can be cooled.

The bursting of the bubbles of water vapor at the water surface and any pistonic pumping of liquid watcr out of thc cnds of thc front fluid flow channels 217 may gencratc droplets of liquid waler, and may projecl at leasl some of ihese waler droplets mb the vacuum wilhin ihe rcspcctive vapor manifold 211 abovc thc water surface. As a rcsult, the heat transfer mechanism may be a multi-phase systcm comprising liquid water, water vapor and droplets of liquid watcr, and not just a two-phase system comprising liquid watcr and water vapor only.

The presence of such droplets of water in the vacuum, and any pumping of liquid water out of thc cnds of thc front fluid flow channels 217, may enhance thc rate of vaporization by incrcasing thc surface area of thc watcr cxposcd to the vacuum.

Similarly to thc first embodiment, the watcr vapor in the vacuum within the heat transfcr chamber or vapor manifold 211 travels at a very high speed through the vacuum within the vapor manifold 211 into contact with the exterior surface of the outer tube 234b forming the heat exchanger 207. The travel speed of the hot water vapor in the vacuum is very fast, approximating to the thermal speed of the water vapor mokcules. The water vapor condenses on the external surface of the outer tube 234h, which acts as a heat exchange surface. The condensed waler falls oil the ouber lube 234h to the bottom of ihe vapor mamlold 211, and is returned back into the water 221 within the lower fluid flow channels 218. This generating of hob water vapor within ihe upper fluid how channels 217 and ihe vapor manifold 211, and ihe condensing of the hob waler vapor on ihe ouber lube 234b, iollowed by return of Ihe condensed waler mb the iluid flow-channels 217 and 2! 8, transfers heat energy Irom Ihe heal transfer elemenb 204 to the first!luid within the tuhe 234.

Thus, the working fluid is causcd to circulate on a working fluid pathway insidc thc hcat transfer devicc such that the heat of thc working fluid is transferred to the heat exchangcr in thc heat transfer chamber. in the illustrated example the working fluid pathway is formed by the fluid flow channels 217 and 218 and the heat of the working fluid is absorbed from the cooled surface 204a of the heat transport element 204.

The lirsi Iluid Ilows from ihe support elemeni 206, ihrough the heat transfer elemenL 204, where it absorbs heat, and the heated fluid then returns to the support element 206. In the illustrated second embodiment the first fluid is water and a pumped water supply passes through the support element 206 and Lhe cylindrical Lube 234.

Any liquid water ejected from the front fluid flow channels 217 into a vapor manifold 211 which does not vaporize will also fall to the bottom of the respective vapor manifold 211, and is returned back into the water 221 within the rear fluid flow channels 218 associated with that vapor manifold 211.

The description indicates that water droplets and condensed water falls into the bottom of the vapor manifold 211. In some examples, depending upon the orientation of the collector assembly 202, some or all of this water may fall into the lower fluid flow channels 218 without necessarily contacting the surface of the vapor manifold 211.

The location of the heat exchangers 207 within the heal transfer chambers or vapor marniolds 211 may improve the efficiency of the heat transfer element 204 by providing a short path for water vapor to travel hetween the upper surface of the working Iluid and the heal exchanger 207.

As is explained above all of the froni and rear Iluid flow-channels 217 and 218 in each section 204c Lu 204e of the heat transfer element 204 are interconnected by the respective Iluid manilold 224 formed by the respective gap 223. Accordingly, within each section 204c to 204e of the heat transfer clement 204, it is not important which of the rear fluid flow channels 218 is entered by any liquid water returning from the respective vapor manifold 211.

As is clear from the description above, each heat transfer chamber or vapor manifold 211 generally includes liquid water in addition to water vapor when the hybrid solar energy converter 201 is operating. however, as is also discussed above, if the level of the water in a section 204c to 204e of the heat transport element 204 is too high, so that the upper surface of the waler is loo high wilhin the respective vapor manifold 211, the efficiency of operalion of the heat transport element 204 may be reduced. This reduction in efficiency of operation may S occur because thcrc is insufficicnt spacc within thc vapor manifold 211 abovc thc surfacc of Ihe waler br Ihe movement and evaporalion of the droplels oF liquid waler. This reduction in efficiency of opcration may occur because thc droplcts of liquid watcr and waves and splashing upwardly of the liquid water surface may reducc the open, or water free, cross sectional arca of thc vapor manifold at some locations to a relativcly small amount, or cven to zcro, momentarily closing the vapor manifold. This reduction in thc open, or water frce, cross sectional arca of the vapor manifold may interfere with the movcment of the watcr vapor in the vacuum within thc vapor manifold 211.

in a similar manner to the first embodiment the bubbles 222 of watcr vapor will tcnd to move upwardly through the liquid water in the front fluid flow channel 217 because of the lower density of the water vapor compared to the liquid water 221, which will result in an upward buoyancy force on each bubble 222. Further, the movement of the bubbles 222 of water vapor will lend lo drive the Uquid water 221 in Ihe Froni Iluid how channd 217 upwardly, particularly in examples where pistonic driving takes place. As a result, the bubbles 222 of water vapor cause Ihe waler 221 in the Fronl and rear fluid flow channels 217 and 218 in each section 204c to 204e to circulate, with relatively hot liquid water and bubbles 222 of water vapor flowing upwards along ihe front fluid blow channels 217, and relalively cool liquid water flowing downwards along Ihe rear Iluid how channels 218. The Fronl and rear hluid flow channels 217 and 218 are inierconnected by the vapor manihifid 211 and the hluid manihold 224, as explained above. According'y, Ihe relatively hot liquid waler hiowing upwards along the front fluid flow channels is continuously replaced by rclativcly cool liquid water from the rcar fluid flow channels 218. Ibis circulation is drivcn primarily by the difference in density bctwccn the water vapor and the liquid water. However, this circulation may also be drivcn by convection as a result of the diffcrcnce in density betwccn the relatively hot liquid water in the front fluid flow channels 217 and the relatively cool liquid water in the rear fluid flow channels 218, in a similar manner to a thermosiphon. Accordingly, the front fluid flow channels 217 may be regarded as riser channels, while the rear fluid flow channels 2! 8 may he regarded as sinker channels or relurn channels.

As the bubbics 222 of water vapor travel upwardly along the front fluid flow channcls 217 the pressure head acling on Ihe hubbies 222 decreases, so thai Ihe hubbies 222 lend Lu expand. As a rcsult, the tcndency of thc vapor bubbles 222 to collapse and implode is reduccd by the effccts of the expansion and decreasing pressure as the bubbles 222 move upwardly. When considering this point, it should bc remcmbered that when thc heat transport element 204 is operating thc bubblcs 222 will be forming within cstablished density driven circulation fluid flows and will movc upwardly carricd by thesc flows in addition to the bubbles movement due to their own buoyancy relative to thc liquid water. Further, it is believed that expansion of the bubblcs 222 as they movc upwardly will further increase the spccd of the density driven circulation flow by incrcasing the buoyancy of the cxpanding bubblcs 222. In some examples expansion of the hubbies as they move upwardly may also increase the degree of pistonic driving.

This densily driven circulation may lorm a highly elTeclive heal transporl mechanism because water has a relatively high enthalpy of vaporization, so that the movement of the hubbies 222 oF water vapor may carry a large amounl of heal energy, in addition Lu ihe heal energy carried by the movement of relatively hot water out of the front fluid flow channels 217, and its replacement by cooler water. In arrangemenls where pislonic driving of the how of the Uquid water by the waler vapor huhhles lakes phice ihe effecliveness of the heal Iransport mechanism may he lürther increased by Lhe increase in ihe flow rate of Ihe liquid waler caused by the pislonic driving. This pislonic driving is a componenl oF the overall densily driving producing the density driven circulation, the pistonic driving is causcd by the density diffcrence bctwccn the liquid water and the bubbles of water vapor.

In general, the spced of the density driven circulation increases and thc cffcctiveness of the heat transport mechanism increases as the temperature of the upper shcct 214 of thc hcat transport element 204 increases.

The density driven circulalion ol the waler 221 within the Iluid how channds 217 and 218 is a vapor driven circulating or rolling flow.

The density driven circulalion ol Ihe water 221 wiihin Ihe Iluid flow channels 217 and 218 becomes particularly vigorous, and becomcs particularly effective as a heat transport mechanism, when the tempcraturc of thc upper shcet 214 of the heat transport elcment 204 becomes sufficicntly high that thc watcr 221 within the fluid flow channels 217 and 21R enters a rolling boil state. Ic effectiveness of thc hcat transport mechanism significantly incrcases when rolling boiling of the water 221 commcnces. In general, when other parameters of the systcm remain constant, entry into thc rolling boil state will take placc when the tcmperature of thc front shcet 214 of the hcat transport elemcnt 204 rcaches a specific temperature.

In the illustrated examples using water, the water 221 within fluid flow channels 217 and 218 may enter a rolling boil state at a temperature of about 40°C.

The arrangement of the heat transfer element 204 into sections 204c to 204e with separate fluid flow channels 217 exiending along Ihe heal transporl elemeni 104 may allow the verlical height of the liquid water in each section 204c to 204e of the heat transport element 204 to he reduced compared to emhodimenls in which the densily driven how exiends athng the length oF a heal transporl elemenl, and so reduce the pressure head acting on the liquid waler al ihe hoitom oF the heal transporl elemenl 204. Tn general, increased pressure reduces the lendency oF liquids lo vaporize and so increases the boiling point oF liquids. Accordingly, reducing Ihe pressure head acting on the liquid watcr at the bottom of thc heat transport clcmcnt 204 may incrcase the tendency of the liquid water 221 in the front fluid flow channels 217 to vaporize and produce bubbles 222, and so may improvc thc efficicncy and effectivencss of the hcat transport element 204.

In particular, the reduction of the pressure head acting on the liquid water at the bottom of the front fluid flow channels 217 may reduce any temperature differential along the lengths of the front fluid flow channels helween their the iop and bottom ends by reducing any difference in the tendency of the liquid water to vaporize due to differences in pressure. This may reduce tcmperature diffcrcntials bctwccn thc different points on thc hcat transport clcment 204 and may avoid the lormation ol hot spois in the pholovollaie elements 205. Accordingly, reducing the prcssure hcad acting on thc liquid water at thc bottom of the hcat transport clement 204 may make the temperature of the front sheet 214 of the hcat transport elcmcnt 204 more isothermal.

Thc arrangement of fluid flow channels 217 extending longitudinally along thc heat transport element 204 and interconnected by vapor manifolds 211 extending laterally across the heat transport element 204 may allow a very rapid flow of heat energy along the heat transport element 204 away from any fluid flow channel 217 having a higher temperature. This may reduce temperature differentials between the different points on the heat transport element 204 and may reduce, or avoid, the formation of hot spots in the photovoltaic elements 205.

The provision of the two separate heat transport mechanisms of the movemeni of waler vapor along the vapor manifold 211 and the density driven flow of liquid water and water vapor along each of the front Iluid flow channels 217, respectively acting longitudinally and transverse the length of the heat transport element 204 may tend to equalize the temperature across the entire upper surface of the heal transport elemeni, and thus lend to equalize the temperature across the photovoltaic elements 205 and reduce, or avoid, the formation of hot spots.

The movement of water vapor along the vapor manifold 211 provides a very rapid heat transport mechanism that tends, by the vaporization and condensation of water, to move heat energy from relatively hot locations to relatively cold locations. As a result, the movement of water vapor along the vapor manifold 211 may tend to equalize the temperature of the liquid water surface at different positions across the heat transfer element 204, in addition to transporting heat energy from the heat transport element 204 to the heat exchanger 107 formed by the tube 234. This temperature equalization may have the effect of removing more heal energy from hotler paris of the heal transporl elemeni 204, and so tending to equaliie ihe temperature across the front surface of the heat transport element 204. It is clear that such isothermal cooling will tend to reduce, or avoid, thc formation of hot spots, for example in any pholovoltaic element attached lo ihe front surface of ihe heat transporl elemeni 204.

Similarly to the first embodiment, the rear sheet 215 of thc heat transport element 204 has a plurality of hollow ridges 225 cxtcnding between the flat part of the rcar surface 204b and the semi-cylindrical surface of each outwardly projecting section 210. Each hollow ridge 225 has a V' profile, and the hollow ridges 225 arc located spaced apart at regular intervals along the length of cach outwardly projecting scction. the hollow ridges 225 act as supports for the outwardly projecting sections 210, and also act as drains to rcturn liquid water from the vapor manifolds 211 into the rear fluid flow channels 218 in a similar manner to the hollow ridges 125 of the first embodiment.

The hollow ridges 225 may extend the range of angles of inclination at which the heat transporl element 204 can he used, as explained ahove regarding ihe first embodiment.

Depending upon ihe geomeiry of ihe different paris of ihe heat transport elemeni 204 in any specific design, even when the hollow ridges 225 are used there may still he a minimum angle ol inclination at which the heat transport element 204 can operate withoul the relenlion of liquid water in the vapor manifolds 21 I having adverse eliecis on operation of ihe heal transporl element 204.

The corrugated profile of the central sheet 216 and the bonding of the central shccts 216 to the front shect 214 and the rear sheet 215 increases thc strength and rigidity of the heat transport element 204, and may rcduce or prcvent ballooning for the reasons discusscd regarding the second embodiment. Ibis may make the heat transport element 204 a more rigid structure.

This may tend to reduce the amount of flexing of the hcat transport element 204 in use. Ibis may prevent damage to the photovoltaic elements 205 by reducing the amount of mechanical stress applied to the photovoltaic elements 105. This may allow the front, rear, and/or central sheds 214, 215, 216, to he thinner, which may reduce weight and cosLs. This may allow the front sheet 214 to be thinner, which may improve the transfer of heat from the photovoltaic elcmcnts 205 into the liquid water within the front fluid flow channels 217.

The heat transport clement 204 is a substantially rigid structure. This may minimize changes in the level of the upper surface 232 of the water 221 due to flexing of the components of the heat transport element 204, such as the upper and lower sheets 214 and 215. Such changes in the level of the upper surface 232 of the water 221 may affect the efficiency of the cooling of the photovoltaic elements 205.

As is explained above, the interior of the heat transport element 204 is evacuated, and the heat transport element 104 is located within an evacuated tube 203. Usually the heat transport element 204 and the evacuated tube 203 are evacuated to the same pressure. In the illustrated example of the second embodiment described above this pressure maybe i03 mbar.

The interconnection of the front and rear sheets 2 14 and 215 by Ihe linking surfaces of the central sheet 216 may resist ballooning of the front and rear sheets 214 and 215 and reduce or prevent ballooning. Arranging lbr the linking surfaces of the cenlral shed 216 Lobe straight may increase the resistance to ballooning. Reducing or preventing ballooning may prevent damage Lo the photovoltaic elemenLs 205 by reducing the amount of mechanical stress applied to the photovoltaic elements 205. This may allow Lhe front sheet 214 to he thinner, which may reduce weight and costs and/or may improve the transfer of heat from the photovolLaic elements 205 into the liquid water within the front Iluid how channels 217.

For the same reasons as explained with regard to the first embodiment it is preferred for the sizes of the surfaces of the central sheets 216 in contact with the front shcct 214 to be as small as possible, subject to the contact area between the central sheets 216 and the upper sheet 214 being sufficiently large to fonn a reliable bond of the required strength.

In the illustrated example of the fifth embodiment 0.2 mm thick tin coated mild steel sheets are used Lo lorm the difl'ereni sheds of ihe heal transport demenL Tn alternalive examples other thicknesses may be used, in particular 0.1 mm thick tin coated mild steel sheets may he used.

In thc illustrated cxamplc of the fifth embodiment the spacing betwccn the front sheet 214 and thc parallel parts of the rear sheet 215 is 1,8mm at thc locations of thc recesses. Accordingly, thc thickness of the fluid flow channels 217 and 218 at thc locations of thc recesses is 1.6mm, sincc the thickness of the central shcct is 0.2mm.

lie sheets uscd to form the hcat transport clement may be shapcd by pressing.

In thc illustrated fifth embodiment the heat transport element 204 is arranged to be horizontal transversely to longitudinal axis. [hat is, the vapor manifolds 211 should he honzontal.

however, in practice some deviation from the horizontal may he tolerated without significant impact on the operation of the heat transport element 204. Such deviation from the horizontal will resuli in differences in the kvel of the liquid waler surface relalive to ihe structure ol' ihe heat transport element 204 at different positions along the length of each vapor manifold 211.

As is explained above, ihe level of the liquid water surface may be varied. Accordingly, ihe minor differences in level caused by small deviations from the horizontal may he accommodaled.

The front and rear sheets 214 and 2i5 of the filth emhodimeni have a dimpled prolile similarly to ihe upper and lower metal sheds 114 and 1 15 ol' the second emhodimenL As discussed abovc thc heat transport element 204 has a flat front surface 204a formed by a front shect 214 with a dimpled profile. In addition, the front shcet 214 is has two longitudinal recesses running across in its front surface 204a which form two parallel troughs running along thc upper surface 204a of the heat transport element 204 behind the photovoltaic elements 205. Similarly to the first embodiment electrically conductive ribbons or wires run along the longitudinal recesses between the heat transport element 204 and the photovoltaic elemenis 205. The wires are electrically connecled Lu the pholovollaic elements 205 and lo Ihe conductors 21 which pass through the cap 12 to provide a conductive path to carry the elcctrical powcr gcnerated by the photovoltaic elements 205 out of the sealcd transparent tube 203. This eleclrical power may he supplied to an inverler br voltage conversion andlor for convcrsion to alternating current for supply to a domestic or mains electrical system.

In cxamplcs where adhesivc is used to attach the photovoltaic elements 205 to thc hcat transport clement 204, an electrically insulating adhesive can be uscd in a similar manncr to the second embodiment.

In the fifth embodimcnt thc longitudinal recesses run parallel to thc fluid flow channels 217 and 218. Accordingly, each of the longitudinal recesscs can bc accommodated by rcducing the thickness of one of the front fluid flow channels 217 in each section 204c to 204e of the heat transfer element 204.

Tn ihe illusftaled example of Ihe filth embodiment the spacing heiween the front sheet 214 and the parallel rear sheet 215 is 1.8mm at the locations of the longitudinal recesses 129.

Accordingly, the thickness of the fronl fluid flow channels 217 at Ihe localions of the longitudinal recesses is 1.6mm, since the thickness of the central sheet is 0.2mm.

The heal Iransport dement o1 the filth embodiment may he formed using Ihe same malerials and bonding lechniques as in Ihe first embodiment.

Tn the illustrated example of ihe Iiflh embodiment ihe blow of water vapor and liquid water through ihe heal Iransport elemenl 204 lends lo keep ihe cooled lioni surface of Ihe heat transporl elemenl 204 at a uniForm operaling lemperature during operation. Thai is, Ihe cooled upper surface oF ihe heat Iransporl element 1 04 lends to be kepi isothermaL The isolhermal nalure ol Ihe cooled upper surface of Ihe heat Iransporl element 104 lends to give rise lo isothermal cooling of ihe pholovollaic elements 105, where hotter parts of ihe pholovollaic elements 105 tend to he preferentially cooled so that the photovoltaic elements 105 themselves tend to become isothermal Such isothermal cooling provides further advantages in addition to those provided by cooling.

Tsoihermal cooling may provide the advantage thai the appearance of hot spois or regions in thc photovoltaic clcments 205 produccd by hcating by incidcnt solar radiation can bc rcduccd or eliminated. Such hot spots or rcgions can rcducc thc cfficicncy of the photovoltaic clements 205.

lsothcrmal cooling may simplify the control and wiring arrangcmcnts of the photovoltaic clements 205 by reducing or eliminating any requirement for compensation for differenccs in thc performance of the different parts of the photovoltaic elcmcnts 205 that are at different tempcratures.

Isothermal cooling tends to reduce, or prevent, the formation of hot spots or regions in the photovoltaic elements 205. As is explained above, this may allow the efficiency of the photovoltaic elements 205 to be improved al a specific lemperalure. Further, this may reduce the amount of degradation of the photovoltaic elements 205 caused by higher temperatures.

Still further, this may allow the photovoltaic elements 205 to operate with a given degree of efficiency at a higher temperature than would otherwise he the case. This may allow the solar energy collector assembly 202 including the photovoltaic elements 205 to he operated at a higher temperature without reducing the efficiency with which the photovoltaic elements 205 produce electrical energy.

Onc example of this effcct of isothermal cooling is that the general figure quoted above for silicon photovoltaic elemcnts that thc efficiency of electrical energy gcncration generally drops by about 0.35% to 0.5% for cach degree centigrade of temperature increase above 25°C may not apply to silicon photovoltaic clements that arc isothcrmally coolcd. Such isothermally cooled silicon photovoltaic elements having hotspots eliminated or reduced may have a higher threshold temperature at which the efficiency of electrical energy generation begins to drop and/or may have a reduced rale oF reduction in elliciency for each degree centigrade of temperature increase above the threshold temperature. Further, the temperature at which thcrc is a risk of permanent degradation of thc silicon photovoltaic clements may also he increased For isothermally cooled silicon pholovollaic elements. Similar eFFects may bc found in photovoltaic elements formed of othcr semiconductor matcrials.

In somc examples, onc or morc layers of heat conductivc matcrial may be located bctwccn thc uppcr sheet 214 and the photovoltaic elements 205. Such layers of hcat conductive material may increasc the rate of heat transfer between the photovoltaic elements 205 and the front sheet 214, and thus the rate of heat transfer between the photovoltaic elements 205 and the liquid within the front fluid flow channels 217. Such layers of heat conductivc matcrial may also increasc thc ratc of heat transfer laterally across the photovoltaic clements 205.

Accordingly, providing a layer of heat conductive material may increase the degree of isothermal cooling and further tend to reduce, or eliminate, the formation of hot spots or regions in the photovoltaic dements 205.

The heal transporl element may he used in other applications separately From the rest of the solar energy converter.

In some examples control methods can he used to control the temperature of the solar energy collector assembly 202. In some examples the temperature of the solar energy collector assembly 202 may he controlled by changing the rate of removal of heat energy from the solar energy collector assembly 202.

Tn some examples the rate ol removal ol heat energy from the solar energy cofleclor assembly 202 can he controfled by altering Ihe flow rate oF the Iirst operating fluid passing through the tube 234 Forming the heal exchanger 207.

In some examples the rate of removal of heat energy from the solar energy collector assembly 202 can be controlled by altering the vacuum pressure within the tube 203. This may change the rale oF convective heal loss from Ihe solar energy collector assembly 202 lo the Luhe 203.

In general, heat transferred to the tube 203 will be rapidly lost to the outside environment by convcction and/or conduction.

In somc examples thc ratc of rcmoval of hcat cncrgy from thc solar cncrgy collector asscmbly 202 can bc controllcd by altcring thc vacuum prcssurc within scctions 204c to 204c of thc hcat transport clcmcnt 204. In gcncral, thc tcndcncy of thc liquid watcr within thc front fluid flow channel 217 to vaporize and form bubblcs of vapor 222 will incrcasc as thc vacuum prcssurc is rcduccd, and thc tcndcncy of thc liquid watcr within thc front fluid flow channel 217 to vaporizc and form bubblcs of vapor 222 will dccrcasc as thc vacuum prcssurc is incrcascd. As is cxplaincd above, thc dcnsity drivcn circulation of watcr around thc front and rcar fluid flow channcls 217 and 21S and thc transport of hcat cncrgy along the vapor manifolds 211 and the tubes 219 are both driven by water vapor. Accordingly, altering the tendency of the liquid water to vaporize by altering the vacuum pressure may allow the rate of removal of heat energy from the solar energy collector assembly 202, and the rate of removal oF heal energy Irom the pholovollaic elemenls 205 to he conirolled, and so allow ihe temperature of the solar energy collector assembly 202 and photovoltaic elements 205 to he conlrolled.

Furlher, Ihe lemperalure al which rolling boiling of the water 221 wilhin the front fluid how channels 217 commences will lend to increase as Ihe vacuum pressure is increased, and will lend lo decrease as Ihe vacuum pressure is decreased. Accordingly, in examples where ihe vacuum pressure wiihin the heal transporl elemeni 204 is allered ihe temperalure al which Ihe watcr 221 within thc front fluid flow channcls 217 commcnccs rolling boiling can bc changcd.

As is explained above, thc dcnsity drivcn circulation of watcr around thc front and rcar fluid flow channcls 217 and 21R bccomcs particularly vigorous, and hccomcs particularly effectivc as a hcat transport mechanism, whcn thc water 221 within thc front fluid flow channcls 217 enters a rolling boil state. Accordingly, altering the temperature at which the water 221 within the front fluid flow channels 217 commences rolling boiling by altering the vacuum pressure may allow ihe rate of removal of heat energy from ihe solar energy colleelor assembly 202 and photovoltaic elements 205 to he controlled, and so allow the temperature of the solar energy collector assembly 202 and photovoltaic elcmcnts 205 to be controllcd.

in somc exampics the tcmperaturc of the solar encrgy collcctor assembly 202 may be controlled by changing the amount of solar energy incident on the solar cnergy colicetor assembly 202, and so changing the rate of absorption of heat cnergy by thc solar encrgy collcctor assembly 202.

in some examplcs the amount of incident solar energy may be controlled by changing the oricntation of thc solar energy collector assembly relative to the direction of the incidcnt solar cnergy. Ibis can be carried out using a drive mechanism ablc to rotatc thc solar encrgy collector assembly about one or more axes.

In some examples the amount of incident solar energy may he controlled using adjustable light intercepling or blocking mechanisms in the paLh of Ihe ineideni solar energy. Tn some examples variable filters, shutters, stops, or the like may he used. In some examples these adjustable lighi intercepting or hlocking mechanisms may compnse physical devices. In some examples these adjustable light intercepting or blocking mechanisms may comprise devices having elecironicafly conirolled oplical eharacterislics, such as liquid cryslals.

In examples where the Lemperature oF the solar energy cofleclor assembly and/or ihe phoLovoltaic elemenLs are Lo he conirolled, a temperature sensor and a lemperalure coniroller may be provided, togcthcr with a tempcrature control mcchanism arranged to carry out one, some, or all, of the methods of controlling temperature describcd above.

Thc temperaturc scnsor is arrangcd to measure the temperature of the solar energy colicetor assembly and providc this tcmperature value to the temperaturc controller. Thc temperature controller can then operate the temperature control mechanism in a suitable manner to control the temperature of the solar energy collector assembly to the desired value.

Examples where the temperature of the photovoltaic elements is to he controlled a tcmpcraturc scnsor ananged to measure the tcmpcraturc of a photovoltaic element or elements and provide this temperature value to the temperature conlroller may he provided. This may be additional to, or instead oL the temperature sensor arranged to measure the temperature of the solar energy collector assembly. Ihe temperature controller can then operate the temperature control mechanism in a suitable manner to control the temperature of the photovoltaic clement or elements to the desired value.

in some examples the temperature sensor can be provided on the upper surface of the solar energy collector assembly. in some examples the temperature sensor can be formed on the same semiconductor wafer as a photovoltaic element.

in the illustrated fifth embodiment, the heat transport element 204 is divided into three sections 204c to 204e, each of which has a separate heat transfer syslem comprising a number of front and rear fluid flow channels 217 and 218, a vapor manifold 211, and a tube 234. Each of these separate heal transfer systems operates in a similar manner to the first embodiment described above. Tn other examples the heal transport element 204 may he divided into a dilTerent number of sections, each having a separate heat transfer system.

in the illustrated fifth embodiment the tubes 234 each extend outwardly from the side of the heat transport element 204, then turn through a right angle and extend parallel to the axis of the tube 203 to pass through the end cap 220 of the tube 203. In other examples, the tubes 234 may be arranged differently. In some examples the tubes 234 may be interconnected for mutual support. Ibis may improve the support provided to the heat transport element 204.

The tubes 234 connect the respective heat exchangers 207 to the support structure 206, and may be regarded as a heat exchange network.

In the illustrated fifth embodiment the tubes 234 each extend outwardly from the end of a rcspcctivc vapor manifold 211. In somc cxamplcs thc tubcs 234 may cxtcnd from a diffcrcnt pan ol ihe respective vapor manilolds 21 I. Tn some examples Ihe luhes 234 may exlend Irom diffcrent parts of thc rcspectivc vapor manifolds 211 from one another.

in the illustrated fifth embodiment the differcnt scctions 204c to 204e of the heat transport clement 204 are each divided by a wall 231 extending bctween the front and rear sheets 214 and 215 to form a fluid tight seal betwccn the fluid flow channels of the diffcrcnt scctions. in other examples a different scaling structure could be used. In some examples the front and rear sheets 214 and 215 could be brought into contact to form the fluid tight seal. In some examples the rear sheet 215 could be bcnt towards thc flat front shcet 214 to contact the front sheet 214 and form the fluid tight seal. in some examples the rear sheet 215 maybe shaped by pressing.

The illuslnaled filth embodimeni is a hybrid solar energy convener comprising pholovollaic elements and arranged to convert incident solar radiation into outputs of both electrical energy and hol waler. in other examples ihe photovollaic elements may be omitted to provide a solar energy converter arranged to convert incident solar radiation into an output of hot water.

The illusirated example oF the huh emhodimenl has a heal exchanger comprising concentric luhes according to Ihe third embodimenl. in other examples the filth embodimeni may have a heal exchanger comprising luhes according to Ihose oF the hirsl, second or!ourlh cmbodiments.

in thc illustrated embodiments the hcat exchanger is fonned by simple smooth tubes. in other examples the heat exchanger tube or tubes could be shaped or surface profiled to increase their surfaec area and/or to encourage and increase contact betwcen the different fluids and the surfaces. In some examples the surfaces may he convoluted, threaded and/or spiraled. In some examples the tubes may contain flow controlling or modifying structures to increase or improve ihe conlact helween Ihe firsl Iluid and the walls of Ihe lube or luhes forming Ihe heat exchanger. In some examples the flow controlling or modifying structure may comprise a helical inscrt within the tube.

Temperature Control lie cmbodiments describcd above may further comprise, in addition to thc described hcat exchanger, an additional secondary heat exchanger and a heat transfer control valve. The secondary hcat exchanger may be connected to the vapor manifold by a vapor passage or pipe with thc heat transfer control valve arranged to selectively allow, or prevent, the transfer of heat encrgy from thc heat transport element to the secondary heat exchanger.

The heat transfer control valve is able to selectively allow, or prevent, the transfer or transport of heat energy from the heat transport element to the secondary heat exchanger. Accordingly, the degree of cooling applied to the photovoltaic elements can he varied.

Tn some arrangements the heal energy transferred lo the secondary heat exchanger is transferred into ambient air and allowed to escape and the secondary heat exchanger is used, under Ihe sdeclive contro' 0! the heal transfer conirol valve, to release heal energy in order to regulate the temperature of the solar energy collector assembly.

The irigger temperature of ihe heal iransler control valve at which the valve opens may he predetermined. In some exampks the trigger temperature may he seitable in use, or on installation or manufacture of ihe hybrid solar energy converter. In some examples the trigger temperature may be settable to diffcrcnt values depending on thc intended maximum water temperature of thc water to be heated. In particular, in some examples the trigger temperature may be settable to 65°C when the hybrid solar energy converter is to be used to heat water for a domestic hot water system and may bc settable to 135°C when the hybrid solar encrgy convcrter is to be used to heat water for an industrial hot water system.

In some examples the trigger temperature of the heat transfer control valve may he selected to maximize the generation of electrical energy by Ihe pholovollaic elemenis. in some examples the trigger temperature value may he selected to increase the amount of heat energy transferred to thc first opcrating fluid. in some examples thc triggcr temperature may bc selected lo oplimize ihe overall produelion oF energy, taking mb account holh Ihe amount of electrical cncrgy produccd by the photovoltaic elements and thc amount of hcat cncrgy transferred to thc first opcrating fluid. in some examples thc optimizing may maximizc thc total production of energy. in some examples the optimum overall production of cncrgy may take into account thc rclative dcmand for, or value of, thc diffcrent types of cncrgy, rathcr than simply maximizing thc total amount of cnergy produccd.

As explained abovc, thc isothermal cooling tends to reduce, or prevent, the formation of hot spots or regions in the photovoltaic elements. flis may allow the solar energy collector assembly including the photovoltaic elements to be operated at a higher temperature without reducing the efficiency with which the photovoltaic elements produce electrical energy. This may allow the temperature of the collector assembly to be increased to produce more useable heal energy withoul the increase in lemperabure reducing ihe elTicieney wibh which Ihe photovoltaic elements produce electrical energy. This may allow the trigger temperature to he increased.

in some examples the Irigger bemperabure may he sd to diftereni temperalures during use of Ihe hybrid solar energy converter. This may allow the temperature of the colleebor assembly lo he conirolled to produce difFerenb amounbs of useahle heat energy or electricity depending upon which lype 0! energy is most in demand ala specific lime.

For example, when hot water is more in demand than electricity the valve may be closed to pass hot water vapor from the heat transport element only to the heat exchanger to maximize the amount of heat applied to the water acting as the first operating fluid regardless of any temporary reduction in efficiency of the photovoltaie elements as a result of any resulting increase in temperature of the collector assembly. Further, when hot water is less in demand than electricity, the valve may be opened in order to pass hot water vapor from the heat transporl element Lo both oF Lhe heal exchangers in order Lu cool Ihe photovollaic elements as much as possible and maximize the efficiency of electricity generation regardless of the cffccts on the tempcraturc of thc watcr acting as thc first operating fluid.

Alternative collector arrangements The illustrated embodiments all employ a single substantially flat collector assembly within a tube. Other arrangements may bc used.

In somc examples thc collector assembly may bc curved. The curvcd collector assembly may bc arrangcd to havc a curved outcr surface conccntric with a cylindrical tube within which the collector assembly is mounted. This may allow a collector assembly having a grcatcr surface arca to be fitted within a cylindrical tube of a particular size. I'he curvcd collector assembly may have curved photovoltaic elements mounted on it.

Some examples may mount multiple collector assemblies within a single tube.

Some examples may mount multiple collector assemblies at different angles within a single tube. in examples where the colleclor assemblies and the Lube are lixed Lhis may allow-the efficiency of the collector to he increased by arranging the different collector assemblies at angles adapLed Lu more eliicienLly coiled energy at diliereni Limes of day.

Tn some examples mirrors andlor lenses may be associaLed with Ihe hybrid solar energy converter to direcL or locus incident solar energy onlo Lhe collector assembly. Such minors may bc flat or curved. Such mirrors and/or lcnses may be fixcd or moveablc. in some examples movcablc mirrors or lenses may bc arranged to track thc sun.

In somc examples the transparent tube may incorporate a lens to dircct or focus incidcnt solar cnergy onto the collector asscmbly. in some examples the transparcnt tube may incorporate a Fresnel lens.

Tn the illustrated examples the lirsl Iluid is water. Tn other examples other fluids may he used, which may he liquids, vapors or gasses.

Sun Tracking Thc embodiments dcscribed above are solar encrgy converters which convcrt incident solar radiation into useabic electrical and/or heat energy.

In somc exampics the collector asscmblies of thc solar encrgy convcrters may be arrangcd to change their oricntation to follow the apparent movemcnt of the sun across the sky, or track the sun. this may increase the amount of solar radiation energy incident on the collector assemblics, for well-known gcometric reasons, and so may incrcase thc amount of uscable elcctrical and/or heat energy produced.

Figure 18 shows a general view of a sixth embodiment of a solar energy converter 300 arranged to be able to change orientation to track the sun.

The solar energy converter 300 comprises a sealed transparent tube 301 containing a solar energy cullecior assembly 302 and mounted Lu a heal exchange assembly 303. The solar energy converter 300 may he a solar energy converter according to any of the embodiments disdosed herein. Sun (sacking arrangemenLs may he added Lu any of Ihe embodiments.

Tn Lhe illusiraled example of Lhe sixth emhodimenL ihe sealed Iransparenl lube 301 is cylindrical and has an axis 304. The sealed Iransparent lube 301 is mounied br rolalion ahoul the axis 304 togethcr with the solar cnergy collector assembly 302 mounted within the tube 301. A drive motor 305 is arranged to rotationally drive thc tube 301 through a transmission mechanism 306. h the illustrated example the transmission mcchanism 306 is a cog and chain transmission mechanism.

By selectively operating the drive motor 305 based on the time and date, the sealed transparent tube 301 and solar energy collector assembly 302 can be rotated to follow the sun as the appareni posilion of Ihe sun changes as a result of the rolalion of Ihe earlh.

Adding such a solar tracking drivc system may incrcase thc amount of cncrgy gathcrcd by the solar energy collecior assembly by ahoul 20%.

Figure 19 shows a general vicw of a scvcnth embodiment of an array 307 of solar energy converters 300, in figurc 19 a plurality of solar encrgy convertcrs 300 according to the sixth embodiment arc mounted to form an array 307. Each of the solar energy converters 300 compriscs a scalcd transparent tube 301 containing a solar energy collector assembly 302 and mounted to a hcat exchange assembly 303. Each sealcd transparent tube 301 is mounted for rotation about an axis 304 togcthcr with the solar cncrgy collector assembly 302 mountcd within thc tube 301. The transparent tubes 302 are mounted on the array 310 so that their respective axes of rotation 304 are parallel.

A drive motor 311 is arranged to rotationally drive the tubes 301 of the array 310 in synchrony Lhrough a Lransmission mechanism 3 12. in Ihe illusirated examp'e of the sevenLh embodiment the transmission mechanism 312 is a cog and chain transmission mechanism.

The array 310 is mounted on a turntable 313 for rotation about an axis 314 perpendicular to the axes 304. A drive motor 3i5 is arranged to rolationally drive Ihe tumlahle 313 through a transmission mechanism 316. Tn (be iflusiraled example the transmission mechanism 316 is a geared transmission mechanism.

By selectively operating the drive motors 305 and 315 based on thc time and date, the sealed transparent tubes 301 and solar energy collector assemblies 302 of the array 310 can be rotated to follow thc sun as the apparcnt position of the sun changes as a result of thc rotation of thc earth.

Adding such a dual axis solar tracking drive system may increase the amount of energy gathered by the solar energy collector assemblies 302 by up to about 48%.

In the examples of figures 18 and 19, the operating of the drive motor or motors should take into account the location of the solar energy convertcr or convertcrs 300.

Figure 20 shows a general view of a eighth embodiment of a solar energy converter 400 arranged to be ablc to change orientation to track the sun.

The solar energy converter 400 comprises a scaled transparent tube 401 containing a solar energy collector assembly 402 and mounted to a heat exchange assembly 403. The solar energy convcrter 400 may be a solar energy converter comprising a heat transport device according to any of the first to sixth embodiments described above. Sun tracking arrangements may be added to any of the embodiments.

In the illustrated example of the eighth embodiment the sealed transparent tube 401 is cylindrical and has an axis 404. The sealed transparent tube 401 has two opposed open ends sealed by respective end caps 420. The solar energy cofleclor assembly comprises a heal transport element 404 according to any of the first to sixth embodiments covered by phoLovoltaic elements. The heal transporl element 404 is cooled by heat exchanger supplied with a first fluid through tube sections 405, which pass through the end cap 420 at one end of the transparent Lube 40 I. The heat Lransporl demenl 404 is supporied al one end by Ihe tube sections 405 as discussed above. Tn order lo supporL the oiher end ol ihe heat transporl elemenl 404 inward projecLions 406 are provided on an inner face of the end cap 420. these inward projections 406 are arranged to allow sliding movement of the heat transport element 404 parallel to the axis of the transparent tube 401 in order to accommodate differential thermal expansion of the heat transport element 404 and the transparent tube 401.

The sealed transparent tube 401 is mounted for rotation about an axis 407 midway between the tube sections 405 together with the solar energy collector assembly 402 mounted within the tube 401.

In thc illustratcd cxamplc thc hcat transport clcmcnt 404 is supplicd with fluid through pipcs 405 passing through an end cap 420 al one end only of Ihe transpareni tube 401. In oLher cxamplcs thc hcat transport clcmcnt may bc supplied by a singlc tubc passing through an cnd cap 420 at onc cnd only of thc transparcnt tubc 401, or by tubcs passing through thc cnd caps 420 at both cnds of thc transparcnt tubc 401. In cxamplcs whcrc a singlc tubc passcs through thc cnd cap at cach cnd of thc transparent tubc it is prcfcrrcd that positions whcrc thcsc tubcs pass through thc rcspcctivc cnd caps arc aligncd. In cxamplcs whcrc only a singlc tubc passcs through thc cnd cap at onc or both cnds of thc transparcnt tubc thc transparcnt tubc may bc mountcd for rotation about an axis coincidcnt with thc tubc.

In other examples tube may be mounted for rotation about the axis of the tube.

In other examples the heat transport element 404 may he supported only at one end by the tube secLions 405.

A solar tracking drive syslem may he arranged to sdectively roUte the solar energy converter 400 so that the sealed transparent tube 401 and solar energy collector assembly 402 can he rotated to loflow the sun as Ihe appareni posilion of the sun changes as a resuF. of the rotaLion of Lhe earLh. Carrying out such roLaLion may increase the amouni of energy gaLhered by Lhe solar energy collecior assembly by ahoui 20%.

Figurc 21 shows general vicw of a ninth cmbodimcnt of a solar cncrgy convcrtcr array 500 arrangcd to bc able to changc oricntation to track thc sun.

In figurc 21 a plurality of solar cncrgy convcrtcrs 400 according to thc cighth cmbodimcnt arc mountcd to form an array 500. I'hc solar cnergy convcrtcrs 400 arc mounted horizontally in a frame 501, and are arranged for rotation about their respective axes 407. The solar energy converters 400 are arranged with their respective axes of rotation 407 horizontal and paraflel.

The array 500 comprises suitahie molors and drive mechanisms thcated within the frame 501 to carry out rotation of the solar energy converters 400, hut these are not visible in the figures.

The array 500 is arranged In synchronously rolale Ihe solar energy converters 400 ahoul their respective axes 407. in other examples thc array 500 may be arranged to allow separate rotation of the individual solar energy converters 400.

Thc frame 501 comprises fluid supply tubes 502 and a fluid supply network allowing thc first fluid to be supplicd to and from cach of the heat transport clcments 404 of the solar encrgy convcrtcrs 400. In the illustrated example the first fluid is watcr.

Thc frame 501 is mounted for rotation about a vertical axis on a bearing section 503 to allow the array 500 to change orientation to track the sun. the vertical axis of rotation of the frame 501 is perpendicular to the axes of rotation of the individual solar energy converters 400. The array 500 comprises a suitable motor and drive mechanism located within the frame 501 to carry out rotation of the array 500, hut these are not visible in Ihe ligures.

By seleclively roUting the solar energy converlers 400 and the array 500 based on the time and date, the sealed transparent tubes 401 and solar energy collector assemblies 402 can he rotated to!6Ilow the sun as Ihe appareni posilion of the sun changes as a resuli of the rotalion o1 the earth.

Adding such a solar tracking drive system may increase the amount ol energy gathered by the solar energy collector assembly by about 4S%.

in gencral, it is not necessary to rotate the solar cnergy converters 400 freely, but only through a limited angular range. Accordingly, it may not be necessary to usc fully rotating joints to conncct the tube sections 405 to the fluid supply tubcs 502. in somc examplcs coiled pipes allowing a limited range of angular movement by coiling or uncoiling as the solar energy converters 400 rotate may he used. Where there are two tube sections 405 connected to a solar energy converter 400 they may he coiled in opposite senses to reduce any change in the torsional forces they apply to the solar energy converter 400 as it rotates.

Tn Ihe illustrated example there are six solar energy converters 400 in the array 500-in other examples a diffcrcnt numbcr of converters 400 may bc uscd.

In thc illustratcd cxample thc solar cncrgy convcrtcrs arc arranged horizontally. In othcr examples thcy may be arranged in other orientations, in onc cxamplc thay may bc arranged vertically.

in the illustratcd example the solar energy converters arc arrangcd for rotation about respective horizontal axes. In othcr examples they may bc arranged to rotate about axcs with other onentations. lii one example they may he arranged to rotate about respective vertical axes.

in the iflustraled exampk the array is arranged for rotation about a vertical axis. Tn other examples the array may he arranged for rotation about an axis with a different orientation. In some examples the array may he arranged to rotate about an axes perpendicular to the axes of rotation of the solar energy converters.

in examples where the solar collectors can he rotated about one or two axes to follow the sun, rotation about a single axis may increase the amount of energy gathered by up to about 20%, while rotation about two axes may increase the amount oF energy gathered by up to about 4S%.

in somc examplcs thc solar cnergy collcctor assembly may bc mounted within the tubc for rotation rclativc to the tube and a drivc motor arrangcd to rotationally drive the solar cncrgy collcctor assembly only. in such exampics a drive mcchanism which will not allow air leakage, which would destroy the vacuum within the tube, should he used.

Tn some examples Ihe solar energy collector assemhy, or ihe solar energy collector assembly together with the tube, may be rotated about an axis other than the axis of the tube.

General In thc dcscription abovc the level of water within the heat transport elements of thc diffcrent cmbodiments is referred to. ftc rcfcrences to the levcl of water refer to thc level of water whcn the heat transport clement is cold and the liquid watcr contains essentially no bubbles of water vapor. it will be understood from thc above description that the level of the water will vary during opcration of the heat transport elemcnts as water vapor bubbles are formcd in the liquid water and burst, and as the liquid watcr is vaporized and the water vapor condenscs.

in thc illustrated cmbodiments the heat transport elemcnts may have an operating temperature range from just over 0°C to about 270°C. in practice, the operating temperature range for domestic instillations may he limited to a maximum temperature of 95°C, or of 65°C, for safety, and to comply with legal requirements in some jurisdictions. Where silicon pholovoltaic elements are used the oplimum temperature range lo maximize ihe generation of electricity may he in the range 20°C to 65°C, or in the range 20°C to 3 0°C, or in the range 25°C to 30°C.

The heal transfer rate of lhe heal exchanger, that is the rale al which the heat exchanger can Iransfer heal energy Irom the heal iransier elemenl to the firsl respeclive operaling Iluids, may be maiched lo the heat Iransfer rale of ihe heal transfer element, Ihal is the rale al which ihe heal Iransfer elemenl can iransfer heal from the isolhermally cooled face of ihe coileclor asscmbly to the heat cxchanger assembly, at the expccted operating temperature, or over the expected operating temperature range, of the system. This may improvc efficiency.

in the illustrated embodiments the first operating fluid is watcr to bc in other examples the primary opcrating fluid may be air.

In other examples the first operating fluids may be fluids other than water and air.

In the illustrated embodiments a transparent tube or envelope is used. In other examples this may be replaced by a translucent or partially opaque tube or envelope.

In general, in all of the embodiments it may be preferred to have the photovoltaie elements as thin as possible to ensure effective cooling of the entire thickness of the photovoltaic elements by the heat transport element. Tlis may assist in preventing localized hot spots of elevated temperature developing within the photovoltaic elements, which hot spots may degrade the performance and reliability of the photovoltaic elements. However, in practice there may be a minimum required thickness of the photovoltaie elements for other reasons, for example physical strength.

In the illustrated embodiments degassed distilled water is used. This may provide the advantage that the tendency to vaporize of the water is maximized, increasing the efficiency of the heat transfer by the thermo siphon. Impurities dissolved in the water, including dissolved gasses, will lend to suppress vaponzalion ol Ihe water.

in some examples the waler may contain vapon/alion enhancing additives lo increase the tendency of the water to vaporize. In some embodiments particles of hydrophobic materials may he used, in particular particles of zinc oxide may he used. The particles oF hydrophobic molecules may act as nucleating sites, boosting the lormalion oF bubbles of waler vapor, without lending to suppress vaporization.

in all of the embodiments, nucleation enhancing structures may be added to the surfaces of the riser channels only, and not the return channels. This may encourage the liquid water to vaporize and form bubbles primarily, or only, in the riser channels even when the water in the riser and return channels are at similar, or the same, temperature. Suitable nucleation enhancing structures may include micropores and/or surface roughening.

In all of the embodiments, pores or apertures may he provided in the sheet separating the riser and return channels Lo allow-water to pass from ihe relurn channel to the riser channel. This may improve the circulation of the liquid water and improve the efficiency of the heat transfer.

Tn the iflustraled emhodimenLs water is used as Ihe working fluid within the heal Iransport element to provide the density driven circulation. in other embodiments other vaporizable liquids, solutions or mixtures may be used. in particular a mixture of water and glyeol may be used, ethanol may be used, and a mixture of ethanol and water may be used. Mixtures of dissimilar fluids where one fluid acts as a nucleating agent for another fluid may be used.

In other examples a mixture of 75% water and 25%-ethanol may be used as the working fluid within the heat transport element. When a mixture of 75% water and 25% ethanol is used the mixture may enter a rolling boil state at a temperature of about 22°C. In other embodiments the relative proportions of water and ethanol used as the working fluid maybe varied in order to set the temperature at which a rolling boil commences to a desired temperature.

As discussed above, the effecliveness of the heal Iransport mechanism signilicanlly increases when rolling boiling of the working fluid commences. Accordingly, it applications where it is desirable to keep the temperalure of the cooled face of the collector assembly bdow a specilic temperature, it may be preferred to select a working fluid, or mixture, which commences rolling boiling al a temperalure al or below-said specilic Lemperature al the iniended vacuum pressure conditions within Ihe heal Iransfer device.

In the illusiraled embodimenls the tubes lorming the heal exchanger are localed inside the vapor manifold so that the entire circumference of outer surface of the tube is inside. in other examples the tubes may be arranged so that only a part of the tubes project inside the vapor manifold, In examples where the solar energy collector assembly rotates relative to the evacuated tube a rotating vacuum seal must be provided between them. In some examples a rotating vacuum seal may be provided by a multi-stage seal. In particular a multi-stage 0-ring seal may he used.

Where a multi-stage 0-ring seal is used an advantageous method of manufacture may be to form thc 0-ring seals of the different stages in order from the interior of the evacuated tube to the exierior while evacuating the tube. This will provide a multi-stage o-ring seal with the regions bctwccn thc seals initially having the same vacuum pressure as the interior of the tube.

Such a multi-stage 0-ring seal may support a long lasting vacuum within the tube even when the multi-stage 0-ring seal is used as a rotating vacuum seal.

lie above embodiments illustrate and describe a single solar energy converter. in practice an array made up of a plurality of such units may be used. in such an array each solar energy converter may have a dedicated electrical inverter. Alternatively, a group of a plurality of solar energy converters may share a common inverter.

In an array of solar energy converters it may be preferred to have a primary operating fluid channel running through the primary heat exchangers of all of the energy converters of the array as a common manilold.

Tn an array of solar energy converlers ii may he preFerred for adjacent solar energy converters to have their respective inlet opening and outlet opening connected directly together. This may he done by providing a flange around each inlet opening and outlet opening and clamping together Ihe flanges of the adjacent mId opening and outlet opening of adjacent solar energy converters.

In an array of solar energy converters it may be desirable to be able to extract individual solar energy converters from the array for servicing, or to replace faulty converters, without having to drain all of the fluid from the common manifold. Accordingly, fluid cut off valves may be provided in the support element of each solar energy converter in order to seal the appropriate one of the inlet opening or outlet opening when an adjacent solar energy converter is removed from the array.

The embodimenis described ahove comprise a collecior assembly within an evacualed cylindrical tube. In some examples the collector assembly may he located within an enclosure which is not cvacuatcd. in somc cxamplcs cnclosurcs which arc not cylindrical tubes may bc used.

IThc cmbodimcnts sct out abovc arc dcscribcd in thc contcxt of a hybrid solar cncrgy converter. Fhc diffcrcnt parts of thc dcscribcd hybrid solar cncrgy convcrtcr may bc useablc indcpcndcntly.

in particular, thc solar energy collector asscmbly and thc hcat cxchangc asscmbly may bc uscd in a flat panel dcvicc without a scparatc cvacuatcd transparent tube for thc solar cncrgy collcctor assembly. Such a flat pancl dcvicc may bc cvacuatcd, or alternatively may not bc evacuated.

in particular, the collector assembly may he used as a thermal collector to gather heat energy from incideni solar radialion withoul any pholovoltaic elemenls being mounted on ihe collector assembly.

An array of solar energy converters may comprise both hybrid solar energy converters with pholovoltaic elements mounted on the colleclor assembly and Ihermal solar energy converlers wiihouL pholovollaic elemenis mounted on ihe collector assembly. Such an array may he used Lo heal waler, with ihe hybrid solar energy converters heating ihe waler lo an inlermediale lemperalure and the thermal solar energy converlers heating ihe water from Ihe inlermediale tcmpcraturc to a high temperature. The thermal solar cncrgy convcrtcrs without photovoltaic elements may opcratc at a higher tempcrature than thc hybrid solar cncrgy convcrtcrs bccausc thcy do not havc any photovoltaic elcments to suffcr thcrmal degradation.

In somc examplcs thc collector asscmbly may bc uscd as a thermal collector to hcat air or water in industrial or domestic applications, in some examples the collector assembly may he used as a thermal collector to heat water in a desalination or water purifying application.

In particular, the heat exchange assembly may be used separately in solar energy heat collectors without thc photovoltaic elements and/or without thc hcat transport elcmcnt. this may allow-Ihe problem of slagnalion lobe solved.

in particular, the heat transport clement may provide a density driven heat transport mcchanism uscable in othcr heat transport applications.

in particular, the heat transport elemcnt may provide an isothermal cooled surface uscable in other applications.

in particular, thc isothermal cooled surface may be curved. This may allow curved objects to he cooled more efficiently.

in one example the heat transport element may be used to cool electrical circuits, for example in a compuler.

ii' the heal Iransport element is used in other apphealions, and nol in conjunction wiih photovoltaic elements, the heat transport element may operate at a wider range of lemperalures. In one example the heal transport elemenl using waler as the working fluid may operale at a lemperalure of up lo 280°C. In other examples other Iluids may he used as ihe working fluid. In one exampk of a high lemperalure applicalion sodium may be used as the working fluid within the heat Iransport elemenL in some examples the heat transport element may transport hcat to one or morc electro-thermal powcr generators in place of onc or both heat exchangers. This may increasc the amount of electrical energy generated. in particular thc heat transport element may transport heat to a Stirling engine or engines.

In the illustrated embodiment vacuums are used within the heat transport element having a pressure of ahoul I mhar. Higher or lower pressures may he used. In general, it is expecled that using lower vacuum pressures would improve the performance of the hybrid solar energy converter. In some examples a vacuum pressure of 102 bar or lower may be used. In some examples vacuum pressures of I 06 mhar or I 0 mhar maybe used.

A vacuum pressure of io-mbar is generally the lowest pressure that can be provided by simple vacuum pumps, so that the use of this vacuum pressure is convenient as the necessary vacuum pumps are readily available. The use of this vacuum pressure may be economically advantageous in commercial scale production of hybrid solar energy converters because of the cost of providing a lower vacuum pressure. In other embodiments higher or lower vacuum pressures may be used.

In the illustrated embodiments the hybrid solar energy converter has roof and/or wall mounting brackets. In other embodiments different mounting methods and components may be used.

The description above describes three embodiments. All of the embodiments are closely relaLed and alternatives, explanations and advanlages disclosed in relalion Lo one of the embodiments can generally he applied in an analogous manner to the other embodiments. In particular, elements of one embodiment may he used in Lhe oLher emhodimenLs, and analogous elements can he exchanged between the embodiments.

The above description uses relative location terms such as upper and lower and ironi and rear.

These are used for clarity to refer to the relative locations of the referenced parts in the illustrated figures, and should not be regarded as limiting regarding the orientation and/or location of parts of embodiments of the invention during manufacture or in use.

those skilled in the art will appreciate that while the foregoing has described what are considered to be the best mode and, where appropriate, other modes of performing the invention, the invention should not he limited to specific apparatus configurations or method steps disclosed in this description of the preferred embodiment. Ti is undersiood ihal various modifications may be made therein and that the subiect matter disclosed herein may he implemented in various forms and cxamples, and that the teachings may be applied in numerous applicalions, only some of which have been described herein. It is iniended by the following claims to claim any and all applications, modifications and variations that fall within the true scope of the present teachings. Those skilled in the art will recognize that the invcntion has a broad range of applications, and that the embodimcnts may take a wide rangc of modifications without departing from thc inventive concept as dcfincd in the appended claims.

Claims

Claims: 1. A heat transFer assembly comprising: an elongate envelope: an elongate heat transfer device located within the envelope, the heat transfer device having an elongate heal translèr chamber; and an elongate heat exchanger passing longitudinally through at least a portion of the elongate heat transfer chamber.
2. A heat transfer assembly according to claim 1, wherein the elongate envelope is transparent or translucent.
3. A heat transfer assembly according to claim 2, wherein the elongate envelope is glass.
4. A heat iransier assemffly according Lo any preceding claim, wherein the elongale heat transfer chamber extends along substantially the whole length of the elongate heat transfer device.
5. A heat iransier assemffly according Lo any preceding claim, wherein the elongale heat exchanger extends along substantially the whole length of the elongate heat transfer chamber.
6. A heal iransier assembly according to claim 5, wherein ihe elongale heat exchanger comprises a Lube which passes through a lirsi end of ihe elongate heal transfer chamber, exiends along substantially ihe whole length of Ihe elongale heal Iransfer chamber, and Lurns hack to pass For a second time Lhrough Lhe first end of ihe elongaLe heat transfer chamber.
7. A heal iransier assembly according to claim 6, wherein ihe elongaLe heat exchanger comprises a tube which passes Iwice ihrough a firsL end of ihe dongaLe envelope.
S. A heal iransier assembly according to claim 5, wherein ihe elongaLe heat exchanger comprises a tube which passes through a first end of the elongate heat transfer chamber, extends along substantially the whole length of the elongate heat transfer chamber, and passes through a second end o! the elongate heal Iransfer chamber opposite the first end.
9. A heal transfer assembly according to claim 8, wherein the lube and/or Ihe elongale heal transfer device comprise means lo accommodate differential ihermal expansion heiween the lube and elongale heal Iransfer device.
10. A heat transfer assembly according to claim 9, wherein the means lo accommodate differential thermal expansion comprise a bellows structure of the tube.
11. A hcat transfer assembly according to any one of claims S to 10, wherein the clongate heat cxchanger comprises a tubc which passes through a first cnd of the clongate cnvelope, extends along substantially the whole length of the elongate envelope, and passes through a second end of the elongate envelope opposite the first end.
12. A heat Iransfer assembly according to claim 11, wherein Ihe Lube and/or the elongale envelope comprise mcans to accommodate diffcrcntial thermal expansion between the tube and elongale heat transfer device, and the elongale envelope.
13. A heat transfer assembly according to claim 12, wherein the means to accommodate differential thermal expansion comprise bends in the tube.
14. A heat transfer assembly according to any one of claims S to 10, wherein the elongate heat cxchanger comprises a tubc which passes through a first cnd of the elongate envelope, passcs through thc elongatc heat transfer chamber, and turns back to pass for a second time through the first end of the elongate envelope.
15. A heat transfer assembly according to claim 5, wherein the elongate heat exchanger comprises inner and outer concentric tubes which pass through a first end of the elongate heat transfer chamber and extend along substantially the whole length of the elongate heat transfer chamber, wherein the outer concentric tube is closed at an end remote from the first end of the elongate heat transfer chamber.
16. A heat transfer assembly according to any preceding claim, wherein the elongate envclopc is at least partially evacuated.
17. A heat transfer assembly according to any preceding claim, and further comprising at least one photovoltaic clement mounted on the elongate heat transfer device.tO
18. A heat iransfer assemffly according Lo any preceding claim, wherein the elongale heat transfer chamber is a vapor chamber.
19. A heat transfer assembly according to claim 18, wherein the vapor chamber is at least partially evacuated.
20. A heat transfer assembly according to any preceding claim, wherein the heat transfer assembly is arranged for rotation about a rotation axis.
21. A heat transfer assembly according to claim 20, wherein the elongate envelope is cylindrical and has an axis of symmeiry, and the axis of rolalion is parallel lo the axis of symmetry.
22. A heat transfer assembly according to claim 21, wherein the axis of rotation and the axis of symmetry are coaxial.
23. A heal Iransfer assembly according Lo any one oF claims 20 Lo 22, when dependent Irom one of claims 7 or I I to IS, wherein the axis of rolalion coincides with ihe location of a tube passing through an end of the elongate envelope.
24. A heal Iransfer assembly according Lo any one of claims 20 Lo 22, when dependent from one of claims 7 or 14, wherein the Lube passes twice through ihe lirsI end of ihe elongale envelope and Lhe axis of rotalion passes heLween the locaLions at which the tubes passing through Lhe end of Lhe elongate envelope.
25. A heat transfer assembly according to claim 24, whcitin the axis of rotation passes cenlrally between Ihe thcations at which the luhes passing Ihrough Ihe end of Ihe elongate envelope.
26. A solar collector array comprising a plurality of heat transfer assemblies according to any one of claims 20 to 25 mounted in parallel on a common supporting structure.
27. A solar collector array according to claim 26, and further comprising means for synchronously rotating all of the plurality of heat transfer assemblies relative to the supporting structure about their respective axes of rotation.2K A solar collector array according to claim 26 or claim 27, and furthcr comprising mcans for rotating thc supporting structurc about an axis perpendicular to the axcs of rotation of the heat transfer assemblies.29. A heat transfer device comprising: a pluralily of fluid flow chambers; a common heat transfer chamber serving all of the fluid flow chambers; a heal exchanger passing through at least a portion of the heal transfer chamber.30. A heat transfer device according to claim 29, wherein the heal transfer device comprises more than Iwo Iluid how chambers.31. A heat transfer device comprising: a working fluid pathway; a heat transfer chambcr located on thc working fluid pathway; a hcat exchangcr passing through at least a portion of thc heat transfcr ehambcr.32. A hcat transfer device according to claim 29, whcrein thc heat transfer device comprises a plurality of working fluid pathways.33. A heal translèr device according Lo any one of claims 29 Lu 32, wherein the heat transfer chamber extends along substantially the whole length of the heat transfer dcvicc.34. A heal translèr device according Lo any one of claims 29 Lu 33, wherein the heat exchanger exiends along suhsLantially Lhe whole length of Lhe heal transFer ehamher.35. A heat Iransfer device according to claim 34, wherein Ihe heal exchanger comprises a tube which passes through a first end of the heat transfer chamber, extends along substantially the whole length of the heat transfer chamber, and turns back to pass for a second time through the first end of the heat transfer chamber.36. A heat transfer dcvice according to claim 34, wherein the heat exchanger comprises a tube which passes through a first end of the heat transfer chamber, extends along substantially the whole length of the heat transfer chamber, and passes through a second end of the heat transfer chamber opposite the first end.37. A heal transfer device according to claim 36, wherein the lube and/or the heal transfer device comprise means to accommodate diffcrential thermal expansion between the tube and heat transfer device.3K A hcat transfcr device according to claim 37, whcrein the means to accommodate differential thcrmal expansion comprise a bellows structure of thc tube.39. A heat transfer device according to claim 34, wherein the heat exchanger comprises inner and outer concentric tubes which pass through a first end of the heat transfer chamber and extend along substantially the whole length of the heat transfer chamber, wherein the outer concentric tube is closed at an end remote from the first end of the heat transfer chamber.40. A heat transfer device according to any one of claims 29 to 39, and further comprising at least one photovoltaic element mounted on the heat transfer device.41. A heal transfer device according to any one of claims 29 to 39, wherein the heat transfer chamber is a vapor chamber.42. A heal transfer device according to claim 41, wherein Ihe vapor chamber is at least parlially evacuated.43. A hcat transfer asscmbly comprising a hcat transfer dcvicc according to any one of claims 29 to 42, and further comprising an envelope, the hcat transfer devicc being located within the cnvclope.44. A heat iransier assembly according to claim 43, wherein the envelope is Iransparent or translucent.45. A heat transfer asscmbly according to claim 44, whercin the envelope is glass.46. A heat transfer assembly according to any one of claims 43 to 45, wherein thc hcat exchanger comprises a lube which passes through a first end of the heal transfer chamber, cxtcnds along substantially thc whole length of the heat transfcr chamber, and turns back to pass for a second time through the first end of the heat transfer chamber, and further comprises a tube which passes twice through a first end of the envelope.47. A heat transfer assembly according to any one of claims 43 to 45, wherein the heat exchanger comprises a lube which passes lhrough a lirst end of the heal transfer chamber, exlends along subsiantiafly ihe whole length of ihe heal transfer chamber, and passes through a second end of the heal transfer chamber opposile the!irst end, and further comprises a tube which passes through a first end of the envelope, extends along substaniiálly the whok length of ihe envelope, and passes through a second end of ihe envelope opposite the lirsi end.48. A heat Iransfer assembly according lo claim 47, wherein the lube and/or the envelope comprise means to accommodate differential thermal expansion between thc tube and heal transfer device, and Ihe envelope.49. A heal transfer assembly according to claim 48, wherein the means to accommodate dilierenlial thermal expansion comprise bends in Ihe Lube.50. A heal lransfer assembly according lo any one of claims 43 to 45, wherein the heat exchanger comprises a lube which passes through a firsl end of the heal transfer chamber, extends along substantially the whole length of the heat transfer chamber, and passes through a second end of the heat transfer chamber opposite the first end, and ifirther comprises a tube which passes though a first end of the envelope, passes through the heat transfer chamber, and turns back to pass for a second time through the first end of the envelope.51. A heat transfer assembly according to any one of claims 43 to 50, wherein the heat transfer assembly is arranged for rotation about a rotation axis.52. A heal transfer assembly according lo claim 51 wherein the elongale envelope is cylindrical and has an axis of symmetry, and the axis of rotation is parallel to the axis of symmetry.53. A heat transfcr assembly according to claim 52, wherein the axis of rotation and the axis of symmetry are coaxial.54. A heal Lransfer assembly according lo any one oF claims Si lo 53, when dependent from onc of claims 47 to 50, whcrcin thc axis of rotation coincides with the location of a tubc passing through an end of the cnvelopc.55. A heal Lransfer assembly according lo any one oF claims Si lo 53, when dependent from one oF claims 46 or SO, wherein the tube passes twice ihrough Ihe lirsl end of ihe envelope and Ihe axis of rotation passes between Ihe localions al which the luhes pass through the first end of the envelope.56. A heal Iransfer assembly according lo claim 55, wherein ihe axis of rotalion passes centrally between the locations at which the tubes pass through the first cnd of the elongate envclope.57. A solar collector array comprising a plurality of heat transfer assemblies according lo any one of claims 51 lo 56 mounted in parallel on a common supporting struclure.58. A solar collector array according to claim 57, and further comprising means for synchronously rotating all of the plurality of heat transfer assemblies relative to the supporting structure about their respective axes of rotation.59. A solar collector array according to claim 57 or claim 58 and further comprising means for rotating the supporting structure about an axis perpendicular to the axes of rotation of the heat transfer assemblies.60. A heal iransfer assembly comprising a ph.trality of connected heat transfer devices each according to any one of claims 29 to 42, wherein each heat transfer device has a separale heal iransier chamber; and an envelope: the pluralily of heal transfer devices heing localed within the envelope.61. A heal iransier assembly according lo claim 60, and fttriher comprising a heat exchange nelwork, the heal exchange network connecling the respeclive heat exchangers of the plurality of heat transfer devices.62. A heat transfer asscmbly according to claim 60 or claim 61, wherein the envelope is an elongate envelope.63. A heat transfer assembly according to any one of claims 60 to 62, wherein the envelope is transparent or translucent.64. A heat transfer assembly according to claim 63, wherein the envelope is glass.65. A heal iransfer assembly according to claim 6 I, wherein the heat exchange network compriscs a plurality of tubcs which pass through an cnd of thc cnvclopc.66. A heat transfer assembly according lo any one of claims 60 to 65, wherein ihe envelope is at leasi parlially evacualed.67. A heal iransfer assembly according lo any one of claims 60 to 66, wherein the heat transfer assembly is arranged for rolation about a rolalion axis.68. A heat transfer assembly according to claim 67, wherein the envelope is cylindrical and has an axis of symmetry, and Ihe axis of rotation is parallel to Ihe axis of symmetry.69. A heal transfer assembly according to claim 68, wherein the axis of rolalion and ihe axis of symmetry are coaxial.70. A heat transfer assembly according to any one of claims 67 to 69, when dependent from claim 65, wherein the axis of rotation coincides with the location of a tube passing through an end of the envelope.71. A solar collector array comprising a plurality of heat transfer assemblies according to any one of claims 60 lo 70 mounted in parallel on a common supporting struclure.72. A solar collector array according lo claim 71, and further comprising means br synchronously rolaling all of the plurality of heal Iransfer assemblies relalive to ihe supporling slruclure about their respeclive axes of rotation.73. A solar collector array according to claim 71 or claim 72, and further comprising means for rotating the supporting structure about an axis perpendicular to the axes of rolalion of Ihe heal iransler assemblies.74. A heat transfcr device comprising: a fluid flow means partially filled with a liquid and arranged so IhaL a firsl surface is in themml contact with the liquid in a part of the fluid flow means inclined to the horizontal and containing the liquid; the first part of the fluid flow means being divided into a plurality of first fluid flow channels each having an upper end and a lower end and at least one second fluid flow channel having an upper end and a lower end arranged so that the liquid in the first fluid flow channels is in better thermal contact with the first surface than the liquid in the second fluid flow channel; and the upper ends of the first and second fluid flow channels being connected together by a vapor manifold, and a second surface being located in the vapor manifold; wherein the vapor manifold is at least partially evacuated; whereby, when the first surface is hotter than the second surface, heat energy from the lirsl surface causes Ihe liquid in the lirsl Iluid how channel Lo vaporiIe, and the vapor travels through the liquid in the first fluid flow channel to the surface of the liquid, such LhaL Lhe Uquid circulates around Ihe firsi hluid flow channel and the second Iluid flow channel; vapor Lraveh from ihe surface of the liquid through the vapor manifold lo the second surface and condenses al the second surface; and condensed liquid reLurns from the second surface Lo ihe firsL pan o1 Lhe fluid how means: whereby heat energy is transported from the first surface to the second surface.75. A heat transfer device according to claim 74, wherein the second surface is a surface of a heat exchanger containing a fluid, whereby, when the first surface is hotter than the fluid, heat energy is transported from the first surface to the fluid.76. A heat exchanger according to claim 75, wherein the second surface is an external surface of a Lube containing Lhe Iluid.77. A heat exchanger according to claim 76, whcrein the fluid is arrangcd to flow through Ihe tube.78. A heat exchanger according to claim 76 or claim 77, whcrein the vapor manifold extcnds between first and second opposed surfaccs, and the tubc passes through the first surface, extends through the vapor manifold betwccn the first and second surfaces, and passes through the second surface.79. A heat exchanger according to claim 76 or claim 77, whcrein the vapor manifold compriscs a surface, and thc tubc passes through the surface, extends within thc vapor manifold, and passes through the surface for a second time.80. A heat exchanger according to claim 77, wherein the vapor manifold comprises a surface, Ihe tube passes through Lhe Iirst surface and exlends wiihin Lhe vapor manifold; and an inner lube is arranged wiLhin the Lube, whereby the fluid is arranged Lo how through the inner tube, and to flow between the tube and the inner tube.81. A heal transfer device according Lo any one of claims 74 Lo 80, wherein the firsL pan of Lhe fluid flow means is divided into a pluraliLy of second Iluid how channels.82. A heat transfer device according to claim 81, wherein the number of first fluid flow channcls is the same as the number of second fluid flow channels.83. A heat transfer dcvice according to claim 81 or claim 82, whcrein thc first and second fluid flow channels are located side by side with first fluid flow channcls and second fluid flow channels interleaved.84. A heat transfer device according to any one of claims Si to 83, wherein Ihe cross sectional area of the first fluid flow channels and the cross sectional area of the second fluid flow channcls are cqual.55. A heat transfcr devicc according to any onc of claims 81 to 84, whcrein each first fluid flow channcl is in thermal contact with thc first surfacc across a greater arca than cach second fluid flow channcl.86. A heat transfcr devicc according to any onc of claims 74 to 85, whcrein thc lowcr cnds of thc first and sccond fluid flow channels are connected togcthcr.57. A heat transfcr devicc according to any one of claims 74 to 86, whercin thc first part of the fluid flow means is inclined to the horizontal by an angle of up to 90°.88. A heat transfer device according to any one of claims 74 to 87, wherein the liquid comprises water.59. A heal transfer device according to any one of claims 74 to 88, wherein the Iluid comprises water.90. A heal Iransfer device according to any one of daims 74 to 89, wherein the liquid comprises eihanoL 91. A hcat transfcr dcvicc according to any onc of claims 74 to 90, whcrcin thc liquid compriscs a mixturc of water and ethanol.92. A hcat transfcr dcvicc according to any one of claims 74 to 91, wherein thc part of thc fluid flow mcans above the surfacc of the liquid is at a prcssurc of 1 0 mbar or lcss.93. A heat transfer device according to claim 92, wherein the part of the fluid flow means above the surface ol the hquid is ala pressure of Ift6mhar or less.94. A heat transfcr device comprising: a plurality of first Iluid flow channels each having an upper and a lower end, inclined to the horizontal, and containing a liquid; a second fluid flow channel having an upper and a lower end, connected to the first fluid flow channels and containing the liquid; a vapor manifold connecting the upper ends of the first and second fluid flow channels; a first surface in thermal contact with the liquid in the first fluid flow channel; and a second surface in the vapor manifold; whereby, when the first surface is hotter than the second surface, heat energy from the first surface causes liquid in the first fluid flow channels to vaporize; the vapor travels upwardly along the first fluid flow channels; the vapor drives a flow of liquid from the second fluid flow channel to the first fluid how channels and upwardly along the first fluid flow channels: and the vapor travels from a surface of the liquid to the second surface and condenses at the second surface; whereby heat energy is transported away from the first surface to the second surface.95. A heat transfer device comprising: a first surface: a second surface: a liquid reservoir in thermal contact with the first surface and containing a liquid; wherein the liquid reservoir comprises a plurality of first fluid flow channels inclined to the horizontal and containing the liquid and a second fluid flow channel connected to the first fluid flow channel and containing the liquid; the device further comprising a vapor manifold connecting upper ends of the first and second fluid flow channels; the first surface is in thermal contact with the liquid in the first fluid flow channel, the second surface is in the vapor manilold: and the vapor manifold is at least partially evacuated; whcrcby, whcn the first surfacc is hotter than the sccond surface, heat energy from the lirsi surface causes Uquid in Ihe lirsi fluid flow channel to vapon-ze; the vapor travels upwardly along the first fluid flow channel, into the vapor manifold, and condenscs at thc sccond surface; the vapor drives a flow of liquid from the second fluid flow channel to the first fluid flow channel and upwardly along the first fluid flow channel; and condenscd liquid returns from the second surface to the liquid reservoir; whcreby heat cncrgy is transported away from the first surfacc to the sccond surface.96. An energy gencrator comprising a hcat transfer device or assembly according to any preceding claim, and at least one photovoltaic element, the energy generator having an electrical output and a heated fluid output.97. A heat transFer device suhsLantially as show-n in, or as described with reference Lu, (be accompanying figures.98. A heat transfer assembly substantially as shown in, or as described with reference to, the accompanying figures.