GB2433311A

GB2433311A - A black body solar panel containing granules

Info

Publication number: GB2433311A
Application number: GB0524875A
Authority: GB
Inventors: Martyn Johnson-Townley
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-12-06
Filing date: 2005-12-06
Publication date: 2007-06-20
Also published as: GB0524875D0

Abstract

The black body device includes granules 2 that fill the enclosure behind a transparent planar surface 3 that is part of a container in a solar energy collection device. The random packing of granules 2 leads to a plurality of apertures and matching cavities forming in proximity to the transparent planar surface means 3. These apertures and matching cavities are close approximations to ideal black bodies. Incident sunlight 5, 6, 7 is able to enter the apertures and be absorbed in the cavities associated with the apertures. The granules are themselves good black bodies. Water or fluid flows in intimate contact with the black body device and absorbs useful heat energy from it. The granules may have a cavity or cavities.

Description

A black body device This invention relates to technology to facilitate

the easier fabrication of solar energy driven water-heating units. Much prior art refers to devices that use solar energy to heat water, thereby achieving useful work from the energy in sunlight.

The physical principles of such devices are also well known. The physics of black bodies and black body radiation is well known. To present, the take up of such devices has not been impressive, despite the obvious environmental and economic benefits. For example, in many countries it is not obligatory for new build housing to include such devices. The main issue with prior art is one of expeiise. The present invention addresses a technology that leads to easier manufacture of these devices thereby improving the economic case for more widespread application.

The present invention proposes a black body device including a plurality of granule means that fill the enclosure behind a transparent planar surface means that is part of a container iii a solar energy collection device the random packing of said granule means leads to a plurality of apertures and matching cavities forming in proximity to the transparent planar surface means said apertures and matching cavities are close approximations to ideal black bodies incident sunlight is able to enter said apertures said incident sunlight is absorbed in the cavities associated with said apertures said granule means are themselves good black bodies water or fluid flows in intimate contact with said black body device and absorbs heat energy from said black body device Many devices described in prior art use a fluid as a heat exchange medium, so called "indirect systems'. This heat exchange fluid is conveyed to a solar collector array that is optimised to capture heat from the sun and then permit the heat energy to he transferred to the fluid. The heat contained in the fluid is then available to do useful work, for instance, by transferring its heat energy to water. The water is then made available as part of a hot water supply system.

Many devices described in prior art are "direct systems". Water is conveyed directly to a solar collector array that captures heat that is transferred to the water. The water is then made available as part of a hot water supply system.

Both direct and indirect devices described in prior art use specific configurations of transparent glass or plastic tubing or metal fabrication consisting of networks of tubes to carry heat away from a black body within the solar collector array. These devices are nearly always custom made with all that implies in terms of cost.

The present invention can manifest itself as a direct or an indirect system.

l'he present invention proposes a "generalised" black body device for use in such systems.

Said black body device is a plurality of granule means. A solar panel as described in much prior art will have a transparent flat container means. The transparent flat container means will have one transparent planar surface facing the sun, the other planar surface is normally insulated and is face down against a roof or other structure. Said black body device can he poured or inserted into a transparent fiat container means in order to form the basis for either a direct or indirect solar energy collection device.

Said black body device is easily fabricated. For most solar panel applications it can be fabricated from off the shelf materials. Said black body device also lends itself to a plurality of mass production methodologies. Most of these methodologies are simple to implement.

Some methodologies would be suitable for a low skill, low technology environment such as a third world country.

Provision is made for water or heat exchange fluid to enter and exit the transparent flat container means. The transparent flat container means will also be provided with sensors to detect water or fluid temperature and devices to guard against over heating and frost damage

as is well described in prior art.

The granules of the black body device are exposed to sunlight through the transparent planar surface. The black body device is composed of a granular aggregate. Where the granular aggregate meets the confining transparent planar surface of the container means there are a plurality of opportunities for the granules to form black body cavities. Each such cavity formed by the random packing of the granules amongst themselves is an approximation to an ideal cavity.

The random packing of the granule means will present a plurality of cavities to the incoming sunlight. This happens when granules together take up positions relative to each other such that an opening or aperture to a cavity is presented to the incoming sunlight. This is a random process. So we have "aperture to a cavity formation" which is the classical means to approach as near as possible an ideal black body. However, because of the large number of granule means involved in the filling of a typical solar panel many such random cavities will be formed. To give an idea of orders of magnitude, a typical solar panel is 2.5 m2. This is 2.5 x lO6mrn2. A granule is 3.5 mm maximum overall dimension i.e. -10mm2.

It can be seen that approximately 0.25 x 106 granules present themselves to sunlight. Because of the random nature of the packing of the granules and because of the imperfect mutual lit of the granules there will he a very large number of gaps or apertures between the granules.

l'hese apertures are close against the transparent planar surface and are exposed to incident light. So an approximate model of the present invention is to describe the random settling of the black body device in terms of layers: the first layer of granules is packed tight against the transparent planar surface means of the container means. The second layer is packed tight against the first layer, the third layer is tight against the second. Again, the imperfect mutual fit of the granules in the second layer leads to cavity formation.

The random settlement of the granules layer upon layer leads to the formation of cavities.

Because of the large number of randomly settled granules in the top layer there are a very large number of openings formed in the top layer. These openings will in practically every case connect with a cavity that has lormed at random between the first and second layers.

It is conceivable in the present invention that further cavities can form at random between the second and third layers of granules. Although the cavities are irregular and in many cases not even totally closed they will in most cases approximate to a theoretical black body. Refer to figure 03.

To take this model further we can envisage much smaller granule means, say 1 mm2 (factor of smaller) or even factor of 100 smaller. As the size of the granule means reduces by these factors the rate of"aperture to a cavity formation" increases by the inverse order of magnitude (lOx greater and 1 OOx greater respectively) So from a practical point of view we can make a solar panel which is massively populated with aperture to cavity formation. Moreover the individual granules of the granule means caii be engineered or chosen to have good emissivity. So the formation of black body cavities by the random packing of the granules inter alia is in addition to the black body characteristics of the individual granules of the black body device. So where granules have not formed a cavity through random packing they can still contribute to the heat absorbtion characteristics of the black body device. So depending on materials used and the economics of a particular situation it may be cost effective to coat the granules of the black body device with one of the coatings designed to improve the black body characteristics of a given surface. For example "coating" might be justified for a solar collector destined for northern latitudes. These markets being less price sensitive on average than more equatorial regions but with less power from sunlight available than equatorial regions. To take a practical example, black ABS plastic graiiules as supplied fOr injection moulding can be the granule means in the present invention. The black ABS plastic granules can be used "off the shelf' for the most economical implementation of the present invention. However, it is well known that increasing surface roughness increases emissivity, so the granules can be roughened by tumbling in sharp sand or by chemical means. This refinement will increase the efficiency of the black body device.

The granule means of the black body device are themselves black bodies. In further embodiments of the present invention the granule means of the black body device could be composed of any granule or pellet with suitable black body characteristics: be it spherical, cuboid, or even short rods. The surface of any such granule can be textured to increase surface area. Such texturing can promote heat transfer with the water as well as enhancing black body characteristics. The determining factor in the size and shape of the granule means is that cross section and size of the black body device enables the black body device to be poured or he placed or be inserted or be projected easily into the transparent flat container means of the solar panel.

In a further refinement of the present invention each granule in the granule means of the black body device could be moulded so as to have a cavity or cavities (or possibly dimples). This refinement may or may not be cost effective.

To summarize, the black body device has three distinct modes of absorbing eiiergy from sunlight: -I) The random packing of the granule means of the black body device will present a plurality of apertures to cavities to the incident sunlight. This happens when granules together take up positions relative to each other such that there is an aperture to a cavity.

2) [he surface of each granule of the granule means of the black body device has good black body characteristics.

3) The individual granules can be maufactured so that each one has its own cavity or cavities.

When the container means is filled the random alignment and packing of the granules will ensure that many of these cavity openings are facing the sunlight.

In the present invention the waler or fluid to he heated flows directly through the black body device. I.e. the water or fluid which are both transparent will not affect the optical properties of the aperturc/ cavities of the black body device. heal transfer can take place directly between the granule means and the water or fluid.

A further advantage of the present invention is that the black body device presents a large surface area to the cooling water or fluid. This is because of its granular nature, each granule contributing its own surface area and the large number of granules implying a large surface area, much larger than could be achieved by a similar weight of tubular fabrication. This is in contrast to traditional solar devices that are cooled by tubing or radiator type fabrications.

Ihere are many "off the shelP' materials suitable as granular means in a black body device: -I) Many types of black plastic granules which are suitable.

2) Black glass beads.

3) Black corrosion proof ball bearings.

4) There are a number of "blackadised" metals that would be suitable.

5) Spherical filled nylon. The nylon is black and the spheres have a small diameter compared with the internal dimensions of the transparent fiat container of the solar panel.

The granules of the granule means have a section and shape and size chosen to facilitate an easy production process. The individual granules that constitute a black body device could have any one of a number of commercially available forms or sections or shapes. The material of the granules could he any material that has suitable black body characteristics and is proof against water (direct) or the heat transfer fluid (indirect).

Another example of a material for the granule means of the black body device could he ABS pellets or granules. Each pellet is approximately 3mm long by 2mm diameter -i.e. an irregular cylinder. The walls of the cylinder are often shiny and may need to be dulled in order to increase the effectiveness of the individual granules as black bodies. So one might envisage an industrial process whereby the granules are dulled by, for example, tumbling in sand to roughen their surfaces. Once roughening is complete the granules can be floated off to separate them from the sand. Boiling the granules in caustic soda has also been found to dull the surface of many plastics advantageously.

The water or heal transfer fluid flows in direct contact over the plurality of randomly packed granules that constitute the black body device. As a result the granules give up useful heat energy to the water or heat transfer fluid. This means that the material of the granule means must be proof against water or the heat transfer fluid.

In the case of a large solar panel with one entrance and one exit a means of guiding the flow of water or heat transfer fluid is proposed. This is to ensure that the flow is uniform across the panel and that all of the granules of the black body device are able to contribute heat energy to the flow. The flow guidance means can be simple narrow strips of suitable fluid proof material (such as a plastic). The flow guidance means are disposed within the transparent flat container means in such positions as to guide the flow of fluid or water in, for example, a zig zag Fashion within the transparent fiat container means. In this way the water will address every part of the transparent flat container means.

An advantage of the present invention is that a plurality of simple production processes for solar panels can be envisaged. Many of these processes involve the fabrication of transparent fiat container means in the form of standard flat tanks with a transparent face to the sun and otherwise well insulated. A flat tank can be fabricated complete but with one end left open. In a preferred embodiment of the present invention, a transparent flat container means of internal depth, d is filled with black body device of average maximum granular overall dimension, say, d14. The black body device can be decanted, blown or propelled into the tank. The divisor four is approximate but it is chosen to provide a black body device which can flow easily into the tank. Once filled, the tank would be sealed. The tank is, of course, ready equipped with inlet! outlet for water fluid and sensors as per much prior art.

A further advantage of the present invention is the ability to swap black bodies in the production process. For example the transparent flat container means could be a standard flat glass tank. If a new coating is discovered for the granular means which consitutes the black body device. l'hen the new black body device can be substituted for the old one without impacting the production of the standard flat glass tank.

Frost protection is an issue for solar energy collection devices. The particulate nature of the black body presents an opportunity to add a small percentage of sacrificial crushable particles to the black body device. The sacrificial particles can themselves be "compressible". This compressibility enables them to absorb freezing forces.

The invention will now be described by way of different implementations and with reference to the accompanying drawings in which: -Figure 1 shows a typical transparent fiat container means containing the black body device drawn three dimensionally.

Figure 2 shows cavity and aperture formation and an incident light ray being absorbed. Figure 2 is a simplified vertical section normal to the plane of the transparent planar surface means.

Figure 3 is a development of figure 2 and shows the plurality of close approximations to ideal black bodies achieved by the random positioning of granule means within the black body device. Figure 3 is a simplified vertical section normal to the plane of the transparent flat container means.

Figure 4 shows a flow guidaiice system within the flat container nieans of the solar panel.

Figure 1 shows a typical fiat container means drawn three dimensionally. The layer of granule means corresponding to the black body device is shown as a square latice or hatching. The black body device is confined between a glass or plastic transparent planar surface means 3 that is shown "cut back" and a typical air cavity insulation means 4.

Figure 2 shows a possible aperture and cavity formation due the random packing of the granule means 2 of the black body device. The granule means 2 are packed against the glass or plastic transparent planar surface means 3. In reality there are many other granule means, these are omitted for clarity. I'he granule means 2 in this manifestation of the present invention are black cylindrical granules approximately 3mm long by 1.5mm diameter. The ends of the cylinders are irregular. A possible material for the granule means is black ABS plastic as supplied ready for use in injection moulding machines. An incident light ray 5 is shown making three rellections at the surface of three successive granule means 2. In reality there are many other incident light rays. So figure 2 shows radiation being absorbed in what is, in fact, an approximation to a black body cavity. Assume that the granule means have an emissivity of 0.9. At the first reflection 6 the light is not relected back into space as it would be from a flat surface. Instead it is reflected towards another point in the interior of the cavity 7. At the first reflection 90% is absorbed, leaving 10% of the ray's original energy to reach 7.

The ray 5 has only 0. I x 10% of its original eiiergy after being reflected at 7 that is 1%.

Absorbtion will, of course, continue at further reflections.

Figure 3 shows the plurality of close approximations to ideal black bodies achieved by the random positioning of granule means 2 within the black body device. Figure 3 is a development of figure 2. The six isolated granules in figure 2 are now joined by many other granules. The ray geometry 5, 6, 7 is still visible hut note that there is now a more realistic random packing of granule means with extra "random" granules at 8 and 9 respectively.

Figures 2 and 3 are simplificatioiis of the real three dimensional situation. For instance there would probably be many more granules lying with their axis pointing approximately out of the page such as 10.

In figure 3 there is another incident ray I I. Ray 11 enters a cavity which has formed at random in the same fashion as ray 5. The energy of ray II is absorbed at 12 and is further absorbed at 13 and so on. This random cavity has a completely different geometry to the ray 5 cavity but it is still an effective absorber.

In figure 3 a third incident ray 14 is reflected at 15 and 16. Ray 14 has entered a less than ideal cavity and is finally reflected back into space 16 by the rough end of a granule means.

Ray 14 is less well absorbed than ray II and ray 5. But useful work is still done by ray 14.

Remember that there is a continuous flow of water or heat transfer fluid (not shown) through the granules. Said flow absorbs heat energy from the granules. A pump means (not shown) can provide a water or fluid flow proportional to the incident sunlight as is well described in

prior art.

In figure 4 we see a simple flow guidance system to ensure that all parts of the black body device do useful work. The transparent planar surface means that is visible in figure 1 has been omitted. As in figure 1 the layer of granule means corresponding to the black body device is shown as a square hatching. Cold water 17 is shown entering, water heated by sunlight 18 is shown exiting to the hot water tank. 17 and 18 will, in fact, be inlet and outlet pipes. Flow guide means 19 are provided. The guides have a depth equal to the depth of the transparent flat container means and they are sealed top and bottom by a sealing means. At one end the guide is flush with the tank wall. At the other end there is a gap between the guide and the tank wall. In this way the flow of water or fluid is chanelled advantageously. Without the guides there is the possibility of limited or non existant flow in parts of the black body device because of the homogenous nature of the black body device and the absence of tubing found in conventional solar panels. Note how the flow of water or fluid is forced to zig-zag across the entire panel.

Claims

Claims 1. A black body device including a plurality of granule means

that fill the enclosure behind a transparent planar surface means that is part of a container in a solar energy collection device the random packing of said granule means leads to a plurality olapertures and matching cavities forming in proximity to the transparent planar surface means said apertures and matching cavities are close approximations to ideal black bodies incident sunlight is able to enter said apertures said incident sunlight is absorbed in the cavities associated with said apertures said granule means are themselves good black bodies water or fluid flows in intimate contact with said black body device and absorbs heat energy from said black body device0
2. A black body device according to claim I that is composed of a plurality of granule means.

3. A black body device according to claim 2 that has granule means with dimensions chosen such that the granule means can be packed into a container means as part of a solar energy collection device.

4. A black body device according to claim 3 such that the plurality of granule means are packed against the transparent planar surface means of the container means said container means being a component of a solar energy collection device.

5. A black body device according to claim 4 that is exposed to sunlight through the transparent planar surface means of the container means of the solar energy collection device.

6. A black body device according to claim 5 such that the random packing of the granule means presents a plurality of approximations to black body apertures and cavities to incident sunlight.

7. A black body device according to claim 6 such that said black body cavities absorb useful heat energy from sunlight according to the physics of a black body by multiple internal reflections.

8. A black body device according to claim 7 in which the granule means are themselves good approximations to an ideal black body.

9. A black body device according to claim 8 in which each granule means can have its own engineered aperture and cavity means.

10. A black body device according to claim 9 in which the random alignment and packing of the granule means will ensure that a plurality of engineered aperture and cavity means are facing the sunlight.

II. A black body device according to claim 7 in which the granule means are coated in such a way as to improve the black body characteristics of the granule means.

12. A black body device according to claim 7 in which the granule means are dimpled or roughened in order to improve their black body characteristics.

13. A black body device according to claim Sin which flow guidance means are provided within the container means to ensure that water flows at approximately the same rate through the entire volume of the black body device.

14. A black body device according to claim 13 in which sacrificial crushable granules absorb freezing forces.

15. A black body device composed of a granular aggregate that is contained in a transparent container means as part of a solar energy collection device the granular aggregate forms a plurality of aperture and cavity combinations which can absorb sunlight by multiple reflections inside said cavities the granules themselves of said granular aggregate have a high absorbtivity heat energy is transferred from the black body device directly to a flow of fluids 16. A black body device according to claim 15 that is composed of a plurality of granule means.

17. A black body device according to claim 16 that has granule means with dimensions chosen such that the granule means can be packed iiito a container means as part of a solar energy collection device.

18. A black body device according to claim 17 such that the plurality of granule means are packed against the transparent planar surface meaiis of the container means said container means being a component of a solar energy collection device.

19. A black body device according to claim 18 that is exposed to sunlight through the traiisparent planar surface means of the container means of the solar energy collection device.

20. A black body device according to claim 19 such that the random packing of the granule means presents a plurality of approximations to black body apertures and cavities to incident sunlight.

21. A black body device according to claim 20 such that said black body cavities absorb useful heat energy from sunlight according to the physics of a black body by multiple internal reflections.

22. A black body device according to claim 2 I in which the granule means are themselves good approximations to an ideal black body.

23. A black body device according to claim 22 in which each granule means can have its own engineered aperture and cavity means.

24. A black body device according to claim 23 in which the random alignment and packing of the granule means will ensure that a plurality of engineered aperture and cavity means are facing the sun light.

25. A black body device according to claim 21 iii which the granule means are coated in such a way as to improve the black body characteristics of the granule means.

26. A black body device according to claim 21 in which the granule means are dimpled or roughened in order to improve their black body characteristics.

27. A black body device according to claim 19 in which flow guidance means are provided within -10-the container means to ensure that water flows at approximately the same rate through the entire volume of the black body device.

28. A black body device according to claim 27 in which sacrificial crushable granules absorb freezing forces.

29. A solar energy collection device substantially as herein described above aiid illustrated in the accompanying drawings.