GB2434439A

GB2434439A - Roof tile solar collector containing granular absorbers

Info

Publication number: GB2434439A
Application number: GB0601073A
Authority: GB
Inventors: Martyn Johnson-Townley
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-01-19
Filing date: 2006-01-19
Publication date: 2007-07-25
Also published as: GB0601073D0

Abstract

A black body tile device wherein granule means 2 fill the enclosure behind a transparent planar surface means 3, 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 3, said apertures and matching cavities are close approximations to ideal black bodies and incident sunlight is absorbed. Water 17, 18 flows in contact with the granule means 2 and absorbs heat energy. Black body tile device 4 has the same geometry as conventional roof tiles so it can interlock with adjacent black body tile devices or conventional tiles, said black body tile device having tile like qualities. A plurality of tile devices can be joined together to compose a solar water heating panel to be mounted on a roof. The heat absorbing granules or particles may be black glass beads or ball bearings, "blackadised" metal pellets or nylon spheres. Pellets may be 3mm long by 2mm diameter.

Description

A black body tile device This invention relates to technology to

facilitate the installation and manufacture of roof mounted solar energy panels in the form of black body tile devices. The black body tile devices can be mounted on a roof structure in the same fashion as conventional tiles. The black body tile devices can be physically incorporated in the roof of new build housing using normal tiling skills.

Much prior art refers to devices that use solar energy to heat water, thereby achieving useful work from the energy in sunlight. To present, the take up of such devices has not been impressive. 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 expense. The present invention addresses a technology that leads to easier manufacture of these devices thereby improving the economic case for more widespread application. Moreover the present invention describes a way of making roof tiles that incorporate the ability to heat water using the energy contained in sunlight. The widespread adoption of such roof tiles in new build housing would remove the requirement to retro-fit conventional solar panels.

The present invention proposes a black body tile device wherein a plurality of granule means fill the enclosure behind a transparent planar surface means that is part of the black body tile device to be mounted on a roof as part of a solar energy collector and in said black body tile device the upper transparent planar surface means and the lower insulated surface means and four walls form a container that contains the plurality of granule means 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 and incident sunlight is able to enter said apertures and said incident sunlight is absorbed in the cavities associated with said apertures said granule means are themselves good black bodies and water or fluid flows in intimate contact with said granule means and absorbs heat energy from said granule means said black body tile device has the same geometry as conventional roof tiles so it can interlock with adjacent black body tile devices or conventional tiles in the same fashion that conventional tiles fit together said black body tile device being able to manifest itself as a tile and having tile like qualities in addition to the ability to heat water using the energy of the sun and a plurality of black body tile devices can be joined together such that said plurality of black body tile devices are part of the same water circuit.

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 to permit heat energy to be transferred to the fluid. The heat contained in the fluid is then available to do useful work, for instance, by heating water. The heat exchange fluid is confined to a separate circuit. Many devices described in prior art are "direct systems". Water is conveyed directly to a solar collector array that heats the water. The water is then made available as part of a hot water supply system. The solar collector and the hot water supply system are both part of the same circuit.

The present invention is applicable to both direct and indirect systems.

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. Cost expressed in terms of complexity of manufacture usually precludes the incorporation of such devices in roof tiles.

The plurality of granule means contained within the black body tile device act as black body absorbers. The black body tile device has one transparent planar surface means facing the sky and a lower insulated surface means resting against a supporting structure. The black body tile device has walls in order to form a container. Said granule means can be poured or inserted into the container and then sealed in. This implies a simple manufacturing process whereby, for example, one wall of the container can be left open in order that said granule means can be inserted into the container. Once filling is complete the remaining wall seals the container of the black body tile device. The black body tile device is equipped with an inlet means and an outlet means. Some black body tile devices can also be equipped with sensors to facilitate control as is well described in prior art. Also well described in prior art and equally applicable to the present invention are means to protect against frost and means to protect against overheat conditions.

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

The geometry of said inlet means and outlet means can be arranged so that adjacent black body tile devices can fit together so that the outlet means of one black body tile device is next to the inlet means of the adjacent black body tile device. The objective of such geometry is that a plurality of black body tile devices can be part of the same water or fluid circuit thus composing as large a surface area of solar panel as is deemed necessary.

The walls of the black body tile device may or may not be insulated. Inside a solar panel a black body tile device only looses heat though its walls to adjacent black body tile devices.

However, on the exterior of a panel heat is lost to the environment through the walls-a calculation must be made to determine whether a special black body tile device with insulated walls is cost effective.

The present invention can be used to supply solar heated water to either direct or indirect systems since it is envisaged that and granule means and the material of the black body tile device can be either water or heat transfer fluid proof.

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 black body tile device 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 106mm2. A granule is 3.5 mm maximum overall dimension i.e. 10mm2. In this case we assume that the solar panel is a plurality of black body tile devices.

it can be seen that approximately 0.25 x 106 granules are exposed to sunlight through the transparent planar surface means. Because of the random nature of the packing of the granule means and because of the imperfect mutual fit of the individual granule means there will be a very large number of gaps or apertures between the granules. These apertures are close against the transparent planar surface means and are exposed to incident light. So an approximate model of the present invention is to describe the random settling of the granule means of the black body tile device in terms of layers: the first layer of granules is packed randomly against the transparent planar surface means of the container. The second layer is packed randomly against the first layer, the third layer is packed against the second. The imperfect fit of the granules in the second layer against the granules in the first 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 formed 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 10 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 (I Ox greater and lOOx greater respectively) So from a practical point of view we can make a solar panel from a plurality of black body tile devices that is massively populated with aperture to cavity formation. Moreover the individual granules of the granule means can be engineered or chosen to have good emissivity. So the formation of black body cavities by the random packing of the granules amongst themselves is in addition to the black body characteristics of the granule means. So where granule means have not formed cavities through random packing they can still contribute to the heat absorbtion characteristics of the black body tile 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 tile device with one of the coatings designed to improve the black body characteristics of a given surface.

To take a practical example: black ABS plastic granules 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 tile device.

The granule means of the black body tile device are themselves black bodies. In further embodiments of the present invention the granule means of the black body tile 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 or fluid as well as enhancing black body characteristics. The determining factor in the size and shape of the granule means is that their cross section and size enables them to be poured or be placed or be inserted or be projected easily into the container of the black body tile device.

In a further refinement of the present invention each granule in the granule means of the black body tile 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 tile device has three distinct modes of absorbing energy from sunlight: - 1) The random packing of the granule means within the container of the black body tile device will present a plurality of apertures to cavities to the incident sunlight. This happens when granules together take up positions at random relative to each other such that there is an aperture to a cavity.

2) The surface of each granule of the granule means of the black body tile device has good black body characteristics.

3) The individual granules can be manufactured so that each one has its own cavity or cavities. When the container of the black body tile device 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 water or fluid to be heated flows through the black body tile device in direct contact with the granule means. The water or fluid is assumed to be either transparent or not to markedly affect the transmission of light. Heat transfer can take place directly between the granule means and the water or fluid.

A further advantage of the present invention is that the granule means of the black body tile 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.

There are many off the shelf materials suitable as granule means: -I) Many types of black plastic granules are suitable.

2) Black glass beads.

3) Black corrosion proof ball bearings.

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

5) Spherical filled nylon. The nylon is black and the spheres have a small diameter compared with the internal dimensions of the container of the black body tile device.

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

Another example of a material for the granule means of the black body tile device could be 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.

The water or heat transfer fluid flows in direct contact over the plurality of randomly packed granules that constitute the granule means of the black body tile 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.

A means of guiding the flow of water or heat transfer fluid within the black body tile device is proposed. This is to ensure that the flow is uniform across the black body tile device and that all of the granules of the black body tile 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 container of the black body tile device in such positions as to guide the flow of fluid or water in, for example, a zig-zag fashion within the black body tile device. In this way the water will address every part of the container of the black body tile device.

An advantage of the present invention is that a plurality of simple production processes for black body tile devices can be envisaged. Many of these processes involve the fabrication of a container in the format of a tile with a transparent face to the sun and otherwise well insulated. The container can be fabricated complete but with one end left open. In a preferred embodiment of the present invention, a tile shaped container of internal depth, d is filled with granule means of average maximum individual granule overall dimension, say, d/4. The granules can be decanted, blown or propelled into the container. The divisor four is approximate but it is chosen to provide a granule means that can flow easily into the container. Once filled, the container would be sealed. The tile shaped container is ready equipped with inlet means and outlet means and sensors (if necessary) as per much prior art. Comparisons can be drawn with the ease of fabrication of conventional solar panels.

There will be two types of black body tile device: one with and one without sensors. Black body tile devices will be deployed to make any size of solar panel. Normally, only two sensor equipped black body tile devices would be needed: one at the cold water in and another at the hot water out. However, a further advantage of the present invention is the ability to include intermediate sensor tiles in a large panel.

A further advantage of the present invention is the ability to swap black bodies in the production process. If the black body tile device is produced within the form envelope of a standard ceramic tile and a new granule means is discovered. The new granule means can be substituted for the old one without impacting the production of the standard ceramic tile.

Frost protection is an issue for solar energy collection devices. The particulate nature of the granule means presents an opportunity to add a small percentage of compressible particle means to the granule means of the black body tile device. This compressibility enables them to absorb freezing forces. Once a thaw takes place the particles return to their original volume and shape by virtue of elasticity and "memory" properties. In another implementation the granules of the granule means can be compressible to absorb freezing forces, in addition to the other black body properties herein described. There are many suitable materials that exhibit these characteristics.

Any implementation of the present invention can make use of the many control technologies described in prior art. For example, overheat protection and frost protection.

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 black body tile 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 tile device. Figure 3 is a simplified vertical section normal to the plane of the transparent planar surface means.

Figure 4 shows a flow guidance system.

Figure 1 shows a typical black body tile device drawn three dimensionally. The layer of granule means 2 acting as a black body heat absorber is shown as an irregular lattice. The granule means 2 is confined between a transparent planar surface means 3 that is shown "cut back" and a lower insulated surface means 4. Inlet 17 and outlet 18 means for water or fluid are shown. The walls 20 of the black body tile device can be optionally insulated.

Figure 2 shows a possible aperture and cavity formation due the random packing of the granule means 2 of the black body tile 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 that are omitted for clarity. The 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 reflections 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 reflected 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 0.1 x 10% of its original energy after being reflected at 7 that is 1%. Absorbtion will, of course, continue at further reflections. The absorbtion process will manifest itself as a rise in temperature of the granule means 2.

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 tile device. Figure 3 is a development of figure 2. The six granules in figure 2 are now joined by many other granules. The ray geometry 5, 6, 7 is still visible but 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 simplifications 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 I I enters a cavity that has formed at random in the same fashion as ray 5. The energy of ray 11 is absorbed at 12 and is further absorbed at 13 and so on. This random cavity has a completely different geometry to the ray 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 11 and ray 5. But useful work is still done by ray 14.

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 controlled by a control means 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 tile device do useful work. The transparent planar surface means 3 that is visible in figure 1 has been omitted. As in figure 1 the layer of granule means 2 acting as a black body heat absorber is shown as an irregular lattice. Cold water 17 is shown entering, water heated by sunlight 18 is shown exiting to the hot water tank. Flow guidance means 19 are provided.

The flow guidance means have a depth equal to the depth of the container and they are sealed top and bottom by a sealing means. At one end of the flow guidance means there is no gap between the flow guide means and the container wall. At the other end there is a gap between the flow guidance means and the container wall. In this way the flow of water or fluid is channelled advantageously. Without the flow guidance means 19 there is the possibility of limited or non-existent flow in parts of the granule means 3. Note how the flow of water or fluid is forced to address the entire container. The scheme of flow guidance in figure 4 is one of many patterns of labyrinth that can be conceived to provide a flow guidance system for the present invention.

Claims

Claims I. A black body tile device wherein a plurality of granule means

fill the enclosure behind a transparent planar surface means that is part of the black body tile device to be mounted on a roof as part of a solar energy collector and in said black body tile device the upper transparent planar surface means and the lower insulated surface means and four walls form a container that contains the plurality of granule means 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 and incident sunlight is able to enter said apertures and said incident sunlight is absorbed in the cavities associated with said apertures said granule means are themselves good black bodies and water or fluid flows in intimate contact with said granule means and absorbs heat energy from said granule means said black body tile device has the same geometry as conventional roof tiles so it can interlock with adjacent black body tile devices or conventional tiles in the same fashion that conventional tiles fit together said black body tile device being able to manifest itself as a tile and having tile like qualities in addition to the ability to heat water using the energy of the sun and a plurality of black body tile devices can be joined together such that said plurality of black body tile devices are part of the same water circuit.

2. A black body tile device according to claim I that has a granule means.

3. A black body tile device according to claim 2 that has a container means.

4. A black body tile device according to claim 3 in which the container means has four walls and a transparent planar surface means facing the sky and a lower insulated surface means.

5. A black body tile device according to claims 2 and 3 and 4 that has granule means with dimensions chosen such that the granule means can be packed into the container means.

6. A black body tile device according to claim 5 such that the plurality of granule means are packed sufficiently tightly so as to fill the aperture of the transparent planar surface means of the container means.

7. A black body tile device according to any previous claim in which the granule means is exposed to sunlight through the transparent planar surface means of the container means.

8. A black body tile device according to claim 7 that has an inlet means to allow fluid to flow into the container means and an outlet means to allow fluid to flow out of the container means.

9. A black body tile device according to any previous claim that can manifest itself as a conventional roofing tile.

10. A black body tile device according to claim 8 that has a geometry that allows the fluid outlet means of one black body tile device to be next to the fluid inlet means of an adjacent black body tile device.

11. A black body tile device according to claim 10 such that adjacent black body tile devices can become part of the same fluid or water circuit by connecting the fluid outlet means of a given black body tile device with the fluid inlet means of an adjacent black body tile device.

12. A black body tile device according to claim 11 such that a plurality of black body tile devices are able to become part of the same fluid or water circuit.

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

14. A black body tile device according to claim 13 such that said black body cavities absorb useful heat energy from sunlight according to the physics of a black body by multiple internal reflections.

15. A black body tile device according to claim 2 wherein the granule means are themselves good approximations to an ideal black body.

16. A black body tile device according to claim 2 wherein each granule means can have its own aperture and cavity.

17. A black body tile device according to claim 16 wherein the random alignment and packing of the granule means will ensure that the plurality of apertures are facing the sunlight.

18. A black body tile device according to claim 2 wherein the granule means are coated in such a way as to improve the black body characteristics of the granule means.

19. A black body tile device according to claim 2 wherein the granule means are dimpled or roughened in order to improve their black body characteristics.

20. A black body tile device according to claim 4 wherein sensors to detect temperature can be fitted to facilitate control functions.

21. A black body tile device according to claim 4 wherein 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 granule means of the black body tile device.

22. A black body tile device according to claim 4 wherein compressible particle means absorb freezing forces.

23. A black body tile device wherein a container means contains a granule means said granule means being a randomly packed aggregate of granules that provide a large population of apertures and associated cavities that are approximations to ideal black bodies and the granule means can be heated by sunlight through the transparent planar surface means of the container means and fluid or water circulates through said black body tile device in order to be usefully heated by contact with said granule means said black body tile device can be installed as roofing in the same fashion as conventional roof tiles and a plurality of black body tile devices can be connected together by inlet means and outlet means in order to compose a solar panel of whatever size is required and said black body tile device can be equipped with sensor means for control purposes.

24. A black body tile device according to claim 23 that has a granule means.

25. A black body tile device according to claim 24 that has a container means.

26. A black body tile device according to claim 25 in which the container means has four walls and a transparent planar surface means facing the sky and a lower insulated surface means.

27. A black body tile device according to claims 24 and 25 and 26 that has granule means with dimensions chosen such that the granule means can be packed into the container means.

28. A black body tile device according to claim 27 such that the plurality of granule means are packed sufficiently tightly so as to fill the aperture of the transparent planar surface means of the container means.

29. A black body tile device according to any previous claim in which the granule means is exposed to sunlight through the transparent planar surface means of the container means.

30. A black body tile device according to claim 29 that has an inlet means to allow fluid to flow into the container means and an outlet means to allow fluid to flow out of the container means.

31. A black body tile device according to any previous claim that can manifest itself as a conventional roofing tile.

32. A black body tile device according to claim 30 that has a geometry that allows the fluid outlet means of one black body tile device to be next to the fluid inlet means of an adjacent black body tile device.

33. A black body tile device according to claim 32 such that adjacent black body tile devices can become part of the same fluid or water circuit by connecting the fluid outlet means of a given black body tile device with the fluid inlet means of an adjacent black body tile device.

34. A black body tile device according to claim 33 such that a plurality of black body tile devices are able to become part of the same fluid or water circuit.

35. A black body tile device according to claim 28 such that the random packing of the granule means presents a plurality of approximations to black body apertures and cavities to incident sunlight.

36. A black body tile device according to claim 35 such that said black body cavities absorb useful heat energy from sunlight according to the physics of a black body by multiple internal reflections.

37. A black body tile device according to any previous claim wherein the granule means are themselves good approximations to an ideal black body.

38. A black body tile device according to any previous claim wherein each granule means can have its own aperture and cavity.

39. A black body tile device according to claim 38 wherein the random alignment and packing of the granule means will ensure that a plurality of apertures are facing the sunlight.

40. A black body tile device according to any previous claim wherein the granule means are coated in such a way as to improve the black body characteristics of the granule means.

4L A black body tile device according to any previous claim wherein the granule means are dimpled or roughened in order to improve their black body characteristics.

42. A black body tile device according to claim 26 wherein sensors to detect temperature can be fitted to facilitate control functions.

43. A black body tile device according to claim 26 wherein 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 granule means of the black body tile device.

44. A black body tile device according to any previous claim wherein a proportion of compressible particle means are added to the granule means in order to absorb freezing forces.

45. A black body tile device according to any previous claim wherein the granule means is compressible in order to absorb freezing forces.

46. A black body tile device substantially as herein described above and illustrated in the accompanying drawings.