GB1580803A

GB1580803A - Solar energy collector

Info

Publication number: GB1580803A
Application number: GB20544/76A
Authority: GB
Original assignee: MCGILVRAY I
Current assignee: MCGILVRAY I
Priority date: 1976-05-18
Filing date: 1976-05-18
Publication date: 1980-12-03

Description

(54) IMPROVEMENTS IN OR RELATING TO A SOLAR ENERGY COLLECTOR (71) I, IAN WARNER McGILVRAY, a British subiect, of 108 George Borrow Road, Norwich, Norfolk, England, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to an energy collector, and more particularly relates to a collector adapted to collect energy from light in the form of sun-light. In this specification the word "light" is used in a broad context to mean light, both visible and invisible to the human eye. Thus the term includes infrared radiation.

It has been proposed to utilise collectors to collect energy from light in the form of solar radiation, and such energy collectors have been termed "solar energy collectors". One type of prior proposed solar energy collector takes the form of a closed cycle collector where water is caused to flow through a pipe or conduit which passes through the solar energy collector. The pipe or conduit within the solar energy collector is provided with a matt black surface or is in contact with a panel or other such solar energy collecting member which has a matt black surface. Solar radiation falling on the matt black surface is absorbed, causing the temperature of the pipe or conduit to rise, and heat is thus conducted to the water flowing through the pipe or conduit. Thus the water leaves the solar energy collector at an elevated temperature.

A second type of prior proposed solar energy collector is an open cycle flat plate collector, and in such a collector water is made to run along one or more open channels defined by a substantially flat plate, and solar radiation absorbed by the surface of the flat plate, which is in contact with the water, is effectively transferred to the water, the temperature of the water thus rising. A typical prior proposed solar energy collector of this type takes the form of a housing provided with a tray of aluminium, copper or some other material having a high thermal conductivity, there being a sheet of glass or other transparent material across the open mouth of the tray. The base of the tray may be corrugated or smooth, although the base of the tray is generally planar, that is to say the base of the tray is not provided with any overall curvature.The base of the tray is usually formed to have a dark colour, which is preferably matt black. Located behind the tray within the housing, is a thermally in insulating material to prevent or minimise heat absorbed by the surface of the tray from being transmitted through the tray and being wasted.

It is to be appreciated that hot water generated by a solar energy collector of either of the two types described above can be utilised to heat water in a storage tank, the hot water from the solar energy collector being caused to flow through a heat exchange coil present in the storage tank and subsequently being returned to the solar collector.

One disadvantage of the first described prior proposed solar energy collector, that is to say the energy collector where the water flows through a pipe which is provided with a matt black surface, or which is in contact with a panel having a matt black surface, is that the conduit, and the panel (if provided) and the water contained within the system have a considerable thermal capacity and thus a considerable amount of energy is consumed merely in initially heating up the panel, the conduit and the water flowing through the circuit which includes the solar energy collector.This means that whilst the solar energy collector may well operate satisfactorily when the sun is shining continually, if the sun is only shining for brief periods of time, the solar energy absorbed initially by the device is utilised in raising the temperature of the conduit and the panel (if provided), and as water is continually flowing through a circuit which includes the solar energy collector, the temperature of the water rises only slowly.

Consequently a solar energy collector of this prior proposed type may well not operate satisfactorily in weather conditions such as are experienced in the British Isles in early spring or late autumn, when it is often the case that the sun only shines spasmodically.

A disadvantage of both the above described types of prior proposed solar energy collector is that the collectors are relatively expensive to make. In the case of the first described type of prior proposed collector the pipe or conduit must be formed of a material that has a good thermal conductivity, and similarly the panel must also be formed of a material that has good thermal conductivity. Such materials tend to be expensive. Similarly in connection with the second described type of prior proposed solar energy collector is that the tray must be formed of a material of good thermal conductivity, so that the tray is able to transfer absorbed heat efficiently to the water, and as mentioned above, such materials are relatively expensive.

In utilising the first described prior pro posed solar energy collector certain disadvantages are encountered. Since the collector is part of a "closed" system, the system is usually filled with water and the water is then pumped around the system, between the energy collector and the heat exchange coil present in the hot water tank. Of necessity, a solar energy collector must be located in an exposed position, and thus during the winter months, the solar energy collector is susceptible to frost. In the case of a closed system it is necessary, therefore, either to drain the closed system during the winter months or, alternatively, to fill the closed system with an anti-freeze fluid to prevent the system being damaged by frost.This problem is not encountered, to such a great extent, in connection with the second described type of prior proposed collector since such a collector tends to be "self-draining" and whilst water flowing from the collector will be pumped through a heat exchange coil present in a hot water tank, the water will only be pumped through the solar energy collector when it is in use, and thus, during the winter months, the pump can merely be de-activated, or can be provided with a frost-sensitive thermostat to prevent water from being pumped through the solar energy collector when frost conditions prevail.

Finally, a most serious disadvantage that is experienced with both the above described types of solar collector is that, when the sun shines for a very long period of time, for example during warm mid-summer days, water in the main hot water storage tank associated with the solar energy collector may be raised to an unacceptably high level. It is not, however, possible to stop operating the solar collector since the matt black surface provided on the solar collector is a very efficient absorber of solar radiation, and if the flow of water to the solar energy collector is terminated, the temperature of the energy collector will rise to an unacceptably high level, and it is conceivable that parts of the solar energy collectors would become warped or would even melt, and in the case of the first described collector water in the collector could easily boil.This, of course, is highly undesirable, and means that water must continue to be provided to the solar energy collectors even when the water in the main storage tank has reached an unacceptably high temperature. Thus the water in the tank is heated to an even higher temperature, unless special radiators or other devices are provided to dissipate the unwanted heat. Consequently it has often been found necessary to provide special mixer taps and "anti-scald" devices in houses where the hot water is heated by a solar energy collector of the type generally described above, to reduce the risk of scalding a user.

It will be appreciated, from the foregoing, that there is need for a solar energy collector that can be readily and cheaply manufactured from materials that are not, in themselves, expensive. There is also a need for a solar energy collector that can be utilised in an "open circuit" manner, that is to say which has advantages that water can be pumped through it when necessary, and yet which can be left in a drained or empty condition so that the collector is not damaged by frost. Furthermore there is need for a solar energy collector which can also be drained when the sun shines for long periods of time and when water in the main storage tank associated with the solar energy collector has reached a predetermined maximum acceptable temperature.

Additionally there is need for a solar energy collector which can withstand solar radiation without being damaged when the system is drained or at least when water is not being supplied to the solar energy collector. Furthermore there is need for a solar energy collector which can utilise economically radiation falling on the collector during typical weather conditions experienced during spring and autumn, that is to say during brief sunny spells when the solar radiation is of relatively low intensity and is at a useful level for only brief and spasmodic periods of time. That is to say there is need for a solar energy collector which has a rapid "rise time" and which can produce warm water rapidly when the sun begins to shine.

The present invention seeks to provide a solar energy collector in which the disadvantages and drawbacks of the above described prior proposed solar collectors are minimised or obviated, and also seeks to provide a solar energy collector having some or all of the desirable features listed above.

According to a first aspect of this invention there is provided a solar energy collector for providing a source of useful heat comprising a generally planar member to be mounted, in use, so as to be inclined at an angle to the horizontal, a transparent or translucent member spaced therefrom and defining therewith a chamber, means for introducing a radiation absorbing working fluid into an upper part of the chamber, and for removing such fluid from a lower part of the chamber, so that the fluid runs over said inclined surface, said inclined surface being provided with a member of fibrous or porous material through which the working fluid may flow, said material serving to spread the flow of the working fluid the arrangement being such that the radiation absorbing working fluid will absorb solar radiation falling on the solar energy collector, the nature of the planar member and said fibrous or porous material being selected so as to absorb only a minimum amount of solar radiation.

Conveniently the fibrous or porous material may comprise a woven cloth or a member having an open cell structure, or may comprise merely a plurality of fibres. The most preferred material is a fibre glass open cloth or net.

Preferably the working fluid comprises water having a wetting agent mixed therewith and which supports a suspension of carbon black.

It is to be appreciated that in an embodiment according to this first aspect of the invention, when the working fluid is being pumped through the solar energy collector the fluid will itself be able to absorb the radiation and the temperature of the fluid will rise. However, when the fluid is not being pumped to the solar energy collector the fluid will drain from the fibrous or porous material, and the fibrous or porous material will then present a surface that does not readily absorb solar radiation, and thus the temperature of the solar energy collector will not, under those conditions, rise to an unacceptable level, even if substantial solar radiation is still present.

It is to be appreciated that in such an embodiment of the invention the fibrous or porous material may be in the form of a net with between 10 and 30 per cent of the fibrous material being open and in such an embodiment of the invention said inclined surface should preferably be provided with a white or mirror finish.

According to a second aspect of this invention there is provdied a solar energy collector for providing a source of useful heat comprising a generally planar member mounted, in use, so as to be inclined at an angle to the horizontal, a transparent or translucent member spaced therefrom and defining therewith a chamber, means for introducing a working fluid into an upper part of the chamber, and for removing such fluid from a lower part of the chamber, so that the fluid runs over said inclined surface, said inclined surface being provided with a member of fibrous or porous material through which the working fluid may flow, said material being selected so as to absorb solar radiation and also serving to spread the flow of the working fluid the arrangement being such that the member will absorb energy falling on to the solar energy collector in the form of solar radiation and will transfer that energy to the working fluid.

Advantageously a thin flexible transparent or translucent film may be provided immediately adjacent the said fibrous or porous material to prevent or reduce the evaporation of the working fluid. It is to be appreciated that if such a thin flexible transparent or translucent film is provided the working fluid will flow between the said film and the in dined surface, and the fluid will be spread evenly as a thin film throughout the entire surface of the fibrous or porous material.

Thus, the solar collector will have all the advantages of being a closed system in that there will be no evaporation losses whilst having the advantages of being an open system in that the energy collector may drained when frost conditions and the like may prevail. Additionally the solar radiation will largely be collected almost directly by the working fluid either as a result of being a fluid with good radiation collection properties or by being thinly dispersed over a material having such good properties.

Figure 4A is a cross sectional view on an enlarged scale of part of the apparatus of Figure 1 when it is not in use; Figure 4B is a cross sectional view on an enlarged scale of part of the apparatus of Figure 1 in use; Figure 5 is a diagrammatic cross sectional view of a second form of solar energy collector in accordance with the invention; Figure 6 is a cross sectional view of one side of the collector of Figure 5; Figure 7A is a sectional view on an en larged scale showing part of the collector of Figure 5 when it is not in use; Figure 7B is a sectional view of part of the collector of Figure 5 during use as a light intensity modulator; and Figure 8 is a diagrammatic view of a domestic hot water installation utilising a solar energy collector in accordance with the present invention.

Referring to Figures 1 to 4 of the accom panying drawings a first embodiment of a solar collector in accordance with the present invention comprises a generally rectangular housing 1 which is formed of two com ponents 2, 3 which are each formed, for ex ample, as a G.R.P. (Glass Reinforced Plas tics) injection moulding. Preferably a white plastics material is utilised to form each said injection moulded component, although a material having a reflective finish may be used instead. Each of the components 2, 3 is generally rectangular in configuration and the lower component 3 merely comprises a rectangular bottom wall, upstanding side walls and an outwardly directed peripheral flange 4 provided at the upper ends of the side walls.

The upper component 2 comprises an upper surface which forms a tray 5, depending side walls and a radially extending flange 6 provided at the lower ends of said side walls. The two radially extending flanges 4, 6 are bonded together and the cavity defined between the two components 2, 3 is filled with a thermally insulating material 7, such as fibre glass. The tray 5 is recessed and is provided, at the two shorter ends thereof, with recessed gutters 8, 9 there being an elevated substantially planar portion 10 extending between the two gutters. Adhesively secured to this planar portion is a sheet of fibrous or porous material in the form of fibre glass cloth or net 11, which is formed of "natural" colour fibre glass, the fibre glass cloth being secured in position by appropriate spots of adhesive.The preferred cloth is a net where approximately 10 to 30 per cent of the surface area is open.

Whilst the cloth has been described of being a "natural" colour it is to be appreciated that the cloth may be white or may be of any other desired pale or light reflective colour. The tray is also formed so as to discourage radiation absorption.

Provided in the gutter 8 is a working fluid inlet pipe 12, and this pipe may comprise a pipe which opens into one end of the gutter.

The lip of the gutter is provided with V shaped notches and fluid flows from these notches. A similar working fluid outlet pipe may be provided in the other gutter 9.

The gutters 8 and 9 and the planar portion 10 of the upper component 2 together form a recess in the uppermost moulding and placed over this recess is a sheet of trans parent or translucent material 13 such as, for example, toughened glass. The toughened glass sheet is held in position by appropriate clips or by adhesive.

Provided within the space between the sheet of toughened glass 13 and the glass fibre cloth 11 is at least one temperature or radia tion sensor. This sensor is preferably pro vided with a matt black finish and is adapted to sense when the radiation falling on the collector exceeds a certain pre-determined level, that predetermined level being a level at which it is deemed that the working fluid may usefully be passed through the said space.

Thus, when the level of solar radiation falls above or below said predetermined level the sensor will respond to this and will indicate that working fluid should not be pumped through the solar energy collector when the radiation level is below the selected level and vice versa when the radiation level reaches or exceeds such level.

A solar energy collector as described with reference to Figures 1 to 2 will generally be mounted, when in use in the general direction of the sun and the collector is shown in a typical inclined position in Figures 3 and 4. Figure 3A illustrates the solar energy collector when it is not in use. It is to be noted that no working fluid is passed through the net 11, and consequently the energy collector presents a substantially radiation re flective face to the rays of the sun, and the greater proportion of solar radiation falling on the device is merely reflected away therefrom. The light is reflected from the white, pale or light reflective surface of the net and from the tray and such radiation is easily transmitted back through the toughened glass 13. Reflection from the tray base is illustrated in Figure 4A.

Figure 3B illustrates the device in use, and it is to be noted that fluid is fed to the uppermost gutter 8 and such fluid then flows, under the influence of gravity, down the tray towards the lower gutter 9. In this embodiment the working fluid is selected readily to absorb radiation and is accordingly dark in colour. The working fluid accordingly collects available solar energy and its temperature rises. Preferably the working fluid is black.

In practice this working fluid flows over the net 11 which spreads the fluid as a thin layer across its entire surface to maximise radiation collection.

As illustrated in Figure 4B all wave lengths of solar radiation falling on the dark coloured (preferably black) working fluid is absorbed and the even flow of the fluid all over the surface of the net assists in the efficient working of the apparatus.

If any energy is re-radiated by the black working fluid it is to be appreciated that the greater proportion of any such re-radiated energy will have a low wave length, and consequently the "greenhouse" effect will be experienced, in that the re-radiated energy will not be able to pass back through the glass 13. Thus any re-radiated energy will merely serve to increase the temperature within the space between the working fluid and the glass which will be transferred to the working fluid.

It will be appreciated that in this embodiment since the working fluid is exposed directly to the rays of the sun and since the working fluid traverses the entire surface of the net the working fluid will collect a substantial portion of the solar radiation falling on the collector.

When a drop in the level of radiation be low said predetermined level is detected by the sensor, or when operation of the collecter is to be terminated for any other reason, the pump providing the working fluid to the top gutter 8 is turned off and the working fluid merely drains away via the bottom gutter 9, as illustrated in Figure 3C. The denier of the net 11 and the inclination of the installed collector is, where practical, selected so that the collector is drained of fluid in less than two minutes of ceasing the flow of working fluid.

Figures 5 and 6 of the accompanying drawings illustrate a second embodiment of the invention in which the solar collector is formed predominantly of glass and comprises a substantially rectangular "panel" provided at opposed ends with a working fluid inlet and a working fluid outlet.

The panel comprises, in its simplest form, two sheets of toughened glass 14, 15, which are held in spaced parallelism by a peripheral frame, the frame being formed of a substantially "M" shaped strip 16 of stainless steel, the sheets of glass respectively being located adjacent the inside edges of the downwardly extending arms of the "M" and being secured in position by means of adhesive 17. Whilst this particular frame assembly is preferred it is to be appreciated that many different types of frame could be utilised. Secured to the interior surface of one of the sheets of glass by means of an appropriate adhesive, is a sheet 11 of the previously described glass fibre net material. Pipes are provided at the inlet 18 and outlet 19 and the stainless steel strip 16 accommodates these pipes, the pipes being in communication with the interior of the panel.The panel may be provided with an extra sheet of glass 20 as shown on the right of Figure 5 to provide the panel with a "double glazed" top surface.

The panel may be mounted for use in an inclined position on an appropriate thermal insulator by means of retaining clips or the like, and preferably a layer of reflective material 21 is provided between the panel and the insulating material. This reflective material 21 may comprise aluminised MYLAR film (MYLAR is a Registered ~ Trade Mark) or other reflective material and may be located in contact with the exterior surface of the lowermost sheet of glass or alternatively may be spaced therefrom (see Figure 7A).

As in the first described embodiment a temperature or radiation sensor is provided and in this embodiment said sensor will be within the space defined between the two glass sheets 14, 15, this sensor operating in the same way as hereinbefore described.

Figure 7A illustrates the panel of Figures 5 and 6 when it is not in use. It is to be appreciated that the majority of any solar radiation falling on the panel in this condition will merely pass through the panel and be reflected away again by the reflective material 21 provided under the panel. Since the panel is formed of glass and even the net is formed of glass minimal radiation will be absorbed by the panel.

Figure 7b illustrates the panel of Figure 7A when in use and it is to be noted that the working fluid is fed to the top of the panel via inlet 18, the working fluid flowing downwardly through the panel, being dispersed in to a thin layer throughout the panel surface by the net 11, to the outlet from the panel.

At least some of the radiation falling on to the panel absorbed by the working fluid either directly or via the net 11. However, this panel can be installed to allow radiation to pass through the panel if desired. Thus if a working fluid of adjustable or variable capacity is used then the proportion of radiation absorbed and the amount of radiation allowed to pass through the panel may be con trolled. Such panels may therefore be mounted on, for example, the roofs of greenhouses or the like and may be operated to control the level of the radiation entering the greenhouse to make the best use of all radiation available.

Figure 8 illustrates a solar energy collector 22 in accordance with the present invention when incorporated into part of a domestic hot water supply system.

The domestic hot water supply system comprises a cold storage tank 23 which is provided with water directly from a mains supply 24.

The system also comprises a usual domestic hot water storage tank 25, the storage tank being provided with a heating coil 26 therein, the heating coil 26 being provided with hot water from any heating source, such as a gas or oil boiler. The usual hot water outlet 27 and expansion pipe 28 are provided. The system differs from a usual domestic system in that, between the outlet of the cold water storage tank 23 and the inlet of the said domestic hot water storage tank is a second or intermediate hot water storage tank 29. In this system water leaving the cold water storage tank 23 passes through the second or intermediate storage tank 29 before entering the normal domestic storage tank 25. The said intermediate storage tank 29 is provided with a heating coil 30 which forms part of a pumped circuit of one or more solar energy collecting panels in accordance with the present invention.This pumped circuit includes a small storage tank 31 which is provided to store working fluid and a pump 32 which is provided to draw working fluid from the storage tank and pump it through the heating coil 30 in the intermediate tank 29 to the inlet at the top of the solar energy collector 22. A pipe leads fluid reaching the bottom of the collector back to the said storage tank 31. A control unit 33 is provided which is adapted to control the pump, the control unit 33 being electrically connected to a temperature sensor 34 which is located in the panel of the collector 22 and a temperature sensor 35 located to sense the temperature of the contents of the intermediate storage tank 29.

This control unit 33, with the sensors 34 and 35 is aware of the temperatures at the sensors and the differential temperatures so as to ensure that the pump is stopped should the temperature in the tank 29 exceed the collector panel temperature. Similarly when the tank temperature exceeds a predetermined temperature the pump is stopped irrespective of the sensed collector panel temperature.

In order to describe operation of the system let it be assumed that the main heat source, by a boiler is operational, this boiler maintaining the water contained within the domestic storage tank 25 at a desired temperature as determined by a sensor coupled to the boiler. Whenever hot water is drawn from the domestic storage tank 25, further water will be introduced to the domestic storage tank 25 from the intermediate storage tank 29, the Intermedlare storage tank in turn receiving water from the cold water storage tank 23. Assuming that sufficient solar radiation is available to create a temperature in the collector panel above that of the sontents of the tank 29, (and assuming the contents of the tank 29 are not already at the predetermined temperature), then the control unit will allow the pump to be activated.Working fluid will then flow through the coil 30 and will drain down through the collector 22. The working fluid will rise in temperature as a result of radiation received by it and as this heated working fluid passes through the heating coil 30 in the intermediate tank 29, the temperature of the water stored within that intermediate tank 29 will rise. If, as a result, the temperature of the water within the said intermediate tank rises to the maximum acceptable predetermined temperature, then in response to information received from the sensor 35 the control unit 33 will cease operation of the pump 32. The remaining working fluid in the solar energy collector will drain out of the solar energy collector 22 in to the tank 31. The collector will then merely reflect the greater proportion of any solar radiation incident thereon.

When further hot water is drawn from the domestic storage tank 25, the domestic storage tank will be replenished with preheated water, thereby minimising, or obviating entirely a requirement of further heat from the boiler. The result of drawing hot water from the domestic tank 25 will be that the temperature of water stored within the intermediate storage tank 29 will fall, and when the sensor 35 on the intermediate storage tank 29 detects this fall in temperature this information will be transmitted to the control unit 33 which will signal the pump 32 to pump the fluid, again assuming of course that the sensor 34 confirms that the panel is at a higher temerature than that being sensed by the sensor 35.

Hence, if the solar radiation level at the collector falls to a level where the temperature as sensed by the sensor 34 is lower than that temperature sensed by sensor 35 (possibly overnight, for example,) the pump 32 will not be activated regardless of how low the temperature of the water within the intermediate storage tank 29 drops. Under these circumstances if the temperature in the tank 25 drops as a result of water being drawn from such tank then obviously the boiler will be called upon.

Hence, the use of fuel to heat water is minimised by solar preheating of such water to the maximum extent available for even if the water in the tank 29 is warmed only slightly there is some advantage since if this preheated water is fed to the domestic tank 25 less fuel will be consumed by the boiler than if colder water from the tank 23 was being fed thereto.

Whilst the system described is relatively simple it is to be appreciated that various sophistications could be incorporated into the systems such as time clocks etc.

In a modification of the invention, a thin flexible membrane of polythene, polyethylene, polyvinyl fluoride or some other transparent or translucent plastics material is provided which lies in contact with the porous or fibrous or net material 11 provided in the solar energy collector. As working fluid is pumped through the solar energy collector the flexible membrane lies in contact with the working fluid, to ensure that the fluid flows through the material 11. This prevents any appreciable portion of the working fluid from evaporating and form subsequently condensing on another part of the solar energy collector to impair the efficiency of the solar energy collector.

Whilst the invention has been described with reference to specific embodiments it is to be appreciated that many modifications may be made without exceeding the scope of the invention. Thus, whilst the invention has been described with reference to an embodiment in which a tray is formed by moulding plastics material or glass it is to be appreciated that the invention may be utilised with other materials, such as glass fibre reinforced resin material. The use of such plastics materials or glass is preferred since if aluminium is avoided it is not necessary to effect a regular pH hydroxide monitoring of the working fluid.

Also the use of plastics materials assists in the elimination of electrolytic corrosion. However, the invention may be utilised with some advantage in solar collectors in which a tray formed of alluminium copper or other such material is provided. Furthermore, whilst the invention has been described with reference to an embodiment in which a fibrous porous or net material 11 is utilised, an open cell foamed plastics material, a plurality of fibres or other water absorbent materiaL ~ could be utilised to perform the function performed by the fibrous material.

Solar energy collectors in accordance with the invention may be provided with integrally formed flanges, as illustrated in Figure 2 of the accompanying drawings to enable the panels readily be secured to rafters forming part of the roof of a house or other such structure.

One working fluid that is envisaged, at the present time, is a suspension of carbon black paste in a solution of a wetting agent in demineralised water. Thus, one typical working fluid could be a 0.0035 molar solution of Sodium Lauryl Sulphate with 20 per cent by volume of carbon black paste. Another suitable working fluid is a suspension of carbon black paste in paraffin, but such a working fluid may prove to be objectionable in view of the inherent fire risk. Alternatively (but this is not presently preferred) the working fluid may merely be water and the fibrous or porous material may be black, the intimate contact between the said black material and the water leading to efficient transfer of heat to the water.

It is envisaged that solar collectors as described above may be manufactured cheaply and yet will be reliable and long lasting.

WHAT I CLAIM IS:- 1. A solar energy collector for providing a source of useful heat comprising a generally planar member to be mounted, in use, so as to be inclined at an angle to the horizontal, a transparent or translucent member spaced therefrom and defining therewith a chamber, means for introducing a radiation absorbing working fluid into an upper part of the chamber, and for removing such fluid from a lower part of the chamber, so that the fluid runs over said inclined surface, said inclined surface being provided with a member of fibrous or porous material through which the working fluid may flow, said material serving to spread the flow of the working fluid the arrangement being such that the radiation absorbing fluid will absorb solar radiation falling on the solar energy collector, the nature of the planar member and said fibre is or porous material being selected so as to absorb only a minimum amount of solar radiation.

2. A solar collector according to claim 1 in combination with a working fluid wherein the working fluid comprises water having a wetting agent mixed therewith and which supports a suspension of carbon black.

3. A solar collector according to claim 1 or claim 2, wherein the said inclined surface is provided with a white or mirror finish.

4. A solar collector according to any one of claims 1 to 3 wherein substantially the entire solar collector is formed of glass.

5. A solar energy collector for providing a source of useful heat comprising a generally planar member mounted, in use, so as to be inclined at an angle to the horizontal, a transparent or translucent member spaced therefrom and defining therewith a chamber, means for introducing a working fluid into an upper part of the chamber, and for removing such fluid from a lower part of the chamber, so that the fluid runs over said inclined surface, said inclined surface being provided with a member of fibrous or porous material through which the working fluid may flow, said material being selected so as to absorb solar radiation and also serving to spread the flow of the working fluid the arrangement being such that the member will absorb energy falling on to the solar energy collector in the form of solar radiation and will transfer that energy to the working fluid.

6. A solar collector according to any one of the preceding claims wherein the fibrous or porous material comprises a woven cloth or net or a member of foamed material having an open cell structure, or comprises merely a plurality of fibres.

7. A solar collector according to claim 6 wherein the said material is a fibre glass cloth or net.

8. A solar collector according to any one of the preceding claims wherein a thin flexible transparent or translucent film is provided immediately adjacent the said fibrous or porous material to retain the working fluid in said material and to prevent or reduce the evaporation of the working fluid.

9. A solar energy collector substantially as herein described with reference to and as shown in Figures 1 to 4 of the accompanying drawings.

10. A solar energy collector substantially as herein described with reference to and as shown in Figures 5 to 7 of the accompanying drawings.

11. A solar energy collector installation substantially as herein described with reference to and as shown in Figure 8 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. formed of alluminium copper or other such material is provided. Furthermore, whilst the invention has been described with reference to an embodiment in which a fibrous porous or net material 11 is utilised, an open cell foamed plastics material, a plurality of fibres or other water absorbent materiaL ~ could be utilised to perform the function performed by the fibrous material. Solar energy collectors in accordance with the invention may be provided with integrally formed flanges, as illustrated in Figure 2 of the accompanying drawings to enable the panels readily be secured to rafters forming part of the roof of a house or other such structure. One working fluid that is envisaged, at the present time, is a suspension of carbon black paste in a solution of a wetting agent in demineralised water. Thus, one typical working fluid could be a 0.0035 molar solution of Sodium Lauryl Sulphate with 20 per cent by volume of carbon black paste. Another suitable working fluid is a suspension of carbon black paste in paraffin, but such a working fluid may prove to be objectionable in view of the inherent fire risk. Alternatively (but this is not presently preferred) the working fluid may merely be water and the fibrous or porous material may be black, the intimate contact between the said black material and the water leading to efficient transfer of heat to the water. It is envisaged that solar collectors as described above may be manufactured cheaply and yet will be reliable and long lasting. WHAT I CLAIM IS:-

1. A solar energy collector for providing a source of useful heat comprising a generally planar member to be mounted, in use, so as to be inclined at an angle to the horizontal, a transparent or translucent member spaced therefrom and defining therewith a chamber, means for introducing a radiation absorbing working fluid into an upper part of the chamber, and for removing such fluid from a lower part of the chamber, so that the fluid runs over said inclined surface, said inclined surface being provided with a member of fibrous or porous material through which the working fluid may flow, said material serving to spread the flow of the working fluid the arrangement being such that the radiation absorbing fluid will absorb solar radiation falling on the solar energy collector, the nature of the planar member and said fibre is or porous material being selected so as to absorb only a minimum amount of solar radiation.