TITLE: Solar Energy Collector

Field of the Invention

This invention relates to solar energy collectors.

Description of the Prior Art

Conventionally a solar energy collector comprises a panel having a number of passages through which a liquid passes so that it is heated by absorbing solar energy. The heated liquid may be used in a number of ways, for example it may be supplied to a heat exchanger forming part of a domestic water heating system.

One of the difficulties facing designers of solar energy collectors is that in order to be economic, particularly in the United Kingdom where there is much less solar energy available in the Winter than in the Summer, a collector must be efficient and also simple and inexpensive to manufacture install and maintain.

It has previously been proposed to use extruded plastic panels having a plurality of side-by- side passages for the flow of solar energy-absorbing liquid through the panel but it is thought that the thermal efficiency of such panels could be improved.

Summary of the Invention

According to the present invention there is provided a solar energy collector comprising:

a generally planar panel having:

upper and lower generally planar surfaces;

first and second end regions;

a first planar portion formed with a plurality of passages extending from said one of said end regions to the other for receiving a solar energy-absorbing liquid;

and a respective end closure coupled to each of said end regions of said panel for conducting said solar energy-absorbing liquid to and from said passages;

and wherein each said end closures has upper and lower limbs for sealingly gripping said upper and lower surfaces of said panel.

In a preferred form of the invention said first planar portion is a lower planar portion and said panel further comprises an upper planar portion adapted to allow the passage therethrough of solar radiation and formed with at least one cavity extending from one of said end regions to the other for containing a heat-insulating fluid.

Advantageously, at least one of said end closures has means enabling communication of said at least one cavity with atmosphere. This has the advantage that an accumulation of condensation within the cavity is substantially reduced.

The present invention also provides a kit of parts for a solar energy collector comprising:

a generally planar panel having:

upper and lower generally planar surfaces;

first and second end regions;

a planar portion formed with a plurality of passages extending from said one of said end regions to the other for receiving a solar energy-absorbing liquid;

and a respective end closure adapted to be coupled to each of said end regions of said panel for conducting said solar energy-absorbing liquid to and from said passages;

and wherein each said end closure has upper and lower limbs for sealingly gripping said upper and lower surfaces of said panel.

Preferably, said first planar portion is a lower planar portion;

and said panel further comprises an upper planar portion adapted to allow the passage therethrough of solar radiation and formed with at least one cavity extending from one of said end regions to the other for containing a heat-insulating fluid.

A collector panel of this form can be manufactured relatively inexpensively, particularly as an extruded plastics moulding, and in use the heat-insulating fluid, which is conveniently air, reduces heat loss from the solar energy-absorbing liquid beneath it.

The lower planar portion of the panel preferably has a single group of passages arranged side- by-side. The idea is that in use the panel is installed with the passages extending vertically or at inclination to the vertical, and preferably the solar energy-absorbing liquid is caused to flow upwardly through the passages, for example by pumping it through a pressurised system.

The liquid is conveniently water which may be coloured to provide shade, for example when the panel forms part of a roof.

A further advantage of providing a coloured liquid such as coloured water is that in general the darker the colour of the liquid, the more heat absorbent the liquid will be.

In the examples where a coloured liquid is used, once substantially all the liquid has drained back from the passages in the collector, the collector will be substantially clear. Thus, by switching a pump on or off, an operator can determine whether the collector provides shade

and absorbs heat, for example in the heat of the day, or whether the collector substantially does not provide shade, allowing the majority of the light to pass through, for example, in the early morning or the evening.

A control system comprising valves may be used to permit liquid to flow through all or only some of the passages.

The upper planar portion of the panel is preferably formed with a similar group of passages providing a plurality of the cavities referred to above.

The end closure preferably comprises a channel-section member which is formed or constructed so that when fitted over an end of the panel its limbs grip the panel, the member being provided with an opening arranged to communicate with the passages in the panel to provide an inlet or outlet, as the case may be, for the solar energy-absorbing liquid.

The end closures may be attached to the panel by adhesive, which acts as a sealant for the passages in the panel, in which case the grip exerted by its limbs on the panel enhances the reliability of the attachment.

Preferably, the channel-section member is formed as an extrusion of a resiliently deformable plastics material so that the limbs of the member grip the panel by virtue of their inherent resilience.

The means enabling communication of said at least one cavity with atmosphere prevents distortion of the panel as a result of expansion or contraction of the fluid in said at least one cavity, and condensation. Such means also allow the escape of any gases produced by the sealant.

Conveniently the passages are coupled via the end closures to a reservoir so that the passages communicate with the reservoir allowing flow of the solar energy-absorbing liquid between

the passages and the reservoir.

The reservoir is preferably large enough to store substantially all of the solar energy- absorbing liquid. The coupling of the reservoir to the passages provides a drain back system. Thus, when the pump is switched off, the solar energy-absorbing liquid is allowed to drain back from the passages in the collector to the reservoir.

Brief Description of the Drawings

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:-

Figure 1 is a perspective view from below showing one end of a solar energy collector panel and its manifold or end closure embodying the invention;

Figure 2 is a sectional view showing the end closure fitted to the panel;

Figure 3 is a side view of another form of end closure according to the invention;

Figure 4 shows a solar energy collector according to the invention coupled to a reservoir to form a drainback system, as applied in a greenhouse;

Figure 5 shows a solar energy collector according to the invention coupled to a reservoir to form a drainback system as applied in a conservatory;

Figure 6 shows a graph of the temperature variation for the preferred form of collector panel; and

Figure 7 shows a graph of the efficiency of the collector.

Description

Figures 1 and 2 show a solar energy collector 10 which comprises a generally rectangular panel 12 provided at its ends with manifolds or end closures 14.

The panel 12 is an extruded plastics moulding, for example of polycarbonate, having an upper generally planar portion 16 formed with a series of parallel longitudinal cavities 18, and a lower generally planar portion 20 formed with a corresponding number of similar parallel longitudinal passages 22.

The end closures 14, of which only one is shown in the drawings, each comprises a channel- section member 24 formed as an extrusion of a preferably resiliently deformable plastics material. The member 24 has upper and lower limbs 26, 28 which are relatively thin compared with the thickness of the base 30 of the member. As shown in Figure 2, the member 24 is pushed over the relevant end of the panel 12 and the resilience of the limbs 26, 28 causes them to grip the upper and lower faces 32, 34 of the panel. The member 24 is of such a width that it does not cover the side margins of the upper and lower surfaces 32, 34 of the panel so that glazing bars can engage these margins to mount the panel 12 in position. It also leaves the longitudinal ends of the outermost passages 22 exposed as these are not used. A strip of sealant 36 is provided across the inner face of the upper limb 26 in contact with the upper face 32 of the panel and sealant 37 is provided over the whole of the inner face 46 of the lower limb 28 in contact with the lower face 34 of the panel 12 and also over the internal face of the base 30 of the member 24. The sealant seals the ends of the cavities and passages in the panel to the end closure.

Each end closure 14 is further provided with an opening 38 in its lower limb 28 forming an inlet or outlet port 40, as the case may be, for solar energy-absorbing liquid flowing through the lower portion 20 of the panel 12. The walls of the panel forming the passages 22, except those immediately adjacent to the outermost passages, are cut away as shown in Figure 1 so that all these passages 22 communicate with the inlet or outlet port 40.

Each end closure 14 also incorporates a piece of porous material such as foam plastics material 42 which is located in a groove 44 in the inner face 46 at the base 30 of the closure member 24 so as to be in contact with the ends of all the cavities 18 in the upper portion 16 of the panel 12 except, perhaps, the outermost cavities 18. The foam plastics material 42 connects with atmosphere and serves as breather foam which connects the cavities 18 with atmosphere. It allows the cavities to breathe in order to help prevent condensation.

The base 30 of each end closure forms a substantially U-shaped section with the upper and lower limbs which are substantially planar and formed by the arms of the U. The end closure is of substantially rectangular cross-section and has a thickness approximating to that of the panel thereby to form a generally flat profile with the panel.

In use the solar energy collector is mounted, for example, in the roof of a building so that the passages 22 extend vertically. The intention is that solar energy-absorbing liquid, conveniently water, will flow upwardly through the passages 22. Therefore the opening 38 in the lower closure member constitutes an inlet port and is connected to a pumped supply of water, the opening 38 in the upper closure member constituting an outlet port arranged to return the water to the supply. Preferably the water is coloured, for example by the addition of an appropriate amount of black ink to it, so as to provide shade for the interior of the building. The air in the cavities 18 in the upper portion 16 of the panel provides heat insulation for the liquid flowing through the passages 22 in the lower portion 20, these cavities 18 being allowed to "breathe" through the foam plastics material 42 in each end closure.

Figure 3 of the drawings shows another form of end closure 50 which, like the closure 14, has a member 51 with side limbs 26, 28 and a base 30 to be provided with sealant 36 and 37. In this case, however, the base 30 is formed in two parts 52 and 54 which are joined together by an integral hinge portion 56. As the closure member 51 is made of a resiliently deformable plastics material, the hinge portion 56 enables the closure to be transformed from an open position as shown in full lines in Figure 3 to a closed position as shown in dotted

lines in which the limbs 26, 28 grip the relevant end of the panel 12. The opposite faces of the portions 52 and 54 of the base 30 of the member are formed respectively with a transverse groove 60 and a projecting rib 62 arranged when the member is closed to engage the groove 50 with a snap-in fit, thereby locking the side limbs 26, 28 of the member in position gripping the panel 12.

Alternatively, the base may be formed in two separate parts which are not joined by an integral hinge. The two parts may then be secured in the closed position, for example, by use of securing means such- as screws, or a snap-fit arrangement, so that the side limbs are locked in position gripping the panel.

In the collector as described above with reference to the drawings, the upper and lower surfaces of the panel 12 are generally planar and parallel. This enables the manifold 14 to be manufactured by extrusion and cut to the desired length to be slid onto the end of the panel 12. The manifold 14 seals the end of the panel 12 except for the breather foam 42 which allows the cavities 18 to breath and therefore helps prevent condensation, and the outermost cavities 18 and passages 22 as explained earlier.

The solar energy collector has a low, flat profile which facilitates assembly and entry into roof areas. The manifold is of simple design and clamps both upper and lower surfaces of the panel 12.

Referring to Figure 4 this shows the application of a multi-wall polycarbonate solar collector, 71 similar to that described above, in a greenhouse.

Greenhouses, due to their construction, overheat in hot weather and cool down rapidly requiring night time heating and day time shading and/or ventilation. The design of the collector of the present invention can help to overcome these problems to some extent, replacing the glazing fully or as a retrofit below the existing glazing.

The collector 71, when filled with an ink/water mixture, shades the interior of the greenhouse and at the same time absorbs solar energy in the fluid. The collector is fed by means of small bore flexible tubing 72, through a pump 73. The system is a "drain back" system and has a reservoir 74 large enough to store all of the fluid within the system, when the pump is switched off to allow the fluid to drain back from the collector 71. An outlet tube 75 feeds heated fluid to a pebble bed 76, which may comprise 8mm pebbles and is typically 3 metres long x 600mm wide x 120mm deep topped up with water. Further tubing loops 77 forming a heat exchanger convey the warm fluid around the pebble bed to heat it up. The pebble bed 76 rests on a layer of insulation 78 to minimise heat losses. The upper surface of the pebble bed has a layer of black plastics covering it. This is tucked around grow bags which in the early season have the local warmth from the system to promote plant growth. The black plastics also absorbs a little extra heat, and prevents the growth of algae.

At the height of the summer when there is no need for the pebble bed to be heated but there is still need to shade the plants, the flow can be diverted by closing valve VI and opening valve V2, so diverting the warm fluid along a tube 79 into a standard high gain insulated storage cylinder 80 and returning fluid to the system by way of a tube 81.

Referring to Figure 5, multi-wall polycarbonate solar collectors 85 (only one shown) according to the invention can also be used as an integral part of a conservatory roof. Conservatories also tend to overheat in hot weather and cool down rapidly requiring night time heating and day time shading and/or ventilation. The collector can help to overcome these problems to some extent, replacing the glazing fully or as a retrofit below the existing glazing.

The system of Figure 5 is similar to that of Figure 4 and has the or each collector 85 coupled through small bore flexible tubing 86, 89 and pump 87 to a reservoir 88 which is large enough to store all of the fluid within the system. When the pump is switched off it allows the fluid to drain back from the collector 85. The outlet tube 89 feeds warm water to a heat exchanger coil 90 in a high gain fully insulated storage cylinder 91 and thence back to the

reservoir 88. Expansion of the fluid is allowed by an expansion pipe 92 and the system is controlled by a room thermostat 93 inside the conservatory.

In the situations where the collector is to be used as a retrofit below existing glazing, the upper cavities 18 may be absent.

With regard to the system of Figure 5, Figure 6 shows the variation of temperature with time for the fluid at the panel inlet, the fluid at the panel outlet, the inside air and the external air. A collector of an area of 0.8 sqm with an estimated flow rate of 1.1 L per minute for the fluid was used.

Figure 7 shows the collector efficiencies characteristics where Ti is the inside temperature and the Ta is the external, ambient temperature.