WO2005090873A1

WO2005090873A1 - Solar collector

Info

Publication number: WO2005090873A1
Application number: PCT/CA2005/000439
Authority: WO
Inventors: Dave Gerwing; Neil C. Grant; Konstantin Kouliachev; Stephen R. Tennant
Original assignee: Menova Engineering Inc.
Priority date: 2004-03-23
Filing date: 2005-03-23
Publication date: 2005-09-29

Abstract

A solar collector comprises a linear, concentrator type reflector and an absorber spaced from the reflector. The absorber comprises a first absorber element spaced from the reflector which has a surface oriented towards the reflector for receiving solar radiation therefrom and fluid carrying conduit thermally coupled to the absorber surface. The absorber also comprises a second absorber element having an absorber surface oriented to receive directly transmitted solar radiation, and a fluid carrying conduit thermally coupled to the absorber surface of the second absorber element.

Description

Field of the Invention

The present invention generally relates to solar collectors and more' particularly, but not limited to, one axis tracking, area focus type solar collectors.

Background of the Invention

Many practitioners have presented concepts for solar thermal collectors in an attempt to supply sustainable energy from the sun to be converted into heat in a fluid or gas (WO 01/Q2780-A1) .

Still other practitioners have presented concepts for combining solar thermal and photovoltaic (PV) cells to provide heat and electrical power (US 6,080,927). These concepts allow the sun' s energy to be converted to supply heat and electricity for building space heating, hot water aquaculture, agriculture, industrial processes.

A combined solar thermal/electric collection system typically comprises a concentrator and a receiver or absorber. The concentrator redirects and focuses the optical solar energy on the receiver using mirrors, lenses or a combination thereof. The receiver absorbs the solar radiation producing electricity in the PV cell and converting a portion of that energy into heat due to the inefficiency of the PV cell. Solar collectors are of two basic types. Focusing, which typically requires some type of sun tracking mechanism and control system and non- focusing which tend not to actively track the sun.

Collectors are additionally divided into two categories, namely concentrating and non-ooncentrating. an effective way to co±±ect ana convert soiar o uiyxnid--. energy. In line focused collectors, solar radiation is reflected by a concentrating mirrored reflector surface onto a radiation absorbing tube.

The most common collector is a line focus collector with a parabolic trough-like reflective surface. This type of design can have the collector either above or below the aperture line of the collector, be open or enclosed by a transparent panel covering the aperture and encasing the absorber. Past designs have proposed the merits of the absorber existing below the aperture line with a transparent panel covering the aperture to keep the absorber clean. Art prior to this proposed a collector mounted above the aperture line without any protective transparent panel covering the aperture.

Advantages of the former were claimed to be cleanliness of the collector, space reduction and enhanced wind load resistance.

Summary of the Invention

According to one aspect of the present invention, there is provided a solar collector comprising a reflector and an absorber spaced from the reflector said absorber comprising a first absorber element spaced from the reflector and having a surface arranged for receiving solar radiation reflected from said reflector, the first absorber element comprising at least one conduit for carrying fluid therein and thermally coupled to said absorber surface, and a second absorber element having an absorber surface mere conduits for carrying fluid therein tnermany coupiϋu to the absorber surface of the second absorber element.

Advantageously, providing two or more absorber elements each comprising a conduit for carrying heat transfer fluid in which an absorber element receives reflected radiation from the reflector and the other receives directly transmitted (i.e.. non-reflected) radiation allows the efficiency of the absorber to be significantly improved.

In some embodiments, the reflector concentrates radiation onto the radiation receiving surface of the first absorber element so that the intensity of radiation received by the first absorber element is greater than that received by the second absorber element, leading to a differential temperature between the two elements. The provision of separate absorber elements allows the elements to be thermally insulated from one another to reduce heat loss from the first element to the second element. Thus, in some embodiments, the or at least one conduit of the first absorber element is thermally insulated from the or at least one conduit of the second absorber element.

In some embodiments, a thermally insulating- material is provided to thermally insulate fluid carried in the or at least one conduit of the first absorber element from fluid carried in the or at least one conduit of the second absorber element. The insulating material may be disposed within one or both conduits and/or positioned between the two. In some embodiments, the or at least one conduit of the first absorber element is spaced apart from the or at gap therebetween may assist m providing tnermax ιn3U-<a.--a.<-ji; between the first and second absorber elements and/or their respective conduits. In some embodiments, the absorber surface of the first and/or second absorber element is at least partially planar, which may facilitate mounting an array of solar-to- electrical energy conversion devices thereto.

In some embodiments, the first absorber element comprises a plate supporting the absorber surface and one or more conduits of the first absorber element are thermally coupled to the plate.

^• In some embodiments_/ the first absorber element comprises first and second absorber members, each having an absorber surface for receiving radiation reflected from the reflector, and each having at least one conduit thermally coupled to a respective absorber surface-

In some embodiments, the first absorber element comprises first and second substantially planar oppositely angled surfaces directed to receive reflected radiation from opposite sides of the reflector.

In some embodiments, the solar collector further comprises reflector means arranged to reflect energy reflected from the absorber surface of the first absorber element back to the absorber surface. Advantageously, the reflector means may effectively act as an optical and/or thermal diode to "trap" optical and/or thermal energy in the region adjacent the absorber surface.

In some embodiments, the reflector means is positioned adjacent the first absorber element. first absorber element includes πrst aim -=.<=<-.--.-.-,«. ^rt--~-- longitudinal edges, and the reflector means includes a reflector extending from one of said first and second edges 5 and away from the absorber sur ce.

In some embodiments, the reflector means includes a first reflector extending from a position adjacent the first edge of the absorber surface of the first element and a second reflector extending from a position adjacent the 10 second edge of the absorber surface of the first element.

In some embodiments, distal ends of the first and second reflectors of the reflector means define an aperture for passing solar radiation reflected from the reflector therethrough to the absorber surface. The aperture may

15 assist in restricting the amount of solar radiation impinging on the absorber surface when the reflector is tilted away from the sun and may assist in reducing the tilt angle required to reduce the amount of reflected radiation incident on the absorber surface. In some embodiments, the

20 width of the aperture may be substantially equal to or less than the width of the radiation receiving surface of the first element.

In some embodiments, the second absorber element comprises a plate for supporting its radiation receiving 25 surface and one or more conduits of the second absorber element are thermally coupled to the plate.

In some embodiments, at least one of the first and second absorber elements are detachably mounted to the solar collector. A potential benefit of providing separate 30. absorber elements is that the elements can be removed and replaced independently of one another. For example, this col_lector and modified or replaced wi n anouries^j- , as necessary. In particular, this arrangement allows an absorber element equipped to absorb thermal energy only to be upgraded to an absorber element having an array of solar to electrical energy conversion devices thereon for generating electrical energy. In some embodiments, connection means may be provided for connecting at least one conduit of the first absorber element to at least one conduit of the second absorber element such that fluid which has passed along a conduit associated with the second absorber element (and which has for example absorbed solar heat) is conducted along a conduit associated with the first absorber element for additional heating by concentrated solar radiation incident on the second absorber element. Advantageously/ this arrangement allows fluid to^" be ^• preheated by the second absorber element and then heated to a higher temperature by the first absorber element.

In some embodiments, the reflector has opposed longitudinal edges extending in a direction along its longitudinal axis, and the solar collector further comprises structure positioned between the longitudinal edges and adjacent the reflector and which extends along a major part of the length of the reflector and is arranged to stiffen the reflector in a direction normal to its surface. Advantageously, the structure means can substantially increase the stiffness of the reflector and allow the length of the reflector between support points to be substantially increased. In some embodiments, the solar collector further comprises transparent panel means covering the reflector and spaced from the reflector to form a cavity therebetween . In _lluiα communication witn une cavity to a-Liow air or otner gas to pass into and out of the cavity.

According to another aspect of the present invention, there is provided a solar collector comprising a trough-like reflector having opposed ends and opposed longitudinal edges, an absorber spaced from the reflector for receiving reflected radiation therefrom and structure means positioned between the opposed edges of said reflector and upstanding from a position adjacent said reflector and extending longitudinally and continuously along said reflector over at least a major part of the length of the reflector, and arranged to strengthen the reflector in a direction normal to its surface. Advantageously, the structure means can significantly increase the strength of the reflector in a direction normal to its surface, allowing the length of the reflector between supporting points to be significantly increased. In some embodiments, the structure means comprises at least one panel means, for example upstanding from a position adjacent the reflector. Advantageously, the panel means can be lightweight and effectively provides a similar stiffening effect to the vertical plate of an I-beam. In some embodiments, the structure means may comprise first and second opposed panels spaced apart in a direction transverse to the longitudinal axis to form a space therebetween extending along the longitudinal axis . Advantageously, this arrangement allows the tortional stiffness of the reflector to be significantly increased. tapers towards the other panel n a αirecti-on transverse tu the length of the reflector, and this arrangement may further increase the tortional stiffness off the reflector, In some embodiments, at least o e of the first and second panels tapers towards the other panel as the panels extend away from the reflector.

In some embodiments, the reflector comprises a first side and a second side, each extending longitudinally, and an aperture between the first and second sides and between lower edges of the first and second panels of the structure means to provide access to the space between the first and second panels. In some embodiments, the panels support ^"the absorber ^'and the aperture provides access for mounting and dismounting the absorber from the .solar collector.

In some embodiments, the reflectcpr comprises a first panel forming one side of the reflector and a second panel forming a second side of the reflector, and wherein the first panel of the structure means extends from the first panel of the reflector and the secon<d panel of the structure means extends from the second panel of the reflector.

According to another aspect of tlie present invention,, there is provided a solar coll ctor comprising a reflector defining a substantially concave reflective surface, an absorber having a surface for receiving radiation from the reflective surface, and. reflector means positioned between the reflective surface and the radiation receiving surface of the absorber for reflecting radiation surface of the absoroer.

Advantageously, the reflector means reflects optical and/or thermal energy reflected or radiated from the absorber surface back to the absorber surface to reduce energy losses therefrom and improve the efficiency of the absorber.

In some embodiments, the radiation receiving surface of the absorber includes first and second opposed longitudinal edges, and the reflector means includes a reflector extending from a position adjacent one of the first and second edges and away from the absorber surface.

In some embodiments, the reflector means includes a first reflector extending from a position adjacent the first edge and a second reflector extending from a position adjacent the second edge.

In some embodiments, the distal ends. of the first and second reflectors define an aperture for passing solar radiation reflector from the reflector therethrough to the absorber surface. The width of the aperture may be substantially equal to or less than the width of the radiation receiving surface of the absorber.

.According to another aspect of the present invention,, there is provided a solar collector comprising a reflector for receiving solar radiation, an absorber arranged for receiving solar radiation reflected from the reflector and transparent panel means opposite the reflector and spaced therefrom to define a cavity therebetween_/ and means forming a variable volume chamber in communication with the cavity. chamber in communication with the cavity anσwt. uie effective volume of the cavity to increase and decrease to allow air or other gas in the cavity to expand or contract with temperature, thereby reducing any pressure loading on the cavity and in particular any seals which seal the inside of the cavity from the external environment, including ambient air and moisture.

According to another aspect of the present invention, there is provided a solar collector comprising a reflector for receiving solar radiation, an absorber arranged for receiving solar radiation reflected from the reflector and transparent panel means opposite the reflector and spaced therefrom to define a cavity therebetween and wherein said cavity is defined in part by a flexible wall to allow^' the volume of the cavity to vary.

According to another aspect of the present invention, there is provided a solar collector comprising a reflector having a concave reflective surface, an absorber having a substantially planar surface for receiving solar radiation reflected from the reflective surface, and wherein the reflective surface is shaped to reflect radiation between first and second spaced apart positions on a predetermined plane such that the distribution of intensity over said plane between said first and second positions varies by less that 15%.

According to another aspect of the present invention, there is provided a solar collector comprising a reflector having a concave reflective surface defined by the equation ^"" l+Vl-(l+/c)-c²- ^" -

where z is the axis extending through the surface of the reflector, y is the position transverse to the reflector and c = -3.436E-002, k = 1.300E-001, a4 = -1.Q50E-006, aβ = 1.815E-008, a8 = -1.090E-011, alO = -2.351E-Q15 and al2 - 2.305E-017.

According to another aspect of the present invention, a solar collector comprising a concave reflector being capable of focusing solar radiation reflected therefrom to a focal line or point or zone, and an absorber having a surface arranged for receiving solar radiation reflected from said reflector and being spaced from the reflector such that the focal point or zone is positioned in front of and spaced from said surface. According to another aspect of the present invention, a solar collector comprising a reflector and an absorber spaced from said reflector and having a first surface for receiving radiation reflected from said reflector and a second surface for receiving direct sunlight, a first conduit positioned adjacent said first surface for receiving energy transmitted therefrom and a second conduit positioned adjacent said second surface for receiving energy transmitted from said second surface.

According to another aspect of the present invention, a solar collector unit comprising an elongate reflector formed of sheet material and having a concave inner surface and a convex outer surface, an elongate absorber spaced from said reflector for receiving solar radiation reflected therefrom, a support for supporting said opposed side edges or saiα renec or tmu sow OWSV AO. OIIU transparent panel means connected to opposed side edge portions of said reflector and to said absorber, According to another aspect of the present invention, a solar collector comprising a reflector having a concave reflective surface, an absorber having a surface for receiving radiation from the reflective surface, and reflector means positioned between the reflective surface and the radiation receiving surface of the absorber for reflecting radiation received from the absorber back to the surface of the absorber.

According to another aspect of the present invention, a solar collector comprising a reflector and an absorber, the absorber having a single, planar radiation receiving surface on one side thereof for receiving solar radiation from one side of the reflector and a single, planar radiation receiving surface on the other side of the absorber for receiving radiation from the other side of the reflector.

According to another aspect of the present invention, a solar collector comprising a plurality of trough-like reflectors having a longitudinal axis, the reflectors positioned in series end to end along the longitudinal axis, and an absorber for receiving radiation from the reflectors and which substantially spans the length of said plurality of reflectors.

According to another aspect of the present invention, a solar collector comprising first and second reflectors each having a longitudinal axis and positioned end to end and an absorber having means defining a radiation comprises a single piece which extends across adjacent euua of the first and second reflectors.

According to another aspect of the present invention_/ an apparatus for rotating a rotatably mounted solar collector having a reflector and an absorber, the apparatus comprising a driver for driving rotation of the solar collector about an axis and a controller arranged to control rotation of the solar collector to scan solar radiation across the solar collector to remove moisture therefrom.

According to another aspect of the present invention, a method of removing moisture from a transparent panel positioned between an absorber and reflector of a solar collector comprising rotating the solar collector to scan solar radiation across the transparent panel.

According to another aspect of the present invention, a method of controlling the heat absorbed by a solar collector comprising varying the tilt angle of the solar collector to vary the extent to which incident solar radiation is received by the collector.

According to another aspect of the present invention, a method of cooling the absorber of a solar collector comprising passing fluid through the absorber. According to another aspect, of the present invention, a solar collector comprising a reflector, an absorber and tranaparent panel means extending from the absorber to each edge of the reflector such that the transparent panel constitutes a stressed skin panel. invention, a neat t ansitsL s-y ----!_tun -uuj.

num «, coolant heated by solar radiation comprising a plurality of heat exchangers connected for serially or successively receiving said coolant.

According to another aspect of the present invention, a solar collector comprising a trough-like reflector and an absorber having a longitudinal axis and first and second conduits extending through said absorber along said longitudinal axis and means for connecting the first conduit to the second conduit to cause fluid flowing in one direction along the first conduit to return through the second conduit.

According to another aspect of the present invention, a solar collector in combination with fluid driving means, wherein the fluid driving means is arranged to direct fluid through the first conduit before being returned by the second conduit.

According to another aspect of the present invention, a solar collector comprising any one or more of the features described, claimed or illustrated herein.

According to another aspect of the present invention, an absorber for a solar collector comprising any one or more of the features described, claimed or illustrated herein.

According to another aspect of the present invention, any combination of two or more features described herein, claimed or illustrated herein. invention, a neat transrer system com nt-my -any une ui uιu-.c features described, claimed or illustrated herein.

According to another aspect of the present invention there is provided an area focus type solar collector unit comprising one or more trough like concentrators or reflectors and a long axis radiation receiver fixed beyond the focus line of the reflector or concentrator so as to uniformly distribute the direct solar energy along the short and long axis of one or more surfaces of the collector's absorber, the solar collector unit received within a casing, said casing being formed structurally by transparent panels covering the aperture, external ribs and one or more parabolic surfaces that make up a form support for a geometrically accurate reflector or concentrating surface. The term "'aperture" used herein in the specification may alternatively be used to denote one or more openings or spans of the concentrator or reflector.

In a preferred embodiment, the collector has a long and 'short axis, and one or more areas with a long and a short axis, the long axis of the collector is oriented parallel with the long axis of the reflector or concentrator to provide a flat surface suitable for mounting PV or other thermal/electric device, while one or more conduits for either gas or liquid run parallel to the axis of the collector enabling efficient transfer of heat from the collector flat surface to the fluid conduit of the absorber and to the fluid.

Embodiments of the absorber (or receiver) are removable without disassembling the collector transparent panels on concentrating surface or reflector. accepting one or more absorbers witn eitner a selective emissivity and absorption coating to minimize reflectance, and maximize absorptivity for thermal collection only, or, said collector may be fitted with PV or thermal electric devices which enable the production of heat and electricity.

In embodiments, the one or more reflectors is parabolic or comprise facetted flat reflectors and the one or more absorber is removable and fitted with an integral duct through which heat absorbing gas or liquid flows.

Still preferably although not restricted thereto, the one or more solar collector unit is pivotally mounted and actuated by a single linear actuator forming a one axis sun tracking mechanism and clock work associated sun tracking system.

In embodiments of the present invention, the concentration ratio is defined as

X/W = 1;1.5 to 1:4 or 1:1.5 to 1:6 where X = short axis of the aperture of one or more collectors and = width of the short axis of direct solar radiation receiver.

The area of the collector exposed to total solar radiation may in the first instance fitted with one or more selectively coated absorber positioned under a transparent panel, said absorber being insulated on one or more sides not exposed to the total solar radiation and/or in the second instance said one or more absorbers having one or more PV cells or optical/electric or thermo/electric devices absorber being covered with one or more transparent paneia and being enclosed on one or more sides with low thermal conductivity insulation such as rock or mineral wool. By two specific designs, when PV or thermoelectric cells are not used the one or more collectors shall coated with selective coating to reduce heat loss with emissivity O.03 to 0.09 at up to 300^αC and solar radiation absorption 94 to 99% in the solar spectrum of light to maximize the solar to thermal energy conversion, and minimize radiation energy loss ,

Additionally the one or more direct radiation receiver shall be enclosed on one or more sides with a low thermal conductivity insulation such as rock or mineral wool.

In embodiments, the transparent panels referred to herein before may have a transmission of solar radiation 80 to 99% with an antireflective layer of between 90 an 98% transparent to solar radiation. In accordance with a particular design the dimensions of a collector module (unit) is about 2 to 10 feet wide by 4 to 10 feet long. Preferred dimensions were found to be 5 feet wide by 8 feet long.

An embodiment of a collector may comprise a plurality of modules or units, e.g. six modules, connected in series and actuated by one (linear) actuator with three to six mounting points.

Still a further embodiment has removable absorbers (or receivers) up to ^'24 feet long so as to minimize the system.

In other embodiments, the collector unit comprises a single module having a length in the range of 15 to 50 feet or more.

Some aspects of the present invention provide an improved system based on area focus that combines both direct and total solar radiation capability in a superior format where one or more of the following disadvantages of existing systems are overcome or reduced:

(a) no need for high cost, vacuum tube collectors to attain similar thermal efficiency;

(b) an area focus system of low concentration ratio typically 1:1.5 to 1:15, for example so that geometric accuracy of reflector and^" collector is not as critical as higher concentration ratio systems and stagnation temperatures are in the range of 100 to 300°C versus 400 to 1100°C from the higher concentration ratio systems which makes those systems require more exotic absorber materials such as ceramics and glass to handle the higher temperature. Thus, lower concentration ratio systems will be more cost effective and greatly reduce risks of fire, as well enable use of conventional PV cells which typically operate at temperatures no higher than about 75 ^βC; (c) enable the mounting of conventional (100-125mm) flat solar cells on ^'the absorbe 'surface since the absorber is not a simple round tube; and

(d) ability to capture both total solar radiation as well as direct. This is important (although optional) since the areas of tbxe world is greater, as depicted as siyu-i-c _-w.

Therefore, systems only capturing direct solar energy are at a competitive disadvantage compared to either total solar energy collectors or combination total and direct solar energy collectors (as proposed) , in terms of available solar energy.

The availability of the solar energy is only one component of an efficient system. The second and third components are efficient conversion to electrical and thermal energy as well as efficient transport of the electrical and thermal energy to a useful point for consumption or storage.

Vacuum tubes proposed in prior art suffer a number of drawbacks in both concentrating and non-concentrating systems .

1) The vacuum is difficult to maintain if systems are routinely exposed to temperature extremes, since the seals tend to degrade over time. 2) There is no obvious indication that the vacuum has been lost.

3) Vacuum tubes without vacuum perform thermally similar to low efficiency non-glazed pool heating thermal collectors, not bad in summer, very poor in winter. The attached chart shows efficiencies to be expected of the various systems.

4) Vacuum tubes in non-concentrating collectors present a snow and debris trap (leaves etc.) that can hamper performance. In embodiments of the invention, a combination direct and diffuse solar collector, although somewhat less efficient than a vacuum tube collector, is proposed since it may overcome one or more of the herein before stated drawbacks .

Brief Description of the Drawings

Embodiments of the present invention will now be described by way of non-limiting examples only, with reference to the accompanying drawings in which; Figure 1A shows a perspective view of a solar collector according to an embodiment of the present invention;

Figure IB shows a side view through a portion of the solar collector showing flow of fluid through a conduit in the absorber;

Figure 1C shows a cross sectional side view through a portion of the collector showing fluid flowing through an upper conduit of the absorber in one direction and flowing through a lower conduit in the opposite direction, and an end cap 36 for causing fluid flowing through the upper conduit to return through the lower conduit;

Figure 2 shows a cross-section through the embodiment of the solar collector shown in Figure 1A; Figure 3 shows a cross-sec ional view through the absorber incorporated into the solar collector shown in Figures 1A and 2; Figure 4 shows a cross-sectional view through a solar collector according to another embodiment of the present invention;

Figure 5A s?hows an expanded view of a cross section through the absorber incorporated into the embodiment of Figure 4;

Figure 5B shows a portion "A" of the upper absorber shown in Figure 5A in more detail;

Figure 6A shows a cross-sectional view through part of a solar collector according to an embodiment of the present invention;

Figure 6B shows a sectional view through part of a solar collector according to another embodiment of the present invention; Figure βc shows an expanded view of a bracket for connecting a reflector panel to an absorber support panel of the embodiment shown in Figure 6A;

Figure 6D shows a cross-sectional view through a reflector panel rib or use in embodiments of the present invention;

Figure 6E shows an expanded view of the absorber structure shown in Figure 6A;

Figure 6F shows an expanded view of a side portion of the solar collector shown in Figure 6A; Figure 6G shows a perspective view of a solar collector according - o an embodiment of the present invention having an aperture for connection to a variable volume chamber; Figure 7 shows a cross-sectional view of an absorber assembly according to an embodiment of the present invention;

Figure 8A shows a perspective view of a solar collector according to an embodiment of the present invention;

Figure 8B shows a plan view of the solar collector of Figure 8A rotated about a longitudinal axis in one direction; Figure 8C shows a plan view of the solar collector of Figure 8A rotated about a longitudinal axis in the opposite direction to that shown in Figure 8B;

Figure 8D shows an end view of the solar collector shown in Figure 8A; Figures 9A to 9D show an arrangement of solar collectors mounted on the roof of a building;

Figures 10A to 10D show an arrangement of solar collectors mounted to the side of a building above windows in a manner similar to awnings; Figures 11A to 11D show another mounting arrangement for one or more solar collector units according to an embodiment of the present invention, in which the longitudinal axis is at an angle so that one end of the unit is above the opposite end; Figures 12A to 12D show another mounting arrangement for one or more solar collectors in which the one or more solar collectors are mounted substantially vertically, and in this case to the side of a building; Figure 13 shows a schematic view of a thermal storage and transfer system according- to an embodiment of the present invention;

Figure 14 shows a schematic diagram of a heat transfer system according to another embodiment of the present invention; Figure 15 shows a heat transfer and storage system according to another embodiment of the present invention; and Figure 16 shows a graph of total and direct received sunlight as a function of time.

Description of Embodiments Referring to Figures 1A and 2, a solar collector 1 according to an embodiment of the present invention comprises a concave elongate reflector 3 and an elongate, solar energy absorber 5 positioned above the reflector. The reflector 3 comprises first and second curved portions 7, 9 positioned on either side of a central support 11 which extends from the reflector 3 and supports the absorber 5. The curved portions 7 and 9 are formed of sheet material and define a concave inner surface and a convex outer sur ace. The support 11 comprises first and second opposed upright members 13, 15 which are formed of sheet material and extend upwardly from respective inner edges 17, 19 of the first and second curved portions 7, 9 of the reflector. A flat mounting portion 21 is positioned between upper ends 23, 25 of the upright members 13, 15 to which the absorber is secured, and the upright members 13, 15 taper outwardly from the mounting portion to the reflector to provide access to the lower surface of the mounting portion to facilitate securing the absorber to the mounting portion. The upright member 13 and the reflector element 7 may be integrally formed from the same sheet of material, with the upright member 13 being formed by bending the sheet material upwards at a position corresponding to the inner edge 17. The second reflector element and the second upright member 15 may be formed in a similar manner, and in one embodiment, all of the reflector elements, the first and second upright members and the mounting portion may, for convenience, be integrally formed from the same sheet of material. In other embodiments one or more of these components may be formed separately and connected together, as required.

In one embodiment, the curved portions 7, 9 of the reflector may comprise a single sheet of material whose concave surface constitutes the mirror surface to reflect solar radiation onto the absorber. The curved portions may be formed of any suitable material, such as aluminum. In another embodiment, the curved portions 7, 9 of the reflector may comprise a plurality of sheets of material positioned one above the other. For example, the curved portions may comprise a first lower sheet whichi constitutes a structural substrate and may optionally be integrally formed with the absorber support 11 (or formed separately there rom) , and may comprise any suitable material such as steel or aluminum. The curved portions may further comprise a separate, second sheet of material positioned above the first sheet and whose concave, upper surface constitutes the mirror surface of the reflector for directing solar radiation onto the absorber. These separate mirror elements may be formed of any suitable material, such as aluminum. In one embodiment, the substrate layer is formed of a different material to the mirror elements, and advantageously, the mirror elements may simply float on the substrate layer so that any differential expansion of the upper and lower layers does not distort the shape of the reflective surface. For example, in one embodiment, the lower substrate may be formed of steel and the mirror elements may be formed of aluminum. As particularly shown in Figure 2, when the solar collector is directly pointing towards the sun,, an essential portion of the reflector below the absorber is in shadow and does not receive solar radiation. Embodiments of the solar collector, including that shown in Figure 2 exploit this characteristic by placing an absorber support, for example support 11, in the shadowed region both to support t?h.e absorber and to increase the strength and rigidity of the solar collector structure as a whole. In one embodiment, the support 11 may extend continuously along the lencjth of the reflector/absorber, or the support may comprise a series of individual supports spaced apart along the length of the collector. In the embodiment shown in Figure 2, the sides 13, 15 of the support extend to the edges of thie shadowed region to maximize the stability of the support structure without compromising its ability to collect solar radiation.

A series of rib members 29 are spaced along the length of the reflector and connected to its convex outer surface by any suitable fastening means such as an adhesive (or other suitable fastening means include welding, or mechanical fasteners such as rivets, bolts, screws or other devices) . Advantageously, the use of an adhesive allows the rib members to be secured to the reflector without the risk of deforming the inner, concave reflector sur ace. The mating surface 31 of the rib members conforms to the desired curved profile of the reflector elements 7, 9. The ribs provide a robust mounting structure for pivotally (or otherwise) mounting the solar collector about a longitudinal axis and provide mounting poin (s) for an actuator which actively drives rotation of the solar collector about its pivot point for solar tracking. Advantageously, as the rib members are mounted on the outer surface of the reflector, they do not interfere with or shadow any solar radiation incident on the collector. In the embodiment shown in Figures 1A and 2, an aperture 32 is formed in the rib member 29 which is centrally positioned between the edges of the reflector for receiving a shaft for rotatably mounting the solar collector about a longitudinal axis 30. In other embodiments, the aperture 32 may be formed in the rib at any other desired location, for example offset from its central position. In other embodiments, any other suitable rotary or static mounting system may be secured to one or more rib members .

The rib members also serve to strengthen the reflector and maintain its shape. In this embodiment, the lower edge 33 of the rib members generally follows the same arcuate profile as the mating surface 31 in order to reduce wind resistance, and material used, and thereby save weight and cost. However_/ in other embodiments, the lower edge of the rib members 29 may be of any other suitable shape.

Although, in some embodiments, the pivotal axis of a solar collector may be positioned below the reflector surface, e.g. at a rib member, in other embodiments, the pivotal or mounting point may be positioned about the reflector surface near or at the centre of gravity of the reflector between the top and bottom thereof. Thus, for example in the embodiment of Figure 2, the pivot or mounting point may be positioned at or near the axis 4. The solar collector 1 further comprises a transparent cover generally indicated at 35 which, in this embodiment, is formed by first and second transparent panels 37, 39 which extend from the absorber 5 to respective opposite outer edges 40, 41 of the reflector 3. The panels are rigidly connected to both the absorber and the edges 40, 41 of the reflector and with the reflector form a strong monocoque structure in which each of the panels and the reflector constitute a stressed skin panel to provide the unit with high load bearing capabilities (for example to resist both (longitudinal and/or transverse) bending and torsion) . The panels 37, 39 may be connected to the outer edges of the reflector by any suitable means, and in this particular embodiment, they are connected by brackets 43, 45 which may extend continuously along the length of the reflector (as shown in Figure 1A) , in order to prevent contaminants entering into the space enclosed by the cover and reflector which may change the properties of the critical surfaces and components . The absorber according to an embodiment of the present invention is shown in more detail in Figure 3. Referring to Figure 3, the absorber 5 comprises upper and lower channels 41, 43 for carrying fluid therethrough such as air or other gas. The upper channel 41 has a lower wall 45, two sides walls 46, 47, and inclined upper walls 48, 49 extending upwardly from the side walls to an apex 50. In this embodiment, an array of solar-to- electrical energy conversion devices 51, 52 are mounted on the upper channel walls 48, 49 for generating electrical power when exposed to solar radiation. The solar energy conversion devices may comprise for example photovoltaic cells (PVCs) , thermionic diodes or any other suitable devices known at the present time or which will become available in the future. In this embodiment, the transparent panels 37, 39 described above with reference to Figures 1A and 2 extend to cover the device arrays to protect the devices from weathering and other possible causes of damage, and also to reduce or prevent heat loss due to convection. protrusions such as fins 53, 54 extend from each upper channel wall into the channel passage to increase the surface area from which heat is transferred into fluid flowing through the channel. In use, the arrays of devices receive both direct and diffuse solar radiation (i.e. total solar radiation) and generate electricity therefrom. Advantageously, the electricity can be used to drive a pump, blower or other fluid displacer or impeller to drive heat transfer fluid through the solar collector. The electricity may be used to drive a tracking system actuator or any other electrical load. The absorbed solar radiation is also converted into heat which flows through the devices and upper channel walls 48, 49 into the heat transfer fluid for subsequent use such as space heating, process or hot water heating.

The lower channel 43 comprises an upper channel wall 55, opposed side walls 56, 57, inclined lower walls 58, 59 extending downwardly from the side walls to a truncated apex 60 defined by a narrow bottom channel wall 61 by which the absorber is supported and connected to the support 11 upstanding from the reflector 3. An array 63, 65 of solar- to-electrical energy conversion devices is mounted to the outer surface of each lower channel wall 58, 59 for receiving solar radiation reflected from the reflectors, and generating electrical power therefrom. Protrusions such as fins 66, 67 extend from the inside of the lower channel walls into the .channel passage to increase the surface area from which heat can be transferred into fluid flowing through the passage. Additional fins 68 may also extend from the side walls 56, 57 of the lower channel 43.

The absorber has first and second re-rradiation reflectors 70, 71 arranged to reflect solar and thermal 5 radiation, which is reflected from the surface o the device arrays, back onto the arrays to reduce energy loss and increase efficiency. In this embodiment, the first re- radiation reflector 70 comprises a plate which extends from a position adjacent the lower edge 72 of each lower inclined

.0 channel wall 58, 59 and outwardly of the surface defined by the device array. Similarly, the second re-radiation reflector 71 comprises a plate which extends from a position adjacent the upper edge 73 of each lower inclined channel wall 58, 59, and outwardly of the surface defined by the

L5 device array 65. The ends 74, 75 of the re-radiation reflectors define a respective aperture 76 for ^passing solar radiation from the reflector to the device arrays mounted on the inclined lower walls of the absorber.

In this embodiment, thermal insulation 77 is 20 provided on the other side of the second reflec tor 75 to reduce heat loss theref om into the main enclos ure of the solar collector. Thermal insulation 78 is also provided adjacent the outside of the side walls 46 47, 56, 57 of the upper and lower channels to reduce heat loss therefrom. In 5 this embodiment, additional thermal insulation 79 is also provided to reduce heat transfer between the up»per and lower channels through their respective upper and lower walls 55, 45. In this embodiment, the additional thermai insulation 79 is positioned within the lower cha el 0 passage, although in other embodiments it may hae positioned in the upper channel passage or between the respective lower and upper channel walls. Referring to both Figures 2 and 3, the reflector elements 7, 9 are formed to reflect direct solar radiation to a focal line or zone 80 which is positioned in front of the surface of the device array 65 and spaced therefrom, so that the device arrays receive divergent rays beyond the focal point (line) . It is to be noted that the focal point or zone is actually a line focus which extends along the length of the reflector- Advantageously, the surface of the device array for receiving solar radiation is relatively large and 'allows tolerances on the curvature of the reflector elements 7, 9 in providing a precisely defined focal point or area to be relaxed thereby reducing the cost of the reflector elements without sacrificing performance, and thereby making the unit more robust. Furthermore/ in contrast to a circular absorber, parts of whose surface necessarily present an angle which is almost tangential to the direction of incident radiation and which therefore reflect, rather than absorb, the radiation, the radiation absorbing surface of the present embodiment is arranged so that even the most divergent radiation at the edge of the beam meets the surface at a reasonable angle for absorption. This is achieved by the use of a planar rather than convex surface which is oriented so that incident radiation at the extreme edges of the beam are at similar angles to the surface. Radiation which is not absorbed but reflected or re-radiated from the absorber surface is reflected back to the surface by the first and second re-radiation reflectors 70, 71, and this has been found to significantly improve the efficiency of solar radiation energy conversion in comparison to prior art arrangements.

In any of the embodiments disclosed herein as well as other embodiments, the curvation of the reflector may be such that the reflected radiation is substantially uniformly distributed over a plane between two spaced apart positions^, In one embodiment, the curved surface may have a form substantially defined by the equation:

z(y)

where z is the axis extending through the surface of the reflector, y is the position transverse to the reflector and c = -3.435529E-002, k ■= 1.300109E-001, a4 = -1.049700E-006, a6 = 1.814578E-008, a8 = -1.089380E-011, alO = -2.350870E-015 and al2 = 2.305415E-017. Advantageously, such a curve concentrates solar radiation at a plane with a substantially uniform distribution of intensity between spaced apart positions on the plane.

Advantageously, the efficiency of the absorber in absorbing solar energy and reducing re-radiation and heat loss removes the need for any insulation around the reflector, or the need for the enclosed space between the reflector and transparent panels to be evacuated and sealed, in contrast to the solar collector described in WO 01/02780 (SOLEL-SOLAR SYSTEMS LTD) . This considerably simplifies construction and reduces cost of the unit and additionally reduces maintenance and helps to extend the lifetime of the collecto ,

In use, the upper channel of the absorber may function as a primary fluid heater and the lower channel of the absorber may function as a secondary fluid heater. In this case, fluid is first passed through the upper channel and is preheated by thermal energy absorbed and conducted through the inclined upper channel walls 48, 49. The preheated fluid is then returned through the lower channel in which the fluid is heated further by thermal energy absorbed by the lower inclined channel walls 58, 59.

Examples of different implementations of the absorber are shown in Figures IB and 1C. In Figure IB, fluid flows in one direction through the absorber as indicated by the arrows. In the embodiment of Figure 1C, an end coupling 36 is provided at the end of the absorber channels to reverse the flow of fluid through the absorber 5 so that fluid carried in the upper conduit is returned through the end coupling into the lower conduit.

The amount of heat absorbed by the absorber may be controlled by tilting the solar collector by different amounts towards or away from the sun. For example, when heating is not required and no coolant flows through the absorber, the collector may be tilted away from the sun in order to reduce or minimize the amount of heat absorbed by the absorber and therefore the stagnation temperature of the various absorber elements. Features of the solar collector which individually contribute to minimizing the stagnation temperatures are as follows.

Only parts of the absorber surface are used to receive solar radiation and transfer heat efficiently to the interior of the absorber channel (s). The side portions of the channel (s) are preferably thermally insulated, for example by thermal insulation 77, 78 shown in Figure 3 which reduces the amount of heat transferred into the absorber channel when the side walls are exposed to direct sunlight.

With reference to Figure 3, the radiation absorbing surfaces 63, 65 are positioned behind an aperture 76, which in this embodiment, is defined by re- radiation reflectors 70, 71. When the solar collector is tilted so that solar radiation reflected from the reflector is no longer incident on the aperture 76/ the radiation will not be received by the thermal absorbers, but instead reflected by either one or both of the external surfaces of the re-radiation reflectors 70, 71, thereby significantly reducing the stagnation temperatures of the thermal absorbers 63, 65. In the embodiment shown in Figure 3, this effect is enhanced by the aperture 76 having a smaller width than that of the absorbers 63, 65, and this may reduce the change in tilt angle required to "turn" the solar collector from its full ""o " position in which the collector is oriented to maximise absorption of solar radiation to its "off" position in which the solar collector is tilted such that the lower thermal absorbers 63, 65 do not receive any substantial solar radiation.

Advantageously, the ability to substantially reduce the stagnation temperatures allows the absorber to be made from cheaper and readily available materials, rather than special materials capable of withstanding high temperatures over long periods of time.

A second embodiment of an absorber which is designed for a liquid heat transfer fluid will now be described with reference to Figures 4, 5A and 5B. The absorber 105 comprises an upper absorber 121 for absorbing both direct and diffuse sunlight, and a lower absorber 123 for absorbing direct sunlight reflected from the reflector 103. The upper absorber 121 comprises first and second plates 125, 127 formed of a thermally conductive material and having a generally planar upper surface 126, 128, A conduit 129, 130 for carrying fluid is positioned below each plate and is in thermal contact therewith. Conveniently, the conduit and plate may be formed as an integral unit, (e.g. by extrusion), or in other embodiments the conduits and plates may be formed separately. The plates are positioned within a housing 131 having side walls 132, 133 and a base 134. Thermal insulation 135 is provided below the plates and surrounds each conduit to reduce heat loss therefrom through the housing. In one embodiment, the thermal insulation may at least partially support the plates and conduits.

An array of solar-to-electrioal energy conversion devices 136, 137 is mounted on the upper surface of each plate for receiving solar radiation and generating electrical power therefrom, A transparent cover 138 is mounted above the device arrays to protect them from possible damage, and provides a convective heat loss barrier.

The lower absorber 123 comprises first and second absorber elements or plates 141, 143 each having a generally planar, inclined lower surface 145, 147- A conduit 148, 149 for carrying a heat transfer fluid is positioned above each plate and is in thermal contact therewith. Again, the plate and conduit may be formed as an integral unit or may be formed separately. Thermal insulation 150 is positioned behind the plate and surrounds the conduit to reduce heat loss therefrom. An array 151, 152 of solar-to-electrical energy conversion devices are mounted on the lower surface of each plate for receiving solar radiation reflected by the reflector 103 to generate electrical power.

As for the embodiment shown in Figures 2 and 3, first and second re-radiation reflectors are provided to reflect solar radiation, which is reflected from the device arrays, back onto the arrays to improve efficiency and performance. The first and second reflectors 170, 171 extend from respective lower and upper edges of the absorber elements and converge towards their distal ends 174, 175 thereby defining an aperture 176 for passing radiation from the reflector to the absorber element.

As for the embodiment shown in Figures 2 and 3, the reflector elements 7, 9 are designed to reflect direct solar radiation towards a focal line or zone 180 positioned in front of the absorber elements and spaced therefrom so that trie absorber elements receive divergent radiation from beyond the focal line. The radiation receiving surface of the absorber elements is oriented so that substantially all of the divergent rays make an angle with the surface which promotes absorption, rather than reflection, with the concomitant advantages discussed above in relation to the embodiment shown in Figures 2 and 3 ,

The absorber further comprises a support member 161 for supporting both the upper and lower absorbers and includes a base portion 163 which is mounted on and secured to the top of the support 11 upstanding from the reflector 103,

In this embodiment, the protective covers (transparent panels) 37, 39 are secured between the upper and lower absorbers in a recess 181 formed in the base 134 of the upper absorber housing.

In use, the upper absorber may function as a primary fluid heater and the lower absorber may function as a secondary fluid heater. In this case, fluid is first passed, through the two upper conduits in whioh the fluid is preheated by thermal energy absorbed and conducted through the upper plates, and the preheated fluid is then returned through the lower conduits 148, 149 in which the fluid is heated further by thermal energy absorbed by the lower plates. Alternatively, the fluid may pass through an absorber only once, in one direction. In this case, the absorber may have a single conduit or more than one conduit.

In embodiments of the solar collector, the absorber may include both the upper and lower absorbers, or the absorber may include just the lower absorber without the upper absorber which may be optionally offered to customers and fitted as an upgrade. In some embodiments, the solar collector may be adapted to permit the upper and/or lower absorber to be retrofitted and, for example slid into position from an end of the collector unit to obviate the need for removing the transparent panel and possibly dismantling other components of the solar collector. In this case, access to the space for inserting the elongate upper and/or lower absorber may be gained by removing an end panel of the collector unit or opening some other closure at the end of the unit. The absorber and/or the transparent panel may include at least one retainer for maintaining the upper and/or lower absorber in a predetermined positional relationship therewith, and/or one or more guides for guiding the upper and/or lower absorber into position. An example of an arrangement which allows the lower absorber to be removed from and inserted into the collector unit is shown in the embodiment of Figures 2 and 3 ,

Returning to Figure 3, first and second guide rails 82, 84 are provided on the upper wall 55 of the lower absorber 23 for retaining and guiding the lower absorber into position. Each guide rail 82, 84 has a lower stem 86 and an enlarged upper portion or head 88 which is wider than the stem 86. The lower wall 45 of the upper absorber 21 has first and second grooves 90, 92 formed therein for registering with and receiving a respective guide rail, 82, 84. Each groove has a similar cross section to the guide rail with an elongate slot or opening 94 for receiving the stem 86 of the guide rail and an enlarged channel 96 above the slot for receiving the enlarged head of the guide rail. The enlarged head of the guide rail is wider than the slot so that the resulting coupling between the lower and upper absorbers limits any vertical movement of the lower absorber relative to the upper absorber while allowing the lower absorber to be slid longitudinally under the upper absorber into position. In other embodiments, fewer or more slidable couplings may be provided to secure the lower absorber to the upper absorber, and in other embodiments, the guide rail(s) may be provided on the upper absorber and the groove may be provided on the lower absorber. Numerous other coupling arrangements for guiding and/or retaining the upper absorber in position may be implemented in other embodiments. Advantageously, this arrangement allows a lower absorber element without solar-to-electrical energy conversion devices to be easily upgraded or exchanged with another that includes such devices for generating electrical power. In a similar manner, one or both of the lower absorber elements of Figures 4, 5A and 5B may be withdrawn from the solar collector and upgraded or replaced.

Figures 6A to 6F show cross-sectional views of other embodiments of a solar collector unit and components thereof. Figures 6A and 6B each show a half cross section of an embodiment of a solar collector unit 202, 204 from an outer edge 206, 208 to a centre line 210 and the other half of each embodiment 202, 204 may be a symmetrical mirror image on the other side of the medial line 210. Referring to Figure 6A, the solar collector comprises a concave collector panel 212, an absorber 214, an absorber support 216 upstanding from the reflector panel 212/ a transparent cover or panel 218, an edge bracket 220 and one or more formers or ribs 222. In this embodiment, the absorber 214 comprises an upper generally planar plate 224 having a raised edge region 226 and a flange 228 extending downwardly from the raised edge 226 and which forms a re- reflector plate, as previously described. The raised edge region 226 provides a support for the transparent panel 218 and provides a space 230 between the planar plate 224 and the transparent panel 218 for optionally receiving an array of solar cells for generating electrical power. The absorber further comprises a conduit 232 positioned below and in thermal contact with the planar plate 224, a plate section 234 extending from the conduit 232 and a lower plate 236 coupled to the lower edge of the plate section 234 and which forms another re-reflector plate, as previously described. The various plate sections 224, 228, 234, 236 of the absorber form a cavity or space 238 for receiving a lower absorber (not shown) for receiving radiation reflected from the reflector 212. One or more sections or components of the absorber described above may be integrally formed, for example by extrusion, and in one embodiment, all of the planar plate 224, conduits 232, re-reflectors 228, 234 and the interconnecting plate section 234 may be formed as a one piece 'extrusion.

In this embodiment, the support 216 comprises a discreet panel having upper and lower edges 240, 242 connected to the absorber and reflector, respectively. In this embodiment, the upper edge 240 of the support panel 216 is held in a slot or channel 244 formed at the end 246 of the lower plate section 236 of the absorber 214, as best shown in Figure 6E . The lower edge 242 of the support panel 216 is held in a slot or channel 248 provided in a lower support bracket 250, as best shown in Figure 6C. The support bracket is connected to an upper support surface 252 of the ribs 222 and has a base or flange 254 which extends laterally from both sides of the channel 248 to provide increased surface contact area with the ribs. The underside of the outer portion 256 of the flange 254 has a recess formed therein for receiving the edge of the reflector panel 212. In this embodiment, the ribs 222 may be formed of a sheet material and may be press cut or stamped. The rib 222 may be formed with an upper flange 258, for example by bending an upper portion of the rib after it is cut from the sheet material, and the flange provides both lateral stiffness and an increased surface area 252 for supporting the reflector panel 212 and absorber support bracket 250, as shown in Figure 6D. The rib 222 may be further provided ith an optional lower flange 260 extending in the same or opposite direction as the upper flange 252, again to provide lateral stiffness.

Referring to Figure 6F, the edge bracket 220 comprises an upwardly extending panel 262 having an inwardly directed lower end portion 264 defining a channel 266 therein for receiving an outer edge portion of the upper flange 258 of each rib member 222. The lower end portion of the edge bracket further includes a retaining flange 268 for retaining an edge portion of the reflector panel thereunder. The upper end of the edge bracket has a support structure for supporting the * transparent panel 218 and which, in this embodiment comprises an inwardly extending flange portion 270 and an upwardly extending flange portion 272 at the distal end thereof, and which provides a supporting surface for the transparent panel. The outer edge of the edge bracket 220 has a pair of flanges 27 _r 276 extending therefrom and defining a slot or channel 278 therebetween for receiving a clip member 280. The clip member 280 includes a flange 282 which overlaps an edge portion of the transparent panel 218 and holds the transparent panel against the lower supporting flange 272 of the edge bracket 220.

As can be seen in Figure 6A, the reflector panel, edge bracket, transparent panel, absorber structure and absorber support define a cavity 286 therebetween and the joints between these components may be sealed to form a sealed cavity to prevent the ingress of air, moisture and contaminants. For example, the components may be glued together with a suitable adhesive and the adhesive may provide sealing characteristics. Referring to Figure 6F, a suitable adhesive/sealant may be introduced into the space between the inwardly extending upper flange 270 of the edge bracket 220 and the transparent panel 218 and may provide a degree of flexibility to maintain the integrity of the seal during differential contraction or expansion between the transparent panel or edge bracket.

In use, the solar collector will be exposed to changes in outside temperature between day and night, and on a seasonal basis and the temperature range will vary depending on the country or region in which the solar collector is situated. The unit will also be exposed at different temperatures depending on the extent to which the unit is active, for example whether it is daytime or night time, the amount of available sun, and the extent to which the unit is tilted towards the sun. If the cavity is sealed, this thermal cycling will cause stress on the seals as the air or other gas in the cavity becomes pressurized or depressurized relative to the ambient air outside the unit and cause the seals eventually to break. Once the seal is broken, moisture and contaminants can pass into the cavity and degrade the quality of the internal transparent and reflective surfaces and cause fogging of the transparent panel, degrading the performance of the unit. To solve this problem, one or more expandable chambers may be provided in fluid communication with the cavity to absorb volumetric changes in the air or gas in the cavity thereby reducing or eliminating pressure variations and the resulting stresses or loading on the seals. The expandable chamber may be provided by any suitable means, non-limiting examples of which include a bag, sac, bladder or bellows, each having a flexible wall to allow the space defined by the walls to expand, or the expandable chamber may be provided by a chamber and fluid displacer arrangement such as a dashpot or piston/cylinder combination. An example of an expandable chamber is shown in Figures 6A and 6B. I this embodiment, the expandable chamber comprises a bag 290 having a flexible wall 291 to allow the volume inside the bag to expand and contract as illustrated by the solid and dotted lines, where the dotted lines show the bag in a more inflated state. The bag is conveniently positioned within the well 292 formed between the absorber support panels 216 and has a port 293 mounted within an aperture 297 (see Figure 6G) formed in the absorber support panel 216 to allow fluid communication between the cavity 286 and the bag 290. The junction between the port and the aperture is preferably sealed to prevent leakage of air or gas from the cavity into the ambient and vice versa. The wall(s) of the bag may be formed of any suitable flexible material having the required sealing capability to control or prevent the passage of air, gas and/or moisture through the wall membrane. The wall may for example comprise one or more layers of material such as a polymeric material and may further include a metallic or etalized layer. A desiccant 294, such as silica or other material, may be provided in the bag (or chamber) to absorb moisture from the air or gas which enters from the cavity. The desiccant material may for example be provided near the port 293 to absorb moisture from the air or gas as the air flows into the bag, and/or the desiccant may be positioned elsewhere in the bag.

In operation, when the temperature inside the cavity is relatively high, air or gas passes from the cavity through the port 293 and into the bag where it is optionally dried by desiccant. When the temperature of the cavity subsequently cools, air or gas which has been optionally dried by the desiccant material flows back into the cavity. As the bags are positioned externally of the cavity, they do not interfere with the performance of the solar collector and provide a convenient repository for desiccant to maintain the humidity level in the cavity below the dew point. Although the provision of an expandable chamber in fluid communication with the cavity is desirable fo:r the reasons described above, in other embodiments, a non- expandable chamber may be provided in fluid communication with the cavity for containing a desiccant material which would still be effective in drying the air or gas in the cavity as the air or gas passes into and out of the chamber by natural movement caused for example by diffusion, or convection. In other embodiments, a part of the wall of the cavity may be flexible to allow the volume of the cavity to vary. The well between the absorber support panels 216 may be used to accommodate a portion of the piping 295 which delivers fluid to the fluid conduit 214 of the absorber or returns fluid from the conduit 214. Insulation 296 may be provided around the piping 295 for thermal insulation.

Accommodating a portion of the external piping in the well between the absorber support panels allows the piping to be drawn down at a position intermediate between the ends of the solar collector unit to help protect the piping against damage and to enhance the aesthetic appearance of the solar collector unit in comparison to having the piping extending down from one or both ends of the unit.

Figure 7 shows a cross-sectional view through another example of an absorber according to an embodiment of the present invention. The absorber, generally shown at 219 comprises an upper absorber 221 and a lower absorber 223. The lower absorber 223 comprises an upper, laterally extending plate 225 and opposed edge section 227, 229 at opposite edges of the upper plate 225. Each edge section 227, 229 comprises an upwardly standing portion 231, 233 extending above the upper plate 225 for carrying the upper absorber 221. Each upper portion 231, 233 has a longitudinal channel 235, 237 formed therein which is accessible through a longitudinal slot 239, 241 formed in the inner wall 243, 245 of the support section 231, 233. Each edge section 227, 299 further comprises a downwardly extending flange 247, 249 which acts as a re-reflector as described above, for example with reference to Figures 2 to 6. The lower absorber 223 further comprises two spaced apart wall sections 251, 253 positioned near the middle of the upper plate 225 and extending downwardly therefrom, a lower, laterally extending wall section 255 extending between and positioned at the lower end of the opposed wall sections 251, 253, and outwardly angled flanges 257, 259 extending from the opposed wall sections 251, 253 for providing re-reflectors for the lower absorber, as previously described. Advantageously, the upper plate section 225, the edge sections 227, 229, the opposed wall sections 251, 253, the lower wall section 255 and the angled flanges 257, 259 may all be formed integrally in one piece, and may conveniently be formed by extrusion. A connector may be provided at the lower end of each angled flange 257, 259 to facilitate connection to the absorber support panels 216 which extend from the reflector, as shown in Figure 6A and 6B. The connector may comprise a channel or slot for receiving the upper edge of each panel formed between two flanges 244, 246, as also shown in Figure 6E . The connectors may also be integrally formed with the angled flanges and other components connected thereto. The lower absorber further comprises oppositely angled absorber plates 261, 263, a conduit 265 thermally coupled to the back of each plate and an optional array 267 of solar to electrical energy conversion devices mounted on the front faoe of the plate 261, 263- Each thermal absorbing plate 261, 263 is mounted to the lower absorber main mounting structure by spacers 267, 269 positioned between the re-radiation flanges 247, 257 and opposite edges of the thermal absorber plate 261. Advantageously, the lower flange 257 may be angled sufficiently to prevent downward movement of the spacer 269 to assist in holding the spacer and thermal plate assembly in position. The spacers 267, 269 preferably comprise a material having good thermal insulating properties to reduce heat loss from the plate to other parts of the absorber such as the flanges 247_/ 249. Thermal insulation 271 may be provided at the back of each thermal plate 261, 263 and around the conduit 265, again to prevent heat loss. A section 273 may be pro-vided at the back of each thermal plate to provide an enc losure or the thermal insulation 271 and the conduit 265 and may also be mounted between the spacers 267, 269 and the mally insulated thereby from the main supporting structure o the absorber.

The upper absorber 221 comprises a. laterally extending plate 275 having opposed edges 277^", 279, first and second conduits 281, 283 thermally coupled to the underside of the plate 275 and may optionally include an array of solar to electrical energy conversion devices 285 mounted on the upper surface of the plate 275. Spacers 287, 289 positioned between the edges of the upper absorber plate 275 and the upper support 227, 229 of the edge section of the absorber structure are provided to maintain a spacing between the upper absorber plate 275 and the upper edge sections 227, 229. Advantageously, the spacers can be formed of a thermally insulating material to reduce heat transfer 'between the upper absorber plate 275 and the main absorber structure. Each spacer comprises flange 291 which is accommodated within the channel 235, 237 of the edge supports 227, 229 and a support section 293 having a channel or slot 295 formed therein for rec iving an edge portion of the upper absorber plate 275. Advantageously, the arrangement shown in Figure 7 allows an upper absorber to be easily retrofitted after the solar collector has been installed on site, and also facilitates the assembly process when the uxpper absorber is installed at the factory. For example, when the upper absorber is to be installed, the end panel or closure of the solar collector unit is opened, as necessary, and the Spacers and upper absorber plate assembly are simply slid longitudinally into position in their respective channels 235, 237, 295, in the space between the transparent panel 218 and the upper plate 225 of the main absorber support structure. Advantageously, this minimizes the amount of dismantling of the solar collector unit that must be done to retrofit an upper absorber. Any one or more of the spacers of the embodiment shown in Figure 7 may be formed by extrusion.

The lower absorber elements 261, 263 may also be withdrawn from or inserted into the absorber support structure from an end of the collector unit to allow a lower absorber to be easily upgraded, replaced or repaired.

In some embodiments, any one or more components of the solar collector which at least partially extend from one end thereof to the other end may comprise a single piece or unitary member to simplify manufacture. For example, the or each reflector panel on either side of the absorber support may be formed of a single sheet extending between the ends of the absorber. The or each opposed panel forming the absorber support may be formed of a single sheet extending between the ends of the solar collector. The transparent panel or cover may be formed of a single sheet extending between the ends of the collector. One or more fluid carrying conduits of the absorber may each be formed of a single piece extending between the ends of the solar collector advantageously removing the need to join individual pieces together and reducing the risk of leakage.

Embodiments of the solar collector in which at least one component is made of a single piece between the ends of the collector, may comprise any desired length, for example, any length in the range between 6 and 50 feet or more. In one embodiment, a collector in which at least one component is a single piece component extending between the ends of the collector unit has a length of between 30 and 45 feet, for example about 40 feet. In this embodiment, any one or more of the reflector panels, absorber support panels, absorber, transparent panel and any other components which extend end to end may comprise a single piece.

An example of a solar collector unit in which at least one component is made of a single piece between the ends of the unit is shown in Figures 8A to 8D. In this embodiment, the solar collector 251 comprises reflector panels 253, 255, absorber support panels 257, 259 and an absorber 229. One or more of these components may comprise a single piece component extending between the ends 217, 219 of the collector. A plurality of transverse rib members 216 may be provided on the outside of the reflector panel 253 and spaced apart along the length of the collector. The collector unit comprises opposed end panels 226, 228 to close the ends of the unit and which may be removable or have a cover or closure to allow access to the inside of the unit, for example to allow one or more additional absorbers and/or an array of solar-to-electrical energy conversion devices to be inserted or removed from the end of the unit. Two supports 221, 223 are provided for supporting the unit, and in this embodiment are positioned adjacent the ends of the collector unit, although in other embodiments, one or more of the supports may be positioned more inwardly towards the middle of the unit. In this embodiment, the supports support the solar collector unit from structure below the reflector so that the supports do not obstruct sunlight. In other embodiments, the collector is mounted near or at the centre of gravity between the top and bottom thereof. The mounting structure may be provided for example by a rib member on the external side of the reflector panel. The solar collector is mounted on the supports such that it can rotate about a longitudinal axis for solar tracking. Figures 8B and 8C show top views of the solar collector when in oppositely tilted positions. One or more actuators 232 (Figure 8D) may be provided to tilt the solar collector to the required angle.

Although more than two supports can be provided along the length of the solar collector, providing just two supports can be beneficial. For example, if the solar collector is mounted on the ground, the supports may be susceptible to vertical movement due to settling of the ground or freezing during winter. Providing just two supports relieves the unit of stresses that would otherwise be caused by differential vertical movement of the supports.

Mounting and Tracking

Embodiments of the solar collector may be mounted on a tracking system which tilts the collector towards the sun as the sun's position changes over time. In one embodiment, the solar collector may be mounted with its longitudinal axis generally directed along the East-West direction, and the tracking system rotates the collector about a longitudinal axis as the sun's position changes in the North-South direction over the course of a year. As the change in the sun's North-South position over the period of a year is very gradual, only small changes in the ^"tilt angle of the collector are required over time. An example of a collector mounted in this manner is shown in Figures 9A to 9D. The solar collector system 201 shown in Figures 9A to 9D comprises first and second solar collectors in which each collector may comprise a linear array of solar units, (i.e. with the units in each array connected end to end). The arrays are mounted horizontally, with the second collector 205 positioned behind and above the level of the first collector 203, to ensure that neither collector overshadows the other over the operating range of tilt angles. In this embodiment, the collector system is mounted on the rooftop 207 of a building 209 (in this case a multiple dwelling unit (MDD) ) , although the system may of course be mounted on the ground or at any other suitable or desired location. The collectors are mounted with their longitudinal axes directed substantially along the East-West direction, and are shown tilted towards the South, which corresponds to the relative position of the sun. In this embodiment, each collector comprises a linear array of six collector units, and is mounted on three supports 211, 213, 215, one at each end_/ and one positioned centrally between the third and fourth units. However, it will be appreciated that other embodiments of the collector may comprise any number of units and any number of supports positioned at any desired locations along the collector.

The system 201 includes an actuator (not shown) for rotating the collectors about a longitudinal axis and controller (not shown) , for controlling their rotation to the required the tilt angle.

The actuator may be electrically operated, and in one embodiment, the actuator may be driven by electrical power generated by the solar collectors themselves so that the collectors are effectively self-driven. Only a single actuator may be provided to drive both collectors, or each collector may be driven by one or more actuators.

Heat absorbed by heat transfer fluid flowing through the collectors may be supplied to various points of use (i.e. heat sinks) within the building, for example, for use in space and/or water heating. Electrical power generated by the collectors, if any, may be used to drive heat transfer fluid through the collectors to the heat sinks or various points of use.

In another arrangement, one or more solar collectors may be mounted to the side of a building and an example of such an arrangement is shown in Figures 10A to 10D. In this arrangement, one or more collectors 303, 305, 307 are mounted substantially horizontally to a suitably directed wall 309 of a building 311, which in this embodiment is a multi-storey multiple dwelling unit. In this embodiment, the wall 309 to which the collectors are mounted generally faces south and the collectors may be rotated about their longitudinal axis as the North-South position of the sun changes over the period of a year.

In this embodiment, the collectors are mounted above one or more windows 313, 315, 317 of each floor and may be positioned to reduce the amount of direct sunlight to which each window is exposed. This may be particularly advantageous when the outside temperatures are higher than the desired inside temperature of the building, for example during summer time when cooling of the building may be required. If one or more collectors are capable of generating electricity, the electrical power generated by the solar collecto (s) may be used to drive an air conditioning system, for example, and/or the secondary function of the solar units in shading the windows may reduce the load on the air conditioning system.

In other embodiments, the collector may be mounted with its longitudinal axis directed generally along the North-South direction, and the tracking system rotates the collector about a longitudinal axis as the sun' s position changes during the course of a day. An example of such an arrangement is shown in Figures 11A to 11D. Referring to Figure 11A, a solar collector 401 is mounted with its longitudinal axis generally directed along the North-South direction and with its Northern end 403 positioned above its Southern end 405. The collector is mounted for rotation about its longitudinal axis on first and second supports 407, 409, and in this embodiment, the first support 407 is positioned at about one-third of the length of the collector from the Northern end and the second support is positioned at the Southern end 405. An actuator 411 drives rotation of the solar collector about a longitudinal axis and a controller (not shown) controls the tilt angle. In one embodiment, the tilt angle is controlled to track the sun's movement over the period of a day. If the collector is equipped to generate electricity, electrical power generated by the solar collector may be used to drive rotation.

Another solar collector arrangement is shown in Figures 12A to 12D. In this arrangement, generally shown at 501, one or more solar collectors 503, 505, 507, 509 are mounted to the side of a building 511, with their longitudinal axes (e.g. axis 515) oriented substantially vertically. The side 513 of the building to which the solar collectors are mounted generally faces South to maximize their exposure to the sun (for locations in the Northern Hemisphere, and may face North for locations in the Southern Hemisphere) . Each solar collector is mounted for rotation about a longitudinal axis thereof, and one or more actuators (not shown) are provided to drive rotation of the collectors. A controller (not shown) controls the tilt angle so that each collector is directed towards the sun and tracks movement of the sun over a daily period.

In any of the embodiments described herein_/ if the collector includes a means for generating electrical energy from solar energy, at least part of the energy may be used to drive the actuators and/or tilt angle controller, and/or pump for driving heat transfer fluid through a collector.

Heat Transfer Systems Figure 13 shows a heat transfer system according to an embodiment of the present invention for use in applications where the coolant passed through the solar collecto (s) is air (or possibly other gas). The system 601 comprises a blower 603 for driving fluid through the solar collector (s) 605, a damper or other valve 607, an air-to- water heat exchanger 609 for receiving air from the blower 603 and an air return line 611 for returning air to the solar collector (s) 605. The solar collector may for example comprise any of the embodiments described above with reference to Figures 1 to 3, or variants thereof. The system further includes a hot water storage tank 613 , a pump 615 for pumping water from the air-to-water heat exchanger 609 to the hot water storage tank 613 and a return line 617 for returning water from the hot water storage tank to the heat exchanger 609. A water-to-water heat exchanger 619_/ which, in this embodiment is in the form of a coil, is positioned within the hot water storage tank 613 and has an inlet 621 situated near the bottom of the storage tank 613 for receiving water from a water supply 614 and an outlet 623 positioned near the top of the storage tank and which is connected to a hot water supply tank 625 (near the bottom thereof) for supplying hot water to a building.

The heat transfer system further includes a forced air heat exchanger 627 which may be selectively connected to receive air from the heat exchanger 609 by means of a valve for example an air damper 629. In one embodiment, the forced air heat exchanger comprises an existing forced air furnace. A cold air return system 631, which may include a cold air return plenum 633, for returning cold air to an existing forced air furnace is connected to the solar collector return line 611 for returning cold air from the building to the solar collectors to be heated thereby and returned for use to the heat transfer system.

In this arrangement, the highest grade heat available, i.e. that contained in the air of the output of the solar collectors is used to heat hot water (in the heat exchanger 609) ; residual, lower grade heat from the heat exchanger is used for space heating, and cold air returned from the inner space of the building is supplied to the input of the solar collector (s) . This arrangement ensures that heat is supplied to each point of use at a temperature which is similar to that required at the point of use so that heat energy is transferred efficiently. This arrangement also ensures that the inlet temperature of fluid to the solar collector is relatively low. This both minimizes heat loss from the fluid between the final point of use and the inlet to the collector, and also increases the differential temperature of the fluid between the inlet and outlet of the collector to increase the heat absorption capacity of the fluid Joetween the inlet and outlet.

The heat transfer system has a bypass line 635 which allows return air to selectively bypass the solar collector_/ as required, and which may be controlled by an air damper (or other valve) 637. The bypass line 635 is connected to (the low pressure side of) the blower 603. The return air may bypass the solar collectors at night_/ for example_/ and stored heat from the hot water storage tank 613 may be used for space heating.

The air damper 607 may be controlled to vent or exhaust air from the solar collector when high temperature heat is no longer required within the building. Furthermore, the inlet of the solar collector may be selectively opened, for example by the air damper 637, to outside ambient air so that air is simply drawn through the collector by the blower 603 to cool the collector. Advantageously, the h>lower 603 may be driven by solar-to- electric energy conversion devices mounted on the solar collector or mounted elsewhere and provided separately.

Nσn limiting examples of the temperatures of fluids in the system of Figure 11 are as ollow . When active (i.e. during daytime)_/ the inlet temperature to the solar collector may ? e between 10°C and 25^QC and the outlet temperature of the collector may be for example between 50°C and 100°C or more. The temperature of water from the fresh water supply may be between 5^αC and 15°C, for example 10°C and the output air from the solar collector may heat the water for the hot water storage tank via the air-to-water heat exchanger 609 to a temperature of for example between 30°C and 8Q^ώC. The water supplied to the hot water tank 625 may be in the range 30 "C to 65 ^ήC and the hot water tank may supply water to the building at approximately 60 °C. Air from the air-to-water heat exchanger which is fed from the air damper 629 into the existing forced air heating system may have temperatures in the range of 50 to 100°C Low pressure air which is returned from the forced air heating system to the input of the solar collector may be in the range of 15°C to 25^DC, for example.

Figure 14 shows an example of a heat transfer system according to another embodiment of the present invention in which air driven through and heated by a solar collector is used for space heating only. Accordingly, this system is similar to that shown in Figure 13, except that the air-to-water heat exchanger, the hot water storage tank, associated pump and hot water tank have been omitted, and like parts are designated by the same reference numerals. The description of these components described above with reference to Figure 13 applies equally to Figure 14.

Figure 15 shows an example of a heat transfer system according to another embodiment of the present invention in which the heat transfer fluid or coolant driven through the solar collector (s) is a liquid, and which is particularly suitable for use with any of the embodiments of the solar collector described above with reference to Figures 4 to 7, or variants thereof. The heat transfer system comprises a pump 703 connected to the outlet 705 of a solar collector 707, a hot water storage tank 709, a heat exchanger 711 connected to the output of the pump 703 for transferring heat from the coolant (e.g. glyco or other liquid) to water contained in the hot water storage tank, a second heat exchanger- 713 having an inlet 715 for receiving water from a fresh water supply 714 and an outlet 717 for supplying hot water to a hot water supply tank 719 for supplying hot water to one or more points of use, as required. The heat transfer system fu.rth.er includes a space heating system 721 which may include a solar space or existing forced air furnace 723, a fluid-to-air heat exchanger 725, a pump 727 for pumping liquid from the hot water storage tank 709 to the fluid-to-air heat exchanger 725 and a cold air return plenum 729. Water from the fluid-to-air heat exchanger 725 is returned to the hot water tank 709 via a return line 739- In this embodiment, an optional hydraulic 2one control system is positioned between the pump 727 and the fluid-to-air heat exchanger 725. The pump 727 may be activated by any suitable means to provide space heating when required, and in some embodiments may be activated or controlled in response to one or more temperature sensors, or other call for heat such as a switch. A temperature sensor may be positioned to sense the temperature of water in the storage tank, and may comprise an aquastat, for example. A signal from the aquastat may be used to control the pump 727 and/or the coolant pump 703. For example, if the temperature of water in the storage tank falls below a threshold value, the signal may activate the coolant pump 703, and/or possibly turn off the water pump 727.

The heat transfer system may further include one or more fluid-to-fluid heat exchangers 733, 735, 737 connected to the output of the first fluid-to- luid heat exchanger 711 in the hot water storage tank 713. This embodiment comprises three £luid-to—fluid heat exchangers which are connected in series so that the first fluid-to- fluid heat exchanger 733 receives coolant/heat transfer fluid from the first heat exchanger 711, the second fluid- to-fluid heat exchanger 735 receives coolant from the first fluid-to-fluid heat exchanger 733 and the third heat exchanger 737 receives coolant from the second heat exchanger 735. In this embodiment, coolant from the third heat exchanger 737 is returned to the inlet 741 of the solar collector (s) 707. The heat exchangers 733, 735, 737 are arranged in descending order of temperature, with the heat exchanger requiring the highest inlet temperature positioned first and the heat exchanger requiring the lowest inlet temperature positioned last. In this particular embodiment, the first heat exchanger comprises a heat exchanger for a hot tub, requiring the highest temperatures, the second heat exchanger is that for a swimming pool, and the third heat exchanger is a ground heat exchanger which exchanges heat with the ground. In other embodiments, any other arrangement of one or more heat exchangers may be used. In some embodiments, the additional heat exchangers may be omitted altogether, so that the solar collector heat is used for space heating and/or hot water heating, or for any other purpose.

Aspects of the present invention and advantageous embodiments thereof include the following.

A heat and/or heat and electricity production combination total and area-concentrated direct solar radiation collector unit comprising one or more trough-like concentrators or reflectors and a longitudinal solar radiation absorber surface positioned beyond the focus line of the one or more concentrator or reflector, wherein the absorber is placed above the aperture line of the casing reflector, said casing having one or more transparent panels provided over the one or more apertures of trie concentrator or reflector, said transparent surface and reflector or concen_trator acting as stressed elements also forming the case, and the system tracks the sun.

A combination solar collector where both total (diffuse) and direct solar radiation are collected and converted to heat only or heat and electricity using photovoltaic (PV) or thermonic diode (s) and a heat collector with thermal or integral fluid path to carry away heat using air or liquid. A combination solar collector unit where the total solar radiation is collected by a one-sun thermally optimized thermal/electric absorber by means of heat sink fins and the direct or reflected solar radiation is collected by an electro optical device over area and thermal energy transferred to air by heat absorber fin.

A combination solar collector where the air is first passed through the total absorber tube and then turned 180° by an air duct at the end of a module or row on n. modules to return and pick up additional heat in direct absorber tube.

A combination solar collector where the absorbers are thermally insulated on at least one and preferably all sides not exposed to optical radiation.

A total absorbers and where the absorber is covered by a transparent panel,

A direct thermal absorber where an optical/thermal diode is created by optical and thermal reflector panels in such a way as to "trap" direct beam solar radiation, both optically and thermally minimizing radiation heat loss and optical reflection heat loss from solar cell or thermonic diode. A total solar radistion electrical/thermal capture absorber where optionally itte photovoltaic or thermal diode first transforms total solar radiation to electricity then to heat which is efficiently transferred into one sun thermal absorber air flow path preferably by means of highly thermal conductive absorber and optional heat sink ins .

A combination sola r collector which uses external ribs and to provide structurally sound mounting points for system actuation and pivot point mounting that do not interfere/shadow any solar radiation incident on the collector .

A system having any solar collector unit described above with a low concentratd_on ratio 1:2 to 1:6

X/P = 1:2 - 1:6

X = width of aperture of direct solar radiation

W — width of radiation receiver

A system with radiation receiver arranged for solar intensity uniformity.

A direct solar absorber that is removable from the collector system without ef cting the structural integrity of the solar collector system and can optionally be fitted with opto-electric or opto- thermal devices to produce electricity.

A direct solar atssorber that can span multiple collector modules to reduce or minimize fluid and electrical interconnects between modul-es connected in series. A combination heat and electric collector system where up to n panels can be connected in series with minimal mounting hardware and base suppor .

A solar thermal collect system arranged so one actuator can move between 1 and 6 or more collectors simultaneously to track the sun.

A system including a solar collector where the longitudinal axis of the collector is substantially vertical . A system including a solar collector where the long axis of the collector is inclined at latitude.

A system where the collector panels have an opening in the shadow area of the absorber to aid assembly.

A combination solar collector where the liquid absorber tube has a shape arranged or optimized for minimum mass and fluid volume as well as maximum heat transfer from the solar collection surface to the fluid.

A liquid absorber that has been optimally thermally insulated on all sides not receiving direct or total solar radiation.

A liquid absorber having a shape arranged or optimized for the application of PV or thermonic diodes to provide maximum heat transfer to fluid.

An electronic control system for the panels may comprise at least one of:

(a) track the motion of the sun in the sky with 1/16° increments (or of less than 1°) as a function of day of year, time of day, latitude or longitude,- (b) control the fan or fluid pump flow to maintain a constant system output temperature from the absorber;

(c) measure and store the electrical and ther nal energy captured as a function of time of day and/or day of year; (d) optionally transmit this data to a centra 1 computer system;

(e) provide a "defrost" or fog clear cycle fear the multi- sun aperture,"

(f) record and alert remote devices in the event of system failure or performance; and

(g) the defrost cycle will be accomplished b^ off tracking the sun so the area of focused solar energy t-raverses the transparent panels of the collector enclosure .

An air absorber where air f om a bu ilding may be recirculated through the absorber to heat the building.

An air absorber where 100% or a n% of fresh outside air may be drawn through the absorber- (s) to supply fresh make up air to buildings.

A system where the solar collector unit(s) or module (s) is/are not air sealed but vented, optionally with a Gortex or similar air permeable water repe3_lent vent.

A system where moisture absorbing cdesiccants encapsulated in the solar collector unit or the module system, A system where the direct thermal «and/or PV electrical energy can be turned off by tiltimg the collector about 10° away from pointing directly at the sun, while the one-sun PV panel still captures total solar energy,

A system where the multi-sun PV cells are cooled in summer by ambient air or cooled air or liquid or sourced or river/pool liquid.

In embodiments of the present invention, the solar collector may comprise at least one end panel, and the or each end panel may comprise a transparent material.

In embodiments of the present invention, any one or more components of the reflector may comprise a plastics material, for example the reflector may comprise concave support elements formed of a plastics material, and a central support member also formed by a plastics material, and these elements may either be formed integrally e.g. moulded or formed separately and connected together. The concave reflector elements may also comprise a plastics material which is coated with a reflective coating by any suitable technique. In one embodiment, the reflector may comprise plastic concave support members for supporting separate reflector elements in which the reflector elements comprise aluminum, or a plastics material.

In other embodiments of the present invention, any feature described above or claimed herein may be combined with any other feature described above or claimed herein. In embodiments of the present invention_/ the absorber may comprise any number of different configurations. For example_/ the absorber may comprise a lower absorber having one or more conduits therethrough for receiving reflected radiation from the reflector, and may optionally include a field replaceable or permanently mounted upper absorber which absorbs total sunlight and the upper absorber may include one or more fluid carrying conduits therethrough or may simply comprise one or more solar to electrical energy conversion devices. In one embodiment, the absorber may be adapted to carry either liquid or gas such as air, or the absorber may be adapted to carry both liquid and gas, such as air.

In embodiments of the present invention, the absorber may be adapted to carry fluid in one direction only, and in another embodiment, the absorber may be adapted to include a plurality of conduits which enable fluid to make multiple passes through the absorber.

The conduit material of the absorber may comprise any metal or metallic material or other highly thermally conductive material and may include one or more coatings to increase its thermal absorption.

Insulating material around conduits of the absorber may comprise any suitable material, for example spun rock or other material. In embodiments of the present invention, the surface of the absorbers which receive radiation reflected from the reflectors may include a simple surface without any solar to electrical conversion devices so that this portion of the absorber converts solar radiation into thermal energy only rather than both thermal and electrical energy.

The upper portion Of the absorber may also be adapted to convert total solar radiation to thermal energy only and not include any solar to electrical energy conversion devices. Further aspects of the invention comprise a combination of any one or more components disclosed herein.

Modifications to the embodiments described herein will be apparent to those skilled in the art.

Claims

CLAIMS :

1. A solar collector comprising a reflector and an absorber spaced from the reflector, said absorber comprising a first absorber element spaced from the reflector and having a surface arranged for receiving solar radiation reflected from said reflector, the first absorber element comprising at least one conduit for carrying fluid therein and thermally coupled to said absorber surface, and a second absorber element having an absorber surface arranged for receiving directly transmitted solar radiation, and one or more conduits for carrying fluid therein thermally coupled to the absorber surface of the second absorber element.

2. A solar collector as claimed in claim 1, wherein the second absorber element is positioned above the first absorber element.

3. A solar collector as claimed in claim 1 or 2, wherein the or at least one conduit of said first absorber element is thermally insulated from the or at least one conduit of said second absorber element.

4. A solar collector as claimed in claim 3, comprising a thermally insulating material between the or at least one conduit of said first absorber element and the or at least one conduit of said second absorber element.

5. A solar collector as claimed in any preceding claim, wherein the or at least one conduit of said first absorber element is spaced apart from the or at least one conduit of said second absorber element.

6. A solar collector as claimed in any preceding claim, wherein said absorber surface of said first absorber element is at least partially planar.

7. A solar collector as claimed in any preceding claim, wherein the absorber surface of said second absorber element is at least partially planar.

8. A solar collector as claimed in any preceding claim, wherein said first absorber element comprises a plate supporting said absorber surface, and said one or more conduits of said first absorber element are thermally coupled to said plate.

9. A solar collector as claimed in any preceding claim, wherein said first absorber element comprises first and second absorber members each having an absorber surface for receiving radiation reflected from said reflector, and each having at least one conduit thermally coupled to a respective absorber surface.

10. A solar collector as claimed in any preceding claim, wherein said first absorber element comprises first and second substantially planar oppositely angled surfaces directed to receive reflected radiation from opposite sides of said reflector.

11. A solar collector as claimed in any preceding claim, further comprising reflector means arranged to reflect energy reflected from the absorber surface of the first absorber element back to the absorber surface.

12. A solar collector as claimed in claim 11, wherein said reflector means is positioned adjacent said first absorber element.

13. A solar collector as claimed in claim 11 or 12, wherein the absorber surface of the first absorber element includes first and second opposed longitudinal edges, and the reflector means includes a reflector extending from one of said first and second edges and away from said surface.

14. A solar collector as claimed in claim 11 or 12, wherein the radiation receiving surface of the first absorber element includes first and second opposed longitudinal edges, and the reflector means includes a first reflector extending from a position adjacent said first edge and a second reflector extending from a position adjacent said second edge.

15. A solar collector as claimed in claim 14, wherein distal ends of the first and second reflectors define an aperture for passing solar radiation reflected from said reflector therethrough to said absorber surface.

16. A solar collector as claimed in claim 11 or 12, wherein said reflector means comprises first and second spaced apart reflectors having opposed ends defining an aperture for introducing solar radiation reflected from said reflector onto the radiation receiving surface of said first absorber element.

17. A solar collector as claimed in claim 11 or 12, wherein said first absorber element comprises a first absorber surface for receiving reflected radiation from one side of said reflector and a second absorber surface for receiving radiation reflected from the other side of said reflector, and reflector means disposed between said reflector and said first absorber element arranged to reflect energy reflected from the first and second surfaces of said first absorber element back to said radiation receiving surfaces .

18- A solar collector as claimed in claim 15, wherein the width of said aperture is less than the width of the radiation receiving surface of said first element.

19- A solar collector as claimed in any preceding claim, wherein the second absorber element comprises a plate for supporting said radiation receiving surface, and said one or more conduits of said second absorber element are thermally coupled to the plate.

20. A solar collector as claimed in any preceding claim, wherein at least one of said first and second absorber elements are detachably mounted to said solar collector .

21. A solar collector as claimed in any preceding claim, wherein said absorber comprises a support structure for releasably supporting at least one of said first and second absorber elements.

22. A solar collector as claimed in any preceding claim, further comprising means for slideably mounting at least one of said first and second absorber elements on said solar collector.

23. A solar collector as claimed in claim 22, wherein said solar collector has opposed ends and a longitudinal axis therebetween, and said slideable mounting means is arranged to permit at least one of said first and second absorber elements to slide in a direction along said longitudinal axis.

24. A solar collector as claimed in claim 23, further comprising a releasable cover at an end of said solar collector for permitting at least one of said first and second absorber elements to be introduced or withdrawn from the end of said solar collector.

25. A solar collector as claimed in any preceding claim, wherein said first absorber element comprises one or more solar energy conversion means for converting solar energy into electrical energy arranged to receive reflected radiation from said reflector.

26. A solar collector as claimed in any preceding claim, wherein said second absorber element comprises one or more solar energy conversion means for converting solar energy into electrical energy and arranged for receiving direct solar radiation.

27. A solar collector as claimed in any preceding claim, wherein said reflector has a concave profile and extends substantially linearly along a longitudinal axis in a direction transverse to its concave profile.

28. A solar collector as claimed in claim 27, wherein the first and second absorber elements extend along said longitudinal direction.

29. A solar collector as claimed in claim 27 or 28, wherein said reflector has opposed longitudinal edges extending in a direction along said longitudinal axis and said solar collector further comprises structure positioned between said longitudinal edges and adjacent said reflector and which extends along a major part of the length of said reflector and arranged to stiffen the reflector in a direction normal to its surf ce.

30. A solar collector as claimed in claim 29, wherein said structure comprises one or more panel means extending from said reflector.

31. A solar collector as claimed in claim 30, wherein said structure comprises first and second opposed panels extending in a direction along said longitudinal axis and spaced apart to provide a space therebetween which also extends along said longitudinal axis.

32. A solar collector as claimed in claim 31, wherein at least one of said panels tapers towards the other of said panels in a direction transverse to said longitudinal axis.

33. A solar collector as claimed in claim 32, wherein said first and second panels are positioned within the trough formed by the concave profile of said reflector,

34. A solar collector as claimed in any one of claims 30 to 33, wherein said structure is arranged to support said absorber.

35. A solar collector as claimed in claim 30, further comprising transparent panel means extending between the edges of said reflector,

36, A solar collector as claimed in claim 35, further comprising means forming a chamber disposed within the space between said first and second panels, said chamber being in fluid communication with the space between said reflector and said transparent panel, and wherein the volume of the chamber can at least one of expand and contract.

37. A solar collector comprising a reflector and an absorber spaced from the reflector, the absorber comprising a first absorber element spaced from the reflector and having a surface arranged for receiving solar radiation reflected from the reflector, the first absorber element comprising at least one conduit for carrying fluid therein and thermally coupled to the absorber surface, and the solar collector further comprises attachment means for securing a second absorber element to the solar collector for receiving directly transmitted solar radiation.

38. A solar collector as claimed in claim 37, wherein said attachment means comprises a slideable attachment means to allow the second absorber element to be slideably attached to the solar collecto .

39. A solar collector as claimed in claim 37 or 38, wherein said attachment means is arranged to allow said second absorber element to be mounted above said first absorber element.

40. A solar collector as claimed in any one of claims 37 to 39, further comprising a transparent panel and a space between the transparent panel and the first absorber element for receiving the second absorber element.

41. A solar collector comprising a trough-like reflector having opposed ends and opposed longitudinal edges, an absorber spaced from the reflector for receiving reflected radiation therefrom and structure means positioned between the opposed edges of said reflector and upstanding from a position adjacent said reflector and extending longitudinally and continuously along said reflector over at least a major part of the length of the reflector, and arranged to at least one of stiffen and strengthen the reflector in a direction normal to its surface.

42. A solar collector as claimed in claim 41, wherein said structure means comprises at least one panel means.

43. A solar collector as claimed in claim 42, wherein said structure means comprises first and second opposed panels spaced apart in a direction transverse to said longitudinal axis to form a space therebetween extending along said longitudinal axis.

44. A solar collector as claimed in claim 43, wherein at least one of said panels tapers towards the other panel in a direction transverse to the length of said reflector.

45. A solar collector as claimed in claim 44, wherein at least one of said first and second panels tapers towards the other panel as the panels extend away from said reflector.

46. A solar collector as claimed in any one of claims 42 to 45, wherein said reflector comprises a first side and a second side each extending longitudinally and an aperture between said first and second sides and between the lower edges of said first and second panels to provide access to the space between said first and second panels.

47. A solar collector as claimed in claim 46, wherein said aperture comprises a longitudinal slot formed between opposite sides of said reflector.

48. A solar collector as claimed in claim 46 or 47/ wherein said reflector comprises a first panel forming one side of said reflector and a second panel forming a second side of said reflector and wherein the first panel of said structure extends from the first panel of said reflector and the second panel of said structure extends from the second panel of said reflector.

49. A solar collector as claimed, in claim 43, wherein at least one of the first panels and the second panels are integrally formed.

50. A solar collector as claimed in claim 48, wherein at least one of the first panels and the second panels are separate panels joined and connected together.

51. A solar collector as claimed in claim 50, further comprising bracket means for joining at least one of (1) the first panels together, and (2) the second panels together.

52. A solar collector as claimed in any one of claims 41 to 51, wherein said structure supports said absorber,

53, A solar collector as claimed in claim 52, wherein said absorber comprises a first radiation receiving surface for receiving radiation from one side of said reflector and a second radiation receiving surface for receiving radiation from a second side of said reflector, and said structure is connected to said absorber between said first and second radiation receiving surfaces.

54. A solar collector as claimed in any one of claims 41 to 53, further comprising transparent panel means extending between the edges of said reflector.

55. A solar collector as claimed in claim 54, further comprising closure means for closing the opposed ends of said solar collector.

56, A solar collector as claimed in claim 55, wherein said structure means, said transparent panel, said reflector and said closure means form a cavity therebetween.

57. A solar collector as claimed in claim 56, wherein said cavity is partially or completely sealed.

58. A solar collector as claimed in claim 56 or 57, further comprising means forming a chamber in communication with said cavity and wherein said chamber is arranged such that the volume of said chamber can vary.

59. A solar collector as claimed in claim 58, wherein said structure means defines a housing and said chamber forming means is disposed in said housing,

60. A solar collector as claimed in any one of claims 41 to 59, further comprising one or more rib members adjacent said reflector and extending transversely of said longitudinal axis, and wherein said structure means is connected to at least one of said reflector and at least one rib member.

61. A solar collector comprising a reflector defining a substantially concave reflective surface, an absorber having a surface for receiving radiation from the reflective surface, and reflector means positioned between the reflective surface and the radiation receiving surface of the absorber for reflecting radiation received from the absorber back to the radiation receiving surface of the absorber.

62. A solar collector as claimed in claim 61, wherein said reflector means is positioned adjacent said absorber.

63. A solar collector as claimed in claim 61 or 62, wherein the radiation receiving surface of the absorber includes first and second opposed longitudinal edges, and the reflector means includes a reflector extending from a position adjacent one of said first and second edges and away from said surface.

64. A solar collector as claimed in any one of claims 61 or 62, wherein the radiation receiving surface of the absorber includes first and second opposed longitudinal edges, and the reflector means includes a first reflector extending from a position adjacent said first edge and second reflector extending from a position adjacent said second edge.

65. A solar collector as cl imed in claim 64, wherein distal ends of the first and second -reflectors define an aperture for passing solar radiation reflected from said reflector therethrough to said absorkoer surface.

66. A solar collector as cl imed in claim 61 or 62, wherein said reflector means comprises first and second spaced apart reflectors having opposed ends defining an aperture for introducing solar radiation reflected from said reflector onto the radiation receiving surface of said absorber.

67. A solar collector as clai esd in claim 65 or 66, wherein the aperture defined between distal ends of said first and second reflectors has a width which is substantially equal to or less than the width of the radiation receiving surface of said absorber.

68. A solar collector as claimed in any one of claims 61 to 67, wherein at least a portion of the absorber surface is planar.

69. A solar collector as σlaimed in any-one of claims 61 to 69, further comprising solar energy conversion means disposed on the radiation receivi g surface of said absorber.

70. A solar collector as claimed in claim 69, wherein at least a major part of the radiation receiving surface of the absorber is planar.

71. A solar collector as claimed in any one of claims 61 to 70, wherein the absorber comprises first and second radiation receiving surfaces positioned on each side thereof,

72. A solar collector as claimed in claim 71, wherein said reflector means comprises first reflector means positioned between the reflective surface and the first radiation receiving surface of the absorber for reflecting radiation received from the absorber back to the first radiation receiving surface and second reflector means positioned between the reflective surface and the second radiation receiving surface of said absorber for reflecting radiation received from the second radiation receiving surface back to the second radiation receiving surface.

73. A solar collector as claimed in any one of claims 61 to 72, including an absorber support positioned between said first and second radiation receiving surfaces of said absorber.

74. A solar collector as claimed in any one of claims 61 to 73, wherein said reflector comprises a troughlike reflector having a longitudinal axis extending between opposed ends thereof and said reflector means extends in a direction along said longitudinal axis.

75. A solar collector as claimed in claim 74, wherein said at least one reflector extends substantially linearly in a direction along said longitudinal axis.

76. A solar collector as claimed in any preceding claim, wherein the reflector and the edge of the absorber define an aperture therebetween, and the ratio of the width of the aperture to the width of the radiation receiving surface of the absorber is between 30:1 and 1.1. :1, and may be between 25:1 or 20:1 and 1.1:1 or between to 10:1 and 1.1:1, and further may be less than 10:1 or 4:1.

77. A solar collector comprising a reflector for receiving solar radiation, an absorber arranged for receiving solar radiation reflected from the reflector and transparent panel means opposite said reflector and spaced therefrom to define a cavity therebetween and means forming a variable volume chamber in communication with said cavity.

78. A solar collector as claimed in claim 77, wherein said chamber forming means comprises at least one flexible wall to allow the volume of said chamber to at least one of expand and contract.

79. A solar collector as claimed in claim 78, wherein said flexible wall comprises at least one layer of a sheet material.

80. A solar collector as claimed in any one of claims 77 to 79, wherein said chamber forming means comprises a chamber wall at least a portion of which comprises a material, structure, coating or film that is substantially impervious to at least one of moisture and a predetermined gas.

81. A solar collector as claimed in any one of claims 77 to 80, further comprising a housing positioned between opposed edges of the reflector and wherein said chamber forming means is disposed in said housing.

82. A solar collector as claimed in claim 81, wherein said chamber has an opening for fluid communication with said cavity and wherein said opening is substantially sealed to a wall of said housing.

83. A solar collector as claimed in any one of claims 77 to 82, further comprising a desiccant material disposed within said chamber and/or said cavity.

84. A solar collector as claimed in any one of claims 77 to 83, further comprising a plurality of chamber forming means each forming a chamber in fluid communication with said cavity.

85. A solar collector comprising a reflector having a concave reflective surface, an absorber having a substantially planar surface for receiving solar radiation reflected from the reflective surface, and wherein the reflective surface is shaped to reflect radiation between first and second spaced apart positions on a predetermined plane such that the distribution of intensity over said plane between said first and second positions varies by less that 15% or less than 10%.

86. A solar collector as claimed in claim 85, wherein said plane substantially coincides with the planar surface of said absorber.

87. A solar collector as claimed in claim 86, wherein said predetermined positions are adjacent opposed edges of the planar surface of said absorber.

88. A solar collector as claimed in any one of claims 85 to 87, wherein the planar surface of the absorber is angled to receive reflected radiation from one side of said reflector.

89. A solar collector comprising a reflector having a concave reflective surface defined by the equation - [a4 + y² - [a6 + y² - [aS ι- yX (alQ + y² - a ) J]

where z is the axis extending through the surface of the reflector, y is the position transverse to the reflector and C = -3.436E-002, k = 1.300E-QQ1, a4 = -1.Q50E-QQ6, a6 = 1.815E-008, a8 = -1,090E-011, alO = -2.351E-015 and al2 = 2.305E-017.

90. An absorber for a solar collector as defined in any preceding claim.

91. A solar collector comprising a reflector having a concave reflective surface defined by the equation y⁴ - [a4 + y²

- [a% + y - {al0 + y~ - u) ]]}

where z is the axis extending through the surface of the reflector, y is the position transverse to the reflector and c = -3.4355E-002, k = 1.3001E-001, a4 = -1.0497E-006, a6 = 1.8146E-008_/ aS = -1.0894E-011, alO = -2.3509E-015 and al2 = 2.3054E-017.

92. A solar collector comprising a reflector having a concave reflective surface defined by the equation

where z is the axis extending through the surface of the reflector, y is the position transverse to the reflector and c ^« -3.435529E-002, k = 1.30O1O9E-O01, a4 = -1.049700E-006, a6 = 1.814578E-008, a8 = -1. OS9380E-011, alO = -2.350870E-015 and al2 = 2.305415E-017.

93. A solar collector unit mounted to the side of a building.

94. A solar collector unit mounted above a window door or other aperture in the side of a building.

95. A solar collector unit as claimed in claim 94, mounted substantially horizontally,

96. A solar collector unit as claimed in clai_m 93, mounted substantially vertically.

97. A solar collector unit as claimed in any one of claims 93 to 96, comprising a solar collector as cLaimed in any one of claims 1 to 92,

98. A solar collector unit as claimed in any preceding claim, wherein the absorber comprises a planar sur ce for receiving reflected radiation from the reflector and having a width of at least one centimetre, for example between 1 and 10, 1 and 15 or 1 and 20 centimetres or more.

99. A solar collector as claimed in any preceding claim, wherein the reflector is arranged to concent xate reflected radiation to a plane between two positions spaced apart by at least one centimetre, for example between 10 and 1 and 20 or 15 or 20 centimetres or more.