WO2007135419A2

WO2007135419A2 - Solar collector

Info

Publication number: WO2007135419A2
Application number: PCT/GB2007/001885
Authority: WO
Inventors: James Madden
Original assignee: James Madden
Priority date: 2006-05-24
Filing date: 2007-05-22
Publication date: 2007-11-29
Also published as: GB0610296D0; WO2007135419A3

Abstract

A solar collector comprises a tube ( l) through which, in use, a f luid f lows and which absorbs solar radiation through its wall; characterised in that the tube incorporates a portion ( 7, 10, 12 ) which has a width (w), which is greater than its depth (d).

Description

SOLAR COLLECTOR

Field of the Invention

The invention relates to solar collectors.

Review of Art Known to the Applicant

Known collectors enclose a conventional collecting tube which is circular in cross-section in a glass container where the glass seals the tube to form a container. The tube may be vacuum-sealed within the container. The vacuum prevents loss of collected heat by convection from the hot tube to the container's wall and allows the tube to remain clean. Known collectors also employ coated tubes and special glass formulations to maximise the absorption of radiation.

Problems to be Solved

One problem to be solved is the difference in thermal expansion between the tube and the collector container.

Another problem to be solved is how to reduce the overall size of a tube collector. A further problem to be solved is how to increase the thermal collection of a tube. Other problems are solved by the following inventive aspects of the invention.

A further problem to be solved is how to resist the atmospheric pressure from crushing the solar collector's enclosure, whilst containing a vacuum chamber within.

A further problem to be solved is how to evacuate all matter from the cavities contained within the solar collector's enclosure, from one common extraction point.

Summary of the Invention

In its first broad independent aspect, the invention provides a solar collector comprising a tube through which, in use, a fluid flows and which absorbs solar radiation through its wall; characterised in that the tube incorporates a portion which has a width (w) that is greater than its depth (d).

The above configuration allows a tube contained within a collector container to present substantially more of the tube's surface area to the solar radiation. The tube will therefore be able to collect solar radiation with greater efficiency than prior art solar collectors with conventional circular cross-section tubes. In addition, a reduced bending radius can be achieved if the tube is bent across the narrower axes (d), which allows the tubes to be housed in smaller collector containers.

In a subsidiary aspect in accordance with the invention's first broadest independent aspect, said portion is elliptical in cross-section.

The advantage of having portions of the in a elliptical cross section is that the elliptical shape has the desired characteristics of having a width (w) that is greater than its depth (d) whilst substantially retaining its strength in order to withstand elevated temperatures and pressures.

In a further subsidiary aspect, the said tube is asymmetrically flattened. The advantage of having a tube, which is asymmetrically flattened, is that a decreased bending radius can be achieved. An alternative configuration for the above is to use a wholly circular tube in the solar collector, which incorporates a portion of reduced diameter tube. The reduced diameter portion would enable a reduced bending radius as stated in the above flattened tube configuration.

In a further subsidiary aspect, said tube incorporates at least one bend whose width (w) is greater than its depth (d).

This is advantageous for example because it would allow a solar collector which would ordinarily incorporate a single tube located longitudinal through a container to accommodate multiple runs of tube within a conventional collector because the tube can be bent with improved compactness. Furthermore, if a single U-shaped bend is opted, the inlet and outlet pipes may be located at the same end of the solar collector. This results in the solar collector being relatively straightforward to install by having both the inlet and outlet pipes in close proximity.

In a further subsidiary aspect, said tube is located in proximity to a reflector, which is shaped and configured' to focus radiation onto said portion.

The advantage of having the tube located in close proximity to a reflector which is shaped and configured, to focus radiation onto the tube is that the reflector may collect an increased amount of radiation and focus all the collected onto the tube. This increases the efficiency of heating the tube as little or no radiation, which penetrates the solar collector, is wasted by not being reflected onto the tube.

In a further subsidiary aspect, said solar collector further comprising a housing and the tube is free at one end of the housing and held to the housing at the opposite end of the housing.

This configuration is particularly advantageous because it allows the tube to freely expand at its free end so that the tube may have different thermal expansion properties to the rest of the collector. In a further subsidiary aspect, said solar collector further comprises a housing equipped with one or more lenses for focussing radiation on said tube located within said housing.

This configuration is particularly advantageous because increased collection efficiency is achieved as the solar collector is focussed onto the tube by lenses, which are integral to the housing structure. The use of lenses may increase the efficiency of the heat transferred to the tube in varying light conditions.

In its second broad independent aspect, the invention provides a solar collector comprising a plurality of neighbouring walled portions through which fluid flows and which absorb solar radiation through their respective walls; and housing portions forming cavities in which said walled portions are located; characterised in that said housing portions contain said walled portions in a vacuum.

The above configuration allows heating fluid to be contained within the solar collector, while being heated from its exposure to solar radiation. The temperature of the heating fluid is dependent upon the flow rate of the heating fluid through the tube array, the length of the tube array within the solar collector which is exposed to solar radiation and the level of solar radiation which is being collected by the solar collector.

Another advantage of the above configuration is that vacuum cavities formed within the solar collector; thermally insulate the heating fluid, while the heating fluid is exposed to solar radiation. This increases the heating efficiency of the solar collector and prevents thermal leakage from the heating fluid while it is contained within the solar collector.

In a subsidiary aspect in accordance with the invention's second broad independent aspect, said solar collector further comprising internal apertures between neighbouring cavities.

The advantage of having internal apertures is that all the cavities within the solar collector are linked together. This enables a vacuum to be created across all the cavities within the solar collector from one extraction point.

In a further subsidiary aspect, said solar collector wherein said housing portions are formed from at least one sheet which incorporates a plurality of part cylindrical cavities in rows. The advantage of having housing portions formed from at least one sheet incorporating a plurality of part cylindrical cavities in a row is that atmospheric pressure is sustained on the outside surface without crushing the housing portions.

In a further subsidiary aspect, said solar collector wherein said housing portions are formed from at least two mating sheets with a plurality of raised portions.

This configuration is particularly advantageous because it allows the assembly of the solar collector's housing portions about the solar collector's tube array, which incorporates a supporting member.

In a further subsidiary aspect, said solar collector further comprising one or more spacers located between the sheets.

The advantage of having one or more spacers is that they create the apertures required to link together all the cavities, within the solar collector.

In a further subsidiary aspect, said solar collector wherein both said first sheet and said second sheet incorporate raised portions; the raised portions of said first sheet coincides with the raised portion of said second sheet.

This configuration is particularly advantageous because it allows atmospheric pressure applied to the sheet's surface, to be concentrated on to the raised portions which contact the tube array's supporting member. By aligning the raised portions from the bottom sheet so that they coincide with the raised portions from the upper sheet, the atmospheric pressure loads from the upper and lower enclosures are balanced.

Brief Description of the Figures

Figure 1 shows a side view of a solar collector with a U-shaped tube with elliptical cross- sections along line X and line Y respectively.

Figure 1A shows perspective top view of a tapered portion of tube incorporating tapered twist. Figure I B shows perspective top view of tube incorporating tapered twists and ¹U' bend configuration.

Figure 2 shows a side view of a solar collector with a U-shaped tube with cross-sections along line X and line Y respectively.

Figure 3 shows a side view of a solar collector with a U-shaped tube with cross-sections along line X and Y respectively.

Figure 4 shows a collector integrated into a domestic water heating system.

Figure 5 shows a side view of solar collector with a jacketed tube configuration.

Figure 5A shows a side view of heating fluid being expelled from a jacketed tube configuration.

Figure 6 shows a plan top view of a solar collector's tube array fixed upon a supporting member.

Figure 6a shows a side view of the solar collector's tube array incorporated within a supporting member.

Figure 7 shows perspective top view of a solar collector's lower enclosure.

Figure 8 shows a side view of an enclosed solar collector's tube array incorporated within a supporting member.

Figure 9 shows a cross-sectional side view of a cavity formed between two welded metal sheets during fabrication.

Figure 10 shows a cross-sectional side view of a solar collector's tube soldered onto a supporting member. Detailed Description of the Figures

Figure 1 shows a solar collector, which consists of a tube 1 that is housed in a cylindrical container 2, which is transparent to solar radiation. Tube 1 incorporates a portion, which has a circular cross-section 3. This portion functions as the inlet coupling for the solar collector in which the heating fluid is supplied. Tube 1 incorporates a tapered portion 4, which encompasses a transition from an initial circular cross-section to an elliptical cross- section. The circular cross section is adjacent to portion 3 and the elliptical cross section is adjacent to portion 5. Tube 1 incorporates a portion, which has an elliptical cross-section

5, which is adjacent to portion 4. The portion of elliptical cross-section 5 is greater in width on axis YY than axis Y, as shown in cross-section Y. Tube 1 incorporates a tapered portion

6, which has an elliptical cross-section that is adjacent to portion 5. Portion 6. is twisted in relation to portion 5. Tube 1 incorporates a portion, which has an elliptical cross-section 7 that is adjacent to portion 6. The tube 1 portion of elliptical cross-section 7 is rotated on axis X as indicated, as shown in cross-section X. Tube 1 portion 7 is positioned parallel to the horizontally straight inside wall 8 of cylindrical container 2.

Tube 1 incorporates a tapered portion 9, which has an elliptical cross-section that is adjacent to portion 7. Portion 9 is twisted in relation to portion 7. Tube 1 incorporates a portion, which has an elliptical cross-section 10, which is adjacent to portion 9. The portion of elliptical cross-section 10 is identical to the cross-section Y. The elliptical cross-section is greater in width on axis YY than axis Y. This cross-section is an example of tube portion, which has a greater width than its depth. Tube 1 incorporates a tapered portion 11, which has an elliptical cross-section that is adjacent to portion 10. Portion 11 is twisted in relation to portion 10. Tube 1 incorporates a portion, which has an elliptical cross-section

12 that is adjacent to portion 11.

The tube 1 portion of elliptical cross-section 12 is rotated on axis X as indicated, as shown in cross-section X with a width (w) and a depth (d). The tube 1 portion is positioned parallel to the horizontally straight inside wall 8 of cylindrical container 2. Tube 1 incorporates a tapered portion 13, which has an elliptical cross-section that is adjacent to portion 12. Portion 13 is twisted in relation to portion 12. Tube 1 incorporates a portion, which has an elliptical cross-section 14, which is adjacent to portion 13. The portion of elliptical cross-section 14 is identical to cross-section Y. The portion of elliptical cross- section 14 is greater in area on axis YY than axis Y. Tube 1 incorporates a tapered portion 15, which has an initially elliptical cross-section, which encompasses a transition to a circular cross-section. The elliptical cross section is adjacent to portion 14 and the circular cross-section is adjacent to portion 16. The tube 1 incorporates a portion, which has a circular cross-section 16 this portion functions as the outlet coupling for a solar collector in which the heating fluid is transferred from the solar collector. The glass end cap 17 is hot fused to the cylindrical container 2. End cap 17 is assembled from two glass components 18 and 19, which are fixed together around tube 1 portions 5 and 14, along axis Y. When the end cap 17 is hot fused to the cylindrical container 2, the enclosed cavity within the cylindrical container, in which tube 1 is located, is evacuated to form a vacuum cavity 20.

Tube 1 portion 10 incorporates a bend 21. The bending radius of tube 1 portion 10 is reduced by utilising the elliptical cross-section in tube 1 portion 10 (identical to cross- section Y) by bending the tube 1 across axis Y. Bend 21 incorporated in tube 1 configures tube 1 into a "U" shape which is symmetrical about axis Z.

Figure IA shows an enlarged view of the portions 5, 6 and 7 of tube 1 with an alternative form of cross-sectional area 71, which consists of the tube 1 being flattened and rectangular in cross-section. Portion 6 incorporates a transition in the form of a twist. Portion 6 is adjacent to portion 7.

Figure 1 B shows an alternative embodiment in an enlarged view of portions 7, 9, 10, 11, 12 of tube 1. The figure shows an alternative form of cross-sectional area 71, which consists of the tube 1 being flattened. Portions 9 and 11 incorporate vertical transitions in the form of a twist. Portion 9 is adjacent to portion 7. Portion 10 is adjacent to portion 9. Portion 10 incorporates a ¹U' shaped bend. Portion 10 is adjacent to portion. Portion 11 is adjacent to portion 12. The angle of portion 9 is identical to the angle of portion 11, therefore enabling portions 7 and 12 to face the solar radiation at a predetermined angle.

Figure 2 shows an alternative embodiment of a solar collector, which consists of tube 30 that is housed in a cylindrical container 31, which is transparent to solar radiation. Tube 30 incorporates a portion, which has a circular cross-section 32. This portion functions as the inlet coupling for the solar collector in which the heating fluid is supplied. Tube 30 incorporates a tapered portion 33, which is adjacent to portion 32. Tube 30 incorporates a portion, which has an elliptical cross-section 34, which is adjacent to portion 33. The portion of elliptical cross-section 34 is greater in area on axis YY than axis Y, as shown in cross-section Y. Tube 30 incorporates a tapered portion 35, which is adjacent to portion 34. Tube 30 incorporates a portion, which has an elliptical cross-section 36 that is adjacent to portion 35. Elliptical cross-section 36 is rotated on axis X as indicated in cross section X. Portion 30 is positioned parallel to the horizontally straight inside of wall 137 of cylindrical container 31. Tube 30 incorporates a tapered position 37, which is adjacent to portion 36.

Tube 30 incorporates a portion, which has an elliptical cross-section 38, which is adjacent to portion 37. The portion of elliptical cross-section 38 is identical to figure 1 tube 1 position 10. The elliptical cross-section is greater in area on axis YY than axis Y (in figure 1). Tube 30 incorporates a tapered portion 39, which is adjacent to portion 38. Tube 30 incorporates a portion, which has an elliptical cross-section 40 that is adjacent to position 39. Elliptical cross-section 40 is rotated on axis X as indicated, as shown in cross-section X. The tube 30 portion is positioned parallel to the horizontally straight inside of wall 137 of cylindrical container 31. Tube 30 incorporates a tapered position 61, which is adjacent to portion 40. Tube 30 incorporates a portion which has an elliptical cross-section 42 with a width (w) and a depth (d) and which is adjacent to portion 41. The portion of elliptical cross-section 42 is greater in area on axis YY than axis Y. Tube 31 incorporates a tapered portion 43, which is adjacent to portion 42. Tube 31 incorporates a portion, which has a circular cross-section 44. This portion functions as the outlet coupling for the solar collector in which the heating fluid is transferred from the solar collector.

The metal end cap 45 is hot fused to the glass cylindrical container 31. End cap 45 is manufactured from metallic material and tube 30 portions 32 and 44 are inserted through two circular orifices 48 and 49, which are situated in the metal end cap 45. The metal end cap 45 incorporates a locating edge 46, which locates inside the cylindrical container 31 that is hot fused to cylindrical container 31. The enclosed cavity within the cylindrical container 31, in which tube 30 is located, is evacuated to form a vacuum cavity 149.

Tube 30 portion 38 incorporates a bend 47. The bending radius of portion 38 is reduced by utilising the elliptical cross-section, in tube 30 (identical to cross-section Y in Figure 1) by bending the tube 30 in axis Y (Figure 1). Bend 47 incorporated into tube 30 configures tube 30 into a "U" shape, which is symmetrical about axis Z.

Figure 3 shows a further embodiment of a solar collector, which consists of tube 50 that is housed in a cylindrical container 51, which is transparent to solar radiation. Tube 50 contains a portion, which has a circular cross-section 52. This portion functions as an inlet coupling for the solar collector in which heating fluid is supplied. Tube 50 incorporates a tapered portion 53, which is adjacent to portion 52. Tube 50 incorporates a portion, which has an elliptical cross-section 54, which is adjacent to portion 53. The portion of elliptical cross-section 54 is identical to Figure 1, tube 1, and portion 10. The elliptical cross-section is greater in area on axis YY than axis Y (in Figure 1). Tube 50 incorporates a tapered portion 55, which is adjacent to portion 54. Tube 50 incorporates a portion, which has a circular cross-section 56 that is adjacent to portion 55. This portion functions as the outlet coupling for the solar collector in which the heated fluid is transferred from the solar collector.

End cap 56 is manufactured from metallic material or glass. The end cap 56 is abutted to the cylindrical container 51 and hot fused into position. The enclosed cavity within the cylindrical container 51, in which tube 1 is located, is evacuated to form a vacuum cavity 59.

Portion 54 incorporates a bend 57. The bending radius of tube 50, portion 54, is increased by utilising a cross-section 58 in tube 50 which is D shaped as an example of an asymmetrical cross-section about the Y axis. Bend 57 incorporated in tube 50 configures tube 50 into a "U" shape, which is symmetrical about the axis Z.

In an alternative embodiment of the invention, circular tubes may be implemented by flattening the "U" bend portion only. This embodiment may be further improved by incorporating smaller bore tube into the "U" bend portion only. The transition between the large and small tubes is accomplished by installing diameter reducing fittings. Therefore, two "U" shaped tubes may be installed inside a collector, which originally could only accommodate one "U" shaped tube. The use of two tubes within a collector will increase the amount of heat imparted to the heating fluid. Figure 4 shows a solar collector 65 connected to a closed circulation heating system. When domestic storage cylinder 67 demands heat, the hot side pump 70 starts to pump the heating liquid in the solar collector 65 once the heating liquid has reached the set temperature. The heating liquid is pumped around a hot side closed circuit 66. The heated fluid is pumped through a plated heat exchanger 71. The heat from the heating fluid is transferred to the cold side closed circuit 68. The heated cold water is pumped into the domestic storage cylinder 67 by operation of the cold side pump 69. When the domestic storage cylinder 67 has reached the desired temperature, both hot and cold side pumps 69, 70 are stopped. When the hot and cold pumps 69, 70 stop, the solar collector 65 will still be collecting radiation from the sun. In these conditions, the tube will be expected to sustain a stagnation temperature of approximately 170° and a pressure from the heating fluid of around 6 bar. Copper or stainless steel tubing is typically able to sustain this pressure and temperature criteria. Other materials may also be suitable for this use.

Figure 5 shows a further embodiment of a solar collector, which consists of a linear tube 81 that is housed within another linear tube 82. Tube 82 is an outer tube, which is sealed 85 around tube 81, close to inlet coupling 86, in which heating fluid is applied. A cavity 84 is formed between tubes 81 and 82. Tube 82 incorporates an outlet coupling 87, which is fixed perpendicular to the outer wall, in which heating fluid is expelled. Tube 82 incorporates a sealed portion 89 about tube 81 at the opposite end to input coupling 86.

Outer tube 82 is enclosed in a cylindrical container 90, which is transparent to solar radiation. The cylindrical container 90 is sealed around tube 82 by an end cap 91. The end cap 91 is hot fused to the cylindrical container 90 and outer tube 82. The enclosed cavity within cylindrical container 90 is evacuated to form a vacuum cavity 92.

The heating fluid is supplied to inlet coupling 86 of tube 81. The heating fluid flows along tube 81 until expelled against the sealed portion in outer tube 89. The heating fluid then flows along the cavity 84 between tube 81 and outer tube 82. The heating fluid is expelled out of the cavity 84 by an outlet coupling 87.

Both the inlet and outlet couplings are in close proximity to each other. Figure 5A shows an enlarged view of heating fluid being expelled form tube 81 into outer tube 82. The heating fluid is expelled against the sealed portion in outer tube 89 and into the cavity 84, which exists between tube 81 and 82.

Figure 6 shows a tube array 95 that is fixed upon a rectangular, supporting member 96.

The tube array 95 transports the heating fluid through the solar collector, along a configuration, which is substantially longer than a direct point-to-point path that incorporates no deviations.

The configuration regulates the exposure of the transported heating fluid within the tube array 95 to solar radiation. Therefore, by communicating the heating fluid through the tube array 95 of a predetermined length, at a predetermined flow rate and at a known level of solar radiation, the heating fluid's temperature may be determined.

A coupling portion 119 extends perpendicularly from the rectangular supporting member 96 along the vertical axis AA. Coupling portion 119 is connected to a substantially linear portion 98 of the tube array 95.

Linear portion 98 substantially traverses the supporting member 96 along vertical axis AA. Linear portion 98 is connected to a "U" shaped portion109, which extends to the right along axis BB. "U" shaped portion 109 is connected to a substantially linear portion 99, which substantially traverses the supporting member 96 along vertical axis AA. Linear portion 99 is substantially in parallel with linear portion 98. Linear portion 99 is connected to a "U" shaped portion 114, which extends to the right along axis BB. "U" shaped portion 114 is connected to a substantially linear portion 100, which substantially traverses the supporting member 96 along vertical axis AA. Linear portion 100 is substantially in parallel with linear portion 99. Linear portion 100 is connected to a "U" shaped portion 110, which extends to the right along axis BB. "U" shaped portion 110 is connected to a substantially linear portion 101, which substantially traverses the supporting member 96 along vertical axis AA. Linear portion 101 is substantially in parallel with linear portion 100. Linear portion 101 is connected to a "U" shaped portion 115, which extends to the right along axis BB. "U" shaped portion 115 is connected to a substantially linear portion 102, which substantially traverses the supporting member 96 along vertical axis AA. Linear portion 102 is substantially in parallel with linear portion 101. Linear portion 102 is connected to a "U" shaped portion 111, which extends to the right along axis BB. "U" shaped portion 11 1 is connected to a substantially linear portion 103, which substantially traverses the supporting member 96 along vertical axis AA. Linear portion 103 is substantially in parallel with linear portion 102. Linear portion 103 is connected to a "U" shaped portion 116, which extends to the right along axis BB. "U" shaped portion 116 is connected to a substantially linear portion 104, which substantially traverses the supporting member 96 along vertical axis AA. Linear portion 104 is substantially in parallel with linear portion 103. Linear portion 104 is connected to a "U" shaped portion 112, which extends to the right along axis BB. "U" shaped portion 112 is connected to a substantially linear portion 105, which substantially traverses the supporting member 96 along vertical axis AA. Linear portion 105 is substantially in parallel with linear portion 104. Linear portion 105 is connected to a "U" shaped portion 117, which extends to the right along axis BB. "LJ" shaped portion 117 is connected to a substantially linear portion 106, which substantially traverses the supporting member 96 along vertical axis AA. Linear portion 106 is substantially in parallel with linear portion 105. Linear portion 106 is connected to a "U" shaped portion 113, which extends to the right along axis BB. "U" shaped portion 113 is connected to a substantially linear portion 107, which substantially traverses the supporting member 96 along vertical axis AA. Linear portion 107 is substantially in parallel with linear portion 106. Linear portion 107 is connected to a "U" shaped portion 118, which extends to the right along axis BB. "U" shaped portion 118 is connected to a substantially linear portion 108, which substantially traverses the supporting member 96 along vertical axis AA. Linear portion 108 is substantially in parallel with linear portion 107. Linear portion 108 is connected to coupling portion 120 which extends perpendicularly from the rectangular supporting member 96 along the vertical axis AA.

Figure 6a shows an alternative embodiment of the tubular array showing in figure 6, which is embedded within a rectangular supporting member 96, which extends horizontally along axis CC. Each linear portion shown in figure 6, 98 to 108 is shown to be embedded centrally within supporting member 96. Each linear portion 98 to 108 is equally spaced from one another 121 to 130 horizontally along axis CC. Figure 7 shows a perspective top view of the solar collector's lower enclosure member 131. The lower enclosure member 131 extends along axis DD and incorporates two part cylindrical cavities 169 and 170, which are adjacently connected to each other along rectangular portion 141. Each part cylindrical cavity 169 and 170 incorporates an outer convex surface 132 and 133 and a concave surface 134 and 135, which extends along axis DD.

Each part cylindrical cavity 169 and 170 incorporates a front surface 135 and 136, which are flat and part cylindrical that extends horizontally along axis EE and vertically along FF.

The lower enclosure member 131 incorporates rectangular portions 140 to 142, which extends along axis DD. Rectangular portion 141 is located where part cylindrical cavities 169 and 170 intersect each other. Rectangular portions 140 to 142 incorporate three raised rectangular surfaces 143 to 150, which extends along axes FF and DD. Raised rectangular portions 143, 146 and 149 are located at the left most extremities of rectangular portions 140 to 142. Raised rectangular sections 144, 147 and 200 are located substantially central on rectangular portions 140 to 142. Raised rectangular sections 145, 148 and 150 are located at the right most extremities of rectangular portions 140 to 142.

Arrows 151 to 153 indicate the upward atmospheric pressure load on the lower enclosure 131, along axis FF. The indicated upward pressure 151 to 153 is concentrated onto raised rectangular sections 143 to 150, which abuts the tubular array's supporting member.

Arrows 154 to 156 extend downwards vertically along axis FF to indicate atmospheric pressure load on the raised rectangular sections 143 to 150 from the upper enclosure (not shown), which abuts the tubular array's supporting member. The lower atmospheric load is balanced by an equal upper atmospheric load, exerted from the upper half enclosure. Arrows 157 extending up along vertical axis FF indicates atmospheric pressure on the outer convex surfaces 132 and 133, sustained by the design of the enclosure.

Figure 8 shows the linear tube portions 98 to 108 embedded within the tube array's supporting member 96, which extends horizontally along axis GC. Both upper and lower enclosing portions 160 and 161 abut the tube array's supporting member 96. Each linear portion 98 to 108 is enclosed by upper portion 160 and lower portion 161.

Figure 9 shows a cross-section area view of an alternative embodiment of the linear tube, which incorporates a linear cavity 166, which is formed between two metal sheets 167 and 168. The cavity is formed by applying a high pressure gas to un-welded area between the two metal sheets 167 and 168.

Figure 10 shows a cross-sectional view of a linear portion of the tube array 98 (see figure 6), which shows a circular outer surface 162 and an inner circular area 163. The linear tube portion 98 is fixed to the tube array's supporting member 96 by soldering areas 164 and 165 of linear tube 98 to tube array's supporting member 96 (see figure 6). The linear tube portion 98 is fixed so that it abuts the tubular array's supporting member 96.

In an alternative embodiment of the invention, the enclosing members may incorporate an insulating cavity within each enclosing member's body. This cavity will increase the overall insulation performance of the solar collector.

Claims

1. A solar collector comprising a tube through which, in use, a fluid flows and which absorbs solar radiation through its wall; characterised in that the tube incorporates a portion which has a width (w), which is greater than its depth (d).

2. A solar collector according to claim 1, wherein said portion is elliptical in cross-section.

3. A solar collector according to claim 1, wherein said tube is asymmetrically flattened.

4. A solar collector according to any of the preceding claims, wherein the tube incorporates at least one bend portion whose width (w) is greater than its depth (d).

5. A solar collector according to any of the preceding claims, wherein the tube is located in proximity to a reflector, which is shaped and configured to focus the radiation onto said portion.

6. A solar collector according to any of the preceding claims, further comprising a housing and the tube is free at one end of the housing and held to the housing at the opposite end of the housing.

7. A solar collector according to any of the preceding claims, further comprising a housing equipped with one or more lenses for focusing radiation on said tube located within said housing.

8. A solar collector comprising a plurality of neighbouring walled portions through which fluid flows and which absorb solar radiation through their respective walls; and housing portions forming cavities in which said walled portions are located; characterised in that said housing portions contain said walled portions in a vacuum.

9. A solar collector according to claim 9, further comprising internal apertures between neighbouring cavities.

10. A solar collector according to either of the preceding claims, wherein said housing portions are formed from at least one sheet which incorporates a plurality of part r cyvlliinnHdrriircaall r caavviittiipesς i inn r rnowwsς.

11. A solar collector according to any of claims 8 to 10, wherein said housing portions are formed from at least two mating sheets with a plurality of raised portions.

12. A solar collector according to claim 11, further comprising one or more spacers located between the sheets.

13. A solar collector according to either of the preceding claims, wherein both said first sheet and said second sheet incorporate raised portions; the raised portions of said first sheet coincides with the raised portion of said second sheet.

14. A solar collector substantially as hereinbefore described and/or illustrated in any appropriate combination of the accompanying text and/or figures.