GB2091412A

GB2091412A - A Solar Collector Having an Evacuated Interior

Info

Publication number: GB2091412A
Application number: GB8138255A
Authority: GB
Original assignee: Messerschmitt Bolkow Blohm AG
Current assignee: Airbus Defence and Space GmbH
Priority date: 1980-12-24
Filing date: 1981-12-18
Publication date: 1982-07-28
Also published as: GB2091412B; DE3049119A1

Abstract

The collector comprises a trough- like housing 1 which is open on one side and a cover plate 6 which is pervious to radiation. A radiation absorption system is arranged in the evacuated interior. Provided between the housing base 5 and the cover plate 6 are supporting plates 4 which support the latter. The supporting plates 4 may be mounted in slots of a profile plate 9 resting on the housing base 5 and having, for example, sinusoidal profile bulgings. The outside pressure may be transmitted by way of load-bearing elements 14 to the profile plates 9 or respectively the supporting plates 4. <IMAGE>

Description

SPECIFICATION A Radiation Collector Having an Evacuated Interior This invention relates to a radiation collector having an evacuated interior which comprises a trough-like housing open on one side and a cover plate pervious to radiation which rests on the edge of the housing opening, having a radiation absorption system provided in the interior as well as having supporting elements arranged between the cover plate and the housing base.

Such a radiation collector is known, for example, from German Gebrauchsmuster No.

79 09 689 wherein a solar flat collector in various embodiments is described, and depicted, the housing of which comprises a metal trough, on the edge of which is superposed, in sealing manner, a glass plate. In the interior of the collector, which is evacuated as far as a specific residual pressure prior to being put into operation, a radiation absorption system is provided in the form of a plate or sheet incorporating flow channels for a heat transportation medium. In order to withstand the pressure which bears on the glass plate as a consequence of the differential pressure between the housing interior and housing exterior supporting elements in the form of, for example, glass rods or glass tubes are situated between the glass plate and the housing base and extend through openings in the plate or sheet.The glass tubes or rods, having a very small diameter compared to the collector dimensions, result in a mulitiplicity of support points, distributed in net-like manner, for the glass plate.

The disadvantage of such an arrangement obviously lies in the type and the multiplicity of the supporting elements, which all have to be anchored individually on the housing base and thus cost a considerable amount to mount. The aforesaid almost punctiform supporting of the glass plate may, in the event of pressure loading, lead to severe stresses. Furthermore, there is a danger that, with the necessary multiplicity of tube-shaped or rod-shaped supporting elements, certain individual elements might break during continuous operation of the collector, for instance due to material fatigue or because these elements were already defective when installed not recognised as such. In general, this known radiation collector is still in need of improvement with respect to apparatus for supporting the glass cover plate.

An object of the present invention is the provision of a radiation collector of the kind mentioned at the beginning hereof in which the pressure difference prevailing between the evacuated housing interior and the surrounding exterior atmosphere is reliably withstood by simple means, so that the resultant structure is as far as possible stable, light and at the same time simple to produce and assemble.

With this object in view, the present invention proposes that the supporting elements comprise supporting plates. It has been shown that the bending tensions occurring in a glass cover plate can be reduced by a multiple when parallelextending rows of supporting rods or tubes are replaced by similarly parallel-extending supporting plates. An arrangement of supporting rods or tubes distributed in net-shaped manner can thus be replaced by one of parallel-arranged supporting plates, in which respect the supporting spacings can be considerably enlarged without the bending tensions thereby increasing. As a whole the number of requisite supporting elements can be reduced by a multiple and the expenditure connected with mounting the support elements is also considerably reduced.The few supporting elements can be examined prior to mounting more thoroughly and with altogether less expenditure of time for their susceptibility to breakage. The stability of the entire collector structure is as a result favourably influenced.

In order to further increase the stability of the overall structure of the radiation collector, particularly with respect to the pressure loadings, acting on the housing walls, a preferred embodiment of the invention provides that the supporting plates are mounted in slots of a profile plate resting an the housing base and loadbearing elements are provided between the housing walls on the one hand and the side edges of the supporting plates as well as the ends of the profile plate on the other hand.

In this way there results a supporting and retaining structure in which on the one hand the supporting plates are mounted simply and in a defined manner on the housing base, and which on the other hand the pressure loadings acting on the housing walls are absorbed and transmitted to the profile plate or the supporting plates respectively.

In a particularly advantageous further development of the invention provision is made for situating strips of elastic material between the cover plate and/or the profile plate as well as the respectively associated edges of the supporting plates. Thus on the one hand unevennesses of the edge of a supporting plate facing the cover plate may be compensated for and on the other hand impacts or vibrations emanating for instance from the housing base can be damped.

It is possible to subdivide the profile plate into several profile elements which are joined together when mounted on the housing base. This measure can, circumstances permitting, bring advantages during production and transportation of the profile elements. The profiles themselves may have, in cross-section, for example the shape of sine half-waves or of open rectangles.

The load-bearing elements associated with the side edges of the supporting plates may have, in cross-section, for example substantially a Ushape. These preferably butt with their arching against the side walls, whilst the limbs are supported on the side edges of the supporting plates. The ends, corresponding to the limbs of the U-shape, of the load-bearing elements can be slotted to receive the side edges of the supporting plates.

In order to prevent shifting of the load-bearing elements along the housing walls, it is proposed to fit the elements, associated with the side edges of the supporting plates, in extensions, also substantially U-shaped in cross-section and butting partly against the housing wall, of the profile plate or respectively profile elements.

Since the profile plate is restrained by the supporting plates on the housing base it is ensured as a result of the extensions which are shaped as mentioned that the actual load-bearing elements cannot be shifted along the housing wall.

For reasons of saving weight, the supporting plates are preferably formed with the least possible thickness. This naturally has the result that the loadability of the supporting plates in bending becomes even less. Problems may occur, particularly at those points where the supporting plates are let into the slots of the profiles, wherein the outside pressure acts on the supporting plates by way of the load-bearing elements and the profiles. If the slots are not formed extremely accurately, the forces transmitted to the supporting plates may be uneven so that severe bending stresses arise.In order nevertheless to be able to use very thin supporting plates, it is proposed to sub-divide the supporting plates into two part plates which are supported on one another with the part plate associated with the housing base extending substantially as far as the profiles of the profile plate or respectively of the profile elements in the direction of the cover plate.

It is also proposed, to produce said lower part plate.s from a material which has a greater bending strength than the material of the part plate associated with the cover plate. For example the lower part plates pushed into the slots of the profiles may be produced from steel sheet and the upper part plates arranged over these may be made from glass. The radiation absorption system can then be arranged above the line of separation of the two part plates, so that no shadow effect occurs due to the part plates made from steel sheet.

In the above respect, it is particularly advantageous if one of the two part plates of each supporting plate is supported on the other, in each case, by way of strips of elastic material which are inserted between them. Although this elastic material holds the upper part plate onto the lower part plate which is let into the slots, it is advantageous to supplement the guidance of the superimposed upper part plate by pushing guide platelets into the slots of the profiles of the profile plate or respectively of the profile element, on both sides of the supporting plate. Such guide platelets should extend into the region of the upper part plate associated with the cover plate.

However, such platelets need not be present in all the slots; on the contrary it will generally suffice that supporting platelets are provided only for the two respectively furthest outwardly situated slots associated with each supporting plate.

For similar reasons of weight reduction as in the case of the supporting plates, the profile plate or respectively profile elements are also formed as thin as possible with the result that the transverse forces transmitted from the vessel base would in a radiation collector as hitherto described soon cause too large loadings. This is particularly so at locations where the slots cut into the bulged profiles encounter the flat parts of the profile plate or respectively of the profile elements. The transmitted transverse forces can easily lead to tearing of the profile base at these locations, if too thin a material is used.In order to circumvent these difficulties without having to form the profile plate or respectively the profile elements from substantially thicker material supporting strips for the absorption of the transverse forces transmitted from the housing base are preferably inserted under the support plate in the slots associated with the supporting plate. It is particularly advantageous if the supporting strips have a greater width between the profiles than where they extend through the slots. The transverse forces become directly effective precisely between the slotted profiles, that is to say where the profile plate or the profile elements respectively rest flat on the housing base.

Therefore, it is advantageous that the supporting strips should have greater width at these locations. The supporting strips advantageously comprise a material of great bending strength. For example, in the same way as the guide platelets, the profile plate or respectively the profile elements, possibly the lower part plate inserted into the slots, as well as the load-bearing elements, these supporting strips may be made of steel sheet or flat steel.

In general, as in the case of the known solar flat collector described at the beginning hereof, the radiation absorption system arranged in the interior of the collector housing is a tube system which is provided with absorption surfaces. In the known solar flat collector having supporting bars or tubes respectively, arranged in net-like manner, there is a multiplicity of possibilities of the arrangement of the tubes. The presence of the supporting plates in accordance with the invention requires that the tube arrangement must be adapted specially to the new spatial structure. In this respect, it is proposed that the tubes extend in a plane, substantially parallel to the cover plate, between and around the supporting plates. This arrangement is possible because due to the presence of the load-bearing elements sufficient space is available between the side edges of the preferably rectangular supporting plates and the housing walls. An alternative arrangement is that the tubes extend through openings in the supporting plates. In any case it is advantageous to arrange the absorption surfaces, which are connected, in a good heatconducting manner, with the tubes intended for conducting the heat absorption medium, in a plane parallel to the cover plate.

A particularly favourable tube arrangement comprises two individual tubes which extend in each case in U-shaped loops around the supporting plates, in such a way that respectively alternately one and three supporting plates are enclosed. The resulting loop sequences of the two individual tubes are mutually staggered by two supporting plates. In this arrangement each said tube extends respectively between and parallel to two consecutive supporting plates. At the side edges of the supporting plates, where the individual tubes loop around them, the two tubes extend for a short distance side-by-side or one above the other respectively. In comparison with an arrangement in which only a single individual tube extends around or between each of the consecutive supporting plates, the above arrangement offers the advantage of better heat removal with a lower pressure differential.

Moreover, individual tubes are then shorter, and they may be formed with half the previously required cross-section area while still affording better heat exchange conditions by virtue of the surface which is enlarged in relation to the crosssectional surface area.

As well as the requirement that the material of the supporting plates be suitable to withstand the pressure stresses which occur, consideration should also be given to the thermal stress which occurs due to the arrangement of the radiation absorption system around and between the supporting plates. This system reaches very high temperatures when working, so that a great deal of heat energy is radiated on to the adjacent regions of the supporting plates resulting in thermal stress. If, for example, the supporting plates are made of favourably priced window glass, which is capable of withstanding the pressure stresses throughout and additionally seems favourable because of its transparency, it may happen that, under certain circumstances this material cannot withstand the thermal stresses which occur.In order to avoid the insertion of more expensive glass which is capable of withstanding high thermal stress supporting plates of metal, in particular V2A-steel or steel alloyed with nickel may be used. Also other materials which are impermeable to radiation are suitable, so long as they are capable of withstanding both the pressure and thermal stresses which occur.

Furthermore it can be an advantage to produce the supporting plates as apertured plates, since in the region of the apertures no reflections of radiation, connected with losses of heat to the housing elements and elsewhere, can occur.

Moreover a considerable reduction in weight of the supporting plates results. Supporting plates which have grooves on their edges facing towards the cover plate may also be used. Such plates may be described as comb-like and supporting battens may be mounted upon and extend between several of the supporting bars which remain between the grooves.

The radiation collector in accordance with the invention is suitable for the utilisatlon of any type of radiation for which absorber materials converting the radiation into heat exist. In particular, it is suitable for the infra-red part of the solar radiation spectrum. It is possible to connect a large number of such solar collectors in parallel for the generation of heat on a large scale, or alternatively to use individual collectors for small-scale consumption. Special fields for use which should be mentioned are the generation of process heat, the operation of cooling installations as well as water desalination plants.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a plan view of a first embodiment of a radiation collector in accordance with the invention; Figs. 2 and 3 are perpendicular partial crosssections along respective lines 11--II and Ill-Ill of the radiation collector in accordance with Fig.

1; Fig. 4 is a horizontal partial cross-section, along the line IV--IV of Fig. 3, of the radiation collector in accordance with Fig. 1; Fig. 5 and Fig. 6 are partial cross-sections of respective second and third embodiments of a radiation collector in accordance with the invention; Fig. 7 is a plan view of a corner region of the second embodiment of the radiation collector in accordance with Fig. 5; and Fig. 8 is a plan view showing a tube system intended for use in any embodiment of a radiation collector in accordance with the present invention; Fig. 9 is a partial cross section through the trough-like housing of a further embodiment of the radiation collector with a supporting plate shown in side view; Fig. 10 is a side view of an individual supporting plate formed as an apertured plate; Fig. 11 is a side view of an individual supporting plate provided with grooves along its upper edge; Fig. 12 is a cross-section along the line A-A of Fig. 9; Fig. 13 is a view similar to Fig. 12 of a further embodiment of the radiation collector of the invention; Fig. 14 is a cross-section along the line BMlB of Fig. 11.

Fig. 1 is a highly simplified plan view of a first embodiment of a radiation collector of the invention. The collector comprises a trough-like housing 1 made from metal and having walls 3 which extend substantially perpendicularly to edges 2 which is bent into a horizontal plane. A glass cover is placed onto the edges 2.

Supporting plates 4 are arranged perpendicularly in the interior of the housing 1 parallel to the shorter walls 3. Further details can be gathered from the following Figures.

Fig. 2 shows a perpendicular section along the line 11-Il in Fig. 1. The housing 1 is arched in the transitional regions between the horizontally extending edge 2, the perpendicularly-extending walls 3 and the housing base 5, in order to be able better to withstand the pressure difference between housing interior and exterior. A glass cover plate 6 rests on the edge 2 of the housing opening. The interior of the housing 1 is insulated by a seal 7 against the outside pressure. A strip 8 of elastic material is situated between the upper edge of the perpendicularly-standing supporting plate 4 and the cover plate. The strip 8 may, for example, comprise silicon rubber.

On the housing base 5, the supporting plate 4 is mounted in slots in a profile plate 9. This plate 9 has profiles which extend perpendicularly to the drawing plane of Fig. 2, which have approximately the shape of sine half-waves and which are provided with slots which extend in the plane of the drawing and into which the supporting plate 4 is fitted. A strip 10 of elastic material is also provided between the housing base 5 or the profile plate 9 respectively and the supporting plate 4. Between the arched-up profiles, which are interrupted by the slots for the reception of the supporting plates 4, the profile plate 9 has plane portions 11 extending adjacent the housing base 5.The profile plate 9 may be subdivided in the region of these plane portions 11, so that several contiguous profile elements arise, which for example, each comprise a profile and adjacent plane sections, extending perpendicularly to the drawing plane. The profile plate may have, towards the wall 3, an extension 13 which is substantially U-shaped in cross-section and which butts partly against the wall. Fitted into this extension 13 are load bearing elements 12 which are, in cross-section , also approximately Ushaped, and the limbs thereof are slotted at the ends for reception of the supporting plates 4.

Fig. 3 shows a different perpendicular section through a region of the radiation collector of Fig. 1 along the line Ill-Ill. A profile of the profile plate 9 in the longitudinal direction as well as the supporting plate 4 fitted into a slot of this profile are clearly shown.

Between the shorter wall 3 of the housing 1 of the radiation collector and the profile plate 9 there are load-bearing elements 14. These ensure a slight spacing between the profile plate 9 and the housing wall 3 and serve in the same way as the load-bearing elements 12 to transmit the pressure acting on the housing walls, to the profile plate 9 or respectively the supporting plates 4. Thus, as a whole the aforesaid structure is inherently stable, and is able to absorb the forces which occur.

Fig. 4 shows a perpendicular section through a corner region of the radiation collector along the line IV-IV, in Fig. 3. It is clearly indicated in this drawing that each extension 13 of the profile plate 9, which is bent upwards in substantially Ushaped manner, extends continuously along each longer wall 3. In contrast thereto, the loadbearing elements 12 fitted into the extension 13 extend merely over the narrow region adjacent the side edges of the supporting plates 4. The load-bearing elements 14 also extend along the shorter walls 3. They rest on the highest-archedup points of the profiles of the profile plate 9 and engage with the aid of straps 1 5 under these profiles.

The profile plate 9 as well as the load-bearing elements 12 and 14 advantageously comprise steel sheet.

The embodiment of Fig. 5 differs from that of Fig. 2 mainly in that the supporting plate is subdivided into two part plates 24 and 25. One of these is located directly above the other and a strip 26 of elastic material, for example silicon rubber, is inserted between them. The lower part plate 25 associated with the vessel base 5 can be made from flat steel, whilst the upper part plate 24 associated with the cover plate 6 comprises, for example, glass. The tube system (not shown) is disposed approximately at a level half way up the upper part plate 24, whereby shadow effects by virtue of the steel parts are avoided. Adjacent the wall 3, the lower part plate 25 is mounted with the aid of the load-bearing element 21.This has a portion which butts directly against the wall 3 as well as a portion which butts against the side edge of the part plate 25, in which respect both portions are connected by a portion which extends transversely of the wall 3 and of the side edge of the part plate 25. Transmission of force from the wall 3 acted upon by outside pressure to the steel part plate 25 is thus ensured. Instead of a profile plate, profile elements 20 which are joined together are provided. These consist of relatively thin steel sheet. Inserted into the slots of the profile elements 20 are supporting strips 23, which extend underneath the lower part plate 25 between the load-bearing elements 21 of the two opposing walls 3.The supporting strips 23 are, as can clearly be seen in Fig. 7, wider between the arched-up profiles than where they extend through the slots beneath the supporting plate where they necessarily cannot be wider than the width of the slot. The transverse forces transmitted from the housing base 5 may thus be absorbed considerably more effectively than previously.

Guide platelets 22 are provided for the retention or guidance of the upper part plate 24 associated with the cover plate 6. These guide platelets 22 are inserted into the slots on both sides of the two-part supporting plate. To facilitate the platelets 22, the profile edges have appropriate recesses adjacent the slots. The guide platelets 22 are only inserted into the slots of the two profile elements 20 which respectively lie furthest outwards, since this is fully adequate for satisfactory retention of the upper part plates 24.

The embodiment of the radiation collector of the invention as shown in Fig. 6 is distinguished in that the upper part plate 24 associated with the cover plate 6 has substantially a trapezoid shape, and in that the housing wall 3 lying adjacent the side edges of the supporting plate or lower part plate 26 has, in cross-section, the shape of a quarter arc, the arching of which is directed towards the interior of the housing. The edge 27, corresponding to the longer of the two parallel trapezoid sides, of the upper part plate 24 faces towards the cover plate 6.The relatively large radius of curvature of the housing wall 3, which depends to some extent bn the height of the collector, brings with it the advantage that, where the housing wall 3 merges into the housing base 5, no bending moment occurs so that the loading of the housing wall 3 is particularly small and the latter can consist of very thin material. The upper edges 27 of the part plates 24 should project outwardly as far as possible so that the loading acting on the projecting edge of the cover plate becomes particularly small.

One result of the special shape of the housing wall 3 in the case of the radiation collector of Fig.

6 is that the load-bearing element 21 has only to absorb forces transmitted from the housing base 5 and therefore does not need to butt against the housing wall 3. However, whenever the transition from the housing wall 3 to the housing base 5 is formed as an arch, the radius of curvature of which is noticeably different from zero, bending moments occur in this region, and it is advisable to provide load-bearing elements which butt against the housing wall 3. In the present extreme case, the lower part plate 25 associated with the housing base 5 is not supported on the limbs of the load-bearing element 21 which is approximately U-shaped in cross-section, but instead is inserted into the "U". Additionally, a metal ledge 28 of the same width as the part plates 24, 25 is inserted between the guide platelets 22.

A trapezoid-shaped upper part plate 24 is, of course, usable not only in the case of a housing wall structure corresponding to Fig. 6, but also, for example, in the case of a collector in accordance with Figs. 5 and 7. The advantage of the upper edge 27 drawn far outwards are of similar importance in such embodiments.

Fig. 8 is a plan view, in schematic manner of a radiation collector without the cover plate, but with supporting plates 4 and a tube system for conducting of a heat-absorbing medium. Two collecting tubes 1 6 and 1 7 are provided, which extend through the housing walls 3 and also communicated with one another by way of two individual tubes 18 and 19. The individual tube 18 forms three U-shaped loops between the collecting tubes 17 and 1 6. These loops extend around initially one, then three, and then again one supporting plate 4.The individual tube 19 also forms three U-shaped loops between the collecting tubes 1 7 and 1 6, in which respect the loops also extend twice around one and once around three supporting plates 4, but this is offset by two supporting plates with respect to the individual tube 18. The entire tube system is located in a plane parallel to the drawing plane.

Absorption surfaces with which the tubes are connected in a good heat-conducting manner, and which also extend between the supporting plates 4 in a plane parallel to the drawing plane, are not shown.

Fig. 9 is a schematic partial section through a trough-like housing 1 of a further embodiment of the radiation collector. A glass cover plate 6 rests on the edge 2 of the housing opening. The interior of the radiation collector, which is evacuated when the collector is in use, is sealed against the external pressure by the sealing ring 7. A supporting plate 4, formed as an apertured plate, serves to stabilise the evacuated housing in relation to external pressure. The supporting plate 4 has an upper portion 32 orientated parallel to the cover plate 6, 2 base portion 33 directed parallel to the housing base 5 as well as supporting bars 34 running perpendicular to the cover plate 6. The supporting plate 4 is made of V2A-steel or nickel steel and several supporting plates can be produced simultaneously by stamping out from a pile of steel plates.A strip 35 approximately U-shaped in cross-section and of elastic material, for example, silicon rubber (see also Fig. 12) is mounted upon the upper portion 32 of the supporting plate 4. On the housing base 5 lies a profile plate 9 having profiles which extend perpendicularly to the drawing plane of Fig. 9 and which have the shape of sine halfwaves. These profiles also have slots parallel to the plane of the drawing for the reception and guidance of the supporting plates 4. A plurality of supporting plates 4 are fitted with a clearance between them, one behind the other, parallel to the plane of the figure in adjacent rows of slots.

The profile plate 9 may, for example, comprise sheet steel. A supporting strip 36 is inserted into each slot which receives a supporting plate 4.

These supporting strips 36 suitably comprise sheet titanium. This material is advantageous because it possesses a particularly low heat conductivity and heating up of the housing elements themselves must be avoided as far as possible. The side edge of the supporting plate 4 is supported adjacent the curved portion of the housing, which connects the housing base 5 with the side wall of the housing 1, with the aid of a load-bearing element 21 which extends perpendicularly to the plane of the figure. The load-bearing element 21 suitably comprises sheet steel.

The supporting plate 4 shown schematically in side view in Fig. 10 is differentiated from the one shown in Fig. 9 by the provision of circular holes 37 as well as grooves 31 on the lower edge. The circular holes 37 contribute to a further diminution of the weight of the supporting plate 4 and cause increased resistance to heat conduction to the lower edge of the plate 4. The grooves 31 contribute to the further diminution of heat conduction to the housing base 5.

Fig. 11 shows a supporting plate 4 which has deep grooves in its upper edge. Such comb-like supporting plates may, for example, be made by milling piles of plates, Once the grooves have been formed only supporting bars 29 remain standing. Supporting battens 30, which are U shaped in cross section (see also Fig. 14), are mounted upon these supporting bars 29. Strips of elastic material 38 are inserted between these supporting bars 30 and the cover plate 6.

Fig. 12 and Fig. 13 show in a schematic manner how supporting plates 4 may support the pressure-stressed cover plate 6 in the embodiment in accordance with Fig. 9. Strips 35 of elastic material are either laid directly on upper portion 32 (Fig. 12) or alternatively profile strips 39, possibly also made of steel, may firstly be placed upon the upper portions 32 and strip 40 of elastic material inserted between said profile strips 39 and the cover plate 6 (Fig. 13).

Claims

1. A radiation collector having an evacuated interior which comprises a trough-like housing open on one side and a cover plate pervious to radiation which rests on the edge of the housing opening, having a radiation absorption system provided in the interior as well as having supporting elements arranged between the cover plate and the base of the housing, characterised in that the supporting elements comprise supporting plates.

2. A radiation collector as claimed in claim 1, characterised in that the supporting plates are mounted in slots in a profile plate resting on the housing base and load-bearing elements are provided between the housing walls on the one hand and the side edges of the supporting plates as well as the ends of the profile plates on the other hand.

3. A radiation collection as claimed in claim 1 or 2, characterised in that strips of elastic material are situated between the cover plate and/or the profile plate on the one hand and the respective associated edges of the supporting plates on the other hand.

4. A radiation collector as claimed in any of claims 1 to 3, characterised in that the profile plate is subdivided into several profile elements which are joined together.

5. A radiation collector as claimed in any preceding claim, characterised in that the profiles of the profile plate or respectively of the profile elements have substantially the shape of sine half-waves.

6. A radiation collector as claimed in any of claims 1 to 4, characterised in that the profiles of the profile plate or respectively of the profile elements have substantially the shape of open rectangles.

7. A radiation collector as claimed in any of claims 2 to 6, characterised in that the loadbearing elements which are associated with the side edges of the supporting plates have, in crosssection, substantially a U-shape.

8. A radiation collector as claimed in claim 7, characterised in that the load-bearing elements are fitted into extensions of the profile plate or respectively profile elements, which extensions are also substantially U-shaped in cross-section and butt partially against the housing wall.

9. A radiation collector as claimed in any of claims 2 to 8, characterised in that the supporting plates are each subdivided into two part plates one of which is supported upon the other and the part plate which is associated with the housing base extends substantially as far as the profiles of the profile plate or respectively of the profile elements in the direction of the cover plate and is made from a material which has a greater bending strength than the material of the part plate which is associated with the cover plate.

1 0. A radiation collector as claimed in claim 9, characterised in that one part of each two-part plate is supported upon the other by way of strips of elastic material which are inserted between them.

11. A radiation collector as claimed in claim 9 or 10, characterised in that inserted into the slots in the profiles of the profile plate or respectively of the profile elements at both sides of each supporting plate are guide platelets which extend into the region of the part plates which are associated with the cover plate.

12. A radiation collector as claimed in claim 11, characterised in that supporting platelets are provided only for the two slots which are respectively situated furthest outwards of the slots which are associated with each supporting plate.

1 3. A radiation collector as claimed in any of claims 2 to 12, characterised in that supporting strips for absorption of transverse forces transmitted from the housing base are inserted under the supporting plate in each slot associated with a supporting plate.

14. A radiation collector as claimed in claim 13, characterised in that the supporting strips have a greater width where they extend between adjacent profiles than where they extend through the slots.

1 5. A radiation collector as claimed in any of claims 9 to 14, characterised in that the part plates which are associated with the cover plate are substantially trapezoid in shape and the edges corresponding respectively to the longer of the two parallel trapezoid sides face towards the cover plate.

1 6. A radiation collector as claimed in claim 15, characterised in that the housing walls lying opposite the side edges of the supporting plates have, in cross-section, substantially the shape of quadrant arcs, in which respect the arching is directed towards the interior of the housing.

1 7. A radiation collector as claimed in any preceding claim, characterised in that the radiate absorption system is a tube system which is provided with absorption surfaces and the tubes of which extend in a plane, substantially parallel to the cover plate, between and around the supporting plates.

18. A radiation collector as claimed in claim 17, characterised in that the tube system comprises two individual tubes which respectively extend around the supporting plates in U-shaped loops alternately enclosing one and three supporting plates, and the loop sequences of the two individual tubes are mutually offset by two supporting plates.

1 9. A radiation collector as claimed in any of claims 1 to 16, characterised in that the radiation absorption system is a tube system which is provided with absorption surfaces and the tubes of which extend through openings in the supporting plates.

20. A radiation collector as claimed in any of claims 1 to 8, characterised in that the supporting plates are formed as apertured plates.

21. A radiation collector as claimed in any of claims 1 to 8 characterised in that the supporting plates have grooves on their edges which face towards the cover plate and that supporting battens are mounted upon and extend between several of the supporting bars which remain between said grooves.

22. A radiation collector as claimed in claim 21 characterised in that the supporting battens are approximately U-shaped in cross-section.

23. A radiation collector as claimed in any of claims 1 to 8 or 20 to 22 characterised in that the supporting plates have grooves on their edges which face the housing base.

24. A radiation collector having an evacuated interior substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.