The present invention relates to a solar-heat absorbing device comprising two elongate, thin, 5 flexible lengths of material placed one upon the other and joined along lines in a manner such as to form one or more fluid channels between said lengths. The device is primarily intended for use in the construction of solar-collector systems 10 covering large areas, including a heat-absorber section having high heat-absorbing and heat- transmission properties, and optionally a trans¬ parent cover means, where both the absorber sec¬ tion and the cover means are flexible and .can be 15 rolled-up on bobbins, and where the 'absorber section is fully resistant to corrosion attack by water having a high salt content and is able, at the same time, to withstand high temperatures. The device, however, can also be used, to advantage. 20 as a solar collector in roof or outer-wall struc¬ tures of buildings.

In the thermodynamic conversion of solar energy to electricity and/or the desalination of salt water, a collector array having a surface

:25 area m the order of 15,000m 2 is required to pro¬ duce 1 MW of electricity. In addition to this collector array, there is required a further

2 collector surface area of 50,000m for short- term solar-heat storage, in order to allow the •!30 plant to be operated for 24 hours a day, which is a condition for acceptable viability. Calcu¬ lated per square meter, solar-energy collectors known today are excessively expensive, and are difficult to transport and erect or instal in

remote and difficultly reached geographical loca¬ tions, which applies to the majority of countries in the equatorial belt. Above all, the known collectors possess unsatisfactory properties- with regard to their efficiency and their resistance to corrosion against sea water of high salt con¬ tent-in combination with temperatures reaching from 80 to 90°C.

The object of the invention is to eliminate all of the aforementioned disadvantages. 'This object has been realised with a solar-heat absorb¬ ing device having the characteristics set forth in the Claims. Thus, the solar-heat absorbing device according to the invention has an absorber which is made of a corrosion-resistant material having a high heat-passage number, and which, subsequent to being completed in the factory or plant, can be rolled-up onto bobbins and then unrolled at a selected site, the square-meter price of the col- lector on site not exceeding 150 Swedish Crowns. In turn this enables prices of between 20-30 Swe¬ dish Ore per kilowatt hour to be achieved when converting solar energy to electricity ther o- dynamically, and also provides for low prices per cubic meter of desalinated sea water. In accor¬ dance with the invention, the absorber section may, for example, comprise two 0.10-1.15mm thick copper foil of suitable width placed one upon the other and εealingly joined along their long edges to form a tube-like passage for either water, air or some other medium to be heated by solar energy. The absorber section thus constructed and com¬ prising thin metal sheets can be readily rolled-up on bobbins during manufacture, and when placed in

position on site can be inflated or expanded to oval or circular cross-sectional shape, or some other cross-sectional shape, by the pressure of the medium circulating and enclosed in said ab- sorber section. Experiments have shown that the most difficult step in the manufacture of such absorbers is,that of joining the two thin metal foils along their edges. Different methods have been tested, such as bonding with bonding resins of the araldite or silicone type. Neither of these adhesives has been found suitable in con¬ junction with water at temperatures reaching 80 - 90°C. Tests have also been made with both seam welding and cold welding using two rolls under high pressure. These methods have been found complicated and difficult to execute, be¬ cause of the small thickness of the copper foil ^* . In accordance with the invention, these difficul¬ ties encountered in manufacture can be eliminated by using heat-resistant rubber strips which by vulcanizing along the edges of the thin metal foils join the upper and the lower copper foils together in a corrosion-resistant, flexible and heat-tolerable fashion. It is known that when -rubber is vulcanized on metal, rubber diffuses into the outer surface of the metal, thereby to create an extremely strong joint. -Since rubber can also be vulcanized onto material other than metal, a metal sheet, e.g. foil, comprising the upper part of the absorber section and answering for the good heat-absorbing and heat-transmission properties, can be combined with another, less expensive material, which comprises the lower part of the absorber. Since rubber can be

vulcanized onto plastics and other materials, the combination possibilities are prolific with re¬ spect to the upper part of the absorber, which is turned to face the solar radiation and the lower part of the absorber, enabling a minimization of the price for the absorber section. The absorber section can be completed with a transparent cover material. The absorber section and the cover can, in both cases, be rolled-up onto bobbins during manufacture, and then unrolled from the bobbins on site, which is one of the prerequisites for obtaining a low total pric for .solar collectors calculated per square meter when incorporated in wide collector arrays- All of the aforemen- tione*d properties are also of value in solar collectors intended for installation on roofs and outer-wall structures of buildings

The invention will now be described in more detail with reference to the accompanying drawings, which illustrate the mode of use of the invention. Figure 1 is a cross-sectional view of a first embodiment of a solar collector according to the invention,

Figure 2 is a cross-sectional view of a second embodiment of a collector having a rubber base part,

Figure 3 is a cross-sectional view of another embodiment of a solar collector having a trans¬ parent cover means, Figure k is a top plan view of the collector illustrated in Figure 1,

Figure 5 is a cross-sectional view of a preferred solar collector intended for buildings, and

Figure 6 is a side view, partially in section, of a connection to one end of the collector illu¬ strated in Figure 5.

The collector illustrated in Figure 1 is manufactured by bonding an upper part 1 comprising metal foil or thin sheet metal of good heat-trans¬ mission properties to two rubber strips 4 and 5 by vulcanizing along surfaces 2 and 3 , and by bond¬ ing a lower part or base 6 made of a material suit- able for vulcanization to said rubber strips 4 .and 5 by vulcanizing along surf ces 7 and 8 , in a manner to form a water-tight flow passage capable of being shaped to an,oval or circular cross- section, or to some other form suitable for the absorber section of the collector, by the prevail¬ ing water pressure, the cross-sectional shape of the passage being shown in broken lines in Figure 1. In Figure 2, rubber strips 9, 10, correspond¬ ing to the rubber strips 4 and 5 in Figure 1, are joined by a rubber length 11 and comprise a unit which is attached. by vulcanizing along surfaces 12 and 13. to an upper, thin metal plate 14 having good heat-transmission properties.

The broken lines shown in Figure 2 illustrate the change in shape to which the collector is sub¬ jected by the pressure exerted by a flowing medium within the collector.

In Figure 3 , the reference 15 identi ies a schematically drawn support surface, which may be the ground, sand or ground-laid insulating material comprising, preferably mineral wool, the solar collector resting on said support surface.

16 and 17 identify two rubber strips, each of which is provided with a slot 18 and 19 into which

a respective end of a thin absorber plate 20 is inserted, said plate being attached to the rubber strips 16 and 17 by vulcanizing along the inner surfaces 21 and 22 of the slots 18 and 19. An underpart 24 of the collector also com¬ prises thin metal sheet and is bonded to the rubber strips 16 and 17 by vulcanizing along sur¬ faces 25 and 26 in the slots 18 and 19. The solar collector is also provided with a transparent cover material 27, preferably a UV-radiation re¬ sistant material, such as a PVF ₂ -plastics sold under the name "Tedlar". The cover 27 is bonded to the rubber strips 16 and 17 by vulcanizing along surfaces 28 and 29, and also to rubber support strips 30, which in turn are vulcanized to the absorber plate 20. The cover 27 is attached to the rubber strips 16 and 17 via rubber support strips 30 in a manner such that when the absorber 20, 24 is flat the cover lies loosely between the rubber strips 16, 17 in folds 27. This excess of cover material between said rubber strips enables the absorber section of the device to extend from a planar or flat state to an oval or circular state, as a result of the prevailing water pressure, without the cover 27 being unnecessarily stretched. The broken lines in Figure 3 illustrate the confi¬ guration taken by the solar collector as a result of the pressure exerted by the circulating water. Figure 4 illustrates an end piece of a solar collector which can be connected to a water supply. A rubber sealing strip 31 having a slot indicated by broken line 32 is sealingly attached by vulcani¬ zing to the rubber strips 16 and 17 and to the end of the upper absorber plate.20, and to the lower

absorber plate 24 (not shown in Figure 4) in an analogous manner. The rubber sealing strip 31 is also provided with a hole 33 which coincides with a hole in the upper absorber plate 20, facilitating the supply and draining of water.

When the solar collector is used in the con¬ struction of large arrays , some suitable form of pivotable, heat-insulating flaps or the like can be arranged to enable the collectors to be covered during the night. These flaps may comprise an extension of the flexible lower material web (when it comprises rubber) externally of one long side of the collector, so that the width. of the lower material length is at least double. This extension of the flexible lower material length can then be folded back over the absorber section of the col¬ lector, with the aid of suitable means, such as pulling ropes or the like.

Figures 5 and 6 illustrate a highly efficient,* preferred embodiment of a solar collector according to the invention intended for installation on the roof and/or outer-wall structure of a building. In this embodiment the heat-absorbing section com¬ prises a thin metal sheet 41 to which a rubber mat 42 having upstanding ribs 43 is firmly vulcanized at surfaces 44. Formed between the ribs 43 is a plurality of passages having a width of at most about 10mm and a depth of about 2-3mm. A connect¬ ing block 46 made of rubber and having a connect- ing pipe 47 protruding into respective passages 45 is εearingly vulcanized to the ends of said plate 41 and said mat 42. The connecting pipes 47 extend from a distributor pipe 48 connected to a pipe-line (not shown) from which the circulation

water of the solar collector is supplied. The pipes 47 and 48 are also vulcanized in the block 46. In this embodiment, the rigidity of the plate 41 and the rubber mat 42 is such that the passages 45 will not be deformed to any great extent by the pressure of the water in said passages. This ensures a high degree of efficiency in operation, and enables the solar collector to be readily mounted on the roof or walls of a building, substantially by bonding to the support structure, for example to a sheet- metal roof.

Wide possibilities in variation are possible within the scope of the invention, to obtain sig¬ nificant reductions in price per square meter of solar collector in relation to solar collectors known hitherto. Preferably, such a reduction in price is achieved with respect to the absorber section of the collector, while retaining maximum heat-transmission ability, resistance to corrosion and to heat, by making the upper part of the col¬ lector, said upper part being exposed to solar radiation, from copper foil, for example, and the lower part from inexpensive aluminium foil or galvanized, thin iron sheet, which may be- coated with a thin layer of rubber, thereby providing the lower~part of the collector with the same resistance to corrosion as that exhibited by the much more expensive copper foil. Thus, the rubber layer on the lower part of the absorber section can be used as a means of sealingly connecting the lower part of the absorber section to the upper part thereof, by vulcanizing at suitable locations. This possibility of vulcaniz¬ ing the upper, solar-heat receiving part of the

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absorber to the lower part thereof can also be achieved with other material combinations possible within the scope of the invention, which minimizes the total price of the absorber and therewith also the solar collector.

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