CA1215281A - Solar-heat absorbing device - Google Patents

Abstract

A solar-heat absorbing device has first and second elongate, thin, flexible lengths of material placed one upon the other and joined together along parallel, continuous longitudinally extending lines to form fluid passages between the lengths of material. The first length of material is a thin metal sheet for exposure to solar radiation and formed, for example, of copper, brass, stainless steel or the like. The second length of material is a heat-resistant rubber material having mutually parallel upstanding ribs onto which the first material length is firmly vulcanized so as to form the passages between ribs.

Description

iZ~31~

A SOLAR-HEAT AB~ORBING ~EVIC~
___ _ _ The presen-t inven.ion relates to a solar-heat abscrbing device comprising two elongate, thin, 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 coverin~ 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 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, ~O 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 area in the order of 15,000m2 is required to pro-duce 1 MW of electricity. In addition to this collector array, there is require~ a further collector surface area of 50,OOOm for short-term solar-heat storage, in order to allow the 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 difflcultly reached geographical locations, which applies to the majority of countries in the equatorial belt. Above all, the known collectors possess unsatisfactory properties with regard to their efEiciency and their resistance to corrosion against sea wa-ter of high salt content in combination with tempera-tures reaching from 80 to 90C.
It is an object of the present invention to mitigate at least some of the aforementioned disadvantages.
The present invention provides a solar-heat absorbing device comprising first and second elongate, thin, flexible lengths of material placed one upon the other and joined -together along a plurality of parallel, continuous, longitudinally extending lines to Eorm a plurality of fluid passages between the first and second lengths of material, the first length of material comprising a thin metal sheet for exposure to solar radiation and the second length of material comprising a heat-resistant rubber material having a plurality oE
mutually parallel upstanding ribs vulcanized onto the first material length and thereby forming the plurality of passages between the ribs.
Thus, the solar-heat absorbiny device according to the invention may be made from corrosion-resistant materials having a high heat conductivity, 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 collector on site not exceeding 150 Swedish Crowns. In turn this enables prices of between 20-30 ~wedish Ore per kilowatt hour to be achieved when converting solar energy to electricity thermo-dynamically, and also provides for low prices per cubic meter of desalinated sea water.
The first layer may, for example, comprise a 0.10-1.15mm thick copper foil of suitable width placed upon, and sealingly joined along its long edges to, the second layer formsa tube-like passage for either water, air or some other medium to be heated by solar energy. The device thus constructed can be readily rolle~-up on bobbins during manufacture.
Experiments have shown tha-t -the most difficult step in the manufacture of absorbers comprising thin metal foils is that of joining -the 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 have been found suitable in conjunction wi-th water at tempera-tures reaching 80 - 90C. 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, because of the small thickness of the copper foil. In accordance with the invention, these difficulties encountered in manufacture can be eliminated by using a heat-resistant rubber material which by vulcanizing along the edges of the thin metal sheet join the first and the second material lengths together in a corrosion-resistant, flexible and heat-resistant 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 first material length and providing gooa heat~absorbing and heat-transmission properties, can be combined with another, less expensive material, which comprises the second material length. Since rubber can be vulcanized onto plastics and other materials, the combination possibilities are prolific wi-th respect to the upper part of the absorber, which is turned to face -the solar radia-tion and the lower part o the absorber, enabling a minimization of the price for the device.
The device can also include a transparent cover material. The device and the cover can be rolled-up onto bobbins during manufacture, and then unrolled from the bobbins on site, which is one of the prere~uisites for obtaining a low total price for solar collectors, calculated per square me-ter, when incorporated in wide collector arrays. All of the aforementioned properties are also of value in solar collectors intended for installation on roofs and outer wall structures of buildinys.
Embodiments of the inven-tion will now be described in more detail with reference to the accompanying drawings, in which:
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 r Figure 4 is a top plan view o the collector illustrated in Figure 1, Figure 5 is a cross-sectional view of a preferred solar collector intended for buildings, ana ~,~

2~
d , , ~ i~ure 6 is a side view, partially in section, or d connection to one end of the collector illu-stra~ed in Figure 5.
The coilector illustrated in Figure 1 is 5 manu~actured by bondin~ an upper part 1 comprisin~
nletal foil or thin sheet metal of ~ood heat-trans-mi.ssion.proper-ties to two rubber strips 4 and 5 by vulcanizing along surfaces- 2 and 3, and by ~ond-ing a lower par-t or base 6 rnade of a material suit-able for vulcanization to said rubber strips 4 and5 by vulcanizing along surfaces 7 and R, in a manner to form a water-tight flow passage capable of being shaped to an oval or cireular cross-section, or to some other form suitable for the absorber section of the colleetor, by the prevail-ing water pressure, the cross-seetional shape of the passage being shown in broken lines in Figure 1. In Figure 2, rubber strips 9, 10, eorrespond-ing to the rubber strips 4 and 5 in Figure 1, are 2~ joined by a rubber length 11 and eomprise a unit which is attaehed;by vuleanizing along surfaees 12 and 13,to an upper, thin metal plate 14 having good heat-transmission properties.
The broken lines shown in Figure 2 illustrate the ehange in shape to whieh the eolleetor is sub-jeeted by the pressure exerted by a flowing medium within the eollectorA
In Figure 3, the referenee 15 identifies a sehematieally drawn support surface, which may be the ground, sand or ground-laid insulating material eomprising5 preferably mineral wool, the solar eolleetor resting en said support surfaee.
l6 and 17 identify two rubber strips, each of whieh is provided with a slot 18 and 19 into whieh a respective end of a thin absorber plate 20 is inserteZ, said pla~e bei.ng attached to -the rubber s,rips ].6 and 17 by vulcanizing along the inner surfaces 21 and 22 of the slots 13 and 13.
hn underpart 24 of the co~lector also com pri5e~; 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 co~lectcr is also prcvided with a transparent ~0 cover mcl-Lerial 27, preferably a UV-radi.ation re-sistarlt ~lateri.al, such as a PVF2-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 ~0, 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 fro~
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 1ines in Figure 3 illustrate the conii-guration taken by the solar collector as a result of the pressure exerted by the circulating water.
~igure 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 1~ 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 an-l~,Fou5 rmanner. The rubber sealin~ strip 31 is also provided with a hG1e 33 which coincidec Wit}l a hole in the U~L-)PCr ab.-sc)rber p1ate 20, facilitatin the su~ply and drainin~ of water~
When t}~e sc,lar co1iector is usec in the cor,-struction cf lar e ar~ays, some suitab~e form of pivotable, heat-insu1ating f~aps or the 1i~e can be arranged to enab~e the collectors tc be covered lG durin~ the night. These flaps may comprise an extension of the flexible lower materia1 web (when it comprises rubher) externally of one long side of the collector, so that the widt-h 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 7 such as pulling ropes or the like.
~igures 5 and 6 illustrate a highly efficient, preferred embodiment of a solar collector according to the invention intended for installatior, 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 plurali~ty of passages having a width of at most about lOmm 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 passages45 issealinqly vulcanized to the ends of said plate 41 and said mat 42. The connecting pipes 47 extend from a distributo~ pipe 48 connected to a pipe-line (not shown) from which the circulation water of the solar co]lector is supplieZ. The pipe.-.
~7 an~ 4~ are also vulcanized in t:he block 46. In -thi.~ embocliment-, the rigidity of the plate 41 and the rubber mat 42 is such t},at the paSsaEes 45 will r, nGt be cicfc,rmed tc, any great e~:tent by the pressure Gf -the water ir, sai.cl passaQes. This ensures a high degree of efIicierlcy in operation, and enables the solar collector tc, be readily mourl-ted or, the roof or wa~lr oi ~ buildin~, su.)stantially by bonding tc~-th~ supl.ort structure, for exarrlple to a sheet-metal roof.
~ Jide possibilities in variation are possible withir, the scope of the invention, to obtain sig-nificant reductions in price per square meter of solar collector in relation to solar collec-tors known hitherto. Preferably, such a reduction in price is achieved with respect to the absorber section of the collector, while retaining maximum heat-transmission a.bility, 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 galvani.zed, 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 52~3~

absorber tG the lower part t}-~ereof can also be achievec with other material combinations possible withiri the scope G' the inventic,n~ which minimi7~es the -tota~ price of t},e absorber an- therewith also the s, ar col~ector.

Claims (2)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows

1. A solar-heat absorbing device comprising first and second elongate, thin, flexible lengths of material placed one upon the other and joined together along a plurality of parallel, continuous, longitudinally extending lines to form a plurality of fluid passages between said first and second lengths of material, said first length of material comprising a thin metal sheet for exposure to solar radiation and said second length of material comprising a heat-resistant rubber material having a plurality of mutually parallel upstanding ribs vulcanized onto said first material length and thereby forming said plurality of passages between said ribs.

2. A device according to Claim 1, wherein said two material lengths are of such rigidity, and said ribs are located with such small spaces therebetween, that said material lengths will not be deformed to any substantial extent by pressure exerted by the fluid on the walls of said passages.