Solar collector with foil absorber

Abstract

The present invention provides a solar collector comprising a collector device and a heat-transfer device which includes a heat conductive conduit for heat-transfer fluid, the conduit being in physical contact with the collector device, characterized in that: the collector device comprises flexible metallic foil of which at least one side is adapted for exposure to solar radiation by the presence thereon of a heat absorptive coating; and the physical contact is maintained by tension effective to stretch the foil over the conduit. In an embodiment of the invention the tubes 5 of the conduit are arranged in one plane, the tension is maintained by bars 10 arranged in another plane, substantially parallel to the plain of the tubes. Foil 8 is placed so as to contact alternately with the tubes and with tension-maintaining bars 5.

1 . An apparatus for utilization of solar energy which comprises a collector device and a heat-transfer device which includes at least one heat conductive conduit for heat-transfer fluid, the conduit being at least partially in physical contact with said collector device, characterized in that: 
     (A) said collector device comprises at least one flexible metallic foil of which at least one side is adapted for exposure to solar radiation by the presence thereon of a heat absorptive coating; and 
     (B) said physical contact is maintained by tension effective to stretch said at least one foil over said at least one conduit. 
   
   
       2 . The apparatus according to  claim 1 , which is further characterized by at least one of the following features: 
     (a) said at least one conduit comprises a plurality of tubes adapted for serial or parallel transport of said heat-transfer fluid; 
     (b) said at least one foil is in contact with said at least one conduit at a wrap angle value between: 10 degrees to 60 degrees; 
     (c) said foil has a thickness in the range of 40 to 200 μm; 
     (d) said tension is produced by at least one device is selected from springs, weights and combinations thereof; 
     (e) said foil comprises aluminum or an aluminum alloy having preferably a value of ultimate tensile strength greater than 180 Mpa; 
     (f) said coating comprises at least one layer produced by vacuum deposition; 
     (g) said coating comprises a mixture of aluminum and alumina; 
     (h) said coating has a thickness of between 100 nm and 1000 nm. 
   
   
       3 . The apparatus according to  claim 2 , wherein said at least one conduit comprises a plurality of tubes adapted for serial or parallel transport of said heat-transfer fluid, and said plurality of tubes is configured as an array of tubes in one plane or in a plurality of substantially parallel planes. 
   
   
       4 . The apparatus according to  claim 3 , wherein part of said plurality of tubes is in contact with said foil at a location on said tubes not facing the direction of solar radiation. 
   
   
       5 . The apparatus according to  claim 3 , wherein said plurality of tubes is configured as an array of substantially parallel tubes in a single plane. 
   
   
       6 . The apparatus according to  claim 5 , wherein said tubes are in contact with said foil in a manner which alternates between a location on said tubes not facing the direction of solar radiation and a location on said tubes facing the direction of solar radiation. 
   
   
       7 . The apparatus according to  claim 3 , wherein said plurality of tubes is configured as an array of tubes in two substantially parallel planes, defined as an upper plane nearest to the direction of solar radiation and a lower plane furthest from the direction of solar radiation. 
   
   
       8 . The apparatus according to  claim 7 , wherein the tubes in each of said planes are arranged with spaces between the tubes, the tubes in the lower plane being so disposed in a staggered manner in relation to the tubes in the upper plane, such that the tubes in the lower plane are exposed to solar radiation penetrating the spaces between the tubes in the upper plane. 
   
   
       9 . The apparatus according to  claim 8 , wherein said tubes are in contact with said foil in a manner which alternates between a location on said tubes not facing the direction of solar radiation and a location on said tubes facing the direction of solar radiation. 
   
   
       10 . The apparatus according to any one of  claims 1  to  9  wherein said heat absorptive coating is characterized by different values of absorptance and emittance in the foil loci with different temperatures of heat-transfer fluid. 
   
   
       11 . The apparatus according to  claim 1 , substantially as hereinbefore described. 
   
   
       12 . The apparatus according to  claim 1 , substantially as hereinbefore described, with particular reference to and as illustrated in the accompanying drawings.