Solar collector element

Abstract

The invention relates to a solar collector element having an absorber part and a tube for a heat transfer liquid connected thereto on a first side. The absorber part consisting of a composite material having a metallic substrate and an optically active coating on a second side of the substrate. The coating is a multilayer system having three layers. The top layer is a dielectric layer, preferably an oxide, fluoride or nitride layer of chemical composition MeO z , MeF r , MeN s , having a refractive index n<1.8. The middle layer is a chromium oxide layer of chemical composition CrO x . The bottom layer is gold, silver, copper, chromium, aluminium and/or molybdenum. The indices x, z, r and s indicate a stoichiometric or non-stoichiometric ratio in the oxides, fluorides or nitrides.

1 . Solar collector element comprising an absorber part and a tube adapted to contain a heat-transfer liquid, the tube being connected to the absorber part on a first side, the absorber part being a composite material having a metallic substrate and having an optically active coating on the substrate on a second side (A), the coating further comprising a multilayer system having three layers, the top layer being a dielectric layer having a refractive index n<1.8, the middle layer being a chromium oxide layer of chemical composition CrO x , and the bottom layer being of a material selected from the group consisting of gold, silver, copper, chromium, aluminium and molybdenum, the index x indicates a stoichiometric or non-stoichiometric ratio.  
     
     
         2 . Solar collector element according to  claim 1 , wherein the top layer is a silicon oxide layer of chemical composition SiOy, the index y indicating a stoichiometric or non-stoichiometric ratio.  
     
     
         3 . Solar collector element according to  claim 1  wherein the top layer is of a chemical composition selected from the group consisting of MeO z , MeF r  and MeN s  the indices z, r and s indicating a stoichiometric and non-stoichiometric ratio.  
     
     
         4 . Solar collector element according to  claim 1  wherein an intermediate layer is applied to the substrate beneath the multilayer system.  
     
     
         5 . Solar collector element according to  claim 1  wherein a lower layer is applied to the substrate on the first side thereof.  
     
     
         6 . Solar collector element according to  claim 1  wherein the substrate is formed of aluminium.  
     
     
         7 . Solar collector element according to  claim 6  wherein the aluminium is more than 99.0% pure.  
     
     
         8 . Solar collector element according to  claim 4  wherein the intermediate layer is formed of anodically oxidized aluminium.  
     
     
         9 . Solar collector element according to  claim 4  wherein the intermediate layer is formed of electrolytically brightened and anodically oxidized aluminium.  
     
     
         10 . Solar collector element according to  claim 5  wherein the lower layer is formed of anodically oxidized aluminium.  
     
     
         11 . Solar collector element according to  claim 5  wherein the lower layer is formed of electrolytically brightened and anodically oxidized aluminium.  
     
     
         12 . Solar collector element according to  claim 1  wherein the substrate has a rolled structure of grooves which run substantially parallel to one another in a preferred direction.  
     
     
         13 . Solar collector element according to  claim 1  wherein the substrate is formed of copper.  
     
     
         14 . Solar collector element according to  claim 1  wherein the stoichiometric or non-stoichiometric ratio x lies in the range 0<×<3.  
     
     
         15 . Solar collector element according to  claim 2  wherein the stoichiometric or non-stoichiometric ratio y lies in the range 1≦y≦ 2 .  
     
     
         16 . Solar collector element according to  claim 1  wherein the bottom layer includes a plurality of partial layers, arranged one above the other and be formed of at least one material selected from the group of gold, silver, copper, chromium, aluminium and molybdenum.  
     
     
         17 . Solar collector element according to  claim 1  wherein at least one of the top and middle layers are sputtered layers.  
     
     
         18 . Solar collector element according to  claim 17  wherein the layers are produced by reactive sputtering.  
     
     
         19 . Solar collector element according to  claim 1  wherein at least one of the top and middle layers are produced by vaporization.  
     
     
         20 . Solar collector element according to  claim 19  wherein vaporization is by electron bombardment.  
     
     
         21 . Solar collector element according to  claim 19  wherein the vaporization is by thermal sources.  
     
     
         22 . Solar collector element according to  claim 1  wherein at least one of the upper and middle layers are CVD layers.  
     
     
         23 . Solar collector element according to  claim 1  wherein at least one of the upper and middle layers are PECVD layers.  
     
     
         24 . Solar collector element according to  claim 1  wherein the bottom layer is a sputtered layer.  
     
     
         25 . Solar collector element according to  claim 1  wherein the bottom layer is a layer produced by vaporization.  
     
     
         26 . Solar collector element according to  claim 25  wherein vaporization is by electron bombardment.  
     
     
         27 . Solar collector element according to  claim 25  wherein vaporization is from thermal sources.  
     
     
         28 . Solar collector element according to  claim 1  wherein the multilayer system is applied in vacuum order in a continuous process.  
     
     
         29 . Solar collector element according to  claim 1  wherein the top layer has a thickness in the range of 3 nm to about 500 nm.  
     
     
         30 . Solar collector element according to  claim 1  wherein the middle layer has a thickness in the range of 10 nm to about 1 μm.  
     
     
         31 . Solar collector element according to  claim 1  wherein the bottom layer of the optical multilayer system has a thickness (D 6 ) of at least 3 nm and at most approximately 500 nm.  
     
     
         32 . Solar collector element according to claims  1  wherein a total light reflectivity on second side is less than 5%.  
     
     
         33 . Solar collector element according to  claim 1  wherein a total light reflectivity on the second side under a thermal load of 430° C./100 hours undergoes changes of less than 7%.  
     
     
         34 . Solar collector element according to  claim 33  wherein the change is less than 4%.  
     
     
         35 . Solar collector element according to  claim 1  wherein the absorber part is of plate-like form and has a thickness in the range of 0.1 to about 1.5 mm.  
     
     
         36 . Solar collector element according to  claim 35  wherein the thickness is in the range of about 0.2 to about 0.8 mm.  
     
     
         37 . Solar collector element according to  claim 1  wherein the tube is formed of copper.  
     
     
         38 . Solar collector element according to  claim 1  wherein the absorber part and the tube are connected to one another by means of a material-to-material laser welded bond.  
     
     
         39 . Solar collector element according to  claim 38  wherein the bond is formed by a pulse welding process.  
     
     
         40 . Solar collector element according to  claim 38  wherein the bond between the absorber part and the tube is made up of only of the respective materials of the absorber part and of the tube.  
     
     
         41 . Solar collector element according to  claim 24  wherein the absorber part and the tube with the absorber part having a substrate made from aluminium and the tube is formed of copper, is formed by a series of molten balls which have solidified on the absorber part and predominantly made up of aluminium and by diffusion of the aluminium into the copper of the tube.  
     
     
         42 . Solar collector element according to  claim 24  wherein the tube and the absorber part are joined where they are in abutment with one another by weld seams running on both sides of the tube and are formed from weld spots which are spaced apart from one another.  
     
     
         43 . Solar collector element according to claim  41  wherein the tube and the absorber part, with the absorber part having a thickness in the range of about 0.3 to about 0.8 mm and a diameter of the molten balls in the range of about 0.2 to about 3.2 mm spaced at a distance in the range of about 0.5 to about 2.5 mm between centers of the molten balls.