Method and Device for Producing a Highly Selectively Absorbing Coating on a Solar Absorber Component and Solar Absorber Having Such Coating

Abstract

The invention relates to a method for producing a selectively absorbing coating on a solar absorber component comprising the steps of: Providing a substrate having a metallic surface, Determining the inner surface of the metallic surface, Determining the charge quantity per unit area required for producing the absorbing coating according to the inner surface, Electrolytically producing the absorbing coating by direct-current anodising the metallic surface of the substrate, forming a porous oxide layer, and then alternating-current pigmenting the pores of the oxide layer; until the charge quantity per unit area determined for the respective step from the inner surface is reached, wherein the ratio between the charge quantity per unit area for the direct-current anodising and the charge quantity per unit area for the alternating-current pigmenting is 0.65 to 0.8. In addition, the invention relates to a solar absorber component produced according to this method.

1 . A method for producing a selectively absorbing coating on a solar absorber component comprising the steps of:
 Providing a substrate having a metallic surface,   Determining an inner surface of the metallic surface,   Determining a charge quantity per unit area required for producing the absorbing coating according to the inner surface,   Electrolytically producing an absorbing layer in a first step by direct-current anodising the metallic surface of the substrate, forming an oxide layer having pores, and in a second step by alternating-current pigmenting the pores of the oxide layer, wherein the direct-current anodising and the alternating-current pigmenting are carried out until the charge quantity per unit area determined for the respective step from the inner surface is reached,   wherein the ratio between the charge quantity per unit area (ρ A ) for the direct-current anodising and the charge quantity per unit area (ρ P ) for the alternating-current pigmenting ρ A /ρ P  is =0.65 to 0.8.   
     
     
         2 . The method according to  claim 1 , wherein the substrate is a metallic component, in particular a plate-like or tubular component. 
     
     
         3 . The method according to  claim 2 , wherein the substrate is a metallic component, in particular a steel or stainless steel component, having an adhesion-promoting metallic surface coating. 
     
     
         4 . The method according to  claim 3 , wherein the adhesion-promoting metallic surface coating is an aluminium or copper layer. 
     
     
         5 . The method according to  claim 2 , wherein the substrate is an inflated cushion absorber which is produced from two metallic sheets in the roll-bond process. 
     
     
         6 . The method according to  claim 2 , wherein the substrate is cylindrically formed and the adhesion-promoting layer is applied by pulling over an aluminium or copper tube. 
     
     
         7 . The method according to  claim 1 , wherein the substrate is foil-like and in particular is formed as an aluminium or copper foil. 
     
     
         8 . The method according to  claim 1 , wherein the substrate is a glass substrate, in particular a TCO-coated glass substrate. 
     
     
         9 . The method according to  claim 1 , wherein the inner surface of the metallic surface of the substrate is determined by means of atomic force microscopy. 
     
     
         10 . The method according to  claim 1 , wherein the absorbing layer deposited onto the substrate surface by direct-current anodising is an Al 2 O 3  or copper oxide layer. 
     
     
         11 . The method according to  claim 1 , wherein the alternating-current pigmenting is carried out using a metal from the group Consisting of Ni, C, Al, Mg, Ca, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Ag and Sn. 
     
     
         12 . The method according to  claim 1 , wherein the solar absorber component is cylindrically formed, wherein the absorbing layer is electrolytically produced with the solar absorber component positioned standing in a container filled with an electrolyte, wherein the cylindrical solar absorber component is arranged coaxially to a surrounding cylindrical counter electrode. 
     
     
         13 . The method according to  claim 1 , wherein the solar absorber component is cylindrically formed, wherein the absorbing layer is electrolytically produced with the solar absorber component positioned lying in a container filled with an electrolyte, wherein the cylindrical solar absorber component is arranged essentially coaxially to a gutter-shaped counter electrode with an essentially cylindrical inner surface. 
     
     
         14 . The method according to  claim 13 , wherein the cylindrical solar absorber component with respect to its circumference is only partly immersed in the electrolyte. 
     
     
         15 . The method according to  claim 1 , wherein a transparent anti-reflection layer is applied onto the electrolytically produced absorbing layer. 
     
     
         16 . The method according to  claim 15 , wherein the anti-reflection layer is formed from a material from the group consisting of Al 2 O 3 , TiO 2 , 3-mercaptopropyltrimethoxysilane (MPTMS), cerium oxide, sodium silicate, SiO 2 , SiO 2 /SnO 2  or pyrolytic SnO 2  or F:SnO 2  (FTO or fluorine-doped tin oxide). 
     
     
         17 . The method according to  claim 1 , wherein the substrate is an aluminium or copper strip (C, C*) or a steel strip coated with an aluminium or copper coating which is coated in a roll-to-roll process. 
     
     
         18 . A solar absorber component produced according to the method of  claim 1 .