Application and Testing of Coating for Solar Absorber Surfaces

Abstract

Solar absorbers are used widely in many applications. The absorber surface must have a maximum absorptivity and minimum emissivity of solar radiation. This is achieved by application of selective coating on the absorber surface. This study is directed towards studying the effect of different parameters on the optical properties of a CoCuMnOx selective coat by using sol gel technique on steel and stainless steel substrates. The dip coat sol gel technique is based on dipping the substrate into a solution containing metal alkoxides. First, the effect of substrate surface preparation was studied. The steel surface was coated with chrome layer for corrosion resistance but the adhesion was poor between the coat and the steel. The stainless steel was sand blasted prior to coating and this resulted in good adhesion between the coat and substrate. Then the effect of different molar weights of the solution was investigated and the most promising concentration was molar weight/60 based on the best optical properties which are absorptivity and emissivity. This solution was used for further experiments which included different withdrawal rates and the application of multiple dips to obtain multi-layer coat. For testing the coat, the optical properties were measured in addition to the thickness of the coat and its surface roughness. The relation between the optical properties and the coat thickness and surface roughness was investigated. Finally the thermal stability of the coat on the absorptivity, emissivity and selectivity of the coat were investigated. The most promising optical properties samples were studied using SEM, EDX and XRD. Key words: Solar Energy, Sol gel, CuCoMnOx, Opticalproperties, selective coating.