Rough metallic selective surfaces for solar energy applications

Abstract

Abstract Rough surfaces have been used for many different purposes. One of the best known applications of the rough metallic surface is seen in solar systems as a selective surface. The roughness of the surface has been characterized by two parameters, namely the root mean square roughness and the root mean square slope. We calculated these two parameters from reflectance data measured in the thermal region of the spectrum using an equation suggested by Bennett and Porteus. The theory suggested by Horwitz fitz the reflectance data of the rough surfaces at the solar region of the spectrum reasonably well. The theories mentioned above were applied to rough surfaces, prepared by different processes, for three materials, namely chromium, stainless steel 304 and silicon. We found that for solar energy applications the chromium surface had the best optical properties. The root mean square roughness is about 0.160 μm, while the root mean square slope is about 0.500/Δθ, where Δθ is the acceptance angle of the instrument used.