Paints and Painting Procedures for Solar Energy Collectors

Abstract

A solar collector is a special kind of heat exchanger that transforms solar radiant energy into heat. A large variety of these solar collectors have been designed for trapping the solar energy. These collectors are usually made of copper, aluminium, steel or galvanized iron. A solar collector must have very high absorption coefficient for incident solar radiation and very low emissivity in the long wave length region. Means of enhancing the absorptance values of commonly used solar collectors, black paints and selective absorbers are used. Solar collectors designed for high temperature are given selective coatings, whereas normal paints are applied that are designed for 65 to 70°C. Selective absorbers are usually polished metal surfaces coated with a thin deposit of black oxides of nickel and copper and nickel and zinc sulphides. The most recent commercial selective surface which is being widely adopted in U.S.A. is black chrome. Black paints can economically and efficiently be used up to 65°C and are preferred for solar water heaters. The efficiency of these paints is good as they show a very high absorption coefficient for solar radiation (Table 1). However, they require frequent renewal also.