Surface coatings for solar application

This article covers the upto-date developments of single and multilayer solar coatings which have greater potential and technological applications in the transparent and electrically conducting layers for windshields of the automobiles, spectrally selective layers for solar collectors, antireflection coatings for solar cells, windows of buildings etc. The important parameters for surface coatings have been defined and their importance in obtaining spectral selectivity were considered. Materials with high absorptance/emittance ratio and their current status were reviewed. The recent developments of antireflection coatings and energy efficient windows are briefly discussed. This includes the consideration of the design aspects of the antireflection coatings, oxide layers of SnO2, ZnO and the electrochromic, liquid crystal devices. The optical properties (absorptance, emittance etc.) of various coating materials such as selective absorber paints, transparent metal coatings, low emissivity coatings, and metal oxide absorber layers for solar heating have been discussed. The preparative techniques along with the characterization processes of several important absorber layers for solar heater applications (e.g. black cobalt, black chrome, black nickel, black copper, black molybdenum and cermet coatings) have been considered. The criteria for improving the efficiencies of the solar heating system has also been discussed. The ageing effects of these coatings are very important for practical applications and a good ageing resistance of the various properties of the solar coatings is required. The degradation factors for the absorber layers under the working condition are reviewed.