Nanocoatings: Designed layers for solar thermal applications

Abstract

Solar energy is one of the most used renewable energy source in different applications nowadays. The direct method of harnessing solar energy is the solar thermal conversion method using solar absorbers. Solar thermal collectors are mainly used for heating water and for space heating. They capture incident solar radiation, convert it to usable thermal energy, and transfer the solar energy into a heat transfer fluid. All of these requirements should be accomplished economically with a minimum energy loss. One of the most important components of the solar thermal collector is the solar absorber. To be effective, the absorber should exhibit wavelength selectivity, i.e. have maximum solar absorbtance, minimum solar reflectance and thermal infrared emittance. A high solar absorbtance is required to collect as much of the incident solar radiation as possible and a low thermal infrared emittance contributes to minimize radiant energy losses. Usually, lightweight materials like, copper or aluminium, that have a high thermal conductivity, are used to transfer the absorbed energy from the surface to the media (fluid) which has to be heated. For high coefficient of efficiency of solar thermal collectors, the most important parts are: 1) spectral selective coatings that are composed of islands of metal embedded in a threedimensional matrix of dielectric with a solar absorbtance of α > 0.95 and an emittance of ε

Keywords

• nanocoatings
• solar thermal collectors
• solar energy
• design