Evaluation of Multilayer Thin Film Coatings for Solar Thermal Applications

Abstract

The multilayer thin film coatings are one of the proven technologies for improvement in solar thermal and optical applications. In current solar thermal and optical systems, multilayer thin film coatings find application in many functions such as photovoltaics, heat exchangers, filters, sensor technologies, laser windows, mirrors, reflectors and optics for digital projections. The solar absorptance and thermal emittance of the multilayer thin film coatings are one of the leading factors for its applicability in said areas. The processing conditions, morphology and surface finish influence the solar absorptance and thermal emittance behavior of multilayer thin film coating. Therefore, emphasis has given in this paper to deposit multilayer thin film coatings with an increased solar absorptance and decreased thermal emittance to improve its applicability in solar thermal applications. Multilayer thin film coatings (Al2O3/Ni/W–Al2O3/W) were deposited using DC/RF magnetron sputtering on the stainless steel substrate to improve its applicability in solar thermal receiver tube for power generation. The performance of this multilayer thin film was investigated by measuring the absorptance and emittance using 410 Solar and ET 100 in the solar spectrum region at a variable incident angle from 20° to 60°. The effect of optical properties, microstructure and morphology of the multilayer thin film coatings was also investigated. The maximum absorptance 0.92 and minimum emittance < 0.1 were observed in deposited multilayer thin film coating with the combination of Tungsten, Al2O3 and Nickel, respectively. The observed values indicate the practical applicability of the multilayer coatings in medium-to-high-temperature range of solar thermal receiver tubes.