Solar selective absorber functionality of carbon nanoparticles embedded in SiO2, NiO and ZnO matrices

Abstract

It is possible to design an optical material, through control of the substrate and coatings, to absorb a large fraction of the solar spectrum and to emit very little radiation energy in the near and far infra-red wavelength range. This requires a coating structure that transmits in the ultraviolet and visible, but reflects in the near and far infrared, with a sharp drop in transmission near 2 μm. In this paper, the authors report on selective solar absorber coatings of carbon nano-particles embedded in SiO2, ZnO and NiO matrices, fabricated by a sol-gel technique. The coatings were tested on aluminium substrates. UV-VIS and FTIR spectroscopies were used to determine the spectral response of the composite coatings, from which the solar absorptance and thermal emittance were determined. It is shown that the NiO matrix samples have the best solar selective behaviour, and suggest a theoretical evaluation framework for future comparison of such materials.