Optimisation of optical absorption properties of spectrally selective C-NiO composite coatings

Abstract

The demand for low cost, efficient and environmental friendly energy is increasing rapidly. Solar thermal energy is being widely investigated as a solution. Efficient thermal solar collectors require a spectrally selective material capable of absorbing as much as possible the solar radiation while re-emitting very little in the infrared range, i.e spectrally selective solar absorbers. The manufacturing process for most of the materials used as selective solar absorbers is complicated and expensive. Carbon in Nickel Oxide (C-NiO) composite material has been found to have a very good spectral selectivity1,2. Moreover this material has a potential of low cost large scale fabrication since it can be fabricated by a simple sol-gel technique. In order to make a step from lab to large scale fabrication it is important to first optimise the properties of the material in an easy to control manner. C-NiO coatings were coated on aluminium substrate using a combination of sol-gel and spin coating technique. Different fabrication parameters were varied in order to optimise these C-NiO coatings for absorptance. Optical properties, surface morphology and chemical analysis were performed on these coatings by use of UV/Vis spectroscopy, Scanning Electron Microscopy (SEM), and Energy dispersive Spectroscopy (EDS), respectively. Solar absorptance values of up to 0.85 accompanied by thermal emittance values of as low as 0.08 were realised on these coatings.