Solution-based Ni-Al2O3 Solar Selective Coating using Convective Deposition

Abstract In the past century, an interest in solar energy grows rapidly due to its renewable resource and pollution-free operation. One of the technologies to accumulate solar energy is a concentrating solar power (CSP) system which contains a solar absorber as a key part. A role of solar absorber is to convert solar energy into heat. In this study, a technique called rapid convective deposition was used to produce a thin film of cermet solar absorber. The Ni-Al2O3 cermet solution was prepared with chelating and wetting agents. The rapid convective deposition was used for coating a cermet thin film onto a 304 stainless steel substrate. This technique has capability to control the thickness of coating with less amount of substances compared to other coating techniques. Finally, the coated solution was treated at high temperature where the aluminum ions were converted into a matrix of Al2O3, and nickel ions were converted into nickel nanoparticles embedded in the matrix. The important parameters including mole ratio, total metal ion concentration, and coating speed were examined. The optical properties including solar absorptance and thermal emittance were tested and calculated for the solar selectivity to represent solar-to-thermal energy conversion efficiency. The solar selectivity was enhanced from 5.6 to 6.5 with increasing the mole ratio of nickel and aluminum ions. However, the total metal ion concentration did not significantly improve the solar selectivity. The slower coating speed resulted in higher solar selectivity. Overall performance indicated that the cermet and the rapid convection deposition can potentially be exploited for industrial production of selective absorber.