High-Temperature Stable Spinel Nanocomposite Solar Selective Absorber Coating for Concentrated Solar Thermal Application
Abstract
A new Cu-Ni-Co ternary spinel/SiO2 nanocomposite oxide absorber with tandem layer approach is designed and developed for medium and high temperature solar selective receiver tube in concentrated solar thermal applications. The base absorber layer, developed by combining of nanostructured, transition metal spinel and composite oxides with a series of transition metal based salts (Co, Ni, and Cu) in wet chemical method. By optimising the sol concentration, withdrawal speed and annealing temperature, uniform absorber layer with solar absorptance (α) of 0.91 and emittance (ε) of 0.14 were achieved in a single layer coating with a composite oxide formation. On top of the base absorber layer, coating integrated with silica (SiO2) as an optical enhancement layer has been deposited to make the coating more selective (α: 0.95 & ε: 0.13). A thorough investigation has been done for the optical and physiochemical properties of the samples. Besides, the optimised spinel coating exhibits a low radiative loss at a high temperature of about 0.18 thermal emissivity at 500 °C and 0.90 photothermal conversion efficiency, which indicates that the spinels are a very good candidate for medium and high temperature solar selective absorbers.