High-temperature stable spinel nanocomposite solar selective absorber coating for concentrated solar thermal application

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 optimizing the sol concentration, withdrawal speed and annealing temperature, uniform absorber layer with solar absorptance (alpha) of 0.91 and emittance (epsilon) 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) nanoparticles added as an optical enhancement layer to make the coating more selective (alpha: 0.95 & epsilon: 0.13). A thorough characterization has been done for the optical and physiochemical properties of the samples. Besides, the optimized spinel coating exhibits a low radiative loss of about 0.18 thermal emissivity at 500 degrees C and 89.3 % photothermal conversion efficiency at 500 degrees C, which identifies that the spinels are a very good candidate for medium and high temperature solar selective absorbers.