Solar selective coatings for evacuated flat plate collectors: Optimisation and efficiency robustness analysis

Three CrO/Cr based multilayer coatings were designed, optimised, and sputter-deposited. The selective solar absorbers presented in this study were specifically considered for evacuated flat plate solar collectors (EFPCs) at working temperatures of 100, 200, and 300 °C. The film matrix method and genetic optimisation algorithm were used to simulate and optimise the coatings. Further, the robustness of the performance of the coatings related to the unpreventable errors in layer thickness during the manufacturing stage was incorporated as a binding parameter of the genetic algorithm. This solution allowed the optimisation to converge to the thickness package with the highest performance, thereby ensuring proper robustness for given errors in layer thickness. Thereafter, the robustness of the optimised coatings was analysed, consequently confirming an efficiency loss of less than 2% for layer thickness variation of up to ±20% from the optimal thickness value. The obtained values of solar absorptance as high as 0.97, and thermal emittance lower than 0.05 up to 300 °C, validated through measurements on the fabricated samples, are expected to provide unparalleled performances for the emerging technology of EFPCs.