Multilayers for efficient thermal energy conversion in high vacuum flat solar thermal panels

Multilayer absorbers based on Cr2O3 and Cr, designed to improve the solar-to-thermal conversion efficiency at mid temperatures in high vacuum flat thermal panel, are fabricated via sputtering deposition on bulk copper substrates and characterized by thermal and optical analysis. The refractive index of the single layers has been measured and used to estimate absorber thermal efficiency at the operating temperatures. Multilayers have been produced via sputtering deposition on bulk copper substrates. The absorber multilayers can be 10% more efficient than the commercial alternative at 250 ?C operating temperatures, reaching 380 ?C stagnation temperature without sun concentration. The thermal stability has been checked at temperature of 400 ?C in vacuum for four hours. High vacuum flat thermal collectors, equipped with the produced selective solar absorbers can obtain unprecedented performances and can give important contribution to the energy transition from fossil fuels to renewable energy for efficient heat production. ? 2021