Optimized solar absorber coating for a new concentrating solar collector under high vacuum

A compound parabolic concentrator (CPC) inserted in a flat high vacuum envelope is a novel architecture of solar thermal collectors suitable for mid-temperature applications (200 °C - 400 °C). This novel thermal panel uses very low concentration factors and in commerce there is a lack of selective absorbing coatings properly designed for this purpose. In the present work a multilayered coating has been numerically simulated and its thicknesses have been optimized to increase the overall solar-to-thermal efficiency of the device. It consists of Cr2O3 - Cr - Cr2O3 multilayer deposited on a copper substrate and covered with an SiO2 Anti-Reflective (AR) coating. In order to effectively maximize the thermal conversion efficiency, the absorber infrared emission has been taken in the right consideration with respect to solar absorption. The comparison with the adoption of a commercial coating reveals a sensible improvement in the overall thermal efficiency, increasing the working temperature up to 400 °C.