Enhancing the solar-to-thermal energy conversion in high vacuum flat plate solar collectors

Abstract

In solar flat plate collectors, the high vacuum insulation suppresses the convective losses increasing the collector efficiency. The solar-to-thermal energy conversion efficiency in such solar thermal collectors is mainly defined by the optical and radiation losses of the selective solar absorber. We present the full process of design, optimization, fabrication, and characterization of multilayer coatings specifically thought for working in high vacuum flat solar thermal collectors at different operating temperatures, from 100 °C to 300 °C. We discuss the relative importance of absorptance and emittance in determining the collector thermal efficiency. The robustness of the performance of the coatings related to the unpreventable errors in layer thickness during the manufacturing stage is also considered through a genetic optimisation algorithm.