Enhanced spectral selectivity through the quasi-optical microcavity based on W-SiO2 cermet

Abstract

Improving the spectral selectivity of solar absorbers under certain optical concentration could boom the photothermal conversion efficiency. Here, the spectrally selective absorbing coatings based on a novel quasi-optical microcavity structure are fabricated on the mechanically polished stainless steel substrates by magnetron sputtering. The enhanced spectral selectivity via improving the solar absorptance in quasi-optical microcavity–based absorbers is ascribed to the synergistic mechanisms of cermet and traditional metal–dielectric–metal structure absorptances. The spectrally selective absorbing coatings with optimized quasi-optical microcavity structure demonstrate an excellent performance with solar absorptance of 0.957, thermal emittance of 0.044 (82 °C) and superior thermal stability at 600 °C in vacuum. The suppressing heat loss without degraded solar absorptance is due to the better crystallization and the formation of α-W in infrared reflector layer upon annealing at this temperature. The total conversion efficiency of an ideal system using this coating from solar radiation to electricity would reach around 65% at 600 °C with the focus of 1000 suns.