Simulation of Anti-reflection Coated Carbonaceous Spectrally Selective Absorbers

Abstract

A spectrally selective solar absorber is the essential part of a solar thermal collector. The potential of three carbonaceous materials, graphite, soot and single-walled carbon nanotubes (SWCNT) as spectrally selective absorbers has been evaluated using the thin film simulation software Setfos. These carbon materials are interesting and competitive selective solar absorber candidates owing to their high absorption over the solar spectrum and good chemical stability. To further enhance the spectral selectivity of the solar absorbers, simulations with an anti-reflection (AR) layer consisting of alumina or silica were also performed. Aluminum was chosen as the substrate material. The solar absorptance and thermal emittance of simulated solar absorbers were calculated using the reflectance results from simulations. Soot and SWCNT exhibit good spectral selectivity without an added AR layer, graphite does not. The best selectivity after an added AR layer was achieved for a soot absorber coated with a thin silica layer. A solar absorptance of 0.91 and a thermal emittance of 0.03 were obtained. A graphite absorber with an alumina AR layer achieved a solar absorptance of 0.87 and a thermal emittance of 0.05 while the SWCNT absorber with an AR layer of silica, obtained an absorptance of 0.91 and an emittance of 0.07.