SELECTIVE SOLAR ABSORBERS
KEY WORDS: selective solar absorbers, infrared reradiation, intrinsic absorbers, semiconductor-metal tandems, multilayer tandems, ceramic-metal composites, cermets, textured absorbers, photonic crystals
Efficiently capturing sunlight as heat is useful for a variety of applications, such as solar heating, solar thermal electricity generation, solar thermoelectrics, and solar thermophotovoltaics. This process is most efficient when selective solar absorbers can be used to absorb most of the solar wavelengths found at the earth's surface under standard atmospheric conditions, while suppressing infrared re-radiation induced by heating of the selective absorber. In practical terms, this generally corresponds to absorbing short wavelengths up to a certain cutoff wavelength, and reflecting everything else. There are six classes of selective solar absorbers reviewed here: intrinsic absorbers, semiconductor−metal tandems, multilayer tandems, ceramic−metal composites (known as cermets), textured absorbers, and photonic crystals. It is found that the performance of cermets is the highest of the simple structures, while photonic crystals have the most room for improvement in the future, owing to unique capabilities in terms of selectivity with respect to wavelength, angle, and polarization.
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