Perfect grating-Mie-metamaterial based spectrally selective solar absorbers

Spectrally selective solar absorbers are widely employed in solar thermal energy systems. This work theoretically investigates thermal radiative properties of metamaterials consisting of 1-D and 2-D grating-Mie-metamaterials (tungsten nanoparticles embedded in alumina) on top of multilayered refractory materials (tungsten-silicon nitride-tungsten) as a promising selective solar absorber. The proposed metamaterial shows high absorptance from the ultraviolet to near-infrared lights, while exhibiting low emittance in the mid-infrared regime owing to Mie-resonances, surface plasmon polaritons, and metal-dielectric-metal resonance. The optical properties of designed metamaterial solar absorbers are angular independence of up to 75° and polarization insensitive. The total absorptance of 1-D and 2-D grating-Mie-metamaterials are 90.59% and 94.11%, respectively, while the total emittance are 2.89% and 3.2%, respectively. The photon-to-heat conversion efficiency is theoretically investigated under various operational temperatures and concentration factors. Thermal performance of grating-Mie-metamaterials is greatly enhanced within a one-day cycle, and the stagnation temperature under different concentration factors manifests the potential feasibility in mid and high-temperature solar thermal engineering.