A perfect selective metamaterial absorber for high-temperature solar energy harvesting

Selective absorber is an important component for enhancing the solar-to-heat efficiency in high-temperature solar applications. In this paper, a selective metamaterial absorber possessing four-pointed star prisms was proposed and studied. Firstly, an optimal metamaterial absorber with perfect spectrally selective performance was obtained after optimizing the structure. It was found that the optimal absorber can achieve the high total solar absorptance of 0.958 and the low total emittance of 0.2355–0.4062, thus obtaining the high solar-to-heat efficiency of 92.31%-77.78% at 1000 suns and 1273–1673 K. Secondly, the underlying mechanisms for the good spectral selectivity of the optimal absorber were analyzed. The results showed that the high spectral absorptance in the solar spectrum owes to the impedance matching and the coupling effects of different plasmonic modes. The low spectral emittance within the mid-infrared band can be explained by the impedance mismatching. Thirdly, the effects of the geometrical parameters on the spectral selectivity of the absorber were studied, indicating that the height of the SiO₂ layer above the star and the short diagonal length of the rhomb influence little on the spectral absorptance when they are in certain ranges. However, other parameters have obvious influences on the spectral absorptance. Finally, study on the effects of the polarization angle and incident angle indicated that the optimal absorber exhibits good insensitivities to the polarization angle and the incident angle. These results indicate that the proposed perfect absorber is a promising candidate for high-temperature solar applications.