Theoretical Approach to Simulate Efficient Selective Solar Absorbers With Micro or Nano Structured Arrays
Study of the solar absorber with photonic crystal or micro structures as the heat absorbing surfaces operated at a high-temperature was conducted. Numerical calculations based on rigorous coupled-wave analysis were performed to determine the absorptance of the photonic crystal surface on the absorber. The effect of nano geometry of the photonic crystal in tungsten on the selectivity of the absorber was investigated first, including period (L), aperture (A) and depth (d). A design algorithm for the photonic crystal heat absorbing surface was summarized. Based on the results, a design with combined large and small square patterns was proposed to improve the absorptance, which demonstrated the ability to broaden the absorbing band by mix-period nano patterns. Integration of an anti-reflection coating (ARC) on the photonic crystal using aluminum oxide (Al2O3) was also studied. It was shown that, under a specific thickness of ARC, the absorptance can be further improved. As considering the effect of concentration coefficient on the energy absorption efficiency, it was found that a micro structure fabricated by laser ablation on stainless steel has a conversion rate over 85% in the case using a high concentrate coefficient.