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.

本研究针对以光子晶体（photonic crystal）或微结构作为吸热表面的高温太阳能吸收器展开。研究采用严格耦合波分析（rigorous coupled-wave analysis）开展数值计算，以获取该吸收器光子晶体表面的吸光度。首先探究了钨基光子晶体的纳米几何结构对吸收器选择性的影响，涉及周期（L）、孔径（A）与深度（d）三个参数。本研究总结出一套光子晶体吸热表面的设计算法。基于研究结果，提出了一种结合大小方形图案的设计方案以提升吸光度，该方案证实了混合周期纳米结构可拓宽吸收波段。此外还研究了采用氧化铝（Al₂O₃）在光子晶体表面制备抗反射涂层（anti-reflection coating, ARC）的集成方案。研究表明，在抗反射涂层厚度适配的条件下，吸光度可得到进一步提升。在考量聚光系数对能量吸收效率的影响时发现，采用激光烧蚀工艺在不锈钢表面制备的微结构，在高聚光系数工况下的能量转换率可达85%以上。