Numerical Evaluation About Spectral Reflection Properties of Solar Collector With Microstructure

In recent years, attention is increasingly focused on renewable energy. In order to increase the efficiency of solar thermal power generation which is one of renewable energy, it is important to improve the power generation efficiency by increasing the absorption rate of the solar energy collector while reducing the radiation loss. It is known that spectral characteristics control is possible by applying a microstructure to the surface. In this study, the effect of surface periodic microstructure on solar reflectance characteristics is evaluated. FDTD method is applied for electromagnetic field analysis. As the spectrum of solar radiation is distributed in the visible region and the near-infrared region, reflectance of uneven surface is calculated in the region of wavelength from 0.3 mm to 2.5 mm. Evaluation is performed by giving a plane wave to the dielectric with a periodic microstructure of the depth Lx, the opening length Ly, and the pitch length L, respectively. Poynting vector is used for calculating the reflectance. For the analysis of solar reflectance, calculations were made with reference to JIS K 5602: 2008. It can be seen that when the ratio of the concave portion to the convex portion is 1: 1, the solar reflectance becomes lower than in the other proportions. Also, when the depth was 0.1 mm, the reflectance was the lowest, 0.0350, which was about 31.5% of the solar reflectance of the flat plate