Modification of circumsolar radiation for anisotropic diffuse radiation models: Photovoltaic collectors on sloped planes

Photovoltaic fields are deployed in multiple collector rows on horizontal and on sloped planes, therefore the second (and subsequent rows) sees the sky dome with a smaller angle than the first (front) row. A relatively large number of diffuse radiation models have been proposed based on isotropic and anisotropic models. The anisotropic models include circumsolar radiation and horizon brightening, and refer to single rows of collectors. The present article modifies the anisotropic models by two factors: (a) Sky view factor of a second row, depending on the collector and field parameters, (b) Modification to circumsolar brightening. The present article develops the modification to include collector rows deployed on sloped planes facing the south and north. The modifications are demonstrated on Klucher model for diffuse radiation. The study points out the differences in the diffuse incident irradiation on the front and on the second collector row for isotropic and anisotropic modified (Klucher) models. The study shows that for latitude 32° N and relative low percentage of diffuse radiation, the isotropic model resulted in 10.7% less annual diffuse incident irradiation as compared to Klucher original model for the front collector
row. The isotropic model predicts 5.8% less annual diffuse incident irradiation compared to the proposed modified Klucher model for the second and subsequent collector rows.