Corrections to anisotropic diffuse radiation model

Abstract

Solar diffuse radiation models are based on isotropic and on anisotropic models. The anisotropic models take also into account the circumsolar and horizon brightenings. Both types of models were developed for a single row. A photovoltaic field is deployed in multiple rows, therefore the second (and subsequent rows) “sees” the sky dome with a smaller angle than the first row. Obscuring part of the sky affects the diffuse incident radiation. The present article modifies the anisotropic model by three factors: (a) Sky view factor of a second row (b) Correction to circumsolar brightening, (c) Correction to horizon brightening. The modified model is demonstrated on Klucher model for diffuse radiation. The study compares the differences in the diffuse incident irradiation on rows for isotropic, anisotropic and modified anisotropic Klucher models for the first and the second row. For latitude 32°N and relative low percentage of diffuse radiation, the horizon brightening may not be taken into account in the diffuse radiation calculations as it constitutes only about 0.1%. The isotropic model resulted in 9.56% less annual diffuse incident irradiation as compared to Klucher original model for the front row. The isotropic model predicts 5.83% less annual diffuse incident irradiation compared to the modified Klucher model for the second and subsequent rows. The proposed modified anisotropic model enables to calculate the incident solar radiation on photovoltaic fields more accurately.