Improved Model for Circumsolar Irradiance Calculation as an Extended Light Source and Spectral Implications for High-Concentration Photovoltaic Devices

With concentrator photovoltaics (CPV) technology soon to enter a phase of further development in the USA Sunbelt region, it is imperative to update the predictive tools associated with the technology. This involves modeling the Sun as an extended light source with particular attention to circumsolar irradiance. An improvement to the standard extended light source solar profile model is presented based on an improved parameterization of the circumsolar irradiance. A case study for a solar profile pertaining to a circumsolar ratio (CSR) of 0.3 shows incident direct normal irradiance collection overestimations in the standard model of 0.5%–1.5%. The model presented here mitigates these errors and corrects for a misrepresentation of CSR in the standard model. For an input CSR resolution of 0.01, the mean and standard deviation of normalized output CSR are improved from 0.937 and 0.107 to 1.000 and 0.005. Furthermore, a model extension is presented, incorporating the spectral distribution differences in the central solar and circumsolar regions. A banded spectral analysis of CSR and air mass variation effects are presented, corresponding to the subcells of the multijunction cell architecture. Significant differences are found in the trends of each subcell regarding the relationship between these variables and usable input irradiance.