Spectral modeling and spectral impacts on the performance of mc-Si and new generation CdTe photovoltaics in warm and sunny climates

Solar Energy

This paper presents an analysis of spectral impacts on mc-Si and new generation CdTe in two distinct regions of Brazil: Florianópolis-SC (27°S, 48°W) in the South, and Assu-RN (5°S, 37°W) in the Northeast. As utility-scale PV power plants are progressively being deployed in the Brazilian Northeast, the need for evaluation of the spectral effects of local blue-biased spectra on the energy yield of different PV technologies arises, as well as the need for spectral correction of field peak-power measurements done during commissioning and system performance tests. Considering the high cost of adequate spectral measurement equipment, this paper proposes a new approach for the estimation of spectral impacts without the need for in loco measurements. The proposed methodology consists of the use of satellite data acquired from NASA's Giovanni platform as inputs for the SMARTS 2.9.5 spectra model. Results for measured spectra showed that, for both locations, new generation CdTe (i.e. First Solar Series 4 and 6) has significant spectral gains: up to 10% for Assu-RN (Northeastern Brazil) and 2% for Florianópolis-SC (Southern Brazil). A seasonal variation could also be detected for the Florianópolis site, with lower spectral gains for CdTe - and higher for mc-Si - close to the Southern Hemisphere’s winter solstice, due to higher air mass values and lower precipitable water content of the atmosphere. The proposed method using Giovanni data and SMARTS spectra modeling produced very similar spectra to those measured for clear days in the field at both sites, yielding good results for the calculation of spectral factors for both mc-Si and CdTe. For days with a higher diffuse fraction the results were not as satisfactory, as expected. The proposed method was also applied to instantaneous measurements for three different times (and AM values) of the day for Florianópolis: 9:00, 12:00 and 15:00, yielding satisfactory results for IV curve spectral correction.