Spectral mismatch impact on PV performance: A case study for Romania

The efficiency of a commercial photovoltaic (PV) module is evaluated at manufacturing level under the standard test conditions (STC), which assume 1000 W/m2 incident solar irradiance with a spectral distribution AM1.5G. The PV modules operate naturally in outdoor conditions, where the spectrum of the incident solar radiation only very rarely matches the AM1.5G solar spectrum. In outdoor conditions, the efficiency of a PV module may significantly differ from the standard value evaluated at STC, thus becoming a hidden source of uncertainty in the evaluation of PV plants performance. In this work the influence of spectral solar irradiance distribution on the PV module efficiency is assessed in terms of spectral factor (SF). For a specific PV module, SF quantifies the power gain or loss due to the spectral differences from STC. The theory is illustrated with data from four cities of Romania. The actual solar spectrum is estimated with the Leckner's model, based on atmospheric parameters retrieved from the Aerosol Robotic Network-AERONET. As far as we know, this is probably the first study focused on the assessment of spectral mismatch impact on PV systems operating in Romanian locations.