Atmospheric aerosol effects on spectral mismatch and the resulting uncertainty in photovoltaic performance.

In the operation stage of a photovoltaic (PV) power plant, the output power often differs from the expected value. This deviation is sometimes caused by the so-called spectral mismatch, i.e. the difference between the actual solar radiation spectrum and the standard AM1.5G spectrum, under which the efficiency of a PV module is measured. Spectral mismatch appears as a hidden source of uncertainty in PV production, since for the same measured value of solar irradiance, the output power fluctuates depending on the atmospheric parameters. In this study, the magnitude of the uncertainty induced by the spectral mismatch is assessed. The study was conducted following an innovative methodology based on rigorous simulations of solar spectrum in real geometric-frames and various atmospheric conditions (with a focus on aerosols). The analysis is performed in terms of the familiar spectral factor. Furthermore, the influence of spectral mismatch on PV efficiency is evaluated. Overall findings indicate that under certain conditions spectral mismatch causes a gain or loss in PV efficiency within a rough margin of 10%. Marginal loss can be recorded even under mild conditions: small tilt angle, the Sun close to the horizon and an atmosphere moderately loaded with fine absorbing aerosol.