Quantification and Modeling of Spectral and Angular Losses of Naturally Soiled PV Modules

Spectral and angle of incidence (AOI) losses on naturally soiled crystalline silicon photovoltaic (PV) modules have been investigated in this study. The test modules designated as "moderately soiled (3 g/m² ) " and "heavily soiled (74.6 g/m²)" showed short-circuit current ( I_sc losses of about 10% and 41%, respectively. The spectral reflectance and quantum efficiency (QE) losses were also quantitatively determined. In the wavelength range of 350-1100 nm, the average reflectance of moderately and heavily soiled modules increased (as compared with the clean surface) by 58.4% and 87.2%, respectively. In the moderately soiled module, the 26.3% (average) reduction in QE is mainly because of 23% of absorption and 5.5% of reflection in the dust. In the highly soiled module, the 75.3% (average) reduction in QE is mainly because of 62% of absorption and 31% of reflection in the dust particles. It is also seen that the typical critical AOI of 57° for cleaned PV modules decreased to 38° for the moderately soiled module and 20° for the heavily soiled module. This influence is crucial for fixed tilt modules as they experience a wide range of AOI during daily operation, and a significant fraction of energy is generated at higher AOIs.