Angle of incidence effect on five soiled modules from five different PV technologies

Higher the angle of incidence (AOI), lower will be the photovoltaic (PV) module performance. The AOI investigation for cleaned modules of five different technologies with air/glass interface has already been reported by our research group. However, the modules that are installed in the field would invariably develop a soil layer with varying thickness depending on the site condition, rain fall and tilt angle. The soiled module will have the air/soil/glass interface rather than air/glass interface. This study investigates the AOI variations on soiled modules of five different PV technologies. It is demonstrated that AOI effect is inversely proportional to the soil density - in other words, the power or current loss between clean and soiled modules would be much higher at a higher AOI than at a lower AOI leading to excessive energy production loss of soiled modules on cloudy days, early morning hours and late afternoon hours. Also, in this study, we show that the critical angle shifts from 57° for the clean air/glass interface to 40° for the naturally developed air/soil/glass interface in Mesa, Arizona for the fall season.