Evaluation of the Self-Cleaning Effect on the Performance of PV Plants

Seasonal rain can clean PV panels from dirt and droppings that may have accumulated over time. Therefore, PV installations in regions where rainfall is frequent do not necessarily need mechanical cleaning in order to optimize the financial yield of the PV system. In the present work, the effect of rain events on the performance of several PV plants in Switzerland is evaluated. Collected energy yield data is analyzed and used to calculate the performance ratio (PR) of the investigated PV systems. The PR is calculated before and after various precipitation events. The self-cleaning mechanism is correlated to the intensity of precipitation events. It has been shown that light precipitation can accelerate the soiling of PV modules, while heavy precipitation cleans the modules.. In this paper, a threshold for effective rainfall is calculated and the frequency of such events in the investigated locations is given. It could be shown that for the systems under investigation, precipitation events until 15 mm per day increase soiling, whereas precipitation events above 15 mm clean the modules. However, the uncertainty of these values is big.