Dirt and particles can accumulate on the PV module’s front glass over time. Depending on the environmental conditions, PV plants need different cleaning frequencies. Soiling on the module surface can be so thick that the power loss is significant, as found in this study. Although these sites experience a frequent rainfall throughout the year, the PV modules can still be significantly soiled due to the high amount of dirt and particles in the air. In addition, an inefficient cleaning methodology contributes to concentrate dirt in some areas of the module surface leading to the appearance of hot spots and cell string inactivity.