Power Loss Due to Photovoltaic Module Soiling in a California Utility Scale System

Photovoltaic module soiling is recognized as a significant issue in reducing the performance of photovoltaic installations around the world. Areas that receive regular rainfall are less affected as the panels are regularly rinsed to reduce the amount of built up soiling. A 4.5 MWac installation in San Luis Obispo, California is studied to determine the power loss experienced due to soiling. San Luis Obispo has an average rainfall of 19.02 inches per year with almost all precipitation occurring between Oct 1 - Feb 28. The months of May, June, July August and September rarely receive any precipitation which means that soiling builds up during these months without any natural periodic rinsing from rain. This results in power loss due to soiling that is far more significant in the summer months than in many other areas. The study of power losses from the particular installation allow for decisions to be made on whether and when the modules in the installation should be cost effectively cleaned.