The impact of lower quality water on soiling removal from photovoltaic panels

Soiling, bird droppings, and dust accumulation on the surface of photovoltaic cells, can reduce the solar energy absorption and produce power losses. In solar plants where soiling is a problem, the use of low quality water in lieu of typically used demineralized water could conserve fresh water. Soiling was studied in a group of 264 photovoltaic panels, facing due south with a tilt angle of 32°, located at the West Yard of the City of Las Vegas, Nevada. The panels were grouped into six independent sections and each section was manually washed eight times during 302 days using different cleaning methods. The results show that dust did not seem to have a great effect on the system performance, with the control group experiencing only a 1.88% reduction in mean efficiency due to dust accumulation. Washing with distilled water recovered the mean normalized system efficiency approximately 1.32%, followed by treated wastewater (0.92%), treated wastewater with surfactant (0.73%), vacuum cleaner (0.27%), and groundwater (0.24%). The dust composition analysis indicated the dust particles identified on the surface of the photovoltaic panels were the same from the ground or caused by the light vehicular traffic. Pyrolysis-GC/MS identified that the presence of organic compounds on the surface of the PV panels was related to the local suspended soil, pollen, and vaporized cooking oils. The dissolved minerals in the wastewater and in the groundwater, at this location, negatively impact the performance of the system and can be considered an inefficient cleaning method.