The Impact of Waters of Low Quality on Soiling Removal from Photovoltaic Panels (2020)

Soiling, bird droppings, or the accumulation of dust on the surface of photovoltaic cells, can significantly reduce the solar energy absorption and produce power losses. In solar plants where soiling is a problem, solar facilities use demineralized or distilled water for washing the panels to avoid mineral scale deposits that might interfere with solar irradiance absorption. However, in arid and dusty environments, water is normally scarce. For cleaning solar panels, the use of low quality water in lieu of the industry-standard demineralized water could conserve fresh water. The objectives of this research were as follows: evaluate the impacts of low quality water to wash solar panels on the energy output of photovoltaic systems; determine if the use of water of low quality promotes the deposition of any substances on the solar panel surface that can be detrimental to their performance; determine the chemical composition of the dust accumulated on the panels on the solar system where the research is being performed. A group of 264 photovoltaic panels, facing due south with a tilt angle of 32 degrees, located at the West Yard of the City of Las Vegas, Nevada were studied. The panels have been grouped into six independent sections and each section was washed using the following cleaning methods: distilled water, treated wastewater with surfactant (Sodium Dodecyl Sulfate), treated wastewater, groundwater, and vacuum cleaner (no water Ð dry cleaning). One group of panels was left without cleaning (control). Panel soiling cleaning was performed manually using a soft cleaning brush. Three gallons of water were used to wash each group of panels. In this study, the 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. In this study, the solar panels did not get as dirty as expected because the study site is covered with compacted soil and small rocks specifically intended to abate dust. Furthermore, the results confirmed that cleaning the solar panels with distilled water was more effective when compared with the other cleaning methods. During the cleaning schedule period (8 total), the distilled water recovered a mean normalized system efficiency of approximately 1.32%, followed by the treated wastewater (0.92%), treated wastewater with surfactant (0.73%), vacuum cleaner (0.27%), and groundwater (0.24%). In addition, the results indicated that the dust particles accumulated on the panels contained silicon (Si), oxygen (O), aluminum (Al), carbon (C), chloride (Cl), sodium (Na), potassium (K), and other elements. The dust composition analysis performed by scanning electron microscopy coupled with an energy dispersive spectrometer (SEM-EDS) and the Thermo iCAP 6300 Ð ICP-OES Spectrometer detected that the dust particles identified on the surface of the photovoltaic panels were the same from the ground or caused by the light vehicular traffic in the urban area. The anions found in the dust composition were chloride, fluoride, nitrate, sulfate, and phosphate. Pyrolysis-GC/MS identified that the presence of organic compounds on the surface of the PV panels were related to the local suspended soil, pollen, and vaporized cooking oils. It was concluded that the dissolved minerals in the wastewater and principally in the groundwater negatively impacted the performance of the system (power output). Inadequate or inefficient cleaning methods, such as the use of groundwater to clean PV panels, can end up consuming more time and increasing costs. Evaluation of cost benefits regarding washing solar panels revealed that even when the electricity costs $0.1/kWh, it is not cost effective to wash the panels paying $1 per module. To be worthwhile either the washing cost would have to be lower or price of electricity would have to be higher.