oa Longterm Seasonal Variability of Photovoltaic Surface Soiling and Subsequent Power Loss in Doha Qatar

Dust accumulation or soiling on solar panels' and collectors' surfaces has become a well-known problem, which severely reduces the performance of solar energy conversion systems. The soiling of the solar surfaces is a complex phenomenon influenced by various site-specific environmental and weather factors, and therefore should demonstrate seasonal and weather-dependent trends. Such information of natural PV soiling would be useful not only for modeling the economic impact of surface soiling but also for properly scheduling of cleaning, which is of interest to project developers and operators. The purpose of the study is to investigate the long-term seasonal patterns of airborne dust accumulation on PV modules and soiling-induced PV performance degradation in the desert environment of Qatar. PV performance, ambient dust concentration and meteorological data were collected over the study period of 2014-2017. Results revealed that PV performance due to soiling in terms of daily change in the cleanness index (ΔCI) varied with season, which was attributed to substantial variations in environmental conditions (i.e., rainfall, wind speed, humidity, temperature, airborne dust concentration). Averaged over the four years, the daily ΔCI was − 0.43 ± 1.0% per day for modules cleaned every sixth month, and − 0.46 ± 1.05% per day for modules cleaned every second month or about 14% per month. The annual pattern shows significant seasonal variation of daily ΔCI and cumulative CI during the study period. Daily ΔCI was found to be the most severe during November ( − 0.75%) and least during June ( − 0.19%). The months correspond to the rainy season (i.e., February to April) have moderate values of ΔCI ( − 0.34%). It was observed that average daily ΔCI by month was decreased with increasing PM10 concentration and humidity and increased with that of temperature and wind speed. The intense dust storm and rainy events taking place on specific days of the month are predominantly responsible for the large month-to-month variations of PV soiling. A yearly soiling trend was also determined that could help to reduce uncertainty in energy yield prediction. Monthly dust deposition on PV modules was also determined gravimetrically, which also showed month-to-month variation following the same trend of monthly PV performance loss. In addition to the environmental factors affecting dust accumulation on PV modules, particle size distribution and chemical properties of the monthly-collected dust were investigated and compared as well.