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Photovoltaic performance degradation due to soiling and characterization of the accumulated dust

The objective of this study was to determine the daily loss of energy output caused by dust accumulation on photovoltaic (PV) modules, to quantify the dust accumulation rate on PV panels and to determine the physicochemical properties of dust accumulated on PV panels, and their relations to soiling-induced PV performance and environmental conditions. Averaged over the one-year study period, the PV performance loss due to soiling was −0.52% per day for modules cleaned every sixth month, and −0.55% per day for modules cleaned every second month, in terms of a “cleanness index” (CI). The average dust accumulation rate (DAR) was found to be 260 ±100 mg m−2 day−1, with the winter values higher than the summer ones. The DAR was considerably correlated with dust concentration (PM10), wind speed and relative humidity. A substantial negative correlation was also found between daily ΔCI and DAR. On average, very 100 mg m−2 dust loading led to a ΔCI of −0.5%. Particle size analysis showed that 90 percent of the dust (by volume) was composed of particles less than 36 µm. The mean and median particle size (by volume) was approximately 18 and 14 µm, respectively. Chemical analysis showed that the dust mainly consisted of calcium, silicon, iron, magnesium and aluminum, and calcite, dolomite, and quartz being the dominant mineral forms in dust accumulated on PV panels.