Soiling losses for solar photovoltaic systems in California

• The changes in performance of 186 PV sites were quantified over the course of 2010.
• Changes in performance were compared to rain data to quantify soiling losses.
• Soiling losses averaged 0.051% per day overall.
• 26% Of the sites had losses greater than 0.1% per day.
• Sites with small tilt angles (>5°) had larger soiling losses.

Soiling is the accumulation of dust on solar panels that causes a decrease in the solar photovoltaic (PV) system’s efficiency. The changes in conversion efficiency of 186 residential and commercial PV sites were quantified during dry periods over the course of 2010 with respect to rain events observed at nearby weather stations and using satellite solar resource data. Soiling losses averaged 0.051% per day overall and 26% of the sites had losses greater than 0.1% per day. Sites with small tilt angles (<5°) had larger soiling losses while differences by region were not statistically significant.