Measuring soiling losses at utility-scale PV power plants

The effect of dust, dirt, and other contaminant accumulation on PV modules, commonly referred to as soiling, is an important environmental factor that causes reduced PV power plant energy generation. Accurate monitoring of soiling losses has become increasingly important, especially for utility-scale PV power plants, and soiling measurement systems are now widely deployed at First Solar power plants. In this work we show how soiling monitoring data are indicative of actual power plant performance and we outline how such data should be collected and analyzed. We study soiling levels and rates alongside PV plant performance in the desert southwest of the United States, the Arabian Peninsula, and Western Australia. We demonstrate that soiling loss measurements correlate with actual power plant performance. In addition, we address measurement methodology questions, including measurement precision, site-wide spatial non-uniformity in soiling, and the amount of rainfall required for a full recovery in soiling losses.