Accurately Measuring PV Soiling Losses With Soiling Station Employing Module Power Measurements

Monitoring of PV soiling losses has become increasingly important for both operational PV power plants and pre-construction site surveys. Therefore dedicated soiling measurement stations are now being routinely deployed at many sites. Such stations typically compare the output of a "soiled" PV device with that of a "clean" device. While many stations measure only the short-circuit current of the soiled & clean devices, using the assumption that power output is proportional to short-circuit current, for complete characterization it is often necessary to measure the actual power output in addition to the short-circuit current, especially when using crystalline silicon modules. This is essential in cases where soiling accumulates non-uniformly, such as along the edges or sides of the modules. Small amounts of non-uniform soiling may cause significant power losses that cannot be detected through measurements of short-circuit current alone. We review soiling measurement methodology using both current and power measurements, and present a case study from a pre-construction site-survey soiling station in the US Southwest region. The results illustrate examples of both uniform and non-uniform soiling, demonstrate the ability to detect non-uniform soiling and accurately measure power losses, and illustrate the measurement of site-specific soiling rates.