In-Situ Maintenance-Free Measurement of Soiling-Induced Power Losses in PV Arrays

The accumulation of dust, dirt, and other contaminants, referred to as soiling, is a major contributor to energy loss in photovoltaic (PV) systems, particularly in desert environments. Soiling is primarily quantified by the soiling ratio, representing the ratio of actual PV power output to that expected under clean conditions. Although different types of soiling sensors are available, accurate soiling measurements often require comparing the maximum power output of soiled PV modules to the expected output for clean modules, particularly when soiling accumulates non-uniformly on module surfaces. In-situ module-level I-V measurement units now provide a direct means to measure the maximum power output of soiled modules within a PV array, eliminating the necessity for standalone reference modules. However, determining the anticipated power output in a clean state for modules typically involves a comparison with regularly cleaned reference modules, posing challenges for operations and maintenance. In this study, we assess an instrumentation system designed to measure actual power losses due to soiling without relying on the periodic cleaning of reference devices. In-situ I-V measurements determine the actual power output, while soilingcompensated irradiance measurements are used to determine the expected clean-state power without the need for regular maintenance. Testing is ongoing in the desert environment of Qatar. Results from the first four months of testing reveal good performance in soiling measurement compared to a control system comprising a soiled module and a regularly cleaned module whose power outputs are directly compared.