A simple method to estimate the degraded photovoltaic modules from the string open-circuit voltage in solar pumping systems

Four regression methods are presented to estimate the number of highly degraded solar panels per string affected by severe potential-induced degradation (PID) from the open-circuit voltage measurement of the string. Three case-study plants, initially affected by PID and evolving into additional problems, are shown. In the tenth year of operation, the plants’ energy production dropped 67.58%, 47.22% and 32.06% below the average annual production in the four first years. The plants are on the roof of agro-industrial facilities, supply power to irrigation pumping systems, and are subjected to high temperatures and humidity. The proposed method solves a heat stress health safety problem, prevents water supply failures, and estimates the size of repowering purchases. Days with very high temperatures are the best times to detect PID in the field but they represent a safety problem for the maintenance workforce in very hot areas. The method is fast and it is not necessary to reach the roof. The methods were also designed and used to estimate the number of degraded panels to be replaced, proceeding to purchase orders based on these estimates. Significant adjusted R 2 values between 0.64 and 0.82 were obtained depending on the regression method used. • String open-circuit voltage is used to estimate the number of failing modules. • Severe long-term degradation. PID as initial affection, followed by other failures. • Three cases of photovoltaic plants with high temperatures and humidity are shown. • Regression methods are proposed. Adjusted R 2 in the range of 0.64 to 0.82. • Method used to avoid heat-stress of O&M operators and very fast estimation.