Early Detection of Potential Induced Degradation by Measurement of the Forward DC Resistance in Crystalline PV Cells

Potential induced degradation (PID) is still a serious threat for the photovoltaic (PV) industry and it is expected to aggravate due to the tendency to increase the operating voltage of PV systems. Therefore, a method which can detect PID at an infant stage is necessary in order to increase the reliability of PV systems and preserve their lifetime. This paper provides a pathway (proof of concept) for the early and reliable detection of PID, by using the forward dc resistance (FDCR) of a PV cell since it is a parameter, which is affected by the cell's shunt resistance (R_sh), which in turn is heavily affected by PID before any significant power loss occurs, and could act as a PID detection mechanism. The paper presents simulation results, which examine at which forward bias conditions the FDCR has to be measured for the purpose of using it as a PID detection means at an early stage (<1% power loss). The simulation examined the FDCR variation with shunt resistance, reverse dark saturation current (I₀), and ideality factor (n). Furthermore, an experiment was performed to verify the simulation results, demonstrating detection before 2% power loss occurs.