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

Abstract

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 (Rsh), 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.