Modeling the Electrical Mismatch Caused by Potential Induced Degradation in Crystalline Silicon Photovoltaic Modules and Strings

Potential induced degradation (PID) is known to cause, depending on its mechanism, degradation in the current and/or voltage of a solar cell and affect photovoltaic (PV) modules within a PV string non-uniformly. The purpose of this work is to model and estimate the additional power loss that occurs due to current and/or voltage mismatch in the system, caused by polarization and shunting type of PID. The impact of PID on the current-voltage (IV) characteristics is modeled for a PV array consisting of eight parallelly connected strings with 22 serially connected 60-cell PV modules using PySpice where each solar cell in the PV array is represented by a two-diode equivalent circuit model. The degradation is introduced by adjusting the input parameters of the model to values that are reported in literature. To generate realistic I-V curves, the model considers variability in solar cell performance within a module and string due to non-uniform degradation. The power mismatch loss is calculated for twelve different degradation scenarios to assess the long-term performance of the degraded PV arrays. The PLOSS of the PV array affected with PID-p is ~5.25 % and the ML is 0.72 %. The PV array with PID-s has a PLOSS of ~ 10 % and a ML of 2.35 % at the most degraded stage.