Diagnosing Potential Induced Degradation in Crystalline Silicon Photovoltaic Modules

In this work, current-voltage (I-V) and electroluminescence (EL) characterization methods are used to diagnose shunting (PID-s) and polarization (PID-p) types of PID in crystalline silicon PV modules. A comparative analysis is carried out on the impact of PID-s and PID-p on the typical diagnostic parameters used in characterizing module degradation. The fraction of the absolute change of the I-V parameters is calculated for PID-degraded PV modules using healthy-state PV modules as references to identify PID sensitive diagnostic parameters. The I-V result for PID-s shows that early-stage degradation can be identified by reduction in IMPP and FF whereas a reduction in VMPP and VOC indicate severe degradation. For PID-p, a reduction in ISC and IMPP can be used to identify early-stage degradation. A deeper insight into the degradation behavior, the cell variability in a PV module, and the current dependency of PID-s and PID-p is achieved by evaluating the mean cell EL intensities from the EL images acquired at multiple current bias levels. From the EL images, PID-s affected PV modules show a higher level of current dependency with increase in cell luminescence mismatch at lower current bias levels as opposed to PV modules that are affected by PID-p.