Experimentally derived models to detect onset of shunt resistance degradation in photovoltaic modules

It has been shown that a reduction in the shunt resistance can lead to solar module degradation over time, resulting ultimately in module failure. This paper reports how the effects of reduced shunt resistance on the current–voltage (I-V) characteristics of a PV cell can be used to identify degradation before it becomes critical. Five commercial polycrystalline solar cell samples had their shunt resistance artificially lowered before measuring their I-V characteristics. Analyses of the effect of lowered shunt resistance on maximum power output (P_max), short-circuit current (I_SC), open-circuit voltage (V_OC) and fill factor were conducted. Reduction in shunt resistance was correlated with the cells’ electrical parameters to determine the critical shunt resistance where degradation becomes catastrophic. Linear models were developed relating reduction in shunt resistance to the solar cell's P_max and V_OC. These relationships are proposed as strong predictors and observers of shunt resistance degradation and are suitable for implementation in online monitoring systems for operational PV modules.