A comprehensive study on early detection of PID-affected photovoltaic modules based on PID-recovery experiments

Potential-induced degradation (PID) is a serious disaster for photovoltaic (PV) power plants. However, this problem has never been completely solved, especially in the early stage with high recoverability. In this paper, for the first time, it is found that the leakage current and reverse current of PID-affected PV modules change in a linked manner with the progression of PID. In order to explain this phenomenon, a fine model was first built to analyze leakage current density flowing through PV modules. Then, the impedance spectra of ethylene-vinyl acetate for the PID-affected and PID-free modules were measured by impedance spectroscopy. The result indicates that there are no significant differences in leakage current for PID-affected and PID-free modules. Finally, a PID-recovery experiment was carried out. The changing trends of leakage current and reverse current for PID-affected and PID-free modules were investigated. An important finding is that, for PID-affected modules, there exists the same varying trends for leakage current density and reverse current density. However, for PID-free modules, there is no identical varying trend for leakage current density and reverse current density. This reveals that the possible degradation mechanism leading to cell performance loss in PID-affected modules originates from sodium-decorated stacking faults formed within the pn junction under high system voltage. The obtained results give us a hint that the varying trends for leakage current density and reverse current density could be considered as an accurate indication for detecting PID at an early stage.