Identification of Recoverable and Non-Recoverable Potential-Induced Degradation-Shunted Cells in Crystalline Silicon Photovoltaic Modules

Abstract

Potential-induced degradation (PID) is a severe degradation mechanism in crystalline silicon (c-Si) photovoltaic (PV) modules. In p-type c-Si PV modules, PID results in the formation of shunt paths on the front side of negatively biased cells relative to the grounded frame due to the diffusion of sodium ions (Na⁺), a phenomenon known as PID shunting (PID-s). Various methods for PID-s recovery, which involve the outward diffusion of Na⁺, have been reported. However, whereas some cells show almost complete recovery, others exhibit no recovery at all. Conducting PID-s recovery without knowing the recoverability of the cells is inefficient and wasteful; therefore, a method to identify recoverable and non-recoverable cells prior to recovery is needed. In this work, a method using current-resolved electroluminescence (EL) imaging is proposed to identify recoverable and non-recoverable cells in a PV module by evaluating their PID-s nature as ohmic or non-ohmic, which depends on the concentration of Na⁺ ions. A total of 90 cells from three different modules are subjected to PID-s degradation and recovery. The experimental results show varying degrees of PID-s loss and recovery among the tested cells. The analysis highlights that non-ohmic shunts exhibit greater recovery potential than ohmic ones, a finding further verified using dark lock-in thermography (DLIT). Furthermore, the proposed method qualitatively provides insights into the recovery potential of individual cells, establishing EL imaging as an effective tool for assessing PID-s severity and predicting recovery. This paves the way for future advancements in PID-s diagnostics and mitigation strategies within PV systems.