Quantitative assessment of the local leakage current in PV modules for degradation prediction
Small leakage currents flow between the frame and the active cell matrix in photovoltaic (PV) modules under normal operation conditions due to the not negligible electric conductivity of the module building materials. Even if the leakage current is well below the ground-fault detection threshold, predominantly the DC part can cause significant electrochemical corrosion of cell and frame metals, potential-induced degradation (PID) of the shunting type or PID of the solar cells' surface passivation. In general, it was found that the degradation rate has a high correlation with the leakage current density which is a strong function of position in large-area modules due to the voltage drop between the frame and the cells. In this work we measured material and surface conductivities and subsequently calculated the local leakage current density distribution in large-area PV modules in order to obtain quantitative insight into the local degradation. The shares of leakage currents through individual materials are discussed and, as an example, the width of the circumferential module area threatened by electrochemical corrosion was predicted under accelerated test conditions.