Copper Indium Gallium Diselenide (CIGS) shows a degradation due to a voltage between the solar cell and the ground potential, known from other solar cell technologies as well. This degradation is named potential induced degradation (PID). At the cell level, PID has been studied in laboratory experiments and can be traced back to sodium diffusion, which is accelerated by the mentioned voltage against ground potential. The applied potential will lead to a leakage current, which can serve as an indicator for PID. The question whether PID of CIGS thin film solar modules also occurs in real PV power plants inevitably arises. To solve this question the degradation behaviour will be analysed by accelerated aging tests. Furthermore, the influence of different leakage current pathways will be shown. The results of this study serve as a basis for modelling the lifetime of CIGS thin-film solar modules taking degradation due to PID into account.