The detection and the analysis of in field early degradation of a grid connected photovoltaic system located at the Institute of Energy and Environment of the University of Sao Paulo (IEE-USP) are presented. The PV generator is composed by 260 W photovoltaic (PV) modules made of N-type monocrystalline silicon PV cells. Loss of generation capability during the second year of operation was revealed by the PV system's SCADA. Subsequent measurements showed similarities with strong ageing degradation mechanisms and Potential Induced Degradation (PID) was also detected.