This paper deals with the definition of test procedures specifically conceived to highlight the degradation of PhotoVoltaic (PV) modules and identify the mechanisms that are mainly responsible for this degradation. Several environmental and mechanical test cycles are applied to each set of PV modules under test and suitable characterization procedures are performed at the end of each test cycle, thus providing information related to the degradation rate. The applied stimuli are designed according to the measurements available for outdoor exposed PV plants and the laboratory results will be compared to the degradation estimated for these plants.