In this paper, the results of a degradation analysis over a sample of 17 PV systems with monocrystalline, polycrystalline and EFG modules are presented. The systems have a total installed power of 10 MWp and have been in operation for more than 5 years each. By analyzing long-term time series and extracting data points at similar environmental conditions rates of change for Performance Ratio and solar generator efficiency were derived. As drifts of irradiance sensors can considerably affect the results of a long-term analysis, we performed sensor recalibrations for all systems in the study. Results of the recalibration of 85 sensors in total are presented. Sources of uncertainty are discussed. The findings are that it is not necessary to account for a general dropping module efficiency for mono and polycrystallinesilicon.
