Performance Loss Rates of Different Photovoltaic Technologies After Eight Years of Operation under Warm Climate Conditions

In this paper, the performance loss rates of different technology crystalline silicon (c-Si) and thin-film photovoltaic (PV) systems were estimated and compared over their first eight years of operation at the test site of the Photovoltaic Technology Laboratory, University of Cyprus (UCY) in Nicosia, Cyprus, by applying different statistical trend analysis methods on monthly Performance Ratio, RP, time series. The statistical trend analysis methods include Linear Regression (LR), Classical Seasonal Decomposition (CSD), Holt-Winters exponential smoothing (HW) and LOcally wEighted Scatterplot Smoothing (LOESS) and were applied on monthly constructed time series of RP, calculated from the fifteen-minute average array DC power at the maximum power point, PA, of each grid-connected PV system. The comparison of the estimated performance loss rates for each technology showed that the average performance loss rate of the c-Si systems was 0.75 ± 0.17 %/year. On the other hand, the average performance loss rate for the thin-film systems was 1.95 ± 0.11 %/year for all methods, with a 95 % confidence interval. The good agreement in the results between the different methods for each system also provided evidence that the performance loss rates have started to converge to a steady value. Finally, it was demonstrated that trend extraction techniques produced similar estimates between them and with very low uncertainty, even with less than five years of outdoor exposure, whereas LR was the least robust method for all technologies, since it was greatly affected by the seasonality and outliers of the time series and needed more years of data to produce reliable estimates.