More insights from the monitoring of real world PV power plants - a comparison of measured to predicted performance of PV systems

Since 2000, Fraunhofer ISE prepared yield certificates for some 400 PV systems. The institute also operates monitoring equipment at some 200 PV installations, with some of them for more than 6 years now. For an intersection of more than 30 PV systems, we have access both to the original yield certificates and to data sets of meteorological and plant performance data. On this data base, different comparisons are carried out: BL A straightforward comparison looks at predicted and observed yield, irradiation and performance ratios (PR) BL For systems with DC measurements available we compare the ""DC-PR"" and the ""AC-PR"" BL A more in-depth method is named ""weather adjusted yield certificate"". Here, observed time series of solar irradiation and ambient temperature are fed into the same prediction routines as used with the certificate calculations. In the following, all parameters measured on site may be compared to the relevant values of the prediction routine. The overall deviation in energy yield is +3.7 % with a standard deviation of 4.2 %. Most of the deviation results from higher irradiation in the recent years compared to the long term average. So the average deviation in PR for the systems is 0.7 %-points with a standard deviation of 2.5 %-points. This deviation is covered by the uncertainty estimation in the yield certificate.