German PV systems are regularly generating more power than expected, according to researchers at the Fraunhofer Institute for Solar Energy Systems (ISE).
An investigation by the Freiburg-based institute has revealed that an upward trend in solar radiation levels over the past 30 years has led to 5% higher system yields than originally anticipated.
Fraunhofer said solar resources assessments and therefore PV system yield predictions had in the past been based on the assumption that radiation levels will not significantly change over time.
However, by comparing actual solar radiation in Germany with assumed levels the Fraunhofer ISE team found that since the mid-1980s a process of ‘brightening’ has been in process, with current radiation levels now 5% higher than the average between 1951 and 2010.
The effect of ‘global dimming and brightening’, a consequence of factors such as changing air pollution levels, causes solar radiation levels to increase and decrease over time.
After analysing yield predictions for PV power plants being monitored by the institute, the researchers uncovered similar differences between past yield assessments and actual radiation and yield measurements.
“Relying on average radiation values from the past 30 years causes a systematical underestimation of actual PV system yields in Germany by around 5%,” said Bjorn Muller, project leader at Fraunhofer ISE. “We expect that other regions experiencing the brightening effect are seeing similar underestimations.”
Fraunhofer ISE said that its PV quality assurance specialists had now opted to use a modified database incorporating the investigation findings for system yield predictions.
“Our yield forecasts are based on satellite data from the past decade, which enables us to determine the profitability of PV systems more effectively than before,” said Klaus Kiefer, head of the department Quality Assurance PV Modules and Systems at Fraunhofer ISE. “They provide an improved decision support, for example when buying or re-evaluating a PV power plant. Conducting further analyses when re-evaluating PV systems can also help to significantly reduce investment risks.”