Brighter skies leading to 5% PV yield increases

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Leading German solar research body Fraunhofer ISE announced today that higher-than-expected irradiation levels are leading to PV arrays in Germany exceeding forecasts by 5%. The researchers have concluded that this is due to irradiation levels in Germany themselves being 5% higher in the last decade, than in previous ones.

“Relying on average radiation values from the past 30 years causes a systematical underestimation of actual PV system yields in Germany by around five percent,” said Björn Müller, project leader at Fraunhofer ISE. “We expect that other regions experiencing the brightening effect are seeing similar underestimations.”

Fraunhofer ISE quality assurance services have adapted its forecasting tools to reflect this change.

“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 Quality Assurance PV Modules and Systems at Fraunhofer ISE.

The German commercial research body collaborated with meteorologists from ETG Zurich and the German National Meteorological Service (DWD) to confirm its observation and alter forecast models accordingly. Radiation methods from 1951 to 2010 from a number of locations in Germany was analyzed, with results indicating that irradiation levels today are around 5% higher than they were in this period. The effect has been occurring since the mid-1980s, the Fraunhofer team conclude.

In a virtuous circle of sorts, the researchers conclude that the trend is attributable to factors such as a decrease in air pollution or reductions in the concentration of aerosols in the atmosphere. The Fraunhofer ISE team use the term “global brightening” to describe the effect.

Reacting to the news, BNEF’s Seb Henbest commented on Twitter: “Cleaner air = more incident solar radiation reaching the surface = higher yield from solar PV (+5%).”

The Fraunhofer team monitored output from PV arrays located at its base in Germany’s southwest to confirm the effect of the “brightening” on solar output. The researchers found that accordingly, forecasts relying on data from the past 30 years were also off by 5%.

Fraunhofer ISE is now using satellite data from the last “ten full years” rather than the 30-year data to make its solar forecasts.

“They [the new yield forecasts] provide an improved decision support, for example when buying or reevaluating a PV power plant,” said Fraunhofer’s Kiefer. “Conducting further analyses when reevaluating PV systems can also help to reduce investment risks significantly.”

The researchers will present their findings at next weeks EU PVSEC trade show and conference in Amsterdam.