Partial solar eclipse in Jena, Germany 2011. By Spellsinger (Own work) via Wikimedia Commons.
17 Mar 2015 | Sören Amelang

Solar eclipse to stress test German Energiewende

UPDATE -- While millions of Europeans will look skyward for a glimpse of a rare solar eclipse on March 20, technicians at German power grid operator TenneT will be glued to their controls. When the moon covers parts of the sun, the output of all solar panels in Germany will simultaneously dip – if skies are clear, volatility could be equivalent to switching off and on 20 large power stations. This is why TenneT calls the astronomical event “an extreme challenge” that will “stress test the power system.” The eclipse will provide valuable lessons for the future because the rise in renewables will make fluctuations of this magnitude regular events as soon as 2030.

The solar eclipse poses a particularly severe threat to the German power system because no other European country can remotely match its solar capacity of 39 gigawatts. At full capacity, solar panels can supply around half the country’s peak electricity demand and most cannot be switched off remotely.

In the late morning of March 20, the moon will conceal up to 80 percent of the sun in Germany and solar panels’ output will shrink and then rise much more quickly than at a regular sunset or sunrise. “If the weather is very sunny, feed-in from photovoltaic systems will drop by around 12 gigawatts in the first half of the eclipse and then rise by around 19 gigawatts in the second half of the eclipse, when the sun will be higher in the sky around midday,” explain Germany’s four grid operators in a statement. The challenge is to offset this rapid fluctuation with flexible power generation and demand – for example with gas-fired power plants or pumped storage power stations that can supply or use a lot of electricity at a moment’s notice.


This video from the University of Applied Sciences in Berlin shows how solar power generation will fluctuate in Germany if the eclipse coincides with a sunny day.

The Federal Office of Civil Protection and Disaster Assistance warned it could not rule out blackouts with possibly far-reaching consequences for households on the day of the eclipse, from stopped alarm clocks to stuck elevators. The government agency recommends precautionary measures: “These include preparing emergency supplies, as well as a battery-powered radio and an electric torch.” For anyone unsure of what to do, the office even refers people to its brochure, “How to be Prepared for an Emergency.” 

Grid operators have spent close to a year preparing for the event. For example, they have been coordinating possible responses with other European countries and the Federal Network Agency for Electricity. They have banned holidays for some employees and will do double shifts on the big day. Thanks to this thorough effort, most operators and the government are pretty confident the day will pass without major breakdowns. “The situation is controllable,” a spokesman for the network agency told the Clean Energy Wire. “We don’t have to expect blackouts because grid stability can be ensured with adequate preparation.” But even the confident Network Agency is curious about how the stress test will play out. “It will be a fascinating day,” he said.

The main challenge is that even though the eclipse itself can be predicted with absolute precision, its exact effects on Germany’s power system cannot. Much depends on the weather: In contrast to those gearing up for a rare natural spectacle with protective goggles, grid operators are hoping for a cloudy day. In that case, solar panels won’t produce much electricity anyway and the eclipse would only have a minor impact on the grid.

Additionally, it will only become clear shortly before how much electricity wind turbines will generate during the eclipse. It’s also unclear how the general public will behave. Will everyone switch on their lights when the moon partly blocks the sun’s light, putting additional stress on the system?

Perhaps the lessons learned will help to master future eclipses with more confidence. At least there is still enough time to prepare. The next similar event is expected on June 11 in 2048. By that date, renewables will generate 80 percent of Germany’s electricity according to government plans, compared with around 28 percent today. This steady increase of renewable power in Germany will make large fluctuations comparable to those of the eclipse on Friday commonplace much earlier. According to a study commissioned by energy think tank Agora Energiewende*, the eclipse will provide a taste of 2030.

“If today’s comparatively inflexible power system copes with the solar eclipse, then 2030’s power system will handle similar situations effortlessly,” says Agora head Patrick Graichen. “Because of the Energiewende, the power system must become more flexible anyway.” Many technologies to improve the balance between supply and demand are already available, but they need to be developed further, according to the study by Fraunhofer IWES. A secure future power system will require additional integration with other European power systems, domestic grid extensions, better integration of large consumers into the power market, the development of flexible storage technologies, and highly flexible power plants, argue the study's authors.

See the Fraunhofer study in German here.

*Like the Clean Energy Wire, Agora Energiewende is a project funded by Stiftung Mercator and the European Climate Foundation.

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