What happens when the sun goes out?

How much impact does a solar eclipse have on the electricity grid? People had been asking this question for a couple of months before the eclipse on March 20th 2015, which overshadowed most of Europe.

It sounds like a silly question for people outside of the power industry. After all, the last eclipse in Europe happened in 1999, before ‘the birth’ of the high-penetration renewable energy era (and two years before the birth of Canadian Solar Inc.). The contribution of intermittent renewable energy sources such as solar and wind was next to none at that time. Today, Europe has 81 GW of solar capacity installed and connected to its grid. Germany accounts for 38 GW. Europe draws 3% of its total electricity from solar, while Germany draws 7%.

Indeed, there had been a 15 GW fluctuation of solar power between the points when most of the sun was obscured (about 75%) to full noontime sunshine. The low point was 4.8 GW, while the high point was 20.2 GW. This is equivalent to about 15 nuclear power stations being taken out of and put back into service within a short period of time.

However, the grid operated smoothly without a glitch. The European, in particular the German grid operators did a wonderful job. Thumbs up!

While the prophets of doom were wrong, as they usually are, there are many interesting observations and lessons.

Reuters reported that the “15 GW drop was less than operators had feared. They were able to draw on alternative power sources including coal, gas, biogas, nuclear and hydroelectric energy pumped from storage and were helped by demand reductions from industry, including four aluminum plants.”

Different countries in Europe employed different strategies. According to an article in PV magazine, Italy has the world’s highest level of PV penetration and local grid operator TERNA decided to take no chances. It turned off all of its large-scale (>100 kW) PV plants for the day. Germany and other countries, however, decided not to take such drastic precautions.

The impact of the eclipse was felt on regional electricity markets. According to Bloomberg, “power prices in Germany fluttered as the first eclipse of the emerging solar age passed and utility operators worked overtime to keep the grid supplied.” Prices for electricity in wholesale markets both surged and dipped for a short time.

One can now draw the conclusion that the grid can manage any eclipse or major weather change, even with a high penetration of distributed renewable energy components. After all, the sun does go out every night and comes back every morning. With ever enhanced big data and on-grid energy storage technology, we can enjoy a better world while feel more relaxed during the next eclipse.