Several months in advance of the March 20, 2015, total solar eclipse, the European Network of Transmission System Operators for Electricity (ENTSO-E) began evaluating the risk to Europe’s power grid. Because the European power grid incorporates significant solar generation, the risk of negative impact during a solar eclipse needed to be carefully mitigated in order to maintain the security of power supplies throughout the event.
Although solar eclipses are not typically associated with negative impacts to the earth, risks of negative impact on the power supply have risen with the increase of installed PV energy generation. Initiating a Solar Eclipse Impact Analysis, ENTSO-E concluded that operational coordination among Europe’s TSOs would be critical during the eclipse. Continuous coordination between control rooms across Europe was planned well in advance of the event, to ensure successful deployment of scheduled remedial actions.
European TSOs Team Up for the Challenge
It had been anticipated that, under clear skies, around 35,000 MW of solar energy would decrease from Europe’s electrical system over the course of just over two hours. Occurring in the busy morning hours of a typical workweek, this power loss would be the same as losing nearly 80 medium size conventional energy generation units. Managing such a monumental event offered an unprecedented challenge to European Transmission System Operators (TSOs).
Fortunately, the challenge was met with excellent planning. A statement released by ENTSO-E shortly after the eclipse read, “European citizens and businesses could rely on a secure supply of electricity this morning. The fast variations in solar generation and difficult to anticipate impact on demand were successfully managed by Transmission System Operators (TSO) thanks to meticulous preparation, and strong regional and European cooperation.”
Balancing the European power system is performed in milliseconds. Pierre Bornard, Deputy CEO of the French TSO RTE and Chairman of the Board of the ENTSO-E said, “Europeans are used to just push a button to switch the light on. They tend to forget all the highly technical and complex systems and tasks needed to maintain a constant balance between generation and demand on an interconnected Power System.”
Reinforcing their already tight coordination with doubled staffing, TSOs had to balance the unusually speedy loss of solar energy from the power grid as shadow overtook the sun, beginning at 9:00 am Brussels time. The swift loss of around 17 GW was then followed by an even speedier (three times the normal maximum, according to Reuters) reintegration of 25 GW solar generation as the shadow completed its course. The eclipse event concluded at 12:00 pm Brussels time, but the TSOs were still precision-balancing the fluctuating power on the wires.
Energy Forecasting for the “Worst Case Scenario”
Taking into account the “worst case scenario” — that the eclipse would take place on a sunny day — motivated the TSOs to forecast the impact on solar energy generation as precisely as possible. And, in fact, the sun was shining brightly in Southern Germany and Northern Italy where photovoltaic concentration is higher than anywhere else in the ENTSO-E area. In Berlin, pv magazine reported that its “intrepid – and dare we say, just a little bit too excited – editorial team was out on the street, conducting ad-hoc science experiments, live-blogging, and trying to ignore the funny looks of passers-by as they enjoyed a beautiful 85% eclipse.”
With the largest solar energy generation capacity in the world, Germany is Europe’s economic powerhouse. Now at the epicenter of the solar eclipse impact zone, Germany’s 38.2 GW of solar capacity was literally “on the line.” In Germany, reported ENTSO-E, “solar generation this morning was even exceeding the normal seasonal level, as a result of very sunny weather. But despite this challenge, German TSOs managed very smoothly the high and fast variations of 39 GW of installed solar generation relying on power reserves at national and regional level.”
According to a Reuters report, German TSOs wanted to prove their systems were able to meet the challenge, and were relieved at the lower-than-expected initial drop of 15 GW. Drawing on alternative power sources, such as coal, natural gas, biogas, nuclear, and hydroelectric power drawn from storage, they were also relieved of some industrial demand, including from four aluminium plants.
The most critical moment, according to ENTSO-E, was between 10:45 and 11:15 am, when the supply of solar energy generation started rising again. Coming back in at three times the speed of normal maximum, there was concern all around for possible power disruptions.
Power Grid Security Activities Across Europe
In Italy, power grid operator Terna had decided ahead to reduce its risks by turning off all of its large-scale (>100 kW) PV plants for the day in order to prevent severe energy fluctuations on the grid. Approximately 5 GW PV were taken off the system between 7:00 am and 2:00 pm. After 2:00 pm, Italian TSOs began reconnecting the PV, restoring full capacity.
In many European countries, preparations were made and announced ahead of the solar eclipse. Reuters reported that in the UK, “the National Grid said solar output would be reduced by 850 megawatts but there would be a small drop in demand as people were expected to go outside to see the phenomenon.” Regarding Spain, energy grid firm Red Electrica told Reuters that “reserve levels had been raised and big consumers could have been disconnected.” Italy’s Terna “decided to switch off 30 percent of solar capacity and make it up from other sources.” Norwegian, Danish, and Czech energy grid sources told Reuters that the power supply was kept under control.
As for the view, reported pv magazine, “In the U.K., where the very fact that the sun can be seen at all is usually cause for celebration – particularly on a Friday – observers in England’s southwest and Scotland’s far north were treated to the best spectacles, while those in London were left unimpressed by the low, grey cloud that hovered over the city, blocking out the eclipse entirely.”
“Good Preparations Paid Off”
Ulrike Hoerchens, spokeswoman for TenneT, a high-voltage energy grid firm, told Reuters, “Good preparations paid off, we were able to handle all swings in production.” TenneT operates in the region with the highest share of photovoltaic units.
Congratulating all the staff in the TSO control rooms, ENTSO-E Chairman Pierre Bornard was pleased with their success in managing the unprecedented event. He appreciated the “very important role played by the TSOs’ Regional Security Coordination Initiatives (RSCIs) in keeping the energy system stable.” ENTSO-E noted that RSCIs were set up by European TSOs, “deciding for coordinated answers to more variable power sources as well as more European energy market integration. In the case of the eclipse, the planning information on cross border electricity flows provided by RSCIs complemented the TSOs’ real time operation and allowed for a better coordination of actions.” Bornard stated, “Our management of the challenging solar eclipse is an illustration that the TSOs’ regional and bottom-up approach to an efficient coordination is the right way to go.”
Konstantin Staschus, Secretary-General of ENTSO-E, said, “The solar eclipse is an example of the success of European and regional cooperation organised by ENTSO-E.” Staschus added, “Many other aspects of European electricity market integration are solved in the network codes delivered by ENTSO-E to regulators and the European Commission. It is urgent that we see a swift adoption of the network codes. With the network codes in place, when the next solar eclipse takes place in 2026, the management of such challenging event will be much easier.”
While taking every necessary measure to mitigate energy security risks, ENTSO-E points out that the March 20, 2015, solar eclipse illustrated the current energy challenge perfectly: “Maintaining system security with more and more volatile and dispersed generation is becoming increasingly challenging.” Nevertheless, ENTSO-E points out that all of its work products “are designed to ensure that the transition towards a decarbonised economy is as smooth, efficient, secure and cost effective as possible.”
(Also appeared on CleanTechnica.com)