After months of planning and weeks of apprehension, grid operators in Europe managed to avoid blackouts and huge power fluctuations from a nearly complete solar eclipse Friday morning. Analysts say these were real risks, especially in countries with large solar installations like Germany and Italy.

Those countries passed through Friday's event without incident, but with their transmission service operators (TSOs) each taking a different course of action to keep their power systems in balance between electricity supplies and demand.

In Italy, which has the world's highest level of solar power penetration, the grid operator had already decided to reduce its risks by turning off all of its large-scale (greater than 100 kilowatts) solar plants for the day. In all, roughly 5 gigawatts of solar power was taken off the system between 7 a.m. and 2 p.m. That is roughly the equivalent of losing the power from five large nuclear power plants.

Germany, with roughly half of all European solar installations, retired only a small portion of its industrial output, tackling the problem head-on in what was billed as an important test of its fast-evolving energy transition.

It experienced a 9 GW drop in solar input—falling from 13 GW immediately before the eclipse to 4.8 GW at its lowest point. This was less than the 15 GW drop operators had feared. Nevertheless, it was still an unprecedented fall in energy, both in scale and speed. Yet one hour after it began, solar output had recovered to its starting point, indicating the resiliency with which the system had responded.

Across Europe the quick loss of roughly 17 GW was followed by an even speedier reintegration of 25 GW of solar generation. The European Network of Transmission System Operators for Electricity (ENTSO-E) had been planning for the event for several months and congratulated its TSO control rooms.

"The solar eclipse is an example of the success of European and regional cooperation organized by ENTSO-E," said Konstantin Staschus, secretary-general of 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."

'We passed this test'
But observers say such a scenario misses the point: Fluctuations of the same magnitude are on their way, but the trigger most certainly will be ordinary day-to-day weather changes, like clouds passing over the sun in country X, but not in neighboring country Y. As solar power continues to grow, rapid fluctuations won't require planetary alignment.

The issue is learning how to handle large-scale power flexibility with speed. Germany's power sector has a strong record of grid reliability, yet what will it do in the future when the country doubles or triples its current amount of solar panel installation?

At 38.5 GW of capacity, Germany has more solar photovoltaic arrays installed than any other nation. That it wants to nearly double this number in 15 years worries more than a few energy analysts.

Calculations done by the Fraunhofer Institute for Wind Energy and Energy System Technology indicate that the German power system can cope with the upcoming challenges, but only if it acts now. Many technologies designed to improve the balance between supply and demand are already available, report authors say, but they need to be developed further.

Among the recommendations are 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 the build-out of highly flexible power plants.

"It's getting a lot more difficult for us as a TSO to stabilize the grid because every year we have less conventional energy and more renewable energy which is volatile," said Ulrike Hörchens, representative for one of the four high-voltage grid firms, TenneT, which operates in the region with the highest share of PV penetration.

In 2014, TenneT intervened more than a thousand times to stabilize the grid. The number is increasing, Hörchens said, as is the length of time required to rebalance the energy flow.

For last week's solar eclipse, TenneT drew on 8 GW of reserve capacity from a combination of coal, natural gas, biogas, nuclear and hydroelectric energy drawn from storage. Normally, 4 GW is what it holds in reserve.

"We passed this test because we were very well-prepared," Hörchens said.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC., 202-628-6500