Solar eclipse could shave up to 9.7 GW from Europe's power grids — The Debate

Transmission operators prepared for a brief dip of up to 9.7 GW as the August 12 eclipse darkened European solar farms.

Transmission system operators across Europe have readied contingency measures for the solar eclipse that swept the continent on the evening of 12 August. The event is expected to cut solar output by as much as 9.7 gigawatts for a few hours.

Spain, where the moon's shadow traced a narrow band in the north, expected a drop of roughly 5 GW. Red Eléctrica said this would amount to about 13 % of peak demand on a typical August Wednesday evening. The operator used a geographic model to translate obscuration into generation loss, noting that cloud cover could shift the final figure.

The operator also warned that photovoltaic output in the Balearic and Canary islands would remain largely unaffected.

France's transmission system operator RTE projected a reduction of about 1.8 GW, while Germany's operators expected a decline near 2 GW.

The continent‑wide estimate originated with RTE and was confirmed on 7 August by the ENTSO‑E, which placed the change between 19:15 and 21:30 CEST.

ENTSO‑E identified Spain and Germany as the states facing the highest impact, given the size of their solar portfolios, and noted that solar accounted for roughly 13 % of EU electricity generation in 2025. The loss represents a notable fraction of the EU's goal to reach 45 % renewable electricity by 2030, prompting neighbours to coordinate reserves.

In the United Kingdom, the National Energy System Operator (NESO) projected a fall of between 0.7 and 1.3 GW. NESO expected the moon to block up to 95 % of sunlight over parts of Britain between 18:00 and 20:00 local time, with gas‑fired plants covering much of the shortfall. The coordinated response underscores the importance of the single European electricity market, where cross‑border flows can offset local shortfalls.

Solar photovoltaic systems generate electricity only when sunlight reaches the panels. As the moon obscures the sun, output falls rapidly, and it rises equally quickly when the eclipse ends.

Conventional power stations with large rotating turbines provide inertia that helps stabilise grid frequency during such changes; solar and wind installations do not supply the same inertia.

Spain's grid weaknesses were exposed on 28 April 2025, when the Iberian Peninsula lost power for several hours. The Spanish Government's expert committee and ENTSO‑E's final report both attributed that blackout to a voltage surge of multifactorial origin, with insufficient dynamic voltage control among the causes.

Operators have prepared for the event over several months. Measures include placing gas and coal‑fired plants on standby, activating battery storage, arranging electricity imports and suspending non‑essential maintenance work. Such pre‑emptive steps are now standard practice as solar capacity across the continent has more than doubled since 2020.

Portugal's operator Redes Energéticas Nacionais (REN) said on 10 August that additional hydroelectric or thermal reserves would have to be mobilised, partly to keep the interconnection with the Spanish system stable.

In the United Kingdom, Octopus Energy, the country's largest household supplier, advised customers to avoid running washing machines and dishwashers between 18:00 and 20:00 local time. The company offered an hour of free electricity, capped at 16 kWh, to those who reduced consumption.

The early‑evening timing of the eclipse is seen as advantageous because solar output would already be declining with the setting sun.

The partial eclipse of 20 March 2015 remains the reference case for European operators. Around 90 GW of photovoltaic capacity was then connected across European grids, and ENTSO‑E described the episode as a stress test the system passed without interruption.

A second rehearsal came with the partial eclipse of 29 March 2025, which cut solar generation across the ENTSO‑E area by about 21 GW without incident. Red Eléctrica put the Spanish share of that fall at up to 3.5 GW.

Grid operators across Europe have said electricity supply is expected to remain secure. The event is regarded as a scheduled operational test for power systems that have increased their share of solar capacity in recent years.