Transmission system operators across Europe have activated contingency measures for the total solar eclipse that crossed the continent on the evening of August 12, an event expected to temporarily reduce solar power generation by up to 9.7 gigawatts.
Spain, where the moon’s shadow crossed a narrow band of the north, anticipated a drop of around 5 GW.
Grid operator Red Eléctrica has stated this equates to roughly 13 per cent of peak demand on a typical Wednesday evening in August.
The operator built a mathematical model to calculate obscuration by geographical area and convert it into expected generation loss. It warned that cloud cover could move the final figure in either direction and said the phenomenon would have no relevant effect on photovoltaic output in the Balearic and Canary islands.
France’s transmission system operator RTE forecast a reduction of about 1.8 GW. German operators expected a decline of around 2 GW.
The continent-wide estimate originated with RTE and was confirmed on August 7 by the European Network of Transmission System Operators for Electricity (ENTSO-E), which placed the change between 7.15pm and 9.30pm CEST.
ENTSO-E identified Spain and Germany as the member states facing the highest impact, given the size of their operational solar portfolios. It put solar at about 13 per cent of EU electricity generation in 2025.
In the United Kingdom, the National Energy System Operator (NESO) has projected a fall of between 0.7 and 1.3 GW.
NESO expected the moon to block up to 95 per cent of the sun over parts of Britain between 6pm and 8pm local time, with gas-fired plants covering much of the shortfall.
Solar photovoltaic systems produce electricity only when sunlight reaches the panels. As the moon obscures the sun, output falls rapidly. When the eclipse ends, production rises equally quickly.
Conventional power stations with large rotating turbines provide inertia that helps stabilise grid frequency during such changes. Solar and wind installations do not provide the same inertia.
Spain’s grid weaknesses were exposed on April 28, 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. ENTSO-E concluded the problem lay in voltage control rather than in the type of generation involved.
Transmission system 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.
Portugal’s operator Redes Energéticas Nacionais (REN) said on August 10 that additional hydroelectric or thermal reserves would have to be mobilised, partly to hold the interconnection with the Spanish system steady.
In the United Kingdom, Octopus Energy, the country’s largest household supplier, has advised households to avoid running washing machines and dishwashers between 6pm and 8pm local time.
The company offered customers who cut consumption an hour of free electricity as a reward, capped at 16kWh.
The early-evening timing of the eclipse is viewed as advantageous because solar output would already be declining with the setting sun.
The March 20, 2015 partial eclipse 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 afterwards as a stress test the system had passed without interruption.
A second rehearsal came with the partial eclipse of March 29, 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 stated that 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.
