Eclipse Strips Up to 9.7GW From Europe’s Solar-Heavy Grids

According to Brussels Signal, the eclipse—which cast the moon’s shadow across parts of Spain, France, Germany, and the United Kingdom—forced grid managers to scramble conventional backup capacity to compensate for the sudden loss of renewable generation.

Spain bore the brunt of the disruption, with operator Red Eléctrica anticipating a drop of approximately 5 gigawatts as the eclipse crossed a narrow band in the north. That figure represents roughly 13 percent of peak demand on a typical Wednesday evening in August, the company confirmed.

Red Eléctrica constructed a mathematical model to calculate solar obscuration by region and translate it into expected generation loss. Officials cautioned that cloud cover could shift final numbers either way, and noted that photovoltaic systems in the Balearic and Canary islands would remain largely unaffected.

Continent-Wide Impact

France’s transmission system operator RTE projected a reduction of about 1.8 gigawatts, while German operators expected around 2 gigawatts to disappear from the grid. The Europe-wide estimate originated with RTE and was confirmed on August 7 by the European Network of Transmission System Operators for Electricity (ENTSO-E), which scheduled the disruption between 7:15 PM and 9:30 PM Central European Summer Time.

ENTSO-E identified Spain and Germany as the member states facing the highest impact, given the scale of their operational solar portfolios. The organization estimated solar accounted for approximately 13 percent of EU electricity generation in 2025.

In the United Kingdom, the National Energy System Operator (NESO) projected a fall of between 0.7 and 1.3 gigawatts. NESO expected the moon to block up to 95 percent of sunlight over parts of Britain between 6 PM and 8 PM local time, with gas-fired plants covering most of the shortfall.

The Inertia Problem

Solar photovoltaic systems generate electricity only when sunlight strikes the panels. As the moon obscures the sun, output collapses rapidly—and rebounds just as quickly when the eclipse ends.

Conventional power stations equipped with large rotating turbines provide inertia that helps stabilize grid frequency during such swings. Solar and wind installations offer no comparable inertia, leaving grids vulnerable to sudden disruptions.

Spain’s grid vulnerabilities were dramatically exposed on April 28, 2025, when the Iberian peninsula suffered a multi-hour blackout. Both the Spanish government’s expert committee and ENTSO-E’s final report attributed that failure to a voltage surge of multifactorial origin, with insufficient dynamic voltage control among the root causes. ENTSO-E concluded the problem lay in voltage control rather than the type of generation involved.

Standby Measures

Transmission system operators prepared for the eclipse over several months. Contingency measures included 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) announced on August 10 that additional hydroelectric or thermal reserves would need to be mobilized, partly to maintain stability on the interconnection with the Spanish system.

In the United Kingdom, Octopus Energy, the country’s largest household supplier, advised customers to avoid running washing machines and dishwashers between 6 PM and 8 PM local time. The company offered customers who reduced consumption an hour of free electricity as a reward, capped at 16 kilowatt-hours.

Favorable Timing

The early-evening timing of the eclipse was viewed as advantageous, since solar output would already be declining with the setting sun. The disruption therefore coincided with naturally lower generation levels.

The March 20, 2015 partial eclipse remains the reference case for European operators. Around 90 gigawatts 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 March 29, 2025, which cut solar generation across the ENTSO-E area by about 21 gigawatts without incident. Red Eléctrica estimated the Spanish share of that fall at up to 3.5 gigawatts.

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 dramatically expanded their share of solar capacity in recent years.

With information from Brussels Signal