One European country is offering free energy to households that power down during the eclipse

Energy suppliers and grid operators are preparing for the impact of this week’s eclipse on solar power generation.

On Wednesday 12 August, the sun will be partially blocked across much of western Europe with large swathes of Spain, and smaller segments of Portugal, Greenland and Iceland experiencing a total solar eclipse.

With solar power a major part of Europe's energy mix – accounting for approximately 13 per cent of EU electricity generation in 2025 – the roughly two-hour event could throw power generation off balance.

Solar accounts for an even larger part of Spain’s energy mix – between 21 and 22 per cent. As much of the country will experience a total eclipse, it could be uniquely affected.

• Europeans are making the most of cheap solar panels – by creating green garden fences
• A unique ninety seconds in the 21st century: Spain prepares for historic eclipse trio

Spanish grid operator Red Eléctrica de España (REE) has announced precautionary measures to counter the anticipated impact on photovoltaics (PV), which it expects to be “limited and temporary”.

The phenomenon will hit Europe in the early evening, when solar generation naturally starts to decline. Still, it is expected to reduce output on the Iberian Peninsula by up to 5 GW – about 13 per cent of the peak demand for a typical Wednesday in August – according to REE calculations.

REE says it is coordinating closely with official bodies, other European Transmission System Operators (TSOs), and national generation and distribution control centres, as well as increasing usual reserves and safety margins and continuously monitoring the situation.

Across Europe, PV output could decrease by up to 9.7 GW, according to the European Network of Transmission System Operators for Electricity (ENTSO-E).

UK households encouraged to power down for the eclipse

In the UK, major household electricity supplier Octopus Energy is taking a novel approach to the problem by incentivising customers to join an “eclipse power down”.

“When the sun goes off grid, we want you to do the same,” the campaign says. Households that use less power than normal during the eclipse will receive an hour of free energy on Sunday as a reward.

The freebie will be capped at 16kWh – “more than any regular home could use in an hour (more like keeping the lights on at a small sports stadium!)”, according to Octopus Energy. Customers must sign up to the company's rewards programme to take part.

Octopus’s offer isn’t just a gimmick: to ensure the electricity grid’s frequency stays within its safe operational range – avoiding shutdowns and blackouts – real-time power generation and consumption must be kept in delicate balance.

• Italy could be the next country to build a solar railway after Switzerland’s successful trial

By reducing energy usage at the same time renewable production dips, households could help to prevent the need for polluting fossil gas-fired power plants to switch on to fill the gap.

The company hopes its initiative will reduce strain on the grid as the eclipse could mean “a huge chunk of Britain's solar power will be knocked out – just as millions of people are getting home and electricity demand spikes”. Energy demand for cooling could be particularly high this week as Britain swelters through its fifth heatwave of the year.

However, demand is expected to dip below usual levels during the eclipse as millions of people head outside to watch the phenomenon, according to the UK’s National Energy System Operator (NESO).

The moon is expected to block up to 95 per cent of the sun over parts of the UK on Wednesday evening.

Hydro and thermal generation to provide backup in Portugal

Portugal’s grid operator Redes Energéticas Nacionais (REN) expects it will have to tap additional energy reserves to offset the loss of solar power generation caused by the eclipse.

In a statement released on Monday (10 August), the company said that “additional reserves from hydro and/or thermal generation will have to be mobilised” to rebalance supply and demand in the National Electricity System (SEN).

This will also be necessary to maintain stability in the interconnection between the Portuguese and Spanish grids.

REN anticipates a 450 MW drop in solar generation, representing around seven per cent of consumption and 45 per cent of the average solar output forecast by the National Electricity System forecast for the 6.30-8:30pm timeslot.

The country will experience an “almost total” eclipse, ranging from 92 per cent in the Algarve to 100 per cent in the municipality of Bragança. The village of Guardamil is considered the best place in Portugal to see the eclipse in full.