Solar energy shines as nuclear and other thermal generators wilt in European heatwave

The extraordinary heat waves that swept across Europe in June and early July brought with it the highest solar power production on record, which turned out to be useful because thermal generators, and France’s nuclear fleet in particular, struggled to stay on line as temperatures hit 40°C and more.

A report by climate and energy think tank Ember says June was the highest solar electricity production month on record in the EU, with a total of 45 terawatt hours (TWh), a 22 per cent increase from June 2024 (37 TWh).

In Germany, for instance, solar delivered up to 50 GW of power during the peak heatwave days, delivering around one third of total demand needs on those days, and was supported by 14 GW of battery storage and 10 GW of pumped storage, which helped to store some solar to use when the sun went down.

This was just as well as thermal generators struggled in the heat, and demand surged, over the day and into the evening peaks by around 6 per cent in Germany, and 14 per cent in France.

In Italy, the overheating of cables is cited the likely cause of power outages in Italy on July 1, and the difficulty in cooling thermal power plants led to forced reductions in electricity generation from nuclear power plants both in France and Switzerland.

Ember says the French nuclear fleet was impacted the most, with all but one of the 18 facilities experiencing some type of capacity reduction, and one had to be shut down completely. In total 23 gigawatts (GW) of nuclear capacity was offline for one reason or another, with 7 GW of it described as “forced.”

Ember says that while the heatwaves affecting Europe are a severe challenge for governments and grid operators, they also present an opportunity for clean flexibility solutions.

This means that matching electricity consumption with generation mattered more than ever. Storage assets benefitted from price spreads, charging at low prices and discharging during expensive peak time, reducing the need for costly imported fossil fuels in the evening, and supporting the balancing of the grid.

“Heatwaves will not go away – they will only get more severe in the future,” says Pawel Czyzak, Europe program director for Ember.

“Solutions that can help mitigate their impacts, such as battery storage, interconnection, demand flexibility and dynamic tariffs, should become a key part of grid planning and power market design.

“Luckily, there is no lack of sunshine during heatwaves. The biggest opportunity is to store solar electricity, to help power air conditioning well into the evening.”

Spain and Portugal have also called for more interconnection following their dramatic blackouts in April, and Ember notes that as the heatwave swept across Europe, peaking in Madrid on a Sunday, Paris on Tuesday, Berlin and Warsaw on Wednesday – transmission lines moved electricity to where it was needed most.

Grid operators are also focusing on other projects, many of them focusing on distributed energy and grid forming investors, to boost grid resilience, and to restart the grid in the case of a blackout.

This includes the Distributed ReStart project by the UK National Energy System Operator (NESO), and testing of grid forming assets by the Belgian TSO – Elia. System services markets, like inertia or voltage control markets, are being rolled out in multiple countries, including the UK, Germany, the Netherlands.

It’s interesting to note that Europe is not the only northern grid to benefit from solar in the summer heatwaves.

In New England, in the northeast corner of the US, behind-the-meter solar alone shifted peak demand by 2 hours and almost 3 GW, avoiding a 20-year-old grid demand record, according to Grid Status.

“New England is not the first place you’d think of as a leader in solar generation, but the region’s heavy concentration of behind the meter (BTM) solar was able to meet nearly 6 GW of load over the afternoon of June 24 while utility scale solar produced only 750 MW,” it wrote.

“Even during the shifted evening peak, BTM is estimated to have reduced hourly load by over 800 MW. BTM helped keep prices under control during solar hours, shifting volatility to the evening net load peak when expensive oil generators ramped up to meet ~3.5 GW of load.”

And in Texas, the output of solar hit a record high of 28 GW at 12.40pm local time on Thursday. Less than five years ago, the record stood at just 4 GW.