The combined effects of the heatwave and drought have forced 13 French nuclear reactors offline this week, representing 20.4% of the country’s nuclear generating capacity. The shutdowns, attributed to “environmental constraints” or “external environmental factors,” mark the highest level recorded since 2015, according to an AFP analysis based on data from French state-owned utility EDF.
EDF expects output to decline at the Blayais, Bugey, Cattenom, Chooz, Golfech, Gravelines, and Saint-Alban nuclear power plants over the coming days. Current forecasts indicate that weather conditions could result in a maximum capacity loss of 12,474 MW between August 14 and September 1.
Real-time monitoring data from grid operator RTE show nuclear output at around 32 GW on the morning of Friday, August 14, compared with approximately 45 GW on a typical day in March. At the same time, solar generation has remained exceptionally strong for several weeks, accounting for up to 35% of France’s electricity generation mix.
The trend extends beyond France. A study published on August 13 by energy think tank Ember found that solar generation has been running above normal levels across several European countries during recent heatwaves.
“As demand rises and other energy sources struggle, solar is the only electricity source with output exceeding normal levels: up 17% daily in France and Hungary, and 5% in Spain and Italy,” Ember said. The study examined the heatwaves of late June and July and does not yet include the August heatwave.
France is not the only country experiencing reduced output from thermal and nuclear power plants. In the United Kingdom, five gas-fired plants have cut production. In northeastern Italy, low water levels in the Po River have threatened the operation of thermal power plants. In Hungary, the Paks nuclear power plant, which supplies nearly half of the country’s electricity, sharply reduced output in early August because of exceptionally low water levels in the Danube. Coal-fired plants in Serbia and Poland have also had to scale back operations.
Hydropower has also been affected. Seven of the European Union’s eight largest hydropower producers, accounting for 90% of the bloc’s total hydroelectric output, recorded generation below their five-year averages.
“The rise in solar power generation helped stabilize the grid at a time when other energy sources were struggling to operate normally,” said Chris Rosslowe, an Ember analyst.
The main challenge comes later in the day. During heatwaves, solar generation helps meet electricity demand while other generation sources operate at reduced capacity. After sunset, however, demand remains high, driven largely by air conditioning, while photovoltaic generation falls to zero. The grid must then rely more heavily on dispatchable sources, including gas-fired power plants.
“The challenge with solar energy begins after sunset,” Rosslowe said.
Battery storage could help address this issue by storing electricity generated during the day and releasing it in the evening, when demand remains high. This could reduce reliance on the most expensive thermal generation.
During the heatwaves in late June and early July, average daily electricity prices increased by 119% in Hungary, 44% in France, 13% in Italy, and 7% in Spain compared with the preceding weeks. According to Ember, markets recorded notable price spikes in the early evening.
“Solar power helps us during the day, but battery storage can take over in the evening. Together, they represent one of the cleanest ways to make the European electricity system more resilient during the hottest summers,” Rosslowe said.
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