According to Ember’s latest report, successive heatwaves across Europe in June and July drove up electricity demand as air-conditioning use surged, while simultaneously constraining nuclear, gas, coal and hydropower generation.

“During heatwaves beginning in late June, daily power demand increased by as much as 28% in Italy, 23% in Hungary, 14% in France, and 13% in Spain, compared to the week preceding heatwaves (13–19 June), when temperatures were closer to seasonal averages,” the report found.

At the same time, conventional power generation came under mounting pressure, particularly thermal and hydropower plants. Nuclear, gas and coal-fired facilities often rely on water from rivers or seas for cooling, leaving them vulnerable to extreme heat and drought.

This was particularly evident in Hungary and Romania, where exceptionally low water levels on the Danube curtailed generation at the countries’ only nuclear power plants, which account for around 40% of Hungary’s electricity generation and 15% of Romania’s.

Gas-fired generation also came under pressure during the extreme heat. In Italy, low water levels in the Po River raised concerns that nearly a third of the country’s thermal generation fleet—much of it gas-fired—could face restrictions, while gas plants in France warned of reduced availability as temperatures reached record highs.

Coal generation faced similar challenges. In Poland, critically low water levels in the Vistula reduced cooling water availability, prompting output cuts at the Kozienice and Połaniec power stations and taking roughly 1.3 GW of capacity out of the system.

While conventional generation struggled with the extreme conditions, solar moved in the opposite direction. Output during the heatwaves was 17% higher in France and Hungary and 5% higher in Spain compared with other days in June and July. EU-wide solar generation also reached record levels of 52 TWh in June and 55 TWh in July, supplying a quarter of the bloc’s electricity in both months.

Ember Senior Energy Analyst Chris Rosslowe highlighted solar’s growing role in supporting the power system during extreme heat, saying that “Solar is already doing heavy lifting during heatwaves, but the real challenge starts after sundown”.

He also stressed the importance of energy storage, saying that “storage can carry cheap electricity into the evening, when cooling demand is still high and the grid is most exposed to expensive thermal power.”