Solar generation increased by as much as 17% during heatwave days across several European countries in June and July, helping power systems cope with sharp increases in electricity demand, according to new analysis by Ember.

The analysis found that daily electricity demand rose by up to 28% during the heatwaves compared with pre-heatwave days. Italy recorded the largest increase at 28%, followed by Hungary at 23%, France at 14% and Spain at 13%.

At the same time, solar was the only major power source to perform better than usual during the heatwaves. Average daily solar generation was 17% higher in both France and Hungary than on other days in June and July. In Spain, solar output increased by 5%, while in Italy it remained at a similar level.

“The surge in solar output helped stabilise grids at a time when other power sources were struggling to deliver,” said Chris Rosslowe, senior energy analyst at Ember.

Heatwaves put pressure on conventional generation

Extreme heat and drought affected several conventional power sources across Europe, adding pressure to electricity systems as demand increased.

Nuclear generation was curtailed in France, Hungary, Romania and Switzerland during the heatwaves. In the UK, five gas plants cut 2.5 GW during June's period of high temperatures, while low water levels on Italy's Po River threatened gas generation.

Drought also affected coal-fired generation. Cooling constraints forced coal plants in Poland and Serbia to reduce their output.

Hydropower faced similar challenges. In July, seven of the EU's eight largest hydropower producers recorded output below their five-year averages. Together, these countries account for more than 90% of EU hydropower generation.

The combination of higher electricity demand and reduced availability from several conventional and hydroelectric sources increased pressure on European power systems during the heatwaves.

Electricity prices climbed as temperatures rose

The strain on power systems was also reflected in electricity prices. During the late-June and early-July heatwaves, average daily power prices were 119% higher in Hungary, 44% higher in France, 13% higher in Italy and 7% higher in Spain compared with comparable days in the preceding weeks.

In several markets, prices also spiked during the early evening, when temperatures remained high and cooling demand continued to put pressure on the grid.

Ember's analysis highlights a key limitation of solar generation during extreme heat events: while solar production can increase during the daytime, it falls as the sun sets, just as electricity demand for cooling can remain elevated.

“Solar is already doing heavy lifting during heatwaves, but the real challenge starts after sundown,” Rosslowe said. “In the evening, when cooling demand is still high, the grid is most exposed to expensive gas-fired power.”

Ember points to batteries as the next piece of the puzzle

According to Ember, the combination of solar generation and battery storage could help address this evening pressure. Solar can provide additional electricity during the hottest part of the day, while batteries can store part of that generation and discharge it when demand remains high after sunset.

“While solar saves the day, battery storage can save the evening,” Rosslowe said. “Together, they are one of the clearest ways to make Europe’s power system more resilient in hotter summers.”

The findings suggest that the role of solar could become increasingly important as heatwaves raise electricity demand, while the performance of nuclear, fossil fuel and hydropower generation can be affected by extreme heat and drought. At the same time, greater deployment of battery storage could help extend the contribution of solar into the evening hours, when European grids remain particularly exposed to high prices and tight supply.