European Heatwaves Boost Solar Output but Highlight Evening Power Gaps

Analysis by the energy think-tank Ember shows that during the late-June and early-July heatwaves, daily solar generation rose by as much as 17 % in France and Hungary, 5 % in Spain, and remained unchanged in Italy compared with other June-July days. The same period saw electricity demand climb sharply—up to 28 % in Italy, 23 % in Hungary, 14 % in France and 13 % in Spain—as households ran air-conditioning and fans to cope with soaring temperatures. Ember notes that solar was the only major power source that performed “better than usual” while demand surged.

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The heatwave-driven demand spike translated into sharp price increases. Average daily electricity prices were 119 % higher in Hungary, 44 % higher in France, 13 % higher in Italy and 7 % higher in Spain than on comparable pre-heatwave days. Senior energy analyst Chris Rosslowe explains that the grid remains most exposed in the evening, when cooling demand stays high but solar output falls.

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Concurrent drought conditions limited alternative generation. Low Danube water levels forced Hungary to curtail nuclear output, while hydropower in the Alpine region approached an “all-time low.” In Poland, critically low Vistula River levels compelled a reduction in coal-plant output. These constraints amplified reliance on solar during daylight hours.

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Rosslowe argues that pairing solar with battery storage is essential for resilience. He says that storage can capture excess daytime solar generation and release it when evening demand peaks, reducing dependence on expensive gas-fired power.

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• “While solar saves the day, battery storage can save the evening,” — Chris Rosslowe, senior energy analyst

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