Solar helped Europe's grids withstand summer 2026 heatwaves — but Ember warns the real challenge comes after sundown

This surge was well-timed. Daytime electricity demand spiked sharply as air conditioning use soared: daily demand rose by as much as 28% in Italy, 23% in Hungary, 14% in France, and 13% in Spain compared to the pre-heatwave week . The solar boost helped cover that daytime load and kept grids stable through the hottest hours .

Why other power sources struggled

While solar thrived, nearly every other generation source underperformed under extreme heat and drought conditions:

• Nuclear: In France, up to 18% of nuclear capacity was impacted by low river water levels and high water temperatures needed for cooling. In Hungary and Romania, low Danube levels sharply reduced nuclear output. A Swiss reactor temporarily shut down .
• Gas and coal: UK gas plants lost 2.5 GW of capacity, and Polish coal plants lost approximately 1.3 GW .
• Hydropower: EU hydropower production hit its lowest July level in at least a decade; seven of the eight largest EU hydro producers generated below their five-year averages .

The result was a supply-constrained system facing record demand. Day-ahead electricity prices in Italy and Spain reached their highest levels since the gas crisis winter of 2022/23, driven by high post-sundown demand on a constrained grid .

"The real challenge starts after sundown"

Ember's report notes a critical limitation: while solar excels during the day, "the real challenge starts after sundown" — solar cannot directly meet the high evening demand . Once the sun sets, grids must rely on other sources — but as the heatwave showed, those sources are increasingly unreliable during extreme weather events.

Ember's recommended solutions for grid resilience

Ember identifies two primary solutions to close the evening gap and future-proof Europe's grids:

• Battery storage (primary recommendation): Ember states that "battery storage is one of the clearest ways to make Europe's power system more resilient in hotter summers." Storage can charge cheap solar power during the day and discharge it in the evening when cooling demand remains high and grids are most exposed to expensive thermal power .
• Demand-side flexibility / demand response: The report also calls for greater use of demand-side flexibility to shift or reduce consumption at critical peak times .

Ember emphasizes that "increased flexibility will be needed to future-proof grids" as extreme heat becomes more common, and recommends that governments and regulators move faster on both battery storage and demand response . As climate change drives more frequent and intense heatwaves, the summer of 2026 may be a preview of a new normal — one where solar is the backbone of daytime supply, but only storage and flexibility can keep the lights on after dark.