How Nuclear, Gas, Wind & Solar Power Are Affected by Heatwaves

Heatwaves fueled by climate change are disrupting electricity generation worldwide, reducing output from nuclear, gas, wind and solar power sources as demand surges. In June and July 2026, record temperatures above 40°C across Europe forced nuclear reactors to shut down, lowered gas plant efficiency, weakened wind speeds and strained power networks. While extreme heat affects all energy sources differently, critics often single out intermittent renewables like wind and solar while overlooking the vulnerabilities of nuclear and fossil fuel plants.

During the 2026 European heatwave, daily electricity demand in France jumped nearly 20% over two weeks as households and businesses ramped up air conditioning and refrigeration. The surge in demand, combined with reduced power generation, pushed electricity prices higher, creating additional strain on energy systems. Carbon Brief examines how key power sources respond to extreme heat and clarifies common misconceptions about their reliability during such conditions.

Nuclear power plants, especially those using river water for cooling, face significant challenges during heatwaves. In France—where nuclear accounts for about 70% of electricity generation—three of the country’s 57 reactors shut down during July 2026, with another seven reducing output, causing an almost 9% decline in nuclear power production. Similar disruptions occurred in Romania and Hungary, where low water levels on the Danube River forced nuclear reactors offline. In Switzerland, a nuclear plant was shut down due to high river temperatures.

The cooling process is central to nuclear plant operations. These facilities use fission to generate heat, producing steam that drives turbines connected to generators. Afterward, water from rivers or seas cools and condenses the steam so it can be reused. When river temperatures rise or water levels fall, cooling efficiency drops, reducing overall plant output. Michael Tadrous, a researcher at McMaster University’s DeGroote School of Business in Canada, notes that while the technical impact of heat is gradual, legal limits on water discharge temperatures often trigger shutdowns to protect aquatic ecosystems.

Henry Preston, a spokesperson for the World Nuclear Association, emphasizes that reactor shutdowns due to high river temperatures are typically regulatory responses rather than technical failures. He adds that in extreme conditions, authorities may relax these rules to prioritize energy supply and balance climate risks. However, prolonged droughts—such as the ongoing low water levels in the Danube—can have more lasting effects because river levels may not recover for days or weeks.

As of August 3, 2026, about 2.44 gigawatts (GW), or 40% of southeast Europe’s nuclear capacity, was offline due to Danube drought, according to data company Montel. In France, up to 12% of the nuclear fleet remained offline due to heat-related issues, although that figure was expected to decrease to 7% shortly thereafter. Despite these short-term disruptions, the long-term impact of heatwaves on annual nuclear generation is relatively small. A study co-authored by Tadrous found that heatwaves reduced annual nuclear output by an average of just 0.6% between 2003 and 2022, with only France in 2003 experiencing a loss exceeding 1%.

To adapt to more frequent and intense heatwaves, nuclear operators are implementing measures such as installing additional cooling towers and adjusting maintenance schedules. French utility EDF is exploring new cooling solutions for its most climate-exposed sites. Tadrous highlights that France’s river-cooled nuclear fleet lost 5.5 terawatt hours (TWh) of output during the 2003 heatwave but only 0.5 TWh in 2022—a 90% reduction—thanks to upgrades and improved operational practices.

While nuclear power’s large-scale role in some countries amplifies the consequences of heat-related outages, ongoing adaptations aim to enhance resilience and maintain energy security amid a warming climate.

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