Factcheck: How nuclear, gas, wind and solar power are affected during heatwaves

In late June 2026, extreme heatwaves swept across much of Europe, pushing temperatures above 40°C in several regions. The unprecedented weather conditions placed immense strain on energy systems, affecting multiple sources of electricity generation. Nuclear reactors were forced to reduce output, gas-fired power plants saw declining efficiency, wind turbines operated at lower capacities, and solar panels faced diminished performance. Meanwhile, electricity demand surged as households and businesses relied heavily on air conditioning and refrigeration. In France, daily electricity consumption climbed nearly 20% during a two-week heatwave, contributing to higher power prices and increased stress on the grid. The heatwave began in early June 2026, with temperatures peaking in mid-July. As the mercury climbed, so did the challenges for power producers. French nuclear reactors, which supply approximately 70% of the country's electricity, were among the hardest hit. During the peak of the heatwave, three of France’s 57 operational reactors were temporarily shut down, while another seven experienced reduced output. This led to an estimated 9% drop in national power generation. Similar issues emerged in other European nations, including Romania, Hungary, Serbia, and Switzerland, where nuclear facilities reliant on river water for cooling faced operational constraints due to elevated water temperatures or low flow rates. Nuclear power plants operate by using fission to produce heat, which generates steam to drive turbines and produce electricity. Cooling systems play a crucial role in maintaining safe operating conditions. Most nuclear reactors draw water from rivers or the ocean to condense steam after it passes through the turbine. When water temperatures rise, the effectiveness of this cooling process diminishes, reducing the plant’s ability to maintain optimal thermal efficiency. In addition, during periods of drought or extremely high temperatures, the availability of sufficient cooling water can become limited, forcing operators to curtail production or halt operations entirely. According to Michael Tadrous, a researcher at McMaster University’s DeGroote School of Business, the impact of heatwaves on nuclear power is real but often overstated in public discourse. He explained that even a dramatic 15°C increase in cooling water temperature would result in only a modest reduction, around 6%, in a large reactor’s output. Furthermore, he noted that the effects of heat are typically gradual rather than abrupt. Tadrous emphasized that regulatory compliance plays a significant role in determining whether a reactor must be shut down. Many plants are required to ensure that the water returned to rivers or lakes does not exceed certain temperature thresholds to protect aquatic ecosystems. Industry representatives have echoed this perspective. Henry Preston, a spokesperson for the World Nuclear Association, stated that reactor shutdowns triggered by high river temperatures are usually a result of regulatory requirements aimed at preserving environmental health. He added that in cases of extreme necessity, such as during severe heatwaves, authorities may temporarily suspend these rules to prioritize energy security. However, such exceptions are rare and require careful evaluation to balance ecological concerns with societal needs. The broader implications of these events highlight the growing vulnerability of energy infrastructure to climate-related disruptions. As heatwaves become more frequent and intense, the challenge of ensuring reliable power supply will intensify. While renewable sources like wind and solar face immediate limitations under extreme weather, traditional technologies such as nuclear and gas also encounter operational hurdles. Addressing these challenges will require continued investment in resilient infrastructure, adaptive policies, and diversified energy portfolios.