Conventional power generation has vulnerabilities, particularly at times of extreme cold or heat – just the moment it is most needed.
This summer, newly built solar capacity helped the European grid ride out periods of extreme heat.
Solar can’t do it alone, but as storage gets added, heat waves that are becoming more severe will see solar plus storage fill in some glaring gaps.
Ultimately perhaps, modular nuclear may have a role, particularly for winter extremes, but my dark horse is advanced Geothermal.
Neither of those options will be available at scale til the late 2030s, at best. Rapid deployment of renewables and storage is the only course for now.
Europe’s increasingly frequent heatwaves are placing severe stress on electricity grids. Record solar output is helping to meet high demand, but increased flexibility will be needed to future-proof grids.
In June and July 2026, successive heatwaves pushed temperatures above 40°C in many parts of Europe, driving up electricity demand as air conditioning use soared, while disrupting nuclear, gas, coal and hydropower generation.
Fortunately for Europe’s grid stability, record solar output helped cover increased demand during daylight hours, with high prices and supply scarcity most pronounced in the evenings. As extreme heat becomes more common, governments and regulators will need to make greater use of proven solutions, including battery storage and demand response.
The effects of extreme heat on power systems go beyond increased demand. Every type of power generation is impacted, potentially constraining supplies. Grid equipment also has thermal limits. Overhead power lines, for example, can transmit less electricity when the ambient temperature is high, and other equipment, such as grid transformers, can overheat.
The consequences for consumers can be severe. Extreme temperatures caused a grid failure and blackout in the Northeast US in 2003. In June this year, an overheated transformer was responsible for the temporary disconnection of 70,000 consumers in Brittany, France. Fortunately, however, despite extremely challenging conditions, Europe avoided a major disruption to its power supplies.
As demand has risen, other power sources, particularly thermal and hydro power plants, have been constrained by environmental conditions. Thermal power plants, such as nuclear, gas or coal-fired power stations, are typically cooled using water drawn from rivers or seas. Extreme heat and drought therefore deliver a double blow, lowering the availability and effectiveness of cooling water when plants require it most.
In Hungary and Romania, record low Danube water levels have sharply reduced output from the countries’ only nuclear power stations, which typically provide 40% and 15% of their respective electricity generation. Complete shutdowns may be necessary if water levels do not recover. A reactor in Switzerland also temporarily shut down in June because river temperatures were too high.
In France, Europe’s largest nuclear power producer, environmental regulations prevent cooling water being discharged into rivers above a certain temperature, to protect aquatic life. This means reactors can be forced to shut down when river water exceeds a certain temperature. A maximum of 29 GW (43%) of French nuclear capacity was unavailable on 12 July 2026, which is similar to the maximum of summer 2025 (30 GW), but significantly less than the summer of 2022, when nearly two-thirds of capacity was unavailable. It is difficult to verify exactly how many outages are temperature related, but at least 11 GW of offline capacity on 12 July was marked as either “forced” or due to “environmental issues” by the plant operator, with a further 18 GW of reductions due to planned maintenance and other reasons. This means that the heatwave might have impacted up to 18% of France’s nuclear capacity, compared to an estimated 15% in the June 2025 heatwave.
Gas-fired power plants were also affected. During the UK’s record June heat, five plants reported output reductions, removing 2.5 GW from available supply. Analysts warned that water levels in Italy’s Po river could limit up to 32% of the country’s thermal power fleet, mostly gas-fired. Gas power plants in France also warned of limited availability amid record temperatures.
Coal generation also struggled. In Poland, critically low water levels in the Vistula limited cooling water supplies, forcing Enea to reduce output at Kozienice and Połaniec coal plants and removing around 1.3 GW from the power system. Low water levels in the Danube similarly forced Serbia’s Kostolac coal plants to cut production.
- A series of heat waves has weakened some of Europe’s most historically reliable sources of electricity, forcing the continent to lean more heavily on imported fossil fuels and variable renewable energy.
- France’s river-cooled nuclear plants have suffered a record amount of heat-related outages this summer, and hydroelectric plants in the Alps and Nordic region have been hobbled by hot, dry weather.
- The heat-related strains coincide with a surge in natural gas and coal prices, and the disruptions are poised to push power prices even higher, leaving Europeans facing steeper electricity bills.