On the evening of Friday, June 26, Great Britain reported tight electricity system reserves as a heatwave drove up consumption and power plants generated less output. Consequently, the national grid operator, Neso, requested additional electricity supplies for the period between 7 p.m. and 10 p.m. Fans and air conditioning units drove demand, while low wind speeds and reduced solar output in the evening exacerbated the situation. At the same time, high temperatures limited the output of certain gas and nuclear power plants. However, power outages were not considered an imminent threat.
Reserves become more expensive quickly during hot weather
Neso was seeking around 700 megawatts of additional capacity for the evening. The warning was directed at the electricity market rather than directly at households. However, such announcements indicate that the safety margin between supply and demand is narrowing. The grid operator had already taken similar action on Wednesday.
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By Friday afternoon, NESO had secured additional electricity imports from Europe. The volume was equivalent to the consumption of around three million typical households. However, the price stood at £200 per megawatt-hour, making the cost of ensuring system stability significantly higher than on a typical summer day.
Heat affects both consumption and power plants
The heatwave drove up electricity demand during a season that is usually less critical, as many households turned on fans or air conditioning units. At the same time, stable high-pressure weather conditions reduced wind power generation. In the evening, solar power output dropped off, while residential electricity consumption remained high.
However, heat affects more than just demand; it can also strain power plants. Consequently, some British gas-fired power plants reduced their available output. In France, nuclear power plants also had to take action because river water used for cooling had become too warm.
France’s nuclear power unavailable as a buffer
France is normally a key supplier of electricity imports to Britain. Precisely for this reason, the French restrictions exacerbated the situation in the British market. EDF throttled the output of several reactors to comply with environmental regulations regarding river temperatures. Other European facilities also came under increased scrutiny due to high water temperatures.
Nevertheless, NESO emphasized that the electricity supply was not in immediate danger. The warning did not signal impending power cuts, but it did demonstrate how quickly reserves can dwindle when heat, low wind speeds, and reduced power plant output coincide. In such scenarios, every additional megawatt-hour becomes valuable to the market.
Summer Heat Puts Power Grids to the Test
On June 26, the UK Met Office recorded a temperature of 37.3°C in Santon Downham, Suffolk. This marked the third consecutive day that the UK set a provisional temperature record for June. Rare heat warnings were also in effect, while subsequent thunderstorms brought only delayed relief—too late to cool things down during the critical evening hours.
The heatwave affected not only the UK but large parts of Europe. Consequently, electricity prices rose in neighboring countries as the simultaneous need for cooling and restrictions on power plant operations took their toll. For consumers, the conclusion is clear: the power supply held up, but at significantly higher costs. Extreme summer heat is thus becoming a regular stress test for Europe’s electricity systems.
Author: Blackout News
Sources: The Guardian (26.06.26) – NESO (24.06.26) – Met Office (26.06.26) – Reuters (24.06.26) – Sky News (24.06.26)