Soaring temperatures force UK grid alert as solar and gas stumble under heatwave
Heatwave exposes power system fragility as solar efficiency drops and gas balancing costs surge.
Britain's grid operator issued a second power supply warning in as many days on Friday (2026-06-26), an extremely rare summer alert as a Europe-wide heatwave cut into generation from both solar and gas plants.5
The warning arrived just as Britain was recording a 52.5% renewable generation share for 2025 and exposed a vulnerability in the transition. High temperatures reduce the output of every generator, and solar panels are no exception. A 2024 paper found that for each degree above optimal temperature, solar panels lose around 0.5% efficiency, and when ambient heat pushes panel temperatures to extremes, output can fall by more than 30%.4,2
Wind offered little cover. On Tuesday (2026-06-23), wind provided just 13.9% of demand, or about 4.32 GW, against a 12-month average of 35.2% at 10.84 GW.4 By Wednesday (2026-06-24), the National Energy System Operator had flagged that around 1.3 GW of generation was unavailable owing to constraints, with margins described as looking "a little tight."4
Gas-fired plants stepped in to fill the gap, but at cost. LCP Delta data show gas generators earned roughly £10 million in Balancing Mechanism revenue between June 22 and June 25 — a measure of how expensive it becomes when dispatchable supply is lean.5
Nuclear generation last year was just half of its 2015 level, according to Energy Voice, leaving gas as the principal dispatchable backstop when wind and solar falter.2 Experts told Montel that more frequent heatwaves are expected to put pressure on ageing grids in the years ahead, though solar power and battery storage can provide a partial solution, pointing to the prior year's heatwave as evidence that solar helped stabilise supply rather than strain it.3
The underlying issue is system design. Spain has pursued large investments in wind and solar; gas has set power prices there only 15% of the time this year, compared with 89% in Italy.1 That gap reflects each country's grid flexibility more than its technology choices.
Pakistan offers a parallel. Solar's share of generation rose from 0.7% in 2019 to 10% in 2024, and the country's LNG import bill for the rest of this year is likely $6 billion lower than it would otherwise have been, according to one analysis.1 But a grid split 90% clean and 10% fossil does not consistently deliver that mix. Output depends on when the sun shines and the wind blows.1
For Britain, the immediate constraint is gas availability. Without additional storage or firm low-carbon capacity, the Balancing Mechanism will remain the system's pressure valve during summer heat events. Gas plant earnings through that mechanism are the leading indicator: if payments climb further through this summer, it will signal that Britain's dispatchable cushion is thinner than a record renewables share suggested.3,2