French Power Day-Ahead Jumps 22% as Summer Heatwaves Drain Nuclear Output
Five consecutive heatwaves forced EDF to cut 7.3 GW of nuclear capacity in August, driving French day-ahead prices to €142.5/MWh and lifting European forward curves.
France's day-ahead power prices surged 21.8% to €142.5 per megawatt-hour on Tuesday (2026-08-11), according to LSEG data cited by Reuters, as EDF prepared to cut nuclear output ahead of the mid-day peak. The move came during what oilprice.com described as at least the fifth extremely hot wave to grip France in 2026.5
Nuclear power accounts for roughly 70% of France's electricity mix. EDF data showed France's fleet would shed 7.3 GW on Wednesday (2026-08-05), equal to 12% of total installed capacity, with river cooling constraints tightening as water temperatures climbed during the week of 2026-08-10. When river temperatures exceed regulatory thresholds, plants must reduce output to limit thermal discharge — a constraint that tightened repeatedly as successive heatwaves kept rivers warm.5
The pattern had already established itself through July. EDF cut 6.4 GW from the nuclear fleet amid a prolonged heatwave, equivalent to 14% of national power demand on Monday (2026-07-13) according to oilprice.com, after sustained heat raised river temperatures beyond the limits at which plants can safely operate. The July episode confirmed this as a seasonal vulnerability, not an isolated event.3
Those July cuts moved the futures curve sharply. The EEX-traded French Q4 power contract hit €106.67/MWh on Wednesday (2026-07-15), a multi-year high according to Montel, as a broader European energy complex rallied amid Middle East escalation. The contract was up EUR 2.26 on the day when it reached that level.4
Spot prices had already flagged the pressure earlier in July. Montel EQ data on Friday (2026-07-10) showed French spot power set to exceed €100/MWh in the week of 2026-07-13 — the highest since 30 June — with supply security concerns accelerating the move.2
France's grid held up despite the curtailments, at least through July. RTE data showed France exporting more than 10 GW to neighbouring countries on Monday (2026-07-13), even with 6.4 GW of nuclear generation withdrawn.3 The French nuclear fleet's scale — when running at full capacity, France is a net exporter — means even significant curtailment can leave it supplying the continental grid. But that export buffer erodes as outage durations lengthen and multiple plants face constraints simultaneously.
German front-month power futures were priced at €149.98 per megawatt-hour on Thursday (2026-09-03), signalling that markets have absorbed weeks of French nuclear pressure and are now pricing autumn demand risk into the forward strip.
The longer-term supply picture sits with Brussels. The European Commission launched an investigation on Tuesday (2026-05-19) into France's EUR 73 billion plan to subsidise six new reactors with a combined capacity of 10 GW, according to Montel.1 The probe covers the subsidy structure for both construction and operation. Whatever outcome emerges, new reactor capacity cannot arrive in time to address the heatwave-driven curtailments visible across 2026 — the programme's earliest possible delivery dates lie well into the 2030s.
EDF's ability to restore the 7.3 GW curtailed on Wednesday (2026-08-05) before autumn demand picks up will be the near-term signal. September river temperatures will drive that timeline more than any policy action, and France has run through most of summer with less nuclear margin than its export neighbours had priced in at the start of the year.5