French Balancing Market Corrections Persist Despite RTE Assurances, Traders Say

French Balancing Market Corrections Persist Despite RTE Assurances, Traders Say Retroactive revisions to French balancing settlement data are continuing, traders told Montel, as a mid-July heatwave forces further nuclear curtailments. France curtailed 6.4 gigawatts of nuclear output on Monday (2026-07-13) as a prolonged heatwave pushed river temperatures above the cooling limits that regulators permit, RTE data showed.⁵ The cut was equivalent to roughly 14% of France's power demand at the time and arrived on a market already contending with a separate reliability problem. Traders told Montel in the week of 2026-05-21 that RTE has continued issuing retroactive corrections to French balancing market prices and volumes, contradicting the TSO's assurances that the technical problems behind those revisions had been fixed.^2,5 The ongoing corrections have caused unexpected financial losses for market participants across Europe, traders said. Some described the revisions to Montel as "insane." When a TSO revises balancing settlement data after the fact, balance responsible parties end up holding positions that differ materially from what the real-time price signals had suggested.² The scale of errors seen elsewhere in Europe shows the potential exposure. Italian TSO Terna published a balancing price correction on Friday (2026-05-08) that revised a quarter-hour price in the Nord bidding zone from €187/MWh to €3,770/MWh, a 20-fold upward move that traders told Montel on Monday (2026-05-11) appeared to be a clear error.³ That episode followed an earlier disruption: large-scale revisions to Terna's provisional imbalance price data had been distorting intraday market signals since 7 March, traders told Montel on Friday (2026-03-27), with some revised prices differing by as much as 50% from their initial provisional figures.⁴ France's situation is reported as less extreme in individual revision size, but the pattern has been sufficient to erode participant confidence in settlement data as a reliable basis for real-time trading. If traders cannot trust provisional prices, they have less incentive to place efficient bids, reducing the quality of the balancing market as a mechanism for keeping the French grid stable.² Nuclear power supplies around 70% of France's electricity when reactors are fully operational, and France is typically a net power exporter. The heatwave did not break that status. Even with the Monday (2026-07-13) curtailments, RTE data showed France still sending more than 10 GW to neighbouring countries.⁵ French day-ahead power settled at €146.54/MWh on Friday (2026-07-17), with the country remaining a net supplier to the regional market despite the curtailments.⁵ The heatwave underscores why balancing market reliability matters specifically in France. Seasonal nuclear curtailments driven by river temperatures are recurrent, and the real-time signals that coordinate grid balancing during those curtailments depend directly on the accuracy of the settlement data now being questioned.^5,2 France's energy regulator CRE has opened a consultation on the balancing market's structure, examining whether to strengthen financial incentives for balance responsible parties ahead of a 2029 EU-driven overhaul that will push more grid-balancing responsibility onto market participants.¹ The Italian experience offers a precedent. Data revision problems at Terna accumulated for months before drawing formal scrutiny, with traders saying the disruption to intraday signals had persisted since late 2025. RTE has told the market its technical issues are resolved. Traders say the corrections are still happening. If the CRE's consultation does not produce binding procedural requirements on settlement data timelines and revision limits, the problem is likely to follow the Italian pattern well into the months ahead.^2,1³