RTE outage leaves 100,000 Breton homes dark after heatwave reassurance

A power outage struck southern Finistère on the evening of June 23, leaving up to 106,000 households without electricity the day after France's electricity transmission system operator RTE stated there was no concern for summer supply.

High temperatures triggered a transformer failure at Ergué-Gabéric. Two explosions occurred at an RTE-operated electrical substation around 19:30 and later that evening, according to multiple reports. The incident, confirmed as heat-related by the prefecture with local temperatures reaching 37°C in Quimper, forced the shutdown of equipment weakened by the canicule.

Restoration efforts continued overnight and into June 24. By late morning on June 24, approximately 68,000 households remained without power, with full recovery expected during the day. No injuries were reported, though local evacuations took place in the affected area.

RTE had issued a reassurance statement one day earlier. On June 22, the operator declared there was no concern regarding the availability of electricity supply for the coming summer, even in the event of intense heatwave and drought episodes. France maintains sufficient production capacity to navigate the season without major difficulties, RTE said.

Yet the outage highlights how extreme heat can still strain network infrastructure beyond generation limits. High temperatures reduce nuclear output when river water warms beyond environmental thresholds, lower wind power due to calmer conditions, and increase air-conditioning demand that peaks after sunset.

Demand spiked from air conditioning but stayed manageable overall. RTE reported air-conditioning added around 10 GW of consumption on June 21 and was forecast to reach 12 GW on June 22 compared with normal seasonal temperatures. Each additional degree in summer typically lifts demand by 0.7 to 1 GW, far less than the triple effect seen from a one-degree winter drop.

At peak hours on June 22, gas-fired plants supplied more than 4,000 MW at 7 p.m., up from a few hundred megawatts on a typical evening. Solar generation drops at sunset precisely when air conditioners run at full capacity, forcing greater reliance on gas. RTE maintains the overall generation fleet can cover such surges.

The event underscores that while production capacity holds, localized network vulnerabilities can still produce widespread outages during record heat. June 23 marked a historic average temperature of 29.9 °C, the highest since records began in 1947.