On 23 June, as France sweltered through one of its hottest days on record, exasperated residents painted white chalk on their windows to screen out the sun. The Eiffel Tower closed early. In the town of Ergué-Gabéric, Brittany, the punishing temperatures – around 40C – proved too much for a single electric transformer. The chunky metal box malfunctioned, initially leaving more than 100,000 people without power. Local authorities described it as a “heat related” incident; a spokeswoman for power company RTE confirmed to the BBC that a video posted to social media, appearing to show a plume of smoke rising from the stricken transformer, showed one of the firm’s facilities. The day before the accident, RTE had published a statement saying there was “no concern” surrounding the availability of electricity across its network this summer.
The fragility exposed in Brittany is not an isolated case. Just as human bodies have limits in high temperatures, so too does technology. Electrical and telecoms equipment, railway signalling cabinets – all can falter during a heatwave. Extreme temperatures can even set off alarm systems. In the UK last week, six NHS trusts declared a critical incident after hot weather adversely affected their IT systems, scanners, and cancer and lab equipment.
“A transformer in France failed during a heatwave, leaving 100,000 without power, as UK NHS trusts declared critical incidents.”
Iain Staffell, an energy expert at Imperial College London, explains the physics of the problem: “Anything to do with the electricity network – the power lines, the interconnectors and transformers – they all struggle to keep themselves cool enough. It reduces the efficiency of everything.” Staffell and his colleagues estimate that in temperatures of 40C, the output of gas-fired power stations drops by roughly 10% compared with 20C. Solar panels also become less efficient as the mercury rises, though the effect has become less pronounced with newer generations of panels. Data analysed by Staffell’s team and shared with the BBC reveals a clear threshold: “Once the UK gets above 27C, our solar output plateaus and starts to slowly fall [as temperatures continue to rise].” That said, extended sunny periods during heatwaves can still boost solar output relative to cloudier days before the heatwave hit – something that happened last week, according to comparison website Utility Bidder.
The vulnerability extends beyond power plants. The power lines that swathe the country are made of metal, which expands in heat, causing the cables to droop. Running electricity through them generates even more heat. “There is a limit to how much droop you can allow,” says Simon Hogg, a consultant quoted in the article.
As human-caused climate change drives more frequent and more intense heatwaves, engineers are increasingly adapting infrastructure to cope. But the events in France and England show how quickly the systems we depend on can break down when the mercury climbs – and how little warning we may have.