The National Energy System Operator (Neso) issued a rare summer electricity margin notice on Tuesday, calling on power plant owners to provide additional generation capacity for Wednesday evening as a heatwave intensifies across Great Britain. The notice, which asks for an extra 1,900 megawatts of power, comes as the buffer between supply and expected demand tightens due to extreme temperatures and low wind.
Heatwave Drives Up Demand
Neso, which manages energy systems in England, Scotland, and Wales, expects electricity demand to climb between 7pm and 10pm on Wednesday as households switch on fans and air conditioning to cope with soaring temperatures. The heatwave is forecast to bring record June temperatures of up to 38°C in southeast England on Wednesday, with a possible 39°C on Thursday, easily surpassing the previous June high of 35.6°C.
According to a Neso spokesperson, the notice is due to the impact of extremely high temperatures affecting Great Britain and the continent, combined with low wind speeds. They stressed that the electricity supply is not at risk and the notice does not mean a blackout is imminent.
Rare Summer Warning
Such electricity margin notices are more common during cold winter spells when heating demand surges. This is one of the few times Neso has issued a summer warning. The operator asks generators to provide any extra power available, which can come at significant cost.
Across Europe, electricity prices have risen sharply in recent days as the heatwave grips much of the continent, pushing demand higher and causing power plant outages. An area of high pressure has trapped heat, slowing wind speeds and reducing renewable generation. Some French nuclear plants have also reduced output because high river water temperatures make it harder to cool reactors.
Infrastructure Pressure
The combination of rising demand and falling generation across Europe has pushed market prices to multiyear highs. The sweltering heat is expected to strain UK infrastructure: train operators have urged passengers to travel only if necessary on Wednesday and Thursday, schools have closed in southern England and Wales, and hospital appointments have been cancelled.
Several trade unions, including the Trades Union Congress, the Bakers, Food and Allied Workers Union, and the Fire Brigades Union, have called for workers to walk out on the hottest day. There is no maximum legal temperature for workplaces in the UK, though a minimum of 16°C applies in offices.
