Great Britain grid operator issues rare summer electricity margin warning amid heatwave

Great Britain's grid operator has issued a rare summer electricity margin warning for Wednesday evening as a heatwave intensifies across the country. The National Energy System Operator asked power plant owners to provide any extra electricity they can as the gap between expected supply and demand narrows. The notice was issued late on Tuesday and applies to the period when demand is expected to be highest.

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The operator said it needed an additional 1,900 megawatts of generating capacity to keep the system within normal safety margins. A spokesperson said the warning was linked to extremely high temperatures affecting Great Britain and the continent, together with low wind conditions. The operator also said the electricity supply was not at risk and that the notice did not mean a blackout was imminent.

Demand is expected to rise between 7pm and 10pm on Wednesday as households use electric fans and air conditioning to cope with the heat. The warning is unusual because such notices are more commonly issued during cold spells in winter, when heating demand is higher. Electricity prices have also risen sharply across European markets in recent days as the heatwave has lifted demand and reduced generation in some places.

The situation matters because it highlights how extreme weather can strain power systems even in summer, when electricity networks are usually under less pressure than in winter. Low wind has reduced renewable output at the same time as high temperatures have increased demand, creating a tighter operating margin. The broader European market has also been affected by outages at some power plants and lower output at some nuclear stations in France, where warmer river water has made cooling more difficult.

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The warning comes as record June temperatures of 38C are expected in south-east England on Wednesday, with a maximum of 39C forecast for Thursday. That would exceed the previous June high of 35.6C. The operator manages the energy systems in England, Scotland and Wales, and its request is aimed at avoiding a shortfall while keeping the grid stable during the evening peak.

What remains unclear is how much extra capacity generators will be able to provide and whether the pressure on the system will ease if temperatures and wind conditions change. The notice is a precautionary measure rather than an emergency alert, but it will be watched closely by power market participants and households facing very hot weather. The key test will be whether supply can stay comfortably above demand through the evening peak without further intervention.

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