Great Britain’s grid operator warns again over power supplies in heatwave

Friday evening warning

Great Britain’s electricity system operator, NESO, warned again on Friday that hot weather was tightening power supplies and pushing demand higher across the grid.

The operator issued an Electricity Margin Notice for Friday evening, asking market participants and generators to make any extra capacity available. NESO said the system was under strain because of extremely high temperatures in Great Britain and across the continent.

NESO said electricity supply was not at risk and that a blackout was not imminent.

A second alert this week

The latest notice followed an earlier call for backup earlier in the week, making it the second heat-related warning NESO had issued during the same spell of hot weather.

The Guardian reported that the operator had already triggered around £10 million in balancing costs on Wednesday evening, with most of the payments going to gas-fired power stations. The Financial Times also reported that several major UK gas plants had reduced output because of the heat.

That combination of higher cooling demand and lower usable generation has left margins tight at the point of peak evening demand.

Cost and resilience pressure

Balancing actions are routine for the operator, but repeated interventions during a heatwave can add costs that ultimately flow through the electricity system and, in time, consumer bills.

The episode has also sharpened attention on grid resilience, flexible storage and backup generation. On the same day, Ofgem provisionally approved support for 16 electricity storage projects, a move the Financial Times linked to the stress the heatwave has put on the system.

NESO’s repeated warnings underline how extreme weather can affect both supply and demand at once: cooling needs rise just as output from some plants becomes harder to maintain.

What happens next

The key question now is whether NESO needs to issue further notices over the weekend and whether it publishes a more detailed estimate of the costs of the heatwave-related balancing work.

The operator’s actions are a reminder that Britain’s power system can remain operational while still becoming more expensive to run under extreme weather, especially when heat coincides with tight margins and reduced generation flexibility.