Britain's grid operator calls for more electricity as temperatures soar

Rare summer warning

Britain’s National Energy System Operator issued a rare summer electricity margin notice on Tuesday night, asking power generators for extra supply during the Wednesday evening peak as a heatwave tightened the system’s margins.

The notice covered the period from 7pm to 10pm and was designed to keep a larger safety cushion on the grid while temperatures rose and wind output stayed low.

Neso said it needed about 1,900 megawatts of additional generating capacity. The operator said the request was precautionary and did not mean electricity supply was at risk or that a blackout was imminent.

The warning was notable because electricity margin notices are more often associated with winter demand spikes than with summer weather.

Why the system is under pressure

The immediate pressure came from the combination of extreme heat and weaker generation. Forecasters expected temperatures of about 38C to 40C in parts of the UK, while low wind reduced output from turbines.

FT reporting also said the heat lowered the efficiency of solar panels and gas-fired power stations. That meant the system was facing a squeeze on both demand and supply at the same time.

Neso said the notice was aimed at maintaining normal operating margins during the evening peak, when demand can remain elevated even after the hottest part of the day has passed.

The operator’s request was the first summer notice it has issued and its first margin notice since January 2025.

Wider heatwave effects

The electricity warning came amid a broader heatwave that has also strained transport and other parts of public infrastructure. The Met Office issued a red extreme-heat alert, and rail operators canceled or reduced services because of heat-related safety concerns.

The heatwave has also driven power prices higher across Europe. Reporting from earlier in the week pointed to stronger demand and lower generation, including weaker wind output and some nuclear outages in France, as prices climbed.

That wider European context matters for Britain because a heatwave can tighten supply conditions across interconnected markets at the same time that domestic generation is under pressure.

What to watch next

For now, Neso’s notice is a precautionary step rather than a sign of immediate system failure. The key question is whether the evening peak passes without additional intervention.

The next updates to watch are whether Neso issues any further balancing notices, how much of the extra supply comes from domestic plants versus imports, and whether the heatwave keeps pressure on prices in Britain and across Europe.

The episode underlines how extreme weather can affect the grid in ways that are more usually associated with winter cold snaps than with summer heat.