What is the reason for the UK grid operator's second Electricity Margin Notice on Friday, and how large is the supply shortfall?

The UK grid operator, the National Energy System Operator (NESO), issued a second Electricity Margin Notice for Friday evening due to a projected margin shortfall of 671 megawatts between 7 p.m. and 10 p.m., driven by soaring temperatures across Great Britain and continental Europe; the heat wave has increased cooling demand and forced output cuts at French nuclear reactors—whose cooling relies on river water that has become too warm—while also reducing available generation capacity in the UK due to transmission constraints that prevent about 1.1 gigawatts from counting toward the required 700-megawatt operating reserve.

Does the Electricity Margin Notice mean blackouts are likely in the UK?

No—the Electricity Margin Notice is a routine tool used to encourage generators, interconnectors, and demand-side providers to make additional capacity available, and it does not indicate that blackouts are expected; such notices are more commonly issued during winter, when electricity demand is typically highest, and NESO’s objective is simply to maintain its target 700-megawatt operating reserve to ensure grid stability.

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