A summer margin notice.
And a 26 minute wobble.
Yesterday the grid operator issued an Electricity Margin Notice, in July, warning it was about 1.2GW short for the evening peak. It is the second such warning in two months. Then the grid's frequency sat below its normal level for almost 26 minutes, the longest stretch anyone has on record. Nothing broke. It was closer than it should have been.
📟 What a margin notice actually is
An Electricity Margin Notice is the grid operator saying, in public, that the cushion between what it can generate and what the country wants is thinner than it likes.
It is not a blackout warning. It is closer to a flare. It says: we need more generation to offer itself for tonight, and we are willing to pay for it.
It usually works. Plants respond, prices spike, the evening passes. What is notable here is the season. These are supposed to be January problems.
〰️ Why 26 minutes matters
The grid runs at 50Hz. If demand exceeds supply, frequency sags. It is the most direct physical signal that the system is under strain, and it is normally corrected within seconds.
Yesterday it sat below normal for almost 26 minutes, the longest continuous stretch on record.
Nothing failed. But a system running with that little headroom has no answer if something else goes wrong at the same moment. That is what thin margin means: not that it broke, but that it had nothing left if it had needed it.
💡 The cheapest megawatt is the one nobody uses
The expensive way to fix an evening like that is to build and maintain gas plants that sit idle for most of the year waiting for four bad hours.
The cheap way is to shave the peak. If a few hundred thousand homes delay a car charge, or let a hot water tank coast for an hour, the 1.2GW gap closes without anybody building anything.
That is not a hypothetical. It is precisely what the flexibility service is for, and it is why the grid pays for it. A megawatt you did not need at 6pm costs less than a megawatt you generated at 6pm.
The grid asked the country for 1.2 gigawatts on a hot Thursday evening. There are roughly 1.5 million EVs in Britain, most of them plugged in, most of them not urgently charging. The gap it was short is sitting on driveways, being ignored, at exactly the moment it was worth the most.