ESO issues Capacity Margin Notice for second time this summer

For the second time this summer, National Grid Electricity System Operator (ESO) has issued a Capacity Margin Notice alerting the market to a potential stress event.

Capacity Margin Notices are automatically triggered around four hours ahead of real time if forecast surplus capacity on the transmission network falls below 500MW.

National Grid issued the latest notice shortly after 1.30pm on Thursday (11 August) for 6.00pm in the evening.

At the time, the ESO was expecting 35,511MW of aggregative capacity in the Balancing Mechanism to be available to fulfil its forecast requirement of 35,338MW, covering both demand on the transmission network and the necessary operating margin.

Capacity Margin Notices are intended to alert holders of Capacity Market agreements to the increased likelihood of a system stress event. If a stress events occurs and they are not available on the system, capacity providers will incur penalties, so long as a Capacity Margin Notice has been issued at least four hours in advance.

The ESO gave assurances on Twitter that it was “confident” that electricity margins for Thursday evening would be sufficient, emphasising that the Capacity Margin Notices are issued automatically and do not take into account all of the factors its engineers are working on.

This is in contrast to Electricity Margin Notices, which are issued at the discretion of its control room staff based on operational and engineering judgements – usually when the ESO’s operating margin falls below 500MW.

The Capacity Market Notice on Thursday was the second to be issued this so far this summer. The first was issued on 18 July for 8pm in the evening and withdrawn 20 minutes beforehand.

Apart from one sent out by mistake in June 2017, all previous Capacity Margin Notices have been issued between September and January.