Post: NESO expects “sufficient operational surplus throughout winter”

NESO expects “sufficient operational surplus throughout winter”

The National Energy System Operator (NESO) has set out its initial operational margin expectations for the 2025-26 Winter period, which runs from 31 October 2025 to 31 March 2026.

In its 2025 Early View of Winter Outlook, published on 18 June, NESO said it anticipates an operational margin of 6.6GW (10.9%), which is the highest anticipated margin since the 2019-20 winter and reflects an improved margin of 1GW compared to last year’s Winter Outlook figure of 5.2GW. The current Base Case de-rated margin is 6.6 GW – equivalent to 10.9% of Average Cold Spell (ACS) peak demand. The associated Loss of Load Expectation (LOLE) is below 0.1 hours, which is within the Reliability Standard of 3 hours.

This increase has been driven by the growth in supply from battery storage, at both the national transmission and regional distribution network levels, alongside an increase in the availability of electricity generation from gas, and the commissioning of the Greenlink electricity interconnector.

But NESO warned that there may still be some tight days requiring use of the operational tools it has available including use of Capacity Market Notices (which secured 7.9 GW of capacity for delivery in winter 2025-26) and Electricity Market Notices. 

The same day NESO published its Winter Review and Consultation 2024-25, which noted that last Winter margins were broadly within the expected range of the Winter Outlook report and there was no interruption to customer demand due to unavailable supply.

Adequate margins were maintained at all times across winter but there were a small number of days where system notices were issued. This included automated Capacity Market Notices (CMNs) on 14 October, 3 December and 8 January and an Electricity Margin Notice (EMN) for 8 January. Across winter 2024-25 NESO saw 25 registered DFS providers representing more than 1.7m customers, with a large proportion of this volume coming from domestic demand reduction. NESO procured volume on 18 occasions, with a peak delivered volume of 188MW.