NESO sets out initial expectations for Winter 2025/26

18 June
Press release - 18 June 2025
Wind Turbines in Snow

Key facts
National Energy System Operator (NESO) today publishes its 2025 Early View of Winter setting out its initial operational expectations for managing Great Britain’s national electricity transmission network across winter 2025/26.
In today's report NESO anticipates operational margins - the surplus electricity beyond demand and reserve needs - will be at their highest since 2019.
NESO’s initial view of operational margins this winter are 6.6GW (10.9%), their highest level since 2019/20 and over 1GW higher than expected in last year’s Winter Outlook.
Later this year NESO will produce its Winter Outlook report ahead of the start of winter operations.

Today (18 June 2025) the National Energy System Operator (NESO) publishes its 2025 Early View of Winter Outlook, setting out its initial operational expectations for the 2025/26 Winter period, running from 31st October to 31st March.

NESO’s report sets out its expectations for operational margins across the winter. These margins reflect the excess electricity that is expected to be available, beyond that which is used on a second by second basis to meet national electricity demand and the reserves of electricity held by NESO to ensure the safe and reliable operation of the electricity network. 

This year’s early view of winter report 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.
This increase in anticipated margin has been driven by a variety of factors, reflecting 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 between Ireland and Wales.

Whilst the operational view across the winter period is positive there may still be some tight days requiring NESO’s control room engineers to use the operational tools at their disposal. 

This includes the use of Capacity Market Notices and Electricity Market Notices to inform the owners of electricity generating technologies like wind farms, batteries or power stations, that additional electricity supplies may be required to meet specific operational needs. These notices are standard tools used by NESO’s control room most winters during the tightest periods of the year and do not themselves mean that electricity supplies are not sufficient to meet national electricity demand.

Dr Deborah Petterson, Director of Resilience and Emergency Management, NESO

“Our early view of the winter ahead shows a positive outlook with sufficient margins throughout the colder winter months. We will continue to monitor developments in global energy markets, remaining vigilant in our preparations to ensure that the resilience and reliability of the electricity network is maintained.”

ENDS

About NESO

The National Energy System Operator, NESO, is an independent, public corporation at the centre of the energy system taking a whole system view to create a world where everyone has access to reliable, clean, and affordable energy.

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Notes to editors:

  • NESO’s Electricity Early View of Winter Outlook covers operational expectations for Great Britain’s National Electricity Transmission Network.
  • Alongside the Early View of Winter NESO has also published its Winter Review and Consultation report, looking back at the modelling and analysis detailed in the Winter Outlook 2024/25 report against the actual events during the season.

Early View of Winter Outlook Key Messages

Margins

  • Our analysis shows that margins are expected to be adequate and within the Reliability Standard. 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 higher de-rated margin is due to increased battery storage capacity, an increase in available gas-fired power generation, the commissioning of the Greenlink interconnector and the ongoing growth in renewable generation. This more than offsets an expected increase average cold spell peak demand.

Operational surplus

  • We will continue to meet the challenge of reliably operating a changing electricity system.
  • We expect there to be sufficient operational surplus throughout winter, allowing for natural variations in weather. There may be some tight days and early indications suggest these are mostly likely to occur in early December or mid-January.
  • We continue to develop and adapt balancing services markets to ensure all technologies have clear and efficient routes to support security of supply

Markets

  • In Great Britain, the T-1 Capacity Market auction for delivery in winter 2025/26 secured 7.9 GW of capacity from a diverse range of technologies.
  • Early indicators suggest adequate generation will be availability in key interconnected markets. As in recent winters we will continue close and active engagement with our neighbouring Transmission System Operators (TSO), to determine how interconnector flows can be optimised and co-ordinated to ensure reciprocal support between countries.
  • As a prudent system operator, we prepare for a wide range of eventualities and will work closely with Government, Ofgem and National Gas identify and mitigate potential risks.

Winter Outlook 2025/26

  • NESO expects the full Winter Outlook Report to be published by October 2025.