NESO sets out expectations for strongest winter electricity margins in six years

9 October
Press release - 09 October 2025
Wind Turbines in Snow

Key facts
National Energy System Operator (NESO) 2025/26 Winter Outlook forecasts electricity margins of 6.1GW – the highest since 2019/20 and equivalent to 10% of average peak demand.
Increases in margins compared to last year are driven by the connection of new battery storage, greater availability of gas power stations and the commissioning of the Greenlink interconnector between GB and Ireland.
NESO cautions that some tighter periods might occur over the winter period, requiring NESO to use its operational toolkit to notify the energy industry of required actions to keep the system in balance.

Today (9 October 2025) National Energy System Operator (NESO) has set out its expectations for winter operations on Great Britain’s national electricity network from 31st October 2025 to 31st March 2026 in its 25/26 Winter Outlook.

The main finding of this year’s Winter Outlook report is increased operational margins of 6.1GW, the highest such margins since the 2019/20 winter, reflecting a continuing trend in improved operational margins in recent years.

The 6.1GW of operational margins represents the additional electricity available to NESO, on top of the electricity required to meet national demand across the winter and the electricity reserves that NESO’s control room engineers procure to enable the balancing of supply and demand on the national electricity network on a second-by-second basis. Electricity margins provide NESO with an additional buffer beyond its standard reserves, ensuring that should conditions change across the winter that there is enough resilience in the network to respond.

These operational margins are 900MW greater than last year’s margins, the equivalent to roughly three gas power stations. The increase in operational margins year on year is the result of new electricity generation from battery storage on Great Britain’s national and regional electricity networks, alongside greater availability of gas-fired power generation and the commissioning of the Greenlink electricity interconnector to Ireland.

Despite the improvement in margins in comparison to previous years, NESO stresses that some tighter periods on the electricity system are still possible over the winter months. In those situations, NESO may use its standard operational tools, such as issuing notices to the market, instructing them to increase their output to gives us a larger cushion of spare electricity to work with. Capacity Market Notices and Electricity Market Notices represent the lowest level of warning from the NESO Control room and are amongst the first tools available to NESO when managing potential reductions in operational margins.

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

“A resilient and reliable energy supply is fundamental to our way of life.  At NESO we are looking at the upcoming Winter and can report this year’s Winter Outlook sets out the strongest electricity margins in six years. It is critical that we continue our work with the wider energy industry to prepare for the coming months to build on this foundation and maintain our world leading track record of reliability.”

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 Winter Outlook covers operational expectations for Great Britain’s National Electricity Transmission Network.
  • A separate Winter Outlook covering expectations on Great Britain’s National Gas Transmission Network is published by National Gas.

Winter Outlook Key Messages

Margins

  • Our analysis indicates that margins will be adequate and within the Reliability Standard.
  • Our base case margin for winter 2025/26 is 6.1 GW (representing 10.0% of average cold spell peak demand), with an associated 
    Loss of Load Expectation (LOLE) below 0.1 hours. This is an increase from the 5.2 GW forecast in last year’s Winter Outlook and the highest de-rated margin since 2019/20.
  • This higher de-rated margin is due to increased battery storage capacity, a net increase in gas-fired power generation, an additional interconnector and ongoing growth in renewable generation.
  • Alongside our base case, we produce a range of sensitivities to show how adequacy metrics vary under different conditions and assumptions. LOLE remains within the Reliability Standard under each of our sensitivities. 

Operations

  • Our planning, preparations and balancing tools will enable the reliable operation of the system under varied supply and demand conditions.
  • We expect a sufficient operational surplus throughout winter, although there may still be tight days which require us to use our standard operating tools, including system notices. Current market submissions suggest such days are most likely in early December or mid-January.

Markets

  • Our analysis suggests that imports will be available when required, supported by adequate electricity supply across Europe.
  • Indicators suggest adequate generation availability in key interconnected power markets, but uncertainties remain. We continue to monitor the wide range of factors influencing power prices in neighbouring markets and work closely with our strategic partners to assess potential risks in global energy markets.
  • Prices suggest Great Britain will typically be a net importer across electricity interconnectors this winter, although interconnector flows may be more sensitive to prevailing conditions.