Great Britain’s National Energy System Operator (NESO) expects the strongest winter electricity margins in six years, forecasting 6.1GW of operational headroom for the 2025/26 period.
The figure, outlined in NESO’s Winter Outlook report published today, represents the highest margin since 2019/20 and is equivalent to around 10% of average peak demand.
Operational margins indicate the extra generation capacity available beyond what is needed to meet demand and maintain reserves, providing engineers with additional flexibility to balance supply and demand on the grid.
This winter’s expected 6.1GW margin is 900MW higher than last year – roughly equivalent to three gas power stations – reflecting steady improvement in system resilience.
NESO attributed the rise in capacity to the connection of new battery storage across national and regional networks, improved availability of gas-fired generation, and the commissioning of the Greenlink interconnector between Great Britain and Ireland.
Despite the positive outlook, NESO cautioned that short periods of tighter margins could still occur during the winter months, potentially requiring market notifications to ensure sufficient supply.
In such instances, NESO said it may issue standard operational tools, such as Capacity Market Notices or Electricity Market Notices, to prompt generators to increase output.
Dr Deborah Petterson, director of resilience and emergency management at NESO, said: “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.”
The Winter Outlook covers the period from 31 October 2025 to 31 March 2026, assessing the balance between expected electricity demand and available generation across Great Britain’s national network.