The risk that demand for electricity in the UK will exceed supply, leading to power outages this winter, is the lowest since winter 2019/20.
The National Energy System Operator’s (NESO) Winter Outlook 2025/26 predicts a reduced base case margin of 6.1 GW, representing 10% of average peak demand during cold spells. It is slightly lower than the projection published in the Early view of winter in July.
Last year the margin was 5.2 GW. According to NESO, this year’s larger reduced margin results from the increased storage capacity of battery energy at both the transmission and distribution levels, an increase in gas-fired energy generation and the commissioning of the Greenlink interconnector to Ireland.
By the end of August, Britain will have 7,632 MW/11,455 MWh of installed battery energy storage capacity, with notable projects such as Statera’s 300MW/600MWh Thurrock Battery Energy Storage System (BESS)and that of Great Britain first grid-forming BESSby Zenobē, comes online.
NESO also credits the growth of renewable generation for achieving sufficient supply in the winter. The operator’s forecasts are based on the assumption that all providers with capacity market agreements meet their obligations.
Furthermore, it is assumed that in times of tighter margins, a net import of 6.9 GW will be available via interconnectors. Current prices suggest Britain will be a net importer of electricity in winter, mainly from France, while flows from Belgium, the Netherlands and Denmark will be more variable as prices become more closely aligned.
Under normal circumstances, NESO predicts that Britain will export to Ireland and Northern Ireland. In the longer term this could change as Ireland becomes a… ambition to become a net exporter of electricity as part of its aim to be central to wider European energy plans.
NESO said that while the company expects operational surpluses throughout the winter, there may be “some tight days” that require the use of routine system notifications.
For example, the winter of 2024/25 saw NESO issues an electricity margin notice (EMN). on the evening of January 7 for the period between 4:00 PM and 7:00 PM on January 8, after a system margin shortfall of 1,700 MW and a contingency requirement of 900 MW was forecast.
Under normal circumstances, an automated Capacity Market Notice (CMN) is issued when there is a forecast generation shortfall. An EMN is a stronger signal to the market and reflects NESO’s increased concerns.
During the energy crisis, such measures occurred much more often: on January 8, 2021 the operator issued its second EMN in a week and the fifth for that winter. The system was managed by National Grid ESO at the time.
NESO’s Director of Resilience and Emergency Management, Dr. Deborah Petterson, wrote in a blog post on the release of the Winter Outlook report that while “margins have improved year on year since the impact of the COVID-19 pandemic and subsequently the 2022 invasion of Ukraine, [NESO] understands the importance of vigilance.”
