Energy Storage Strengthens UK Power Security for Winter 2025/2026
UK Winter Power Margin 2025/26 Highest in Six Years Thanks to Storage, Gas, and Interconnectors
The British electricity system operator, National Energy System Operator (NESO), announced that the winter 2025/2026 power margin will be the highest in six years. The forecasted margin of 6.1 GW, representing around 10% of peak demand, is the result of ongoing investments in energy storage systems, increased availability of gas plants, and the commissioning of the Greenlink interconnector between the UK and Ireland.
Winter Outlook 2025/26: Strong system foundations, but vigilance remains essential
In its annual Winter Outlook 2025/26 report, NESO assessed electricity supply security for the winter months. This year’s forecast shows an operational margin increase of 900 MW compared to last winter – equivalent to the capacity of three medium-sized gas plants.
This growth is primarily due to three factors:
- New connections of energy storage systems to national and regional grids,
- Higher availability of gas units,
- Commissioning of the Greenlink interconnector, enhancing energy transfer between the UK and Ireland.
Despite the positive outlook, the operator warns that periods of tight supply may occur during exceptionally high demand. In such cases, NESO will utilize standard market tools, including Capacity Market Notices and Electricity Market Notices.
BESS – the backbone of the modern capacity market
Energy storage systems are playing an increasingly important role in the UK capacity market, securing reserve energy contracts since 2015. These technologies enable rapid response when wind or solar generation drops and demand spikes.
The growing number of BESS projects in the UK addresses the increasing intermittency of renewable energy. Storage systems stabilize the grid, allow for price arbitrage, and reduce the need to start costly, high-emission peaking plants.
The UK government is currently consulting on capacity market rules to better reflect a system increasingly reliant on renewable generation, aiming to ensure reliability even with high levels of variable energy.
New system elements: gas, interconnectors, and storage
NESO’s report highlights that interconnectors and flexible gas generation remain key components of the UK energy mix. The 2025 Greenlink Interconnector, linking Wales with southeast Ireland, enhances energy exchange and system resilience to local power shortages.
Meanwhile, the growing number of grid-scale BESS projects, both stand-alone and hybrid (paired with wind and solar farms), significantly improves grid balancing capabilities. Industry analyses indicate that total storage capacity in the UK could exceed 12 GW by 2030.
Deborah Petterson, NESO’s Director of Resilience and Crisis Management, emphasized the importance of industry cooperation:
“It is crucial to continue working with the sector to prepare for winter, building on current foundations and maintaining our global reputation for reliable electricity supply.”