The National Energy System Operator (NESO) anticipates a summer 2025 marked by record-low electricity demand, driven by unprecedented growth in solar generation across the United Kingdom. According to the Summer Outlook 2025 report, there is a 50% probability of reaching a new all-time low in national demand, falling below 13.4 GW.
“The rise of renewables connected to distribution networks is increasing minimum demand variability,” NESO states in its report. This scenario presents complex operational challenges, particularly during weekends and bank holidays, when favourable weather conditions could see demand drop to 12.6 GW.
While security of supply is assured, the operator’s focus is on managing generation surpluses during low-demand periods. “We expect to use our full range of operational tools, including issuing NRAPM notices,” the organisation warns. These Negative Reserve Active Power Margin (NRAPM) notices are exceptional mechanisms to request additional flexibility from the market.
Operational tools to balance a renewables-saturated system
In response, NESO will leverage balancing services, battery and pumped storage, alongside strategic operations through European interconnectors. However, maintenance outages at pumped storage facilities will reduce flexibility by approximately 1 GW compared to 2024.
“Inflexible generation capacity, combined with renewable output and imports, will exceed demand on certain days,” the report explains. Dynamic management through exports or curtailment of renewable generation will be essential in these situations.
European market dynamics and the role of interconnectors
The UK is set to remain a net importer of electricity this summer, driven by lower wholesale prices in continental Europe, where renewable overcapacity, particularly solar, is generating negative price periods. Price differentials of up to £40/MWh are fuelling imports from France, Belgium, and the Netherlands.
Nevertheless, NESO confirms it has sufficient operational surplus to manage uncertainties in interconnector flows. “We continue to work closely with neighbouring TSOs to ensure flexibility and reciprocal support,” the operator highlights.
Mega solar projects: the root of the challenge
This scenario stems from the UK’s ambitious solar development strategy. According to data gathered by Strategic Energy Europe, over 18 GW of solar mega projects are planned or under construction nationwide. These initiatives not only accelerate the energy transition but also reshape demand and supply patterns on the grid.
Flagship projects like Botley West Solar Farm and Longfield Solar Farm, each exceeding 500 MW, exemplify this expansion. Primarily connected to distribution networks, these plants reduce observed transmission demand, increasing operational complexity during solar peak hours.
Towards a zero-carbon and resilient grid
NESO continues to progress towards its goal of operating Great Britain’s electricity system carbon-free for at least one 30-minute settlement period in 2025. To achieve this, it has implemented innovative services such as Dynamic Containment and reduced the minimum inertia requirement to 120 GVA.s, delivering savings exceeding £200 million.
“The systems and tools developed in support of our zero-carbon ambition will reduce costs, emissions, and ensure safe operations,” the operator asserts. Furthermore, initiatives like the Stability Pathfinders and the integration of grid-forming batteries enhance grid stability.
Review of 2024 and outlook for winter 2025/26
In summer 2024, the UK was a net importer 78% of peak periods, while minimum demand remained within forecast ranges due to cooler-than-average weather.
Looking ahead, NESO is already preparing its Winter Outlook 2025/26, having secured 7.9 GW in the latest Capacity Market auction. “We continue to monitor global energy markets to anticipate any uncertainties that could impact winter operations,” the report concludes.
