Batteries awarded 1.22 GW in UK capacity market auction for 2029 delivery

Grid operator NESO procured 1.22 GW of de-rated BESS capacity in the latest long T-4 capacity market auction for Great Britain’s electricity grid, with under construction projects securing the vast majority of contracts awarded to battery storage.

NESO’s provisional results for the T-4 auction for delivery year 2029/30 show the gird operator procured 40.1 GW of capacity at a clearing price of GBP 27.10 ($36.36)/kW/year – the lowest T-4 clearing price since 2022. The provisional results record 1.22 GW of awarded capacity across 109 capacity market units (CMU) with battery storage listed as the primary fuel. There were 49 battery storage CMUs that exited the auction without a contract, roughly one third of the total entering under the battery fuel type. Contracts awarded to BESS assets across a range of deployment durations, including eight-hour batteries in development.

NESO’s results list just 40 MW awarded capacity for existing BESS while new build storage accounted for 1.18 GW of awarded capacity, across a diverse range of storage durations. This included 431 MW of awarded capacity for two-hour storage, 224 MW for four-hour, 273 MW for five-hour, 16 MW for five-hour and 70 MW for eight-hour energy storage.

The T-4 capacity market auction allows grid operator NESO to secure capacity for Great Britain’s energy grid four years in advance of delivery, while providing project developers with bankable offtake agreements to support project financing. Contract lengths on offer include one, three, nine and 15-year capacity agreements.

Gas generators made up the lion’s share of awarded capacity in the T-4 auction for delivery in 2029/30. NESO’s results record 23.48 GW of awarded capacity went to capacity market units listing gas as their primary fuel. Interconnectors were second place by fuel type, with 7.82 GW of awarded capacity, followed by demand-side response at 2.57 GW. Pumped storage was just ahead of battery storage by listed fuel type, with 1.35 GW de-rated capacity procured. Provisional results show six pumped-storage assets were awarded capacity, with one exiting the auction without an agreement.

The T-4 auction follows NESO’s T-1 top-up auction conducted one week before. NESO’s provisional result for that auction show awarded capacity of 576 MW for battery storage at a clearing price of GBP 5/kW/year.

The results of the T-4 capacity auction are provisional for a period of eight working days after the completion of the auction. During this time, the UK government may annul the auction subject to regulation. The auction concluded on Mar. 10, 2026.