BW ESS, EDF ink 10-year floor for 1.2 GWh British battery

BESS developer, owner and operator BW ESS has signed a 10-year floor agreement with EDF for the first phase of the Hams Hall Battery Energy Storage System (BESS) in North Warwickshire, central England, which will deliver 350 MW of power output and 1,243 MWh of storage capacity.

Floor agreements for BESS are contractual arrangements in which an offtaker guarantees a minimum income level (the floor) to the asset owner, providing downside protection. They help bridge the gap between investor demand for revenue certainty and the merchant nature of battery storage, often incorporating a profit-sharing mechanism when revenues exceed the agreed floor.

Under the agreement, the details of which were not disclosed, EDF will optimise its longest-duration battery contracted to date using its PowerShift platform. This will enable the asset to provide flexibility to the electricity system by balancing supply and demand, supporting grid stability, and facilitating the integration of increasing volumes of renewable generation.

The Hams Hall project will initially deliver 350 MW of capacity, with a second phase adding a further 50 MW to bring total site capacity to 400 MW/1,424 MWh. Currently under construction on the northeastern fringe of Birmingham, the site benefits from proximity to major demand centres and a connection to the nearby Hams Hall 400 kV National Grid substation. The project is expected to reach commercial operation in Q4 2026.

Hams Hall forms a key part of BW ESS’s UK portfolio and is co-owned with infrastructure investor AIP Management, which bought into the developer’s 2.4 GWh UK battery portfolio in September 2025.

Under a deal inked in September 2024,  China’s Sungrow is supplying 280 sets of grid-forming PowerTitan 2.0 liquid-cooled energy storage systems to the Hams Hall project.

Upon completion, it will become BW ESS’s largest project globally – around four times the size of the 100 MW/331 MWh Bramley BESS, which was the UK’s largest battery at the time of its commissioning in February 2025.

The Bramley project made headlines in August 2024 as the first single BESS asset in Great Britain to secure a long-term tolling agreement. The seven-year fixed-price contract was signed by BW ESS and partner Penso Power with Shell Energy Europe Limited.

BW ESS is active across the UK, Australia, Italy, Germany, Spain, and Sweden. The company has more than 540 MWh of operational assets, approximately 11 GWh under or in pre-construction, and a development pipeline of around 8 GW.