Voltwise Power (Sandbrook Capital)
Owns 10 batteries at 9 sites, 446 MW, which is 6.5 per cent of everything operating in Great Britain. It sells none of that power itself. The register names one seller for the whole fleet, EDF Energy Customers Limited.
Who sells its power
The balancing mechanism register names the company allowed to sell each unit's power. That company is usually an optimiser or a supplier working under contract, which is why the registers cannot answer the ownership question on their own. Where the seller is one of the owner's own companies, the row says so.
| Seller | Batteries | MW | Of this fleet |
|---|---|---|---|
| EDF Energy Customers Limited | 10 | 446 | 100% |
What it was paid
The three published lines, added up across the fleet for the 364 days to 6 September 2026. Wholesale trading income is invisible for every owner, not just this one, and nothing here nets the cost of charging. The rate is per kilowatt of current capacity.
| Balancing mechanism, paid to discharge | £3.9m |
| Balancing mechanism, paid out to charge | −£3.2m |
| Response and reserve auctions | £7.2m |
| Capacity market | £2.1m |
| Income across the fleet, per kilowatt | £29.77/kW/yr fleet 35.48 |
| Median battery, all three lines | £18.48/kW/yr |
| Hours at full power, sent out | 68 h/yr |
| Hours at full power, taken in | 97 h/yr |
What the fleet is made of
Duration, by megawatt
Region, by megawatt
Every battery it owns
| Battery | MW | Sold by | Grade | £/kW/yr |
|---|---|---|---|---|
| Wolverhampton West BESS Mid Wales and The Midlands | 56 | EDF Energy Customers Limited | confirmed | 26.51 |
| Newton wood BESS North Midlands and North Wales | 52 | EDF Energy Customers Limited | confirmed | 43.56 |
| Brook Farm BESS Mid Wales and The Midlands | 52 | EDF Energy Customers Limited | confirmed | 41.06 |
| Burwell 1 Mid Wales and The Midlands | 52 | EDF Energy Customers Limited | confirmed | 31.69 |
| Brentwood BESS Essex and Kent | 52 | EDF Energy Customers Limited | confirmed | 17.15 |
| Berkeley BESS Cotswold | 52 | EDF Energy Customers Limited | confirmed | 19.43 |
| Hunningley Stairfoot BESS North Midlands and North Wales | 44 | EDF Energy Customers Limited | confirmed | 43.21 |
| North Tawton BESS West Devon and Cornwall | 32 | EDF Energy Customers Limited | confirmed | 18.48 |
| Erskine BESS South West Scotlands | 30 | EDF Energy Customers Limited | confirmed | 14.39 |
| East Cambridgeshire Mid Wales and The Midlands | 24 | EDF Energy Customers Limited | confirmed | 6.11 |
3 batteries ran under an earlier registration for part of the year, E_BERKB-1, E_BRETB-1, E_BURWB-1. The money earned under the earlier code is in the book above; the capacity is counted once.
How we know
Confirmed means a control filing at Companies House, or the owner's own published statement, names the company. Probable means the evidence is strong and indirect. Named means the register leaves the owner blank, the balancing code carries the owner's initials, and a sibling unit at the same site is already settled. Each chain below is printed once, with the batteries it settles.
Confirmed Wolverhampton West BESS, Newton wood BESS, Burwell 1, Berkeley BESS, Hunningley Stairfoot BESS, North Tawton BESS, Erskine BESS
Companies House: Care Power (Barnsley) is controlled by Care Assets Ltd, whose controller changed from SMS Energy Services to Voltwise UK BESS Opco on 19 May 2025; the sibling SPVs share the same parent. Source
Confirmed Brook Farm BESS, Brentwood BESS, Brentwood (earlier registration)
Voltwise's own project list carries Brook Farm and Brentwood; acquired with the SMS battery business, announced 23 June 2025. Source
Confirmed Burwell Weirs Drove BESS (earlier registration), East Cambridgeshire
The register names no owner. The capacity market holds a site called BURWB1 belonging to Voltwise Power Holdings Limited, which is this unit's own balancing code, and Burwell Weirs Drove is a two phase Voltwise site of about 126 MW operated by Ethical Power. Source
Confirmed E_BERKB-1 (earlier registration)
The register names no owner. The capacity market holds a site called BERKB1 belonging to Voltwise Power Holdings Limited 830 metres away, which is this unit's own balancing code. Source
Attribution. A battery belongs to whoever the documents name today, so a fleet that changed hands during the year credits the whole year to the current owner. Groups are joined only where a filing joins them; a company that holds through several vehicles appears once, under the name at the top of the chain. Directors and registered offices are never used as evidence on their own. Why the registers cannot answer this question