About 550 MW of batteries are running that no market register can see
Every balancing dataset published in Great Britain describes the batteries that register in the markets it covers. That is not the fleet. Reading owners' own project lists, supplier case studies and financing announcements against the registers, we have so far named 10 operating batteries, about 550 MW, that appear in none of them. Each is listed here with what its owner or supplier has published, the document, and the mechanism that hides it. A site on this list is not a rumour: it is a battery somebody has announced, financed or energised, and that the public record of the markets cannot see. A further 4 sites, 168 MW, are listed below but not counted, because the only date their owner has published is a plan rather than a report of operation.
Inside another company's identity: 2 sites, 128 MW
The battery trades under a supplier or aggregator's own registration, so nothing public carries its name. A toll or an offtake makes the counterparty the seller.
| Site | MW | What is published |
|---|---|---|
| Bramley | 100 | 331 MWh; 2025-02-17; owner: BW ESS. Penso Power developed it; BW ESS bought Penso Power outright and merged it into its storage platform in October 2024, so the two names on the 2023 and 2024 announcements are one company now; sells through: Shell Energy, seven year fixed price toll from August 2024, the UK's first single asset BESS tolling agreement; built with: Sungrow, PowerTitan 2.0 (grid forming, AC DC block) confirmed source 1 source 2 |
| Basildon BESS, Eku Basildon, Essex | 28 | 56 MWh; operational per Eku's project list; owner: Eku Energy; sells through: Habitat Energy optimises (ledger); NHOA supplied; built with: NHOA Energy (two Eku southern England projects, 130 MWh together) confirmed (site, operation); possible (truly unseen) source 1 |
Behind a generator unit: 0 sites, 0 MW, and 2 listed but not counted
The battery charges and discharges inside a wind farm's own balancing unit. The tell is a registered demand capacity far larger than a wind farm needs for its own auxiliaries: Harestanes carries 51 MW where ScottishPower's other wind farms carry 2.5.
| Site | MW | What is published |
|---|---|---|
| Harestanes BESS Harestanes windfarm, Forest of Ae, Dumfries and Galloway | 50 | construction from July 2022; commissioning at the end of 2024; operations expected during 2025 (SPR 2024 accounts); listed, not counted: the published COD is a forecast, not a report of operation: construction from July 2022; commissioning at the end of 2024; operations expected during 2025 (SPR 2024 accounts); owner: ScottishPower Renewables (Iberdrola) confirmed (existence, size, hosting unit); probable (operating date) source 1 source 2 |
| Battery@Ray, Ray wind farm, Northumberland | 20 | 45.5 MWh; energisation expected late 2022; listed, not counted: the published COD is a forecast, not a report of operation: energisation expected late 2022; owner: Vattenfall; sells through: Arenko, from November 2022 (its second co-located Vattenfall battery) confirmed (project); possible (truly unseen) source 1 |
Operating, no code joined: 7 sites, 372 MW, and 1 listed but not counted
The owner says it operates and documents say it was built, but no auction or balancing code we hold joins to it. Some will be codes we have not yet joined; some are truly absent.
| Site | MW | What is published |
|---|---|---|
| Bumpers BESS Buckinghamshire | 99 | 198 MWh; 2023-10 (energised); owner: Harmony Energy Income Trust (HEIT), whose assets moved under Foresight; built with: Tesla, Megapack confirmed (site, size, operation); possible (truly unseen) source 1 source 2 |
| Low Carbon trio: Meadow, Sandon Brook, Fern Brook | 70 | 190 MWh; first system online early 2025; owner: Low Carbon; sells through: Habitat Energy, Flexitricity and EDF on revenue share, with KrakenFlex as dispatch and controls across all four; built with: Trina Storage, 0.5P Elementa cabinets confirmed (portfolio); possible (which codes carry it) source 1 source 2 |
| West Bradford, the 58 MW not registered | 58 | completed 2025 (annual report 2025); owner: Gresham House Energy Storage Fund, through UK Battery Storage Limited; sells through: not published by site. The fund had 528 MW under a toll with Octopus Energy at the end of 2025, most of it expiring in 2026, and Octopus's balancing units are supplier aggregates that carry no site name; the annual report does not say which sites the toll covers confirmed (site and size, from the owner); possible (why it is absent) source 1 source 2 |
| Thurcroft, Rotherham | 50 | operational by 31 December 2024 (factsheet); owner: Gresham House Energy Storage Fund, through HC ESS7 Limited; sells through: not published by site. The fund had 528 MW under a toll with Octopus Energy at the end of 2025, most of it expiring in 2026, and Octopus's balancing units are supplier aggregates that carry no site name; the annual report does not say which sites the toll covers confirmed (site and size, from the owner); possible (why it is absent) source 1 source 2 |
| Elland 1, West Yorkshire | 50 | operational by 31 December 2024 (factsheet); owner: Gresham House Energy Storage Fund, through UK Battery Storage Limited; sells through: not published by site. The fund had 528 MW under a toll with Octopus Energy at the end of 2025, most of it expiring in 2026, and Octopus's balancing units are supplier aggregates that carry no site name; the annual report does not say which sites the toll covers confirmed (site and size, from the owner); possible (why it is absent) source 1 source 2 |
| Sambar BESS, near Newquay near Newquay, Cornwall | 48 | 95 MWh; online targeted Q2 2025 (acquired by Varco April 2024); listed, not counted: the published COD is a forecast, not a report of operation: online targeted Q2 2025 (acquired by Varco April 2024); owner: Varco Energy (Adaptogen Capital); built with: GE Vernova: FlexIQ controls, FLEXinverter central inverters, battery DC blocks, with long term service confirmed (project); possible (operating and unseen, or still commissioning) source 1 |
| Tynemouth, North Tyneside | 25 | operational by 31 December 2024 (factsheet); owner: Gresham House Energy Storage Fund, through Tynemouth Battery Storage Limited; sells through: not published by site. The fund had 528 MW under a toll with Octopus Energy at the end of 2025, most of it expiring in 2026, and Octopus's balancing units are supplier aggregates that carry no site name; the annual report does not say which sites the toll covers confirmed (site and size, from the owner); possible (why it is absent) source 1 source 2 |
| Staunch, Staffordshire | 20 | operational by 31 December 2024 (factsheet); a seed asset bought at the IPO in 2018; owner: Gresham House Energy Storage Fund, through Noriker Staunch Limited; sells through: not published by site. The fund had 528 MW under a toll with Octopus Energy at the end of 2025, most of it expiring in 2026, and Octopus's balancing units are supplier aggregates that carry no site name; the annual report does not say which sites the toll covers confirmed (site and size, from the owner); possible (why it is absent) source 1 source 2 |
No register presence: 1 sites, 50 MW, and 1 listed but not counted
Documented, operating, and absent from every register we read, with no explanation yet found.
| Site | MW | What is published |
|---|---|---|
| Overhill Pulse Clean Energy near Aberdeen | 50 | 110 MWh; full commercial operations targeted mid 2025; listed, not counted: the published COD is a forecast, not a report of operation: full commercial operations targeted mid 2025; owner: Pulse Clean Energy (IMCO backed); built with: Powin, Stack750 with StackOS confirmed (project); probable (operating and unseen) source 1 |
| Penwortham Storage Penwortham substation area, Lancashire | 50 | 50 MWh; 2024-05 (online; GRID's 25th operating asset); owner: Gresham House Energy Storage Fund plc (GRID) owns; Statera Energy developed and runs operations and maintenance confirmed (site, owner, dates); possible (which code carries it) source 1 source 2 |
Why it matters
A fleet figure built from the registers alone undercounts what is running, and it undercounts unevenly: the tolled, the aggregated and the co-located are exactly the sites whose owners have chosen not to trade in their own name. Anyone benchmarking a battery against "the fleet" is benchmarking against the part of it that shows. The list grows as the register hunt continues, and a site leaves it the day a code joins to it.
Fordtown left this list on 24 September 2026. Its reserve auction code AG-HEL0CP had been in NESO's results all along. NESO publishes that code without a postcode, and a postcode is how a battery that trades only in the auctions gets onto our map. It now has its own page.
Minety left this list on 27 September 2026. Its two reserve auction codes, AG-HLIM03 and AG-HLIM04, had been in NESO's results all along, at Minety's own postcode. No Elexon unit carries its name, and the site's battery test did not read the codes an aggregator registers. It now has a page for each of its two registrations, Minety (AG-HLIM03) and Minety (AG-HLIM04).
Creyke Beck left this list on 27 September 2026. Its reserve auction code, AG-MSTK01, had been in NESO's results all along under Statkraft, which trades it, with only the postcode district HU16. No Elexon unit carries its name, and the site's battery test did not read the codes an aggregator registers. It now has its own page.
Minety South left this list on 27 September 2026. Statkraft, which trades both of its batteries, sells one reserve auction code in Minety parish, AG-HSTK01, and a second of about the same size in the same region with no postcode, AG-HSTK02, which we take to be the other battery. Both had been in NESO's results all along, under names that say nothing, and the site's battery test did not read the codes an aggregator registers. It now has a page for each of its two registrations, Minety South and Minety South 2.
Pelham left this list on 27 September 2026. Its reserve auction code, AG-ASTK05, had been in NESO's results all along under Statkraft, which trades it, with only the postcode district SG9, where NESO pays no other code of any kind. No Elexon unit carries its name, and the site's battery test did not read the codes an aggregator registers. It now has its own page.
Dunsinane left this list on 27 September 2026. Its reserve auction code AG-EDF01P had been in NESO's results all along. NESO publishes that code without a postcode, and a postcode is how a battery that trades only in the auctions gets onto our map. It now has its own page.
Loudwater left this list on 27 September 2026. Its reserve auction code AG-HSTK07 had been in NESO's results all along. NESO publishes that code without a postcode, and a postcode is how a battery that trades only in the auctions gets onto our map. It now has its own page.
Rusholme left this list on 27 September 2026. Its reserve auction code AG-MCAM01 had been in NESO's results all along. NESO publishes that code without a postcode, and a postcode is how a battery that trades only in the auctions gets onto our map. It now has its own page.
Ferrymuir left this list on 27 September 2026. Its reserve auction code AG-NFLX09 had been in NESO's results all along. NESO publishes that code without a postcode, and a postcode is how a battery that trades only in the auctions gets onto our map. It now has its own page.
From the technical register, checked 2026-09-27. The mechanism is read from the documents, not guessed; "no register presence" means we have found no explanation yet. Methods