Brentwood BESS

Part of Brentwood, one of 2 balancing units at one site totalling 101 MW. This page is the E_BRETB-2 unit alone.

What it is

Who owns it and who trades it

How we know. 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.

Market registers name the party that sells into the market, which for a battery is usually an optimiser under contract rather than the owner. Elexon's balancing mechanism unit register names the seller here and the name is checked against it on every build. How we tell them apart

Until 8 December 2025 this battery sold as E_BRETB-1 under ARENKO CLEANTECH LIMITED, taking £400k inside this page's year. The handover shows in the register as a new code, not a renaming, and the old page keeps its record.

What it earned

Balancing is offer revenue and does not net off the cost of the power. The response and reserve figure is the value implied by the published auction results, award quantity times clearing price times the length of the delivery window, and not a settled payment. Capacity market income is the cleared price raised for inflation where the auction set a base period, split by month on EMRS's weights. Method

Outside the balancing mechanism, derived from the meter

Elexon publishes what this unit's meter recorded every half hour. Take away the balancing volumes NESO accepted and what is left is the position the unit ran outside the balancing mechanism: its wholesale trading, its frequency response delivery, and its losses, together. This unit held a frequency response contract in 7,908 of those half hours. The energy the contract asked of it, contracted megawatts times NESO's published delivery curve at the measured grid frequency, is taken out of the position and valued at the imbalance price, because it sits outside the unit's declared position and that is the price Elexon settles it at. What remains is the traded position, valued at the market index. In 2 half hours a contract was held but the grid frequency is not yet held, so those are left in the traded position. The volumes are measured. The prices are public benchmarks, not this unit's trades. The product is derived, and is shown apart from the three measured lines above. 177 days to 12 September 2026, 33 of them still provisional in Elexon's settlement runs. Method and caveats

When it moved, against when power was dear

Across every half hour this unit was metered the market index averaged £104.61. What it sent out was worth £112.04 a megawatt hour at that same index, 1.07 times the average. What it took in was worth £88.44, 0.84 times. Selling above one and buying below one is a unit positioned into the dear half hours and out of the cheap ones. It measures the half hours it chose, not the price anyone paid it, which is not published.

What it paid to buy energy back

When NESO accepts a bid, this unit delivers less than it had already sold, or takes more in. It pays for the energy it no longer delivers, and that payment is most of what makes the balancing figure above negative. Whether that is a cost or a margin depends on the price it paid. Across 3,214 MWh of accepted bids it paid an average of £67.02 a megawatt hour. The market index averaged £94.30 across those same half hours, so it bought back at £27.28 a megawatt hour below the going price.

On 394 MWh the price was below zero: NESO paid this unit an average of £21.58 a megawatt hour to take energy, £9k in all. That is a constrained network with more generation on it than it can move.

The other direction, offers, is much smaller here: 1,149 MWh where NESO asked for more, paid at an average of £137.68 against an index of £102.22.

Checks this unit did not pass cleanly. Published anyway, because a flagged figure with its flag is more use than a blank.

• only 177 of 364 days metered

Where it stands

Percentiles, so 90 means better than nine in ten of the cohort named beside it, on that measure alone, over the same 364 days. Rates are pounds per kilowatt per year, annualised over the days the unit has been on the system, the same figures the performance league ranks on. A high position in the taken-in table is not a fault: a constraint asset is paid to charge, and charging is its job.

The nearest comparables

The five nearest in size in England and Wales, and this battery among them, ranked by what each was paid for every kilowatt it holds over the 364 days to the same date. They run for about the same length of time. Same market, same rules, same weather.

See it on the map

Open the operating map here

Every figure on this page traces to a published file. If something here is wrong about your asset, the methods section says how to tell us.