Wormald Green BESS

What it is

The power on this page comes from the owner. Harmony Energy Income Trust, which owned the battery when it was built, announced it on 12 September 2024 as 33 MW and 66 MWh, a two hour system. The capacity market and planning records also give 33 MW. Elexon registers the unit at 40 MW. Northern Powergrid's register probably shows the same battery, as Wormald Green Hybrid: 32.5 MW, connected on 18 September 2024, on a connection that allows 43 MW out and 33.2 MVA in, shared with a solar farm not yet built. Harmony Energy, which manages the battery, confirmed on 6 November 2026 that nothing has changed at the site: 33 MW and 66 MWh remain correct and its export has stayed within 33 MW throughout 2026. Elexon's figures for the unit show more than that from April 2026: up to 36.7 MW sent out, and on 12 June 74.3 MWh in one discharge. Harmony Energy explained why. For a battery on a distribution network, the volume Elexon publishes is the site's meter multiplied by the network operator's line loss factor for that half hour. Northern Powergrid moved Wormald Green from its general factors to factors of its own on 1 April 2026, and those reach 1.106 on power sent out. Elexon's data fits that account. Since April the highest half hours sit at two levels, 35.7 MW and 36.6 MW, which are 33 MW multiplied by 1.08 and 1.11. Over the same months the energy sent out rose from 86% to 94% of the energy taken in, more than any battery returns. So the megawatts, megawatt hours, cycles and efficiency read from Elexon's meter figures on this page are up to a tenth above what crossed the site's own meter since April. The money figures stand, because settlement pays on the same adjusted volumes. With thanks to Harmony Energy for the explanation. Every per kilowatt figure on this site is worked from 33 MW. Read the announcement.

Where the duration comes from. Harmony Energy Income Trust announced Wormald Green on 12 September 2024 as 33 MW and 66 MWh, a two hour system. Every megawatt hour figure on this site for this battery is worked from 2 hours.

Who owns it and who trades it

How we know. The HEIT SPV naming; the trust sold its assets to Foresight.

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

What it is built from

From published documents, not from any register: supplier and contractor project pages, owner announcements and the trade press. Confidence: confirmed. Checked 2026-08-30. source 1 · source 2. Fields not shown are not published anywhere we have found, and we do not guess them.

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 7,564 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 14 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. 358 days to 5 November 2026, 42 of them still provisional in Elexon's settlement runs. Method and caveats

This battery connects to a distribution network. For such a unit the volumes Elexon publishes are settlement volumes: the site's own meter multiplied by the network operator's line loss factor for that half hour. The factor is usually within a few per cent of one, so the megawatt hours, cycles and efficiency above can sit a little above or below what crossed the site's meter. The money is settled on the same adjusted volumes. Method and caveats

When it moved, against when power was dear

Across every half hour this unit was metered the market index averaged £104.66. What it sent out was worth £133.14 a megawatt hour at that same index, 1.27 times the average. What it took in was worth £85.44, 0.82 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 18,483 MWh of accepted bids it paid an average of £96.08 a megawatt hour. The market index averaged £130.09 across those same half hours, so it bought back at £34.01 a megawatt hour below the going price.

On 626 MWh the price was below zero: NESO paid this unit an average of £13.47 a megawatt hour to take energy, £8k in all. That is a constrained network with more generation on it than it can move.

The other direction, offers, is much smaller here: 24,180 MWh where NESO asked for more, paid at an average of £119.98 against an index of £88.08.

Physical checks passed on power: the meter never exceeded the registered power by more than fifteen per cent. The year's exports against imports are higher than a battery returns, which the loss factor in the note above explains.

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.

In its distribution register

The distribution register of Northern Powergrid lists this site as Wormald Green Hybrid, 32 MW, connected on 18 September 2024. Matched on a site word in common, 2 km apart.

See it on the Development Atlas

From each operator’s embedded capacity register, read every Monday. How the registers are linked to the units that trade.

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.