Monk Fryston

What it is

Where the duration comes from. Constantine Energy Storage, which owns the battery, announced in February 2025 that its five 57 MW batteries (Ocker Hill, Whitegate, Monk Fryston, Capenhurst and Legacy) are 2.7 hour systems, about 154 MWh each, with Habitat Energy trading the first three and EDF the other two (Solar Power Portal, 17 February 2025, solarpowerportal.co.uk). Sungrow, which supplied the batteries, gave Ocker Hill and Capenhurst as 57 MW and 165 MWh each in March 2023, before they were built, about 2.9 hours (sungrowpower.com). This page takes the later and lower figure. Until 25 October 2026 it gave 2 hours, the capacity market class, which is the duration an agreement was bid in. What the battery declares to NESO is above 2 hours: in the fullest 5% of 790 half hours from 8 to 24 October 2026, the energy it held plus its room to charge came to 132 MWh. A battery declares less than it holds when it sets energy aside for frequency response. SSE's separate 320 MW battery at Monk Fryston is a different project. Every megawatt hour figure on this site for this battery is worked from 2.7 hours.

Who owns it and who trades it

How we know. The project companies are named HD, a number and three letters of the place, so FRY is Monk Fryston and OCK is Ocker Hill. Both are controlled by Constantine Energy Storage Midco LLP, which is controlled by Constantine Energy Storage LLP. Above that the register carries a statement that there is no registrable person, so who owns Constantine is not published anywhere we can read. Both companies were held by Pelagic Energy Development Ltd from 2019 until 2025.

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 (SSE project); probable (HD identity). Checked 2026-08-31. 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 2,116 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. 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

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 £149.97 a megawatt hour at that same index, 1.43 times the average. What it took in was worth £75.75, 0.72 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 21,400 MWh of accepted bids it paid an average of £101.71 a megawatt hour. The market index averaged £134.50 across those same half hours, so it bought back at £32.79 a megawatt hour below the going price.

On 439 MWh the price was below zero: NESO paid this unit an average of £27.48 a megawatt hour to take energy, £12k in all. That is a constrained network with more generation on it than it can move.

The other direction, offers, is much smaller here: 30,122 MWh where NESO asked for more, paid at an average of £109.03 against an index of £77.15.

Physical checks passed: the meter never exceeded the registered power by more than fifteen per cent, and the year's exports against imports are what a battery does.

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.