Every metered battery bought its power back below the market price
On the performance league a battery that works hard in the balancing mechanism often shows a large negative number, and a negative number reads as a loss. It is a purchase. Across 143 metered batteries the fleet paid £134.4m to buy back 1,833,634 MWh of energy that was worth £199.2m at the market index in the same half hours. Not one of the 143 paid above the index on average.
What an accepted bid actually is
A battery sells its output before delivery. When the control room accepts a bid from it, the unit delivers less than it sold, or takes more in, and it pays for the energy it no longer delivers. Settlement records that payment and nothing else, so the money leaving is visible and the sale it cancels is not.
48 of the 143 units end the year with a negative balancing figure, £37.0m between them. Once the position outside the balancing mechanism is derived from their meters and added back, 44 of those 48 are positive.
What was measured
Every accepted bid for every metered unit over the year to 11 October 2026, with the price the unit was paid or charged for it, against the market index in the same half hour. Volumes and prices are Elexon's, the index is the public benchmark, and both are free. Volume weighted across the fleet the units paid £73.30 a megawatt hour for energy the market was pricing at £108.64.
| Unit | Bought back | Paid | Market index | Difference |
|---|---|---|---|---|
| Zenobe Blackhillock (BLHLB-3) | 81,622 MWh | £63.17 | £101.92 | £38.75 |
| Zenobe Blackhillock (BLHLB-4) | 72,467 MWh | £63.08 | £107.21 | £44.13 |
| Zenobe Blackhillock (BLHLB-1) | 71,541 MWh | £62.04 | £104.79 | £42.75 |
| Zenobe Blackhillock (BLHLB-2) | 67,923 MWh | £61.27 | £104.23 | £42.96 |
| Auchteraw | 52,750 MWh | £62.09 | £107.16 | £45.07 |
| Lakeside BESS | 42,892 MWh | £82.40 | £113.22 | £30.82 |
| Little Raith BESS | 42,133 MWh | £65.57 | £103.34 | £37.77 |
| Roaring Hill BESS | 41,256 MWh | £66.96 | £105.19 | £38.23 |
| Thurrock Flexible (THURB-1) | 35,618 MWh | £82.40 | £112.94 | £30.54 |
| Hawthorn Pit BESS | 35,132 MWh | £75.70 | £106.83 | £31.13 |
| Ilmer Lane BESS | 32,455 MWh | £78.19 | £101.78 | £23.59 |
| Skelmersdale Battery | 31,454 MWh | £80.81 | £106.12 | £25.31 |
The twelve largest by volume. Every unit's own table, band by band, is on its asset page.
Scotland buys back cheaper, by half as much again
| Where | Units | Bought back | Paid | Market index | Difference |
|---|---|---|---|---|---|
| Scotland | 35 | 735,413 MWh | £64.12 | £108.99 | £44.87 |
| England and Wales | 108 | 1,098,221 MWh | £79.44 | £108.40 | £28.96 |
This is the same constraint the Scotland finding measures from the other end. North of the boundary the network cannot move what is generated, so the control room is buying output back all day and it does not have to pay much for it.
The grid pays some of them to take power
On 136,384 MWh the price was below zero, so the unit was paid to absorb energy rather than charged for it, £3.0m in all. 141 of the 143 units had at least one such half hour. The four Blackhillock units in Moray take the top four places for it.
What this is not
It is not measured profit. The index is a public benchmark, not the price any of these units sold at. We do not know what they sold for, and nobody outside the trade does. The difference above is what the bought back energy was worth against a benchmark.
The gap is partly the price of being chosen. The control room takes the cheapest bids first. A unit asking more is passed over, so accepted bids are cheap by selection, and some of this difference is that mechanism rather than skill.
Not every bid cancels a sale. A bid accepted while a unit is charging is energy bought through the balancing mechanism instead of the market, and that is a purchase with no cancelled sale behind it. 12 of the 143 units bought back more than their meters took in all year, which can only be cancelled sales; for the rest the two cannot be separated from public data.
One unit shows no difference at all, on two megawatt hours across the whole year. A single instruction is not a measurement.