Ofgem confirmed that 77 projects totalling 28.7 GW cleared the first eligibility hurdle in Window 1 of the Long Duration Electricity Storage (LDES) cap and floor scheme.
Lithium-ion (Li-ion) batteries dominate, but pumped hydro and flow batteries also made it through.
These projects now move into the Project Assessment stage, and Ofgem (with NESO’s support) will run the Multi-Criteria Assessment (MCA) to decide who gets support.
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Which LDES technologies are in the running?
Of the 171 LDES projects (52.6 GW) that applied, 77 projects (28.7 GW) cleared the eligibility stage and now face the multi-criteria assessment.
Li-ion dominates with over 20 GW of eligible projects, representing two-thirds of the total eligible capacity.
How much capacity could win contracts
Ofgem hasn’t committed to a number yet. Instead, the final amount it is willing to procure will depend on the MCA results, NESO’s updated system modelling, and their judgment on consumer value.
Ofgem will consider technology diversity during the assessment stage. It may adjust the shortlist to avoid over-reliance on a single technology, which could mean swapping out some Li-ion battery projects in favour of pumped storage hydro or flow schemes.
LDES project scale and technology mix
Eligible LDES projects range widely in size, from just 50 MW up to nearly 2 GW. For example, at the top end are mega-projects like Nexus 1 (1.8 GW Li-ion), Earba (1.8 GW PSH), and Coire Glas (1.45 GW PSH).
Ten projects reach or exceed 1 GW each. Just a handful of very large sites represent one-third of the eligible capacity mix.
At this stage, Ofgem has only published power capacity (MW). Projects have submitted duration and energy (MWh) data for the next assessment, but Ofgem has not indicated whether that level of detail will be released publicly.
To pass eligibility projects had a duration requirement of eight hours at full power. This would mean at least 230 GWh of energy capacity is currently eligible for the scheme. However, some projects are expected to have higher durations than this, such as SSE’s Coire Glas at 23 hours.
Tracks and delivery timelines
Projects are split into two tracks based on when they are expected to be operational. Ofgem and Government set the delivery windows, but developers self-selected which track to apply for:
- Track 1 (by 2030): 71 projects, 24.5 GW
- Track 2 (by 2033): 6 projects, 4.2 GW
With 24.5 GW planned by 2030, track 1 is heavily front-loaded, reinforcing the scheme’s role in meeting Clean Power 2030 targets.
Ofgem will assess all eligible projects at the same time, but its methodology naturally favours schemes that can deliver sooner. Track 1 projects, due by 2030, are therefore likely to take priority because they align with the Government’s Clean Power 2030 goals.
Deliverability forms a central part of the Strategic Assessment, and Ofgem will judge how prepared each developer is to meet its track deadline.
The framework: three tests every LDES project must pass
The LDES cap & floor selection is based on an "in-the-round" assessment that combines the results of an Economic, Strategic, and Financial Assessment.
In plain terms, the “in the round” approach means Ofgem will look at the full picture rather than rely on a single score, and each assessment has no fixed weighting.
1. Economic Assessment
The Economic Assessment estimates the benefits each project will deliver, capturing both monetised and non-monetised impacts.
At the core is a Benefit-Cost Ratio (BCR), which weighs monetised benefits against project costs. These monetised elements include wholesale price shifts, constraint management, security of supply, and project costs. Ofgem will then adjust the ranking for non-monetised factors, such as:
- avoided curtailment,
- real-time flexibility,
- operability benefits, and
- wider social or environmental impacts.
Ofgem adjusts the BCR using a “swing-weighting” method. This means giving more weight to the non-monetised impacts where projects differ the most, so those differences influence the final ranking.
2. Strategic Assessment
This stage checks whether the overall portfolio aligns with national objectives. It looks at:
- Technology diversity,
- Locational diversity,
- Deliverability and cost overrun risks,
- Robustness across Future Energy Scenarios (FES) and weather years.
3. Financial Assessment
This screens out LDES projects that are likely to sit persistently below the floor (i.e. requiring ongoing consumer subsidy).
- Expected revenues (arbitrage, re-optimisation, ancillary services, Balancing Mechanism non-energy, Capacity Market) are benchmarked as a percentage of the floor.
- A cap and floor financial model sets corridor levels, and a “re-optimisation uplift” is applied to capture intraday and Balancing Mechanism value.
In other words, BESS projects that can credibly demonstrate high re-optimisation revenues, strong ancillary positioning, and cost efficiency will score best.
Looking ahead
Eligible projects now have until 18 November 2025 to submit their data forms and evidence. Ofgem will publish an Initial Decision List in Spring 2026, followed by final cap and floor awards in Summer 2026.
For developers, the message is clear: beyond cost and efficiency, evidence of deliverability, re-optimisation capability, and system operability will be decisive. For the GB system, the outcome will shape how 28.7 GW of long-duration storage competes to secure a consumer-backed revenue floor.
