The UK government has launched a £28m programme to develop energy-storage technologies capable of supplying electricity for more than 100 hours, targeting one of the infrastructure problems created by a power system increasingly reliant on variable renewable generation.
The Ultra-Long Duration Energy Storage Challenge will support technologies including advanced batteries and underground hydrogen storage, with funding delivered through UK Research and Innovation.
Its focus is prolonged periods when wind and solar generation is low. Short-duration batteries already play a growing role in balancing the electricity grid over minutes or hours, but storage lasting more than four days is intended to provide resilience across a fundamentally different timeframe.
The government is dividing the challenge between electrochemical technologies capable of extended discharge and underground hydrogen systems that can store energy at much larger scale.
An initial competition is making up to £3m available for UK-registered businesses to carry out project-development studies for ultra-long-duration battery demonstrators. Applications close on 30 September.
The wider £28m programme forms part of a £102m clean-energy package that also includes £74m for consumer-led flexibility. Those schemes sit within the UKRI R&D Missions Accelerator Programme, through which the government intends to deploy at least £500m by 2030 and attract additional private capital.
Very long-duration storage remains an emerging commercial market. The engineering challenge is only part of the problem: projects must also generate sufficient revenue to justify large upfront investment despite being designed partly for periods that may occur infrequently.
A storage asset capable of providing electricity during several consecutive days of weak renewable output can have considerable system value without operating continuously. Conventional electricity-market revenues do not always capture that resilience, which leaves policymakers and regulators considering how capacity and avoided network costs should be rewarded.
Hydrogen provides one possible route. Surplus renewable electricity can power electrolysers, producing hydrogen that is stored underground and later converted back into usable energy. The process loses energy at each stage, but geological storage could achieve capacities that would be difficult or prohibitively expensive using conventional batteries.
Long-duration battery developers are pursuing different chemistries designed to avoid some of the cost and degradation limitations associated with lithium-ion systems. Their commercial prospects will depend on capital cost, efficiency, safety, lifetime, materials availability, and manufacturing scale.
The government estimates that underground hydrogen storage could contribute to system savings running into tens of billions of pounds between 2035 and 2050. Those projections remain sensitive to future technology costs, power demand, generation capacity, and the design of both electricity and hydrogen markets.
Ofgem is separately working on support for long-duration electricity storage, including projects that could contribute to Britain’s first new pumped-storage hydro capacity in decades.
The technologies are likely to serve different purposes rather than compete directly in every application. Pumped hydro has an established operating record and can provide large-scale storage, but depends on suitable geography and major civil engineering. Batteries can be located more flexibly, while hydrogen offers the potential for very large quantities of stored energy over longer periods.
The need for those options increases as the proportion of wind and solar generation rises. Periods of abundant renewable power can push wholesale prices down, while prolonged low-generation conditions can produce sharp increases and require fossil-fuel plants to remain available as backup.
Storage provides a means of transferring electricity or energy between those conditions. In principle, greater flexibility reduces curtailment when renewable generation is high and lowers reliance on expensive backup generation when output falls.
The £28m programme is small relative to the capital eventually required for commercial infrastructure. Its purpose is to move emerging technologies towards demonstrators capable of generating credible operating, engineering, and financial evidence.
That evidence will determine whether developers can progress from public research support into assets financed on commercial terms. Investors will need confidence not only that systems work technically, but that market arrangements provide durable revenues over operating lives measured in decades.
Ultra-long-duration storage therefore sits at the intersection of technology development, energy security, and market design. The programme can help establish which technologies are viable; deployment at scale will depend on whether the electricity system places sufficient commercial value on the resilience they provide.
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