IN Brief:
- The UK has launched a £28m Ultra-Long Duration Energy Storage Challenge targeting storage beyond 100 hours.
- An initial Innovate UK competition offers up to £3m for electrochemical project-development studies, with demonstrators planned later.
- The wider challenge also includes underground hydrogen storage as government examines technologies capable of covering prolonged renewable shortfalls.
UK Research and Innovation and the UK government have launched a £28m Ultra-Long Duration Energy Storage Challenge aimed at technologies capable of storing electricity for more than 100 hours, pushing development well beyond the durations now common in commercial battery projects.
The programme forms part of the R&D Missions Accelerator Programme and covers technologies including advanced electrochemical storage and underground hydrogen. Its purpose is to develop systems capable of retaining renewable electricity through prolonged periods rather than simply shifting power between neighbouring hours of the same day.
That distinction changes the engineering requirement substantially. Most grid batteries currently operating in Britain are designed for much shorter discharge periods, with developers balancing cell cost, inverter capacity, grid connection, and market opportunities around services such as frequency response, balancing, wholesale trading, and daily energy shifting.
A technology able to sustain useful output for more than 100 hours addresses a different system condition. Several days of low wind, weak solar production, high demand, or transmission constraint can create an energy deficit that cannot be covered economically by a conventional short-duration battery simply by adding more power electronics.
The first electrochemical competition under the programme offers up to £3m for project-development studies. Innovate UK requires applicants to demonstrate a route towards technologies capable of supplying cost-effective electrical power to the UK grid for at least 100 continuous hours and achieving a working life of at least 25 years.
The studies must extend beyond laboratory chemistry. The scope includes technology assessment, engineering design, cost and scale-up roadmaps, market assessment, development planning, and manufacturing and supply-chain plans, placing industrialisation alongside electrochemical performance.
That matters because a promising storage medium is only one component of a grid asset. Large-scale deployment also requires containment, thermal management, fire or process safety, power conversion, transformers, switchgear, protection, controls, civil infrastructure, auxiliary power, communications, maintenance access, and a connection capable of operating across charging and discharge conditions.
Projects must also support a pathway towards a UK demonstration by 2030. A planned second competition phase is scheduled for the middle of 2027, with at least £10m allocated to large-scale demonstrators, subject to the later competition proceeding as planned.
The 25-year operating-life requirement creates another practical hurdle. Electrochemical systems are affected by calendar ageing, cycling, temperature, depth of discharge, and equipment obsolescence, while inverter, control, cooling, and auxiliary equipment may require replacement on different timescales from the primary storage medium.
A credible ultra-long-duration design therefore has to explain not only how much energy it can store on day one but how that performance will be maintained over decades. Augmentation, replacement strategy, maintenance intervals, warranty structures, degradation assumptions, and availability become part of the economic case.
The wider £28m challenge also includes underground hydrogen storage. That approach separates the stored-energy medium more clearly from the electrical equipment: renewable electricity can be converted into hydrogen, stored underground where suitable infrastructure and geology exist, and later converted back into power or used in another energy application.
Hydrogen introduces larger conversion losses than direct battery storage, but efficiency is only one metric for a system intended to hold very large amounts of energy for long periods. Capital cost per stored megawatt-hour, standing losses, storage volume, cycling frequency, site availability, discharge capability, and conversion-plant cost all affect whether a technology is competitive for multi-day use.
Government has cited modelling suggesting underground hydrogen storage could reduce total energy-system costs by between £14bn and £50bn over the period from 2035 to 2050. Those are modelling results rather than guaranteed savings, but they indicate the scale of the problem policymakers expect long-duration storage to address.
The research programme sits alongside Britain’s separate cap-and-floor framework for long-duration electricity storage. Ofgem is developing special licence conditions for the first commercial LDES window, while the new Ultra-LDES Challenge is aimed further upstream at technology development, scale-up, manufacturing, and demonstration.
Keeping those programmes separate is important. The cap-and-floor regime is intended to improve investment certainty for projects approaching commercial deployment; the £28m challenge is intended to determine whether less mature technologies can reach the engineering and manufacturing stage where large-scale deployment is credible in the first place.
For UK manufacturers, that gives the programme an industrial dimension. A technology that can deliver electricity for five days but depends on specialist components with no scalable manufacturing route will remain difficult to finance, while a system based on repeatable modules, established materials, maintainable power electronics, and a realistic supply chain has a clearer route into infrastructure procurement.
The initial electrochemical competition closes at 11:00am on 30 September 2026, with applicants due to be notified in November and projects expected to start from January 2027. The later demonstrator phase will provide the more demanding test: moving beyond feasibility studies into hardware capable of proving that multi-day storage can operate reliably at useful scale.
The technology challenge is therefore less about stretching the duration label attached to existing batteries and more about developing a different class of grid asset. A power system dominated by variable renewables needs fast response, but it also needs energy reserves that remain available long after conventional short-duration batteries have completed their discharge cycle.
