RheEnergise has reached full capacity at its first High-Density Hydro energy storage project near Plymouth, Devon. The 500 kW demonstrator marks a breakthrough for long-duration energy storage technology that can operate on hills rather than requiring mountainous terrain.
The system uses a fluid that is 2.5 times denser than water, allowing smaller installations with the same energy output as traditional hydro pump systems. The breakthrough opens up thousands of potential sites in Britain that were previously unsuitable for hydropower storage.
The Cornwood project, built at Sibelco’s kaolin mine, received £8.25 million in government funding through the Net Zero Innovation Portfolio programme. RheEnergise has announced that this is the case completed mechanical work on site in September last year.
The timeline for commercial implementation is accelerating
Stephen Crosher, CEO of RheEnergise, said: “Everyone on the RheEnergise team, along with our investors, our business partners and the UK government, who have provided valuable support to the project, are delighted that we have achieved full capacity and that it is performing exactly as predicted. We have proven and critically downscaled our high-density hydro technology, allowing us to focus on deploying the solution in commercial-scale LDES systems in the UK and globally.”
The successful operation heralds the next phase of project development on a commercial scale. The company is developing sites in Great Britain, Italy, Poland, Spain and North America, with the first commercial project expected to be operational within three years.
Lord Patrick Vallance, the UK Secretary of State for Science, Innovation, Research and Nuclear Energy, said: “Energy storage will play an increasingly important role in the clean energy transition. RheEnergise’s unique system has the potential to strengthen our future long-term energy storage capabilities.”
The news comes as the UK government pushes to deploy 4 to 6 GW of long-term energy storage by 2030 under its Clean Power 2030 Action Plan. Ofgem is currently assessing 77 projects for cap-and-floor investment support, with decisions expected in summer 2026.
RheEnergise’s analysis has identified around 6,500 potential sites in Britain alone, compared to the limited mountainous sites suitable for traditional pumped hydro. This could accelerate the deployment of the long-term storage needed to balance increasing renewable energy generation.
