RheEnergise commissions first ‘high density hydro’ LDES in UK

A UK startup has commissioned a pilot energy storage project designed to allow smaller, flexible hydro installations to be built in hills rather than mountains. RheEnergise secured a grant from the UK government to support development of the now operational Cornwood project in Plymouth, England.

The energy system uses a low-viscosity, denser-than-water fluid, but otherwise operates like a typical hydro energy storage plant, pumping uphill when electricity demand is low and discharging when demand is high. The low viscosity and higher density of the fluid mean the system requires two-and-a-half times less vertical elevation than a standard hydro plant, according to the RheEnergise, potentially expanding the number of viable sites for pumped energy storage.

The idea has attracted significant backing from UK and European innovation funds. RheEnergise has secured GBP 8.25 million ($11.3 million) from the UK government, as well as grant support from the European Innovation Council (EIC) Accelerator program. The company aims to have commercial-scale projects in operation within the next three years and is currently progressing potential sites in the United Kingdom, Italy, Poland, Spain and North America.  

The Cornwood project will serve as a demonstrator for RheEnergise, providing power to the nearby Sibelco Cornwood kaolin mine. The energy storage installation has 500 kW peak power output capacity and will support the clay mine to decarbonize its operations, according to RheEnergise. Commercial projects are expected to range fro 10 MW to 100 MW power capacity, at four- to 20-hour durations.

In a press release, RheEnergise Chief Executive Stephen Crosher said the project had reached full power and was performing “exactly as predicted.”

“We have proven and critically de-risked our high-density hydro technology, which will allow us to focus on deploying the solution in commercial-scale LDES schemes in the UK and worldwide,” Crosher said.

RheEnergise aims to have commercial-scale projects in operation within the next there years and is currently progressing potential sites in the United Kingdom, Italy, Poland, Spain and North America.  

Cornwood’s commissioning is part of a wider push to accelerate LDES deployment in the United Kingdom. The UK government has targeted between 4 GW and 6 GW of power from LDES by 2030, according to the government’s Clean Power 2030 Action Plan, and support for the industry includes innovation funding and a new cap-and-floor support mechanism, with announcement on the first tranche of successful projects expected in June 2026.