Mercia Power Response, a key provider of flexible power response services to the UK grid, has signed an agreement with RheEnergise to explore the potential deployment of RheEnergise’s new and innovative form of long-duration hydro-energy storage, known as High-Density Hydro® (HD Hydro). Mercia Power Response ("Mercia PR") and RheEnergise will work together to identify suitable sites for additional HD Hydro storage projects. The two companies' initial focus will be the feasibility of getting 100MW of HD Hydro in commercial operation by 2030 by utilising Mercia PR’s existing grid connections.

With 40 sites having a combined capacity of 263MW and a number of sites under development and construction over the next 5-10 years, Mercia PR believes that RheEnergise’s HD Hydro storage technology would be a complementary, low carbon solution to its operating portfolio.

Additionally, Mercia PR's industry partners bring market expertise in energy trading and forecasting, helping RheEnergise to optimise grid-connected energy storage projects.

RheEnergise’s HD Hydro storage system is low-cost, energy efficient and fast to construct.  Rather than using water, it uses an environmentally benign fluid which is 2½ times denser than water, and which can provide 2½ times the power when compared to a conventional low-density hydro-power system. It means that HD Hydro can be deployed beneath the surface of hills rather than mountains, so opening up massive opportunities in the UK and around the world.

Graham White, CEO at Mercia PR said: “It is very exciting to explore how we can engage with RheEnergise's HD Hydro technology, applying our expertise in finding the right locations, developing sites, getting grid connections and operating within the Capacity Market. We see enormous potential for HD Hydro deployment as a future low-carbon replacement to our existing gas-powered assets.”

Stephen Crosher, Chief Executive of RheEnergise said: “Mercia PR’s experience in flexible power response and its deep knowledge of the UK energy system will be hugely beneficial to the RheEnergise team. Our HD Hydro technology can provide medium and long duration energy storage, which is becoming increasingly important as the UK moves towards Net Zero and with a UK energy system that is increasingly reliant on intermittent renewables. We are delighted that Mercia PR has chosen to work with us.”

Sophie Orme, Commercial Director of RheEnergise added: “Given the growing pressure to speed up the decarbonisation of the UK’s energy system, our HD Hydro system can be consented in months rather than years, so we are able to make a meaningful and positive impact on the energy transition over the next decade. With our partnership with Mercia PR, we will have a better understanding of the feasibility of deploying 100MW of long duration storage capacity by 2030.”

Notes to Editors:

How the HD Hydro system works: at times of low energy demand, with associated low costs, the High-Density Fluid R-19™ is pumped uphill between storage tanks (buried underground). The storage tanks are connected by underground pipes. As energy prices rise, the non-corrosive fluid is released downhill and passes through turbines, generating electricity to supply power to the grid. Projects will range from 5MW to 100MW of power and can work with vertical elevations as low as 100m or less. It means that, unlike conventional pumped hydro energy storage, a RheEnergise HD Hydro system can operate beneath small hills rather than mountains; the system requires 2½ times less vertical elevation. It also means that there are many more sites suitable for RheEnergise projects – in the UK and across the world. 

RheEnergise’s analysis of potential project opportunities has indicated that there are c6500 site opportunities in the UK, c115,000 in Europe, c345,000 in North America and c500,000 in Africa and the Middle East.



In November 2022, RheEnergise was awarded a UK £8.25m small business research initiative (SBRI) contract from the UK Government’s Net Zero Innovation Portfolio (NZIP) to deploy a first-of-a-kind demonstrator at a site near Plymouth, Devon.

About Mercia Power Response 

Mercia Power Respose has grown its portfolio quickly since 2016, securing and developing over 40 prime operational power response stations sites, with a combined capacity of 263MW, delivering flexible power to local communities. With an extensive pipeline of power response and battery sites identified, it to grow its gas-fuelled power station capacity to about 300MW by 2025 and complement the portfolio by developing grid-scale battery storage sites.