Partnership will assess sites and develop HD Hydro projects in Italy, with plans to expand across Europe.

Ikigai Energy (the development arm of the Ikigai Group) and RheEnergise are pleased to announce the signing of a memorandum of understanding (MOU) to develop a robust and meaningful pipeline of projects utilising RheEnergise’s innovative form of long-duration hydro-energy storage, High-Density Hydro® (HD Hydro). 

The two companies have started working together to identify sites and develop HD Hydro projects in Italy, with plans to rapidly expand to other European markets. Ikigai brings its experience developing and attracting investment for storage projects while RheEnergise brings the technology solution and engineering. 

HD Hydro is based on traditional pumped energy storage technology but rather than using water, a high-density fluid which is 2.5x denser than water is used in a closed loop. This means the technology needs around 40% of the height of a water-based systems for the same output, opening up hills, mines and brownfield sites rather than mountains. 

Ikigai sees HD Hydro as a cost-effective way to add long-duration storage in Italy and the rest of Europe. RheEnergise will draw on Ikigai's market and project development experience, and the two companies aim to build a pipeline of projects together with the aim of attracting the right investors to support the rollout of these projects in European markets where long-duration storage is fundamental to the support the grid network of the future. 

Commenting on the partnership, which builds on £8.24m of UK Government funding for RheEnergise through the Longer Duration Energy Storage Demonstration Programme, Stephen Hickey CMG, British Ambassador to Italy and San Marino, said:

“This partnership reflects the ambition of our UK–Italy Clean Power for Growth agenda: translating innovation and commercial cooperation into greater energy security, economic opportunities and practical benefits for both our countries. By combining RheEnergise’s British technology with Ikigai’s development experience in Italy, it offers a practical way to advance those shared priorities".

Roberto Castiglioni,

Co-founder and CEO at Ikigai, commented:

“Developing a 2.8GW BESS pipeline across Italy gives us first-hand insight into what it takes to deliver successful projects, supported by strong relationships with key stakeholders, including MASE and Terna. As Italy’s wind and solar capacity grows, so does the need for long-duration storage. Together with RheEnergise, we are identifying sites with suitable topography and viable grid connections, ideally alongside wind farms, with commercial viability and bankability guiding our approach from the outset.”

Stephen Crosher,

Chief Executive of RheEnergise said:

“We are delighted to be partnering with Ikigai to bring HD Hydro at scale to Italy and Europe. Ikigai’s project development experience and deep knowledge of European markets will be a real asset to the RheEnergise team. Our HD Hydro technology provides long duration energy storage, it proves a route to 24/7 power from wind and solar, a vitally important step to create a 100% renewable energy system. We are delighted that Ikigai recognise the benefits that our solution provides and share our confidence in the strength of our innovation. Together we are tackling one of the largest opportunities in the energy sector, delivering best-in-class economics, lowering bills for consumers. It is an exciting time”

About Ikigai Group
Ikigai Group is an energy transition advisory and development group helping investors, infrastructure owners and large energy users decarbonise while improving resilience and commercial performance. It combines commercial, strategic and bankability expertise with practical project development experience.

Ikigai Energy, the group’s development arm, originates and co-develops renewable energy, storage and on-site energy projects. Its activities include a 19.9MW PV at Glasgow airport, 10MW at Luton airport and various PV projects at water utilities in the UK. In Italy, Ikigai Energy is currently developing a 2.8GW BESS portfolio through its GC Storage vehicle. All projects are developed with bankability, scalability and long-term value central to its approach.

About RheEnergise
RheEnergise is an innovative energy storage company pioneering the development of High-Density Hydro® technology. The company's mission is to provide cost-effective and sustainable energy storage solutions that can help accelerate the transition to a low-carbon economy.

How the HD Hydro system works: at times of low energy demand, with associated low costs, the High-Density Fluid is pumped uphill between storage tanks (buried underground). The storage tanks are connected by underground pipes. As energy prices rise, the environmentally benign 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 125m. It means that, unlike conventional pumped hydro energy storage, a RheEnergise HD Hydro system can operate beneath small hills rather than mountains. It also means that there are many more sites suitable for RheEnergise projects 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.

RheEnergise has achieved TRL 7 through our 500 kW/1 MWh demonstrator at Cornwood, Devon. The site contains every subsystem of a commercial project, tanks, pipework, pumps, turbomachinery and control system, operating outdoors on a real site rather than in a laboratory, and it reached full power in December 2025. It has completed over 100 charge and discharge cycles with performance consistently within 1% of our models, validating our high-density fluid, turbine and pump behaviour under the fluid's rheology, and round-trip system efficiency.