High-density hydro transforms UK energy storage

Published: 27 January 2026. The English Chronicle Desk. The English Chronicle Online.

A quiet hillside outside Plymouth has entered Britain’s energy history with a remarkable debut. Engineers confirmed that a pioneering underground hydropower project has begun producing electricity, marking a global first. The site in Devon uses an innovative approach that reimagines pumped storage, allowing clean power to be stored and released without mountains or massive dams. This breakthrough has placed high-density hydro firmly at the centre of future energy discussions within the United Kingdom and beyond.

Hydropower has supported electricity networks for more than a century, yet it traditionally demands dramatic landscapes. Large reservoirs and steep valleys usually define pumped storage schemes. The Devon project challenges that assumption by proving that gentle slopes can also store vast amounts of energy. The system sits almost entirely underground, preserving the surrounding countryside while quietly performing a task once thought impossible on such terrain.

The project has been developed by British firm RheEnergise, whose engineers sought to overcome the limitations of geography. Their answer was to replace ordinary water with a specially formulated mineral-rich fluid. This liquid is more than two and a half times denser than water. By increasing density, the same power output can be achieved with far less height. As a result, high-density hydro opens doors for regions previously ruled out for pumped storage.

At its core, the system still follows familiar principles. When electricity supply is plentiful, surplus power drives pumps that move the fluid uphill through underground pipes. When demand rises or renewable output falls, the fluid is released downward. Turbines convert that movement back into electricity, feeding it into the grid. The difference lies in efficiency and location, rather than concept, making the technology easier to integrate with existing infrastructure.

During testing, the Devon installation consistently generated 500 kilowatts of power. If operated continuously, that output could supply electricity to roughly 400 homes for an entire year. Company data shows the system maintained stable performance across repeated cycles. For engineers, this reliability offered crucial proof that high-density hydro can function beyond theoretical models and laboratory simulations.

Stephen Crosher, chief executive of RheEnergise, described the moment as transformative for energy storage. He explained that the project validated years of research and development. According to Crosher, the Devon site demonstrates that pumped storage no longer belongs only to mountainous regions. He said the results provided confidence as the company prepares to move toward commercial-scale deployment internationally.

Energy analysts have long argued that long-duration storage remains the missing link in renewable transitions. Wind and solar power are abundant but variable, often generating electricity when demand is low. Without storage, excess energy can overwhelm grids, forcing operators to curtail generation. Technologies like batteries help over short periods, but they struggle to provide power for days. This is where high-density hydro could play a decisive role.

The UK government has already recognised the importance of such solutions. More than £69 million has been allocated to support long-duration energy storage development. Officials believe that improving storage capacity could significantly reduce the overall cost of achieving net zero emissions. By storing low-carbon electricity during periods of surplus, the country can rely less on fossil fuels during shortages.

In Devon, the project’s underground design has also drawn praise from environmental groups. Traditional hydropower schemes often face criticism for their visual impact and ecological disruption. By contrast, this system leaves the landscape largely untouched. Most infrastructure sits beneath the surface, and there is no large reservoir altering local ecosystems. Supporters argue this makes high-density hydro easier to approve and faster to build.

RheEnergise has confirmed discussions with independent developers across Europe and North America. Talks are underway in Italy, Poland, Spain, and the United States, alongside further opportunities within the UK. The company expects the first commercial-scale installation to be operational within three years. Larger projects, developed with major utilities, are anticipated during the 2030s.

These timelines align with forecasts for renewable expansion. As offshore wind farms multiply and solar capacity grows, pressure on grids will intensify. Storage systems capable of holding energy for extended periods will become increasingly valuable. Industry observers suggest that high-density hydro could complement existing pumped storage stations, rather than replace them, creating a more flexible national network.

Government ministers have voiced strong support for the Devon breakthrough. Patrick Vallance, the minister responsible for science and innovation, highlighted the strategic importance of energy storage. He stated that as Britain moves toward a clean power system, the ability to store electricity will be critical. Vallance noted that scaling innovations like this could strengthen energy security while supporting economic growth.

Local leaders have also welcomed the project, citing its potential economic benefits. Construction and maintenance create skilled jobs, while the technology positions the region as a leader in clean energy innovation. For Devon, the installation represents not just an engineering milestone but a statement about the future direction of regional development.

Critics remain cautious, pointing to costs and long-term maintenance requirements. They stress that mineral-based fluids must be carefully managed to avoid environmental risks. RheEnergise insists rigorous safeguards are in place, with closed-loop systems designed to prevent leaks. Independent assessments are expected as projects move toward larger scales.

Despite these concerns, the broader energy sector is watching closely. Analysts suggest that if costs fall as projected, high-density hydro could compete favourably with other storage options. Its reliance on proven mechanical components, rather than rare materials, may also reduce supply chain vulnerabilities that affect battery technologies.

For now, the Devon hillside continues its quiet work, pumping and releasing energy beneath the soil. What appears unremarkable on the surface represents a profound shift underground. By redefining where and how pumped storage can operate, the project offers a glimpse into a more resilient energy future.

As Britain accelerates toward its climate targets, innovations like this may determine success or failure. The Devon experiment suggests that solutions can emerge from rethinking old ideas, rather than abandoning them. In that sense, high-density hydro stands as both a technological advance and a reminder that even established energy forms can evolve.

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