First-of-its-kind underground hydro storage begins generating electricity in Devon
A hillside near Plymouth, Devon, has become a landmark in renewable energy as a novel, high-density hydropower system begins generating electricity. The project, described by engineers as the first of its kind, embeds a water‑driven energy storage and generation facility underground, offering a new approach to pairing hydropower with storage and demand for clean electricity.
Hydropower is one of the oldest forms of energy storage — using the gravitational potential energy of water to drive turbines. What makes this Devon project different is its “high-density” design, which compresses storage capacity into a compact underground space and couples it with a hydropower generator that can respond rapidly to electricity demand. In effect, the hillside acts as a giant, hidden battery that can be filled and discharged through controlled water flow.
The motivation behind the project is to improve grid resilience and flexibility. Hydroelectric storage is typically tied to large reservoirs or pumped storage stations with significant land footprints. This underground approach demonstrates how storage density can be increased without sacrificing output or speed. By placing the system underground, engineers aim to reduce environmental footprint, minimize visual impact, and enable efficient siting in a region with high energy demand and ambitious climate targets.
The Devon system operates by circulating water between an underground reservoir and surface facilities, using gravity and pumped flow to convert potential energy into electricity as needed. When demand is high, water is released through turbines to generate power; during excess generation, energy is stored by pumping water back into the underground reservoir. The result is a flexible, dispatchable source of clean electricity that can complement intermittent renewables like wind and solar.
Initial tests indicate the technology can respond quickly to changes in grid demand, a critical capability as electricity markets push for faster ramping capabilities and higher reliability. While the project remains in the early stages, developers say it has the potential to deliver a scalable model for future underground hydro storage projects in other parts of the country and beyond.
Experts describe the project as a step toward a more resilient energy system that leverages existing hydropower know-how while embracing modern storage concepts. In many regions, the challenge is balancing supply and demand in real time while keeping emissions low. High-density underground hydro storage could become a valuable tool in meeting peak demand during cold snaps or heatwaves when electricity use spikes, all while reducing the need for peaking power plants powered by fossil fuels.
The Devon project also highlights the importance of cross-disciplinary collaboration. Engineers, hydrologists, electrical engineers, geotechnical experts, and policy makers have joined forces to assess the site, ensure structural safety, and integrate the system with the broader grid. Ongoing monitoring and data collection will help researchers understand performance, reliability, and environmental impact over time.
As with any innovative infrastructure, there are questions to answer, including long-term durability, maintenance costs, and the economics of scale. Supporters point to the potential for lower land use, reduced construction timelines, and improved aesthetic integration as key advantages. If successful, the technology could unlock new opportunities for other hillside sites and urban pockets where space is at a premium but demand for clean energy remains high.
Looking ahead, proponents envision a future where underground hydro storage complements a diverse mix of technologies. The ability to store energy underground, with compact footprints and rapid response times, could complement batteries, pumped storage, and other grid-scale solutions. Devon’s pioneering system is more than a demonstration project—it’s a practical experiment in rethinking how and where we generate, store, and deploy clean electricity.
In summary, the Devon hillside “battery” marks a bold step in the evolution of hydropower and energy storage. As the system ramps up and more data becomes available, the project will be watched closely by researchers, policymakers, and energy companies seeking scalable, sustainable ways to keep the lights on while reducing emissions.
