Gravity Power, LLC has received a federal award from the U.S. Department of Energy to build a test system for underground pumped hydro, a technology that stores grid-scale energy by raising and lowering heavy masses in sealed shafts rather than relying on reservoirs of water. The $199,649 Phase I grant, which runs from July 22, 2024, through June 21, 2025, funds a concept that could sidestep the biggest constraints facing conventional pumped hydroelectric storage, including water scarcity, land footprint, and geographic dependence on elevation changes. If the approach works at scale, it would offer utilities and grid operators a way to bank renewable electricity in regions where traditional hydro is impossible.
How Underground Gravity Storage Actually Works
Conventional pumped hydro plants move water between two reservoirs at different elevations. When electricity is cheap or abundant, pumps push water uphill; when demand spikes, the water flows back down through turbines. The method accounts for roughly 95 percent of global grid-scale storage capacity, but it demands specific terrain and enormous volumes of water, making new projects slow, expensive, and politically difficult to site. Underground gravity systems flip this model by replacing the upper reservoir with a heavy piston that rides up and down inside a deep, sealed shaft filled with a working fluid. Energy goes in by lifting the piston; energy comes out when the piston descends under its own weight, pressurizing the fluid and driving a turbine at the surface.
The Gravity Power project, formally titled a test system for underground pumped hydro, describes exactly this architecture. Because the shaft is sealed, water losses from evaporation or seepage are essentially eliminated. The system can be sited almost anywhere deep drilling is feasible, removing the need for mountainous terrain or large surface water bodies. That geographic flexibility is the core selling point. Solar and wind farms in flat, arid landscapes, where storage is most needed, could pair directly with underground gravity units instead of waiting years for a pumped hydro dam to clear environmental review. In principle, modular shafts could even be clustered near substations, turning otherwise unused land into long-duration storage hubs.
Federal Funding Signals Growing Interest
The DOE awarded Gravity Power the grant under its Small Business Innovation Research program, contract number DE-SC0025060, according to the federal award portal. Phase I awards are relatively modest, designed to prove technical feasibility before a company can compete for larger Phase II funding. The $199,649 amount reflects that early stage: Gravity Power must demonstrate that its test rig can cycle reliably and that the energy density claims hold up in a controlled environment. Success here would open the door to multimillion-dollar follow-on contracts and, eventually, commercial pilot installations that connect to real distribution or transmission infrastructure.
Gravity Power is not the only company chasing this idea. Quidnet Energy, which pursues a related geomechanical approach that pressurizes water in underground rock formations, announced in November 2022 that it would receive $10 million in federal funding to commercialize its clean energy technology. The gap between a $199,649 feasibility study and a $10 million commercialization grant illustrates where Gravity Power sits on the development curve, but it also shows that federal agencies are placing multiple bets across the gravity storage category rather than picking a single winner. For policymakers, seeding several technical pathways is a hedge against the risk that any one design fails to scale or runs into unforeseen environmental or engineering barriers.
What Peer-Reviewed Research Says About Cost and Efficiency
A key question for any new storage technology is whether it can compete on levelized cost of storage, or LCOS, the metric that captures total lifetime expense per unit of energy delivered. A peer-reviewed paper in the Journal of Energy Storage provides a life-cycle assessment framework comparing gravity energy storage systems against both pumped hydro and compressed air energy storage, known as CAES. The study applies standardized system boundary assumptions and benchmarks efficiency alongside cost metrics such as LCOS and levelized cost of energy, giving independent researchers a baseline for evaluating claims from startups like Gravity Power and their competitors. By modeling different configurations and duty cycles, it highlights where gravity-based systems could be most competitive, such as long-duration applications that cycle less frequently but store large amounts of energy.
That kind of independent benchmarking matters because company-funded projections often assume favorable conditions that may not hold in practice. The Journal of Energy Storage paper offers a techno-economic comparison that accounts for construction, operation, and decommissioning across each technology’s full life cycle, including embedded emissions and material intensity. Pacific Northwest National Laboratory has also published detailed cost-performance data for energy storage technologies through its Energy Storage Grand Challenge, providing another institutional reference point. Together, these sources suggest that gravity-based systems have a plausible path to cost competitiveness, particularly where land constraints or water scarcity rule out large reservoirs. Still, real-world validation at scale is missing. Without operational pilot data, the efficiency and LCOS numbers remain modeled rather than measured, and investors will want to see hardware performance, maintenance profiles, and unplanned outage rates before committing large capital to full-scale deployments.
Why Water Independence Changes the Calculus
The “zero water” framing in gravity storage is not just a marketing angle. Drought conditions across the western United States have already forced conventional hydroelectric plants to curtail output, most visibly at large reservoirs where falling water levels have repeatedly threatened generation capacity and turbine operation. A storage technology that does not consume or depend on surface water avoids that vulnerability entirely. For grid planners in arid states, this removes a major risk variable from long-term resource planning, allowing them to model storage output without tying it to uncertain hydrological futures. It also eliminates the permitting battles that arise when new projects compete with agricultural, municipal, or ecological water demands, which can delay or derail conventional hydro proposals for years.
The tradeoff is that underground gravity systems introduce a different set of engineering challenges. Deep shaft construction is expensive and technically demanding, borrowing methods from mining and oil drilling and requiring specialized contractors. Seal integrity over thousands of charge-discharge cycles has not been proven at commercial scale, raising questions about long-term maintenance and potential leakage of the working fluid. And the energy density advantage, while real in theory because dense materials like concrete or iron can be far heavier per cubic meter than water, depends on achieving tight tolerances in shaft diameter and piston fit. Any gap between the piston and shaft wall means friction losses and reduced round-trip efficiency, while overly tight fits complicate construction and increase costs. These are solvable problems, but they require exactly the kind of iterative testing that the DOE Phase I grant is designed to underwrite, moving the concept from paper studies to instrumented prototypes that can be cycled, monitored, and refined.
What Comes Next for Underground Pumped Hydro
Over the next year, Gravity Power’s task is to turn theoretical promise into empirical data. The company’s test system must demonstrate that the mechanical components can survive repeated lifting and lowering without excessive wear, that the seals and shaft lining maintain integrity, and that the measured round-trip efficiency aligns reasonably with modeled expectations. If those milestones are met, the firm can apply for Phase II SBIR funding, which is structured to support larger-scale engineering and early commercial demonstrations. That second step would likely involve integrating a prototype with real grid signals (charging when wholesale prices are low or negative, discharging during peaks) to validate the operational value of underground gravity storage in day-to-day market conditions.
In parallel, regulators and utilities will be watching the broader gravity storage field, including geomechanical concepts like Quidnet’s and other underground or tower-based designs, to see which architectures mature fastest. For all of them, the bar is not just technical feasibility but bankability: lenders and project developers need robust cost curves, performance guarantees, and clear permitting pathways. Underground pumped hydro offers an intriguing combination of familiar components—turbines, pumps, shafts—and novel configuration, which could ease acceptance if early projects prove reliable. If Gravity Power and its peers can navigate the engineering and financing hurdles, underground gravity storage could join batteries, conventional pumped hydro, and thermal storage as a mainstream tool for balancing high-renewable grids, particularly in regions where water and land constraints make traditional solutions untenable.
More from Morning Overview
*This article was researched with the help of AI, with human editors creating the final content.
