Abandoned mine shafts become testing ground for gravity-based energy storage

Overview

The world has roughly 500,000 abandoned mine shafts. A small group of engineering startups believes these holes in the ground could solve renewable energy's biggest problem: what happens when the sun sets and the wind dies. The concept is deceptively simple—use surplus electricity to winch a massive weight to the top of a deep shaft, then let gravity pull it back down through generators when power is needed.

So far, only one commercial-scale gravity storage system exists anywhere on Earth: a 25-megawatt tower in Rudong, China, commissioned in May 2024. The mine-shaft variant remains unproven at scale. Gravitricity tested a 250-kilowatt demonstrator in Edinburgh in 2021 and has signed agreements to build its first full-scale system in a 530-meter Finnish mine shaft. Energy Vault plans a 100-megawatt hybrid system in a former coal mine in Sardinia. If either succeeds, it could unlock a vast, cheap, long-duration storage network using infrastructure that already exists underground—no new mining, no lithium, no rare earth metals required.

Why it matters

If gravity batteries work at scale, the world's half-million abandoned mines become a ready-made energy storage network requiring no new materials.

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Key Indicators

Operational commercial gravity storage systems worldwide

Energy Vault's 25 MW tower in Rudong, China—the only non-pumped-hydro gravity system feeding a national grid.

Operational mine-shaft gravity batteries

No mine-shaft gravity storage system has been built at commercial scale anywhere in the world.

500,000+

Abandoned mine shafts globally

The International Institute for Applied Systems Analysis estimates these could theoretically provide 7 to 70 terawatt-hours of storage.

80%+

Round-trip efficiency demonstrated

Gravitricity's Edinburgh prototype achieved over 80% efficiency with sub-one-second response time.

90%

Share of global energy storage that is pumped hydro

Pumped hydroelectric storage—the original gravity battery, using water instead of weights—dominates all grid storage worldwide.

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People Involved

Charlie Blair

Leading commercialization of mine-shaft gravity storage

Robert Piconi

Leading diversified gravity and battery storage company

Organizations Involved

Gravitricity

Energy storage startup

Developing first full-scale mine-shaft gravity battery in Finland

Edinburgh-based startup developing gravity energy storage systems that raise and lower heavy weights in disused mine shafts.

Energy Vault

Publicly traded energy storage company

Operating world's only commercial gravity battery; expanding into mine-based systems

Swiss-American company that built the world's first commercial gravity storage system and is now developing a hybrid gravity-battery system in an Italian coal mine.

International Institute for Applied Systems Analysis (IIASA)

International research organization

Published key feasibility research on mine-shaft energy storage potential

Austria-based research institute whose 2023 study estimated that the world's abandoned mines could theoretically store between 7 and 70 terawatt-hours of energy using gravity systems.

Timeline

Gravity battery technology enters critical proof-of-concept year
Assessment

With the Rudong tower operational and mine-shaft projects in Finland and Sardinia targeting construction milestones, 2025 marks the year the technology must demonstrate it can work underground at commercial scale.
January 15th, 2025
ABB partners with Gravitricity on hoist engineering
Industry

Swiss-Swedish engineering giant ABB signs a collaboration agreement with Gravitricity to apply its deep-shaft hoist expertise to gravity storage systems.
December 1st, 2024
Energy Vault plans 100 MW hybrid system in Sardinia coal mine
Industry

Energy Vault and Carbosulcis announce a 100-megawatt hybrid gravity-plus-battery storage project at the former Nuraxi Figus coal mine in Sardinia, Italy.
August 5th, 2024
Rudong gravity battery fully commissioned
Technical milestone

Energy Vault's Rudong system completes testing and commissioning, becoming the world's first fully operational commercial gravity energy storage facility.
May 7th, 2024
Gravitricity announces Finland mine shaft project
Industry

Gravitricity reveals plans to install a 2-megawatt system in the 530-meter auxiliary shaft of Finland's Pyhasalmi mine, which would be the first full-scale mine-shaft gravity battery.
February 6th, 2024
Energy Vault connects Rudong system to China's grid
Technical milestone

The 25-megawatt, 100-megawatt-hour gravity storage tower in Rudong, China, becomes the first commercial gravity battery interconnected with a national power grid.
December 1st, 2023
Gravitricity signs deal for Czech Republic mine project
Industry

Gravitricity and Czech state enterprise DIAMO agree to develop a 4-megawatt gravity storage system in the Darkov coal mine shaft.
February 1st, 2023
IIASA study maps global mine storage potential at 7–70 TWh
Research

The International Institute for Applied Systems Analysis publishes research estimating that the world's 500,000-plus abandoned mines could store between 7 and 70 terawatt-hours of energy.
January 15th, 2023
Gravitricity tests 250 kW demonstrator in Edinburgh
Technical milestone

A 15-meter rig with two 25-tonne weights at the Port of Leith achieves over 80 percent round-trip efficiency and sub-one-second response time, proving the core concept works.
April 1st, 2021
Gravitricity founded to develop mine-shaft gravity batteries
Industry

Edinburgh startup begins developing systems to raise and lower heavy weights in abandoned mine shafts for energy storage.
January 1st, 2019
Energy Vault founded to commercialize solid gravity storage
Industry

Robert Piconi launches Energy Vault in Switzerland with a tower-and-crane design that lifts composite blocks instead of pumping water.
January 1st, 2018
First pumped-hydro storage built in Switzerland
Historical

The original gravity battery—using water instead of solid weights—begins operating, eventually becoming the dominant form of grid energy storage worldwide.
January 1st, 1907

Scenarios

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Predictions leaderboard

Mine-shaft gravity batteries prove viable, trigger European rollout

If Gravitricity's Pyhasalmi project and Energy Vault's Sardinia system both reach operational status by 2027–2028, demonstrating reliable efficiency above 80 percent and competitive costs, the European Commission's existing feasibility funding for coal region transition could rapidly scale into deployment grants. Germany's Ruhr Valley alone has hundreds of suitable shafts. This scenario transforms gravity storage from a curiosity into a cornerstone of Europe's grid flexibility strategy, particularly attractive because it repurposes existing infrastructure with no new mining required.

Discussed by: IIASA researchers, Gravitricity investors, European Commission energy planners

Consensus —

Technology works but can't compete with falling battery prices

Lithium-ion battery costs have fallen roughly 90 percent over the past decade and continue to decline, particularly with the rise of cheaper lithium iron phosphate chemistry from Chinese manufacturers. Even if gravity batteries achieve their technical targets, they may struggle to compete on cost per megawatt-hour for the four-to-eight-hour storage durations that dominate grid demand. Gravity storage's advantage lies in very long duration storage (12+ hours) and 50-year asset life, but if battery recycling improves and costs keep falling, the economic window for gravity may narrow before the technology reaches scale.

Discussed by: BloombergNEF analysts, battery industry executives, grid storage economists

Consensus —

Mine-shaft projects stall, gravity storage remains a niche tower product

Converting a century-old mine shaft into a precision energy system presents engineering challenges that demonstrators haven't yet faced: water infiltration, structural degradation, shaft geometry constraints, and the logistics of lowering 12,000-tonne masses in confined underground spaces. If the Finland or Sardinia projects encounter delays or cost overruns—as many first-of-kind energy projects do—investor confidence could evaporate. Energy Vault's tower-based systems would continue operating in China, but the mine-shaft variant that unlocks the massive global potential would remain unproven.

Discussed by: Energy storage industry analysts, mining engineers, infrastructure investors

Consensus —

Underground pumped hydro outpaces solid gravity in mine reuse

Pumped hydroelectric storage has over a century of proven track record and far more installed capacity than any other storage technology. Several research groups are studying underground pumped hydro in mine shafts—filling and draining water between underground chambers rather than raising solid weights. If this approach proves cheaper and simpler to engineer in existing mines, it could capture the mine-reuse opportunity before solid gravity batteries reach commercial readiness.

Discussed by: Pumped hydro advocates, German mining engineers studying Prosper-Haniel, University of Liège researchers

Consensus —

Historical Context

Pumped hydroelectric storage (1907–present)

1907–present

What Happened

Switzerland built the first pumped-hydro storage plant in 1907, using surplus electricity to pump water uphill into a reservoir, then releasing it through turbines when power was needed. The technology spread globally throughout the twentieth century and now accounts for roughly 90 percent of all grid-scale energy storage worldwide, with over 160 gigawatts of installed capacity.

Outcome

Short Term

Pumped hydro enabled grids to balance supply and demand decades before batteries existed, making baseload nuclear and coal plants economically viable by absorbing their overnight surplus.

Long Term

Despite its dominance, pumped hydro requires specific geography—mountains, valleys, water—limiting where it can be built. This constraint is precisely what makes alternative gravity storage concepts attractive: mine shafts exist in flat terrain where reservoirs cannot.

Why It's Relevant Today

Gravity batteries are attempting to replicate pumped hydro's proven physics in a form factor that works underground, without water, and in locations where traditional pumped hydro is impossible. The question is whether solid weights in shafts can match the economics of water in reservoirs.

Prosper-Haniel underground pumped hydro proposal (2017–present)

2017–present

What Happened

When Germany's last black coal mine, Prosper-Haniel in Bottrop, closed in December 2018, engineers at the University of Duisburg-Essen proposed converting its 600-meter shafts into a 200-megawatt underground pumped hydroelectric facility. The concept received broad public support and government-funded feasibility studies concluded it was technically viable.

Outcome

Short Term

The feasibility studies confirmed the engineering could work, but market and regulatory conditions were deemed unfavorable for investment. No construction has begun.

Long Term

Prosper-Haniel became a cautionary example: technical feasibility alone does not guarantee deployment. The project remains in limbo years after the studies concluded, illustrating the gap between a good idea and a built system.

Why It's Relevant Today

Gravity battery startups face the same challenge Prosper-Haniel encountered—proving that mine-shaft energy storage is not only technically possible but economically competitive enough to attract the billions in investment needed for deployment at scale.

Tesla Hornsdale Power Reserve (2017)

November–December 2017

What Happened

After a statewide blackout in South Australia, Elon Musk bet the state's premier that Tesla could install a 100-megawatt lithium-ion battery in 100 days or it would be free. Tesla delivered the Hornsdale Power Reserve in 60 days. It was the world's largest lithium-ion battery at the time and immediately began stabilizing the grid and saving consumers money.

Outcome

Short Term

The battery earned 2.4 million Australian dollars in revenue in its first week and proved grid-scale batteries could be deployed far faster than traditional power plants.

Long Term

Hornsdale triggered a global wave of grid battery construction. Within five years, battery projects ten times its size were being built. The speed of deployment and falling costs set a competitive bar that every alternative storage technology—including gravity—must now clear.

Why It's Relevant Today

Gravity batteries' biggest competitor is not other gravity systems but lithium-ion batteries, which proved at Hornsdale that they could go from concept to grid-connected installation in weeks, not years. Gravity storage must demonstrate advantages—longer duration, longer lifespan, no material degradation—that justify slower deployment timelines.