Gravity storage: Science and technology
Simple physics, tiny energy per tonne: the core problem
What this tab covers The physics and chemistry: how the energy is stored, which materials it needs (scarcity, toxicity, recyclability) and what makes it age.Gravity storage lifts solid weights (blocks, mine-shaft masses or rail cars) and lowers them to generate power. The physics is simple and benign, but the energy held per tonne lifted is small, so systems must be very large or very deep.
Mechanism
MixedElectric motors raise a mass when power is spare; lowering it turns the motors into generators. Stored energy equals mass times gravity times height, so a 35-tonne block lowered 100 m holds only about 9.5 kWh (calculated). Variants: tall or wide block structures (Energy Vault EVx; the Rudong building is about 148 m high), weights winched in deep mine shafts (Gravitricity), loaded rail cars driven up a slope (ARES), and water tanks raised in towers, which remain conceptual. PNNL states that doubling shaft depth raises stored energy fourfold; on simple physics a longer drop alone only doubles it, so that figure implies a heavier weight as well.410
Energy Vault block mass 35 t4 Energy per 35 t block over 100 m about 9.5 kWh (calculated)4 Shaft depth scaling 2x depth, 4x energy10Material scarcity and toxicity
FavourableThe weights can be concrete, soil, mine waste or steel, all abundant and non-toxic. Energy Vault's Chinese partner plans to make composite blocks partly from construction debris and coal ash, and the company describes its blocks as using waste concrete and industrial aggregate. Motors and power electronics use ordinary copper, steel and some rare-earth magnets.34
Block feedstock concrete debris and coal ash (planned, China); waste concrete and aggregate34Degradation and ageing
FavourableThere is no chemical fade. Wear falls on cables, winches, cranes, wheels and rails, which are maintained or replaced like other heavy machinery. Developers claim long lives: Energy Vault projects 35 years for Rudong and Gravitricity says full-scale systems can exceed 25 years with no loss of output. These are design claims, not operating records.17
Projected life, Rudong EVx 35 years1 Projected life, Gravitricity over 25 years7Variants compared13578
| Variant | Largest example | Size | Status |
|---|---|---|---|
| Blocks and towers (Energy Vault EVx) | Rudong, Jiangsu, China | 25 MW / 100 MWh | Grid-connected Dec 2023; three more Chinese projects under construction in 2024 |
| Mine-shaft weights (Gravitricity) | Edinburgh demonstrator | 250 kW, two 25 t weights | Demonstrated 2021; mine sites in Finland, Slovenia, Czechia, Germany studied |
| Rail cars (ARES GravityLine) | Pahrump, Nevada | 50 MW, 15 min of regulation; 210 cars | Ground broken Oct 2020; no operating data found |
| Water towers | None found | n/a | Concept only |
Sources
- Rudong, China Gravity Energy Storage System Energy Vault, 2025
- Energy Vault China gravity ESS project connected to grid; starts building three others Energy-Storage.news, 2024
- A Swiss company uses gravity and 35-ton blocks to store energy Building Design + Construction, 2026
- Energy storage project breaks ground in Pahrump Pahrump Valley Times, 2020
- Gravitricity celebrates success of 250kW energy storage demonstrator Solar Power Portal, 2021
- European deep mine operators looking into underground energy storage MINING.COM, 2024
- Energy Storage Cost and Performance Database: Gravitational Energy Storage Pacific Northwest National Laboratory, 2024