# Gravity storage: Engineering and performance

Fast response and solid efficiency claims, still unverified

Source page: https://www.materialinsights.org/energy/e_gravity/sg-eng/

What this tab covers Engineering and operating performance: round-trip efficiency, whether power and energy can be scaled separately, footprint and siting, and safety.

Efficiency is claimed at 75 to 80 percent and response is fast, but energy per unit of land or structure is low and no large plant has published operating data.

#### Round-trip efficiency
Mixed

Energy Vault reported above 75 percent for its 5 MW Swiss test tower and projects more than 80 percent for the EVx design at Rudong; both are developer figures. Losses arise in motors, gearing and power electronics. Independent operating figures for the Chinese plants were not found.^[1](https://www.energyvault.com/project-cn-rudong)^[2](https://www.businesswire.com/news/home/20230801653396/en/Energy-Vault-Announces-Commencement-of-Commissioning-of-World)
 EV1 test tower (Switzerland) above 75% (developer claim)^[2](https://www.businesswire.com/news/home/20230801653396/en/Energy-Vault-Announces-Commencement-of-Commissioning-of-World) EVx Rudong (projected) above 80% (developer projection)^[1](https://www.energyvault.com/project-cn-rudong)

#### Power and energy decoupling
Mixed

Power is set by the number and size of motor-generators; energy by the mass and height available. Adding energy means more blocks and a taller or larger structure, or a deeper shaft, so the marginal cost of an extra hour is structural rather than cheap. The four Chinese EVx projects built or under construction are all 4-hour designs.^[3](https://energy-storage.news/energy-vault-china-gravity-ess-project-connected-to-grid-starts-building-three-others)
 EVx duration 4 h (four Chinese projects built or under construction)^[3](https://energy-storage.news/energy-vault-china-gravity-ess-project-connected-to-grid-starts-building-three-others)

#### Footprint and siting flexibility
Mixed

Block systems can be built on flat land next to wind or solar farms, unlike pumped hydro, but they are large buildings for modest energy. Mine-shaft systems reuse existing holes and can host weights of up to 12,000 tonnes, but depend on suitable shafts. Rail systems need a long slope.^[3](https://energy-storage.news/energy-vault-china-gravity-ess-project-connected-to-grid-starts-building-three-others)^[8](https://www.mining.com/european-deep-mine-operators-looking-into-underground-energy-storage/)
 Mine-shaft weight (planned) up to 12,000 t^[8](https://www.mining.com/european-deep-mine-operators-looking-into-underground-energy-storage/)

#### Safety and thermal runaway risk
Favourable

There is no fire or toxic gas risk from the storage medium. Hazards are mechanical: falling loads, cable failure and structural collapse in earthquakes or high wind, governed by lifting and structural codes rather than battery fire codes. Response is fast; Gravitricity reports zero to full power in under one second.^[7](https://www.solarpowerportal.co.uk/solar-projects/gravitricity-celebrates-success-of-250kw-energy-storage-demonstrator)^[8](https://www.mining.com/european-deep-mine-operators-looking-into-underground-energy-storage/)
 Response time under 1 s to full power^[7](https://www.solarpowerportal.co.uk/solar-projects/gravitricity-celebrates-success-of-250kw-energy-storage-demonstrator)

#### Sources

1. [Rudong, China Gravity Energy Storage System](https://www.energyvault.com/project-cn-rudong) Energy Vault, 2025
2. [Energy Vault Announces Commencement of Commissioning of World's First Grid-Scale Non-Pumped Hydro Gravity Energy Storage System](https://www.businesswire.com/news/home/20230801653396/en/Energy-Vault-Announces-Commencement-of-Commissioning-of-World) Energy Vault via Business Wire, 2023
3. [Energy Vault China gravity ESS project connected to grid; starts building three others](https://energy-storage.news/energy-vault-china-gravity-ess-project-connected-to-grid-starts-building-three-others) Energy-Storage.news, 2024
4. [Gravitricity celebrates success of 250kW energy storage demonstrator](https://www.solarpowerportal.co.uk/solar-projects/gravitricity-celebrates-success-of-250kw-energy-storage-demonstrator) Solar Power Portal, 2021
5. [European deep mine operators looking into underground energy storage](https://www.mining.com/european-deep-mine-operators-looking-into-underground-energy-storage/) MINING.COM, 2024

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_gravity/index.md)
- [Overview](https://www.materialinsights.org/energy/e_gravity/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_gravity/correlation/index.md)
- [Science and technology](https://www.materialinsights.org/energy/e_gravity/sg-sci/index.md)
- [Economics](https://www.materialinsights.org/energy/e_gravity/sg-econ/index.md)
- [Impact and additionality](https://www.materialinsights.org/energy/e_gravity/sg-impact/index.md)
- [What to track](https://www.materialinsights.org/energy/e_gravity/tracking/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_gravity/links/index.md)