Gravity storage systems convert surplus electricity into potential energy by lifting heavy masses and discharging by lowering them through generators. The physics are simple and bankable, but project bankability hinges on civil costs, utilization, and local alternatives such as pumped hydro, flow batteries, and CAES.
- Round-trip efficiency (RTE) for modern concepts typically falls in the 70–85% range, lower than Li-ion but comparable to pumped hydro.
- LCOS for first-of-a-kind towers is often estimated at 180–260 USD/MWh, with learning curves potentially bringing this towards 110–160 USD/MWh at scale and high utilization.
- Best-fit applications include 4–12 hour renewables firming, transmission-constrained nodes, and sites where pumped hydro is infeasible but there is structural height, mine shafts, or quarries.
- Key risks are capex overruns in civil works, mechanical reliability of moving masses, and securing long-term offtake for assets designed for 30–40 years.
1. Technology benchmarks: how gravity storage actually performs
Gravity storage is not a single technology but a family of concepts that all exploit the same basic principle: use surplus power to raise a mass and recover energy when the mass descends. What differentiates vendors is how masses are moved (towers vs. shafts), how power electronics are integrated, and how much civil infrastructure is required.
Two families of architectures dominate current discussions:
- Tower-based systems (e.g., Energy Vault EVx) lifting composite blocks along a tall structure, typically targeting 25–100 MW and 4–8 hours.
- Underground or shaft-based systems (various gravity power concepts) using deep shafts or mines, potentially delivering 10–100+ MW and up to 12 hours.
| Parameter | Modern gravity tower | Underground gravity shaft | Li-ion (utility-scale) |
|---|---|---|---|
| Typical power rating | 25–100 MW | 10–80 MW | 50–200 MW |
| Duration sweet spot | 4–8 hours | 4–12 hours | 1–4 hours |
| Round-trip efficiency (AC–AC) | 70–80% (conceptual range) | 75–85% depending on hydraulics & mechanics | 85–92% |
| Expected asset life | 30–35 years | 35–40 years | 12–15 years |
| Degradation per year | <0.5% mechanical wear only | <0.3% | 2–4% |
| Site dependency | High: land, height, permitting | Very high: geology, shaft depth | Low: containerized |
These indicative ranges show why gravity storage is framed less as a direct competitor to 2-hour grid batteries, and more as an alternative to pumped hydro and CAES for long-lived, infrastructure-like assets with relatively stable performance over decades of cycling.
2. Economics and LCOS: what gravity storage really costs
For gravity storage to be viable, it must deliver a levelized cost of storage (LCOS) that competes with alternatives providing the same grid service. For a 6–10 hour application at a congested node, this might mean comparing against flow batteries, CAES, or incremental transmission rather than 2-hour Li-ion.
The economics of gravity storage are dominated by civil and structural capex, utilization (full cycles per year), and the cost of capital. The underlying physics do not degrade meaningfully over time, but if the asset is underutilized, LCOS will remain high even with long lives.
| Cost component | Gravity tower (FOAK) | Gravity tower (Nth-of-a-kind) | Underground shaft (conceptual) |
|---|---|---|---|
| Civil & structural (USD/kWh) | 90–140 | 55–90 | 70–120 depends on shaft depth |
| Mechanical & hoisting | 40–70 | 30–50 | 35–60 |
| Power conversion system | 20–35 | 18–30 | 20–32 |
| Controls & balance-of-plant | 15–25 | 12–20 | 15–25 |
| Total overnight capex (USD/kWh) | 165–270 | 115–190 | 140–235 |
Translating these capex figures into LCOS depends on financing assumptions and utilization. For an asset cycled once per day (365 cycles/year), with a 30-year life and 8% nominal WACC, FOAK gravity towers often land in the 180–260 USD/MWh discharged range. At Nth-of-a-kind capex levels with similar utilization, this can fall towards 120–170 USD/MWh.
This comparison highlights that gravity storage is unlikely to out-compete short-duration Li-ion in raw USD/MWh terms, but can be competitive with pumped hydro and CAES in locations where civil works can be standardized and where land or water constraints limit alternatives.
Model gravity storage LCOS with Energy Solutions tools
Many project teams underestimate the impact of utilization, WACC, and round-trip efficiency on LCOS for long-lived assets like gravity storage. Rather than relying on single-point vendor numbers, build a range of scenarios covering different utilization and capex outcomes.
3. Use cases where gravity storage makes sense
Gravity storage competes best in locations where its unique combination of long life, relatively low degradation, and infrastructure-like asset profile creates value that outweighs higher upfront capex.
3.1 Transmission-constrained renewables hubs
In regions with rapid wind and solar build-out but slow grid reinforcement, gravity storage can absorb surpluses and return power when transmission is unconstrained. The long mechanical life matches asset lifetimes for wind and solar portfolios and can underpin 20-year offtake contracts.
3.2 Co-location with heavy industry and ports
Industrial clusters and ports often have large footprints, crane infrastructure, and long time horizons. Tower-based gravity systems can be designed as functional infrastructure, using local materials for blocks and integrating with electrified process loads or shore power.
3.3 Repurposed mines and quarries
Underground gravity concepts are particularly compelling where suitable shafts already exist. Repurposing disused mines can significantly reduce civil costs and environmental impact, although permitting and safety requirements remain stringent.
Developer takeaway: gravity projects should be screened primarily on site fundamentals (height, geology, land) and long-term grid needs, not just vendor claims on capex. Sites with strong structural advantages can justify gravity even where headline LCOS appears marginal.
4. Case study snapshots (conceptual)
A handful of announced projects illustrate the envelope of where gravity storage is being considered. While public data tends to be limited, the ranges below reflect plausible values under reasonable engineering assumptions rather than marketing extremes.
| Conceptual project | Power / energy | Core use case | Key value driver |
|---|---|---|---|
| Gravity tower at renewables hub | 50 MW / 400 MWh | Solar & wind firming, congestion relief | Deferral of transmission upgrades, capture of curtailed energy |
| Port-integrated tower system | 30 MW / 240 MWh | Shore power and crane electrification | Demand charge reduction, time-of-use arbitrage |
| Repurposed deep mine shaft | 20 MW / 200 MWh | Regional capacity and black-start support | Low incremental civil capex, very long asset life |
In all three conceptual cases, LCOS is only one part of the value story. Transmission deferral, ancillary services, and resilience can materially improve project economics if successfully monetized.
5. Global perspective: where gravity storage is likely to scale
Gravity storage is unlikely to become a universal backbone of LDES in the way pumped hydro has in several countries, but it can achieve material deployment in specific geographies:
- Europe: land-constrained markets with ambitious decarbonization targets and limited pumped hydro options (e.g., Benelux, parts of Germany) show interest in gravity as a long-lived asset.
- Middle East and North Africa: large industrial ports and low-cost renewables create potential for gravity tied to hydrogen production and desalination loads.
- Latin America and Africa: mining regions with existing shafts and high-value resilience needs could host underground gravity assets, provided financing structures can support long-tenor investments.
The most promising markets combine:
- High penetration of variable renewables (wind + solar) with increasing curtailment.
- Constraints on building new large reservoirs or long-distance transmission.
- Policy frameworks that recognize and remunerate capacity, flexibility, and resilience.
6. Devil’s advocate: when gravity storage does not make sense
Developers and investors should be explicit about where gravity storage is a poor fit, to avoid misallocating early-stage effort and damaging confidence in the category.
- Short-duration applications (<3 hours): Li-ion or even demand response typically out-compete gravity in cost and simplicity.
- Sites without strong structural advantages: if there is no meaningful height, shaft, or land opportunity, gravity quickly becomes a civil engineering exercise with weak economics.
- Markets with limited long-term contracting: gravity assets are long-lived; merchant-only revenue stacks expose them to excessive risk.
- Regions with abundant low-cost pumped hydro: in such cases, gravity will only win where permitting or environmental constraints explicitly block new reservoirs.
Investor caution: treat gravity storage as an infrastructure bet rather than a modular product. Diligence should focus on civil risk, mechanical reliability data, and realistic utilization assumptions rather than best-case vendor LCOS slides.
7. Outlook to 2035: scenarios for gravity storage deployment
By 2030–2035, gravity storage could fall into one of three broad deployment trajectories:
- Niche success: a few GW of projects in specific markets (ports, mines, constrained nodes), with gravity seen as a specialist tool in the LDES toolbox.
- Regional platform: standardization of tower or shaft designs leads to gigawatt-scale fleets in 3–5 key markets, with gravity recognized as an alternative to pumped hydro.
- Limited adoption: if civil costs remain high and financing complex, gravity may remain at demonstration scale.
From today’s vantage point, a “niche success” to “regional platform” outcome appears plausible where early projects can demonstrate reliable performance and deliver LCOS in the lower half of vendor projections.
8. Implementation guide: how developers should evaluate gravity projects
For utilities, IPPs, and large energy users considering gravity storage, a structured evaluation process helps move beyond marketing claims to robust investment decisions.
8.1 Screening questions
- Does the site have height or shaft advantages (towers, mines, quarries, industrial structures)?
- Is there a clear 4–12 hour flexibility need that cannot be covered cost-effectively by shorter-duration batteries?
- Can you secure long-term offtake (10–20 years) or at least stable capacity payments?
- Are there policy or ESG drivers that value long-lived, low-impact infrastructure?
8.2 Quantitative steps
- Define the service stack: arbitrage, capacity, reserves, congestion relief, resilience.
- Develop a range of capex scenarios, explicitly separating civil, mechanical, and power electronics costs.
- Model utilization scenarios (e.g., 150, 250, 350 cycles/year) and sensitivities for RTE and outages.
- Calculate LCOS and revenue under each scenario using conservative WACC assumptions.
- Stress-test against alternative technologies, including deferring investment.
8.3 Risk allocation and contracting
Because gravity projects resemble infrastructure more than modular batteries, contracting structures should address:
- Turnkey civil and mechanical risk: EPC guarantees, liquidated damages, and warranty terms.
- Availability guarantees and penalty structures aligned with grid service obligations.
- Performance monitoring for RTE and mechanical reliability over time.
9. FAQ: questions energy teams ask about gravity storage
How does gravity storage really compare to pumped hydro?
From a physics standpoint, gravity storage and pumped hydro are very similar: both convert surplus power into potential energy and recover it later. Pumped hydro typically achieves slightly higher round-trip efficiency and lower LCOS in suitable geographies, but is constrained by water availability, topography, and permitting. Gravity storage can be built in locations where reservoirs are infeasible, at the cost of higher civil complexity per kWh.
Is gravity storage bankable today?
Bankability is emerging but still limited. Investors will look for strong counterparties, robust EPC frameworks, and conservative assumptions on utilization and LCOS. Early projects are likely to resemble infrastructure deals with long-term contracts rather than merchant battery projects.
What round-trip efficiency should we assume in models?
For most current gravity concepts, assuming 70–80% AC–AC is reasonable, with precise values depending on mechanical design, drive systems, and power electronics. It is prudent to model a modest degradation of efficiency over time to reflect wear, even if the physics themselves do not degrade like electrochemistry.
Can gravity storage provide fast frequency response?
Yes, many designs can respond quickly, especially when equipped with modern power electronics, although this should be validated on a project-by-project basis. Developers should clarify control philosophies and response times with vendors.
When should we choose gravity over flow batteries or CAES?
Gravity is most compelling when you have strong site-specific advantages (height, shafts, industrial structures) and long-term visibility on the need for multi-hour flexibility. Where geology supports CAES or transmission can be expanded cost-effectively, gravity may face stronger competition.