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Gravity energy storage (lifted solid masses in a tower or mine shaft): round-trip efficiency, cycling and LCOS

Solid masses lifted by motor-generators in a tower (Energy Vault EVx) or a mine shaft (Gravitricity), from 1 to 1,000 MWh: lifted mass from E = m g h, LCOS in EUR/MWh returned on PNNL 2022 developer costs or on the Rudong as-built investment, with a sourced-domain indicator.

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Open Jack

Founder · OpenJack

Add to project
  • CurrencyEUR 2021
  • Battery limitfully financed
  • 74 documented assumptions
  • Updated2 Nov 2026

Mass and energy balance

What the asset draws and delivers for the case and load you choose.

Reference case

Equivalent full discharges a year you expect to sell. 365 is PNNL's basis (one full cycle a day). The slider stops at 330: below that, at 2 h on the Rudong basis, the LCOS leaves the sourced range. Long durations are also capped by the time a charge plus a discharge takes (PNNL Eq. 2): the cap binds above about 10.7 h at 82 %.

Flows

  • In: Electricity for charging—

Asset

Gravity energy storage (lifted solid masses)

  • Out: Electricity discharged—

Annual quantities at the current usage.

Energy returned to the grid per full discharge (MWh). The catalogue binds products here: Energy Vault EVx Rudong is 100 MWh. Rated power = energy / duration. PNNL's cost data start at 40 MWh (its smallest developer point): below that the cost per kWh is held flat, not extrapolated, and the out-of-domain indicator lights up.

Rated power
— MW
Total lifted mass
— t
Energy discharged per year
— MWh/year
Mass flow at rated power
— t/s

CAPEX

Specific cost at this size, what backs it, and how it behaves with scale.

Specific CAPEX at this size

—

Reference size 400 MWh

PNNL-33283 Tables 4.31-4.32, power-law form by OpenJack

Model value: the reference case above. Customized: your own all-in quote per kWh of energy capacity, used as is at every size; the value is then no longer sourced.

Specific CAPEX by energy capacity

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  1. Ex-factory
  2. Installed
  3. Fully financed· this figure
CAPEX at the battery limit—

Included

  • Equipment and installation
  • Indirect and owner's costs
  • Contingency

Not included

  • Nothing

Added at project level

  • Nothing: project mode uses the figure as is

Lifetime and replacements

Costs this asset carries that project mode does not apply.

Not passed to project mode

Power-equipment replacement part of LCOS is left out of project results: project mode only replaces the whole asset at the end of its lifetime. Add it by hand until it does.

Project figures

Values passed to project mode when this asset is added to a project.

Electricity for charging in
—
Electricity discharged outMain product
—
CAPEX to the battery limit
—
Fixed O&M
—
Variable O&M, excluding feedstocks
0 EUR/year
Asset lifetime
35 years
Power-equipment replacement part of LCOSNot applied by project
—

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Levelised cost of storage

A standalone indicator for a quick read. Project mode recomputes it for the whole system.

—

  • Capital part of LCOS—
  • Power-equipment replacement part of LCOS—
  • Fixed O&M part of LCOS—
  • Charging part of LCOS—

Linked to the balance above

Equivalent full discharges a year you expect to sell. 365 is PNNL's basis (one full cycle a day). The slider stops at 330: below that, at 2 h on the Rudong basis, the LCOS leaves the sourced range. Long durations are also capped by the time a charge plus a discharge takes (PNNL Eq. 2): the cap binds above about 10.7 h at 82 %.

Hours of discharge at rated power. Gravitricity quotes 15 min to 8 h; Rudong is 4 h. PNNL costed 2 h and longer, with a 10 MW / 2-10 h building block: below 2 h the power equipment dominates the cost per kWh and the result is out of the sourced domain.

Average height the masses fall through during a discharge. About 130 m reproduces Rudong (12,600 blocks of 25 t in a tower of about 150 m, derived, not published). Mine shafts: 150 to 1,500 m (PNNL, Gravitricity). Sets the lifted mass only: PNNL's costs are per kWh and per kW, not per tonne or per metre.

Grid-to-grid efficiency of the motor-generators, drives, power electronics and hoist friction over a full cycle. 82 % is PNNL's brick-based estimate; 80-90 % its range for shaft weights; Energy Vault states above 80 % for Rudong. No source splits it by component, so it is an input, not derived.

Average price paid for the charging electricity. Default 25.37 = PNNL's 0.03 USD/kWh at the ECB 2021 rate. Divided by the round-trip efficiency in the LCOS. In project mode the charging electricity is the inlet and is priced by the project.

REAL rate, because every cost is in constant money without escalation. Default 6.52 % = PNNL real WACC. Never enter a nominal rate here. The slider is kept narrow (6-7 %) so that every corner of the inputs stays inside the sourced LCOS range of 50-320 EUR/MWh.

Period over which the CAPEX is annualised. 35 years is Energy Vault's stated operating life for Rudong and the low end of PNNL's 35-50 year calendar life; 20 years is PNNL's economic-life convention. Above 30 years one power-equipment replacement is costed (PNNL Table 6.5).

Levelised cost of storage by full cycles per year

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Benchmarks

This model's figures against published references and reference cases.

Levelised cost of storage, EUR/MWh

109.9 PNNL-33283

Specific CAPEX, EUR/kWh

304.4 PNNL-33283

426.1 PNNL-33283

827.1 Nantong government

Round-trip efficiency, %

80 Energy Vault

82 PNNL-33283

86 PNNL-33283

Reference cases at this size and usage

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All results

Every model output at the current settings, grouped, with the sensitivity charts.

66 outputs · 7 groups · 14 also shown above, dimmed

Levelised cost

8
Levelised cost of storage
ComputingEUR/MWh
Capital part of LCOS
ComputingEUR/MWh
Power-equipment replacement part of LCOS
ComputingEUR/MWh
Fixed O&M part of LCOS
ComputingEUR/MWh
Charging part of LCOS
ComputingEUR/MWh
Capital share of LCOS
Computing%
LCOS at PNNL's 20-year economic life
ComputingEUR/MWh
Total annual cost
ComputingEUR/year

Size and CAPEX

14
Rated power
ComputingMW
Specific CAPEX
ComputingEUR/kWh
Total CAPEX
ComputingEUR
CAPEX per kW
ComputingEUR/kW
Scaled PNNL CAPEX
ComputingEUR/kWh
PNNL CAPEX at the reference size
ComputingEUR/kWh
Rudong as-built CAPEX
ComputingEUR/kWh
Size factor
Computingratio
Masses, structure and balance of system
ComputingEUR
Motor-generators and power conversion
ComputingEUR
EPC, development and grid integration
ComputingEUR
Energy share of direct cost
Computing%
Out of sourced domain
Computingflag
Rudong basis extrapolated
Computingflag

Masses and height

10
Total lifted mass
Computingt
Lifted mass per MWh
Computingt/MWh
Gravitational energy stored
ComputingMWh
Energy per tonne-metre
ComputingWh/(t·m)
Mass flow at rated power
Computingt/s
Equivalent 25 t blocks
Computingblocks
Blocks lowered per hour
Computingblocks/h
Rudong block mass
Computingt
Rudong implied drop height (derived)
Computingm
Rudong drop over tower height (derived)
Computing%

Energy balance

7
Round-trip efficiency
Computing%
One-way efficiency (assumed split)
Computing%
Charging energy per MWh returned
ComputingMWh/MWh
Energy discharged per year
ComputingMWh/year
Energy charged per year
ComputingMWh/year
Losses per year
ComputingMWh/year
Energy discharged over the economic life
ComputingMWh

Duty cycle

8
Effective full cycles a year
Computingcycles/year
Maximum full cycles a year
Computingcycles/year
Cycle-time load penalty
Computing%
Charge plus discharge time
Computingh
Cycles counted the PNNL way
Computingcycles/year
Discharge load hours
Computingh/year
Charging load hours
Computingh/year
Discharge capacity factor
Computing%

Finance and yearly costs

12
Capital recovery factor
Computing1/year
Capital recovery factor at 20 years
Computing1/year
Annualised CAPEX
ComputingEUR/year
Power-equipment replacement cost
ComputingEUR
Power-equipment replacements
Computingcount
Replacement present value
ComputingEUR
Annualised replacement
ComputingEUR/year
Fixed O&M (PNNL table)
ComputingUSD/kW/year
Fixed O&M per kW
ComputingEUR/kW/year
Fixed O&M per year
ComputingEUR/year
Charging cost per year
ComputingEUR/year
Interest during construction (not in LCOS)
Computing%

Reference checks

7
Check: PNNL 100 MW / 4 h
Computingratio
Check: PNNL 100 MW / 2 h
Computingratio
Check: scale law vs PNNL power cost at 10x
Computingratio
Check: scale law vs PNNL energy cost at 10x
Computingratio
Rudong over PNNL CAPEX (nominal)
Computingratio
PNNL charging price
ComputingEUR/MWh
Rate gap to PNNL
Computing%

Sensitivities

6 charts
LCOS components vs full cycles per year

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LCOS components by storage duration (sourced 2-12 h)

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Specific and total CAPEX vs energy capacity

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Lifted mass per MWh vs drop height

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LCOS vs charging price

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LCOS by cost reference case

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Sources

74 documented assumptions · 6 sources

About

Calculator context

Gravity energy storage: solid masses, composite blocks stacked in a tower (Energy Vault EVx) or weights hung in a mine shaft (Gravitricity), are lifted by motor-generators when power is cheap and lowered to generate when it is needed. The calculator sizes the plant by its energy capacity (MWh, the key the catalogue binds to, shared with the LFP battery calculator) and its duration, and answers what a MWh returned to the grid costs and how much mass and height it takes.

Physics. One tonne raised one metre stores 2.724 Wh (E = m g h, g = 9.80665 m/s2). The lifted mass is the energy returned divided by the discharge-side efficiency, divided by 2.724 Wh per t·m times the useful drop. The discharge-side efficiency is taken as the square root of the round-trip efficiency, an assumption: no source splits it. At 100 MWh and 130 m the model needs about 312,000 t; Rudong reports 12,600 blocks of 25 t (315,000 t) in a tower about 150 m tall, which implies an average useful drop of about 129 m at 82 % (derived, not published). In a 1,500 m shaft the mass per MWh falls to about 260 t. There is no self-discharge and no fade with cycling (PNNL Table 4.36; Energy Vault), so the full capacity is returned every cycle for the whole life.

Efficiency. The round-trip efficiency is an input, 80-90 %, default 82 % (PNNL's brick estimate; 80-90 % for shafts; Energy Vault states above 80 % for Rudong). No source publishes the motor-generator, drive and friction losses separately, so the model does not derive it.

CAPEX. Two sourced reference cases. PNNL-33283 (2022), whose heavy-brick figures are Energy Vault's own developer cost data: 180 USD/kWh for the masses, structure and balance of system plus 480 USD/kW for the power equipment, plus 20 % for EPC, project development and grid integration, in 2021 dollars converted at the ECB 2021 rate. This reproduces PNNL's printed totals exactly (360 USD/kWh at 100 MW / 4 h, 504 at 2 h). PNNL reduces costs by about 3 % per decade of size; the model writes that as a power law of exponent 0.9868 applied above 400 MWh, which also reproduces PNNL's 1,000 MW power cost to 0.1 %. Below 400 MWh the cost is flat, as in PNNL. The second case is Rudong as built: 650 M CNY (89.52 M USD) for 100 MWh, about 827 EUR/kWh in 2024 euros, held flat at every size and duration. It is about 2.7 times the PNNL developer figure: the first plant of its kind cost far more than the developer data suggest, and the page says so rather than averaging the two. The Rudong figure is not deflated to 2021 money (no cited index), so it reads as an upper reference. A Customized option takes your own quote.

Domain. PNNL costed 2 h and longer, from a 40 MWh developer point up to 1,000 MW. Below 2 h or 40 MWh, or above 1,000 MW, the model still computes but an out-of-domain indicator is on: below 2 h the power cost per kWh grows steeply (about 2,130 EUR/kWh at 15 minutes). On the Rudong basis a second indicator says when the single point is used away from 100 MWh / 4 h.

LCOS. PNNL Eq. 1 with a capital recovery factor at the real rate and no taxes: annualised CAPEX, the power-equipment replacement PNNL schedules every 30 years (costed when the economic life exceeds 30 years), and PNNL's heavy-brick fixed O&M (8-22 USD/kW-yr over 2-10 h, interpolated), per MWh returned, plus the charging price divided by the round-trip efficiency. Annual energy follows PNNL Eq. 2: up to 365 full cycles, capped when a charge plus a discharge no longer fit in a day (above about 10.7 h at 82 %). With PNNL's 6.52 % real WACC, 30 USD/MWh charging and 35 years, 100 MWh / 4 h costs about 304 EUR/kWh and about 102.6 EUR/MWh (113.7 at PNNL's 20-year economic life); on the Rudong basis about 207.5 EUR/MWh. PNNL itself prints 0.13 USD/kWh (about 110 EUR/MWh, after tax, at 1,000 MW / 10 h, a size beyond this slider). Comparable with the LFP battery calculator: same energy key, same charging convention, same PNNL WACC. Interest during construction is not added (an indicative uplift is shown).

Model

153 variables — inputs, calculations and outputs, with their dependencies.

153 variables shown of 153
VariableValueUnitDepends on
100MWh—
4h—
130m—
82%—
365cycles/year—
1——
0——
305EUR/kWh—
25.37EUR/MWh—
6.52%—
35years—
VariableFormulaUnitDepends on
if((<=)+(<=)+(<=)+(>)+(<=)+(>)+(<=)+(>)+(<)+(>)+(<)+(>)+(<=)+(<)+(<)+(<)+(>)>0,1,0)bool
*kW
*ratio
*ratio
*ratio
*min(/,/max(,))cycles/year
max(,)MWh
+*ratio
if(==,,)EUR/kWh
*ratio
VariableFormulaUnitDepends on
/max(,)MW
%
sqrt()*%
/max(,)MWh/MWh
*/Wh/(t·m)
/max(,)MWh
*/max(*,)t
/max(,)t/MWh
/max(*,)t/s
/blocks
/max(,)blocks/h
*t
*/max(**,)m
/*%
**(+)h
*cycles/year
min(,)cycles/year
(-/max(,))*%
/cycles/year
*h/year
*h/year
/*%
*MWh/year
*MWh/year
-MWh/year
*MWh
(/)^(-)ratio
*(+/max(,))/EUR/kWh
clamp(*(/)^(-),,)EUR/kWh
*/(*)/EUR/kWh
if(>=,,)EUR/kWh
**EUR
/max(,)EUR/kW
/max(+/max(,),)*%
*(-)/EUR
(-)**EUR
--EUR
if(<,/,(*(+)^)/max((+)^-,))1/year
*EUR/year
***/EUR
if(>,,)count
**(+)^(-)EUR
*EUR/year
if(<=,,if(<=,+(-)*(-)/(-),if(<=,+(-)*(-)/(-),if(<=,+(-)*(-)/(-),if(<=,+(-)*(-)/(-),+(min(,)-)*(-)/(-))))))USD/kW/year
/EUR/kW/year
*EUR/year
*EUR/year
+++EUR/year
/max(,)EUR/MWh
/max(,)EUR/MWh
/max(,)EUR/MWh
*EUR/MWh
+++EUR/MWh
/max(,)*%
if(<,/,(*(+)^)/max((+)^-,))1/year
(*+)/max(,)+EUR/MWh
((+)^(*)-)*%
if((<)+(<)+(>)+(<)+(>)>0,1,0)flag
if((==)*(<)*((abs(-)>)+(abs(-)>))>0,1,0)flag
*(+/)/ratio
*(+/)/ratio
*(/)^(-)/ratio
*(/)^(-)/ratio
*/(*)/ratio
/EUR/MWh
-%

Assumptions

74 assumptions used in the calculations

  • Zero term in guards and in the negative exponent of the replacement discount.

    Market range Exact, no range.

    0
    Unit conversion

  • Unit term in the CRF, guards and multipliers.

    Market range Exact, no range.

    1
    Unit conversion

  • Percent (0-100) to fraction.

    Market range Exact, no range.

    0.011/%
    Unit conversion

  • Fraction to percent; also the upper guard of 100 % on the efficiency.

    Market range Exact, no range.

    100%
    Unit conversion

  • MW to kW.

    Market range Exact, no range.

    1000kW/MW
    Unit conversion

  • Tonnes to kilograms in the energy per tonne-metre.

    Market range Exact, no range.

    1000kg/t
    Unit conversion

  • Hours in a day, PNNL Eq. 2 cycle limit.

    Market range Exact, no range.

    24h/day
    Unit conversion

  • MWh to Wh for the lifted mass.

    Market range Exact, no range.

    1000000Wh/MWh
    Unit conversion

  • Million USD to USD for the Rudong investment.

    Market range Exact, no range.

    1000000USD/MUSD
    Unit conversion

  • Mid-construction convention for the indicative IDC uplift.

    Market range No independent range cited.

    0.5
    OpenJack convention

  • Reference case 1: PNNL-33283 heavy-brick costs.

    Market range Not applicable.

    1
    OpenJack DSL convention

  • Reference case 2: Energy Vault EVx Rudong as built.

    Market range Not applicable.

    2
    OpenJack DSL convention

  • E = m g h.

    Market range Exact, no range.

    9.80665m/s2
    NIST CODATA

  • Storage block (masses, structure) and balance of system per kWh.

    Market range 180 (<= 400 MWh) to 175 USD/kWh (> 400 MWh), PNNL Table 4.32.

    180USD/kWh
    PNNL-33283

  • Check of the scale law at PNNL's large size.

    Market range Single PNNL value.

    175USD/kWh
    PNNL-33283

  • Power equipment per kW at 100 MW.

    Market range 480 (100 MW) to 466 USD/kW (1,000 MW).

    480USD/kW
    PNNL-33283

  • Check of the scale law on power.

    Market range Single PNNL value.

    466USD/kW
    PNNL-33283

  • Exponent of the CAPEX scale law on energy capacity, the size the catalogue binds to.

    Market range -3 % per decade of size (PNNL).

    0.986772
    PNNL-33283 Tables 4.31-4.32, power-law form by OpenJack

  • Reference size of the scale law.

    Market range Not applicable.

    400MWh
    PNNL-33283

  • One decade above the reference size.

    Market range Not applicable.

    4000MWh
    PNNL-33283

  • Indirect costs on top of the direct costs.

    Market range Single PNNL value.

    20%
    PNNL-33283

  • Cross-check of the CAPEX reconstruction.

    Market range 504 (2 h) and 360 (4 h) USD/kWh at 100 MW.

    360USD/kWh
    PNNL-33283

  • Cross-check of the CAPEX reconstruction.

    Market range 504 (2 h) and 360 (4 h) USD/kWh at 100 MW.

    504USD/kWh
    PNNL-33283

  • Duration of the 360 USD/kWh check.

    Market range Not applicable.

    4h
    PNNL-33283

  • Duration of the 504 USD/kWh check.

    Market range Not applicable.

    2h
    PNNL-33283

  • Numerical guard of the scale law.

    Market range Not applicable.

    100EUR/kWh
    OpenJack

  • Numerical guard of the scale law.

    Market range Not applicable.

    3000EUR/kWh
    OpenJack

  • Interpolation knot of the O&M table.

    Market range Not applicable.

    2h
    PNNL-33283

  • Interpolation knot of the O&M table.

    Market range Not applicable.

    4h
    PNNL-33283

  • Interpolation knot of the O&M table.

    Market range Not applicable.

    6h
    PNNL-33283

  • Interpolation knot of the O&M table.

    Market range Not applicable.

    8h
    PNNL-33283

  • Interpolation knot of the O&M table.

    Market range Not applicable.

    10h
    PNNL-33283

  • Interpolation knot of the O&M table.

    Market range Not applicable.

    24h
    PNNL-33283

  • Fixed O&M of a heavy-brick plant.

    8USD/kW/year
    PNNL-33283

  • Fixed O&M of a heavy-brick plant.

    12USD/kW/year
    PNNL-33283

  • Fixed O&M of a heavy-brick plant.

    15USD/kW/year
    PNNL-33283

  • Fixed O&M of a heavy-brick plant.

    19USD/kW/year
    PNNL-33283

  • Fixed O&M of a heavy-brick plant.

    22USD/kW/year
    PNNL-33283

  • Fixed O&M of a heavy-brick plant.

    47USD/kW/year
    PNNL-33283

  • Lower end of the sourced efficiency range.

    80%
    PNNL-33283

  • Upper end of the sourced efficiency range.

    90%
    PNNL-33283

  • Longest sourced calendar life.

    50years
    PNNL-33283

  • Year of the single power-equipment replacement.

    Market range Single PNNL value.

    30years
    PNNL-33283

  • PNNL's economic-life convention.

    Market range Single PNNL value.

    20years
    PNNL-33283

  • Cap on full cycles a year.

    Market range Single PNNL value.

    365cycles/year
    PNNL-33283

  • PNNL counting convention.

    Market range Single PNNL value.

    80%
    PNNL-33283

  • Construction time for the indicative IDC output.

    Market range Single PNNL value.

    3years
    PNNL-33283

  • Lower duration of the sourced domain.

    2h
    PNNL-33283

  • Smallest sourced size.

    40MWh
    PNNL-33283

  • Largest sourced power.

    1000MW
    PNNL-33283

  • Deepest sourced drop.

    1500m
    PNNL-33283

  • Energy of the Rudong reference plant.

    Market range Single plant.

    100MWh
    Energy Vault

  • Duration of the Rudong plant.

    Market range Single plant.

    4h
    Energy Vault

  • All-in investment of the Rudong plant.

    Market range Single plant: 650 M CNY = 89.52 M USD.

    89.52MUSD
    Nantong government via China Daily regional

  • Block count of Rudong.

    Market range Single plant.

    12600blocks
    Energy Vault / CNTY press release

  • Mass of one Rudong block, also used to count equivalent blocks.

    Market range Single plant.

    25t
    Energy Vault / CNTY press release

  • Height of the Rudong structure.

    Market range About 150 m.

    150m
    Energy Vault / CNTY press release

  • Converts PNNL costs to EUR 2021.

    Market range Single value.

    1.18274USD/EUR
    ECB

  • Converts the Rudong investment to EUR 2024.

    Market range Single value.

    1.08238USD/EUR
    ECB

  • PNNL's charging price.

    Market range Single PNNL value.

    30USD/MWh
    PNNL-33283

  • PNNL's real cost of capital.

    Market range Single PNNL value.

    6.52%
    PNNL-33283

  • Reference efficiency for bricks.

    82%
    PNNL-33283

  • Reference efficiency for shafts.

    86%
    PNNL-33283

  • Reference efficiency for Rudong.

    Market range Above 80 %.

    80%
    Energy Vault

  • External reference on the LCOS ruler.

    109.92EUR/MWh
    PNNL-33283

  • External reference on the CAPEX ruler.

    Market range 426 (2 h) to 304 (4 h) EUR/kWh at 100 MW.

    304.38EUR/kWh
    PNNL-33283

  • External reference on the CAPEX ruler.

    Market range 426 (2 h) to 304 (4 h) EUR/kWh at 100 MW.

    426.13EUR/kWh
    PNNL-33283

  • External reference on the CAPEX ruler.

    Market range Single plant.

    827.07EUR/kWh
    Nantong government

  • Levelised cost per MWh returned to the grid; the charging electricity is an input cost divided by the round-trip efficiency.

    Market range Not applicable.

    —
    PNNL-33283 Eq. 1

  • Real or nominal: real.

    Market range Not applicable.

    —
    Scope note

  • Sizes the mass for the energy actually returned.

    Market range No independent range cited.

    —
    OpenJack assumption

  • Full capacity returned every cycle for the whole life.

    Market range Not applicable.

    —
    PNNL-33283 / Energy Vault

  • One cost basis for towers and shafts.

    Market range No independent range cited.

    —
    Scope note

  • O&M independent of the CAPEX basis.

    Market range No independent range cited.

    —
    Scope note