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CO2 battery energy storage plant (Energy Dome type): round-trip efficiency, CO2 inventory and LCOS

Closed-loop CO2 phase-change storage (dome, compression, packed-bed heat store, liquid CO2 at ambient temperature, turbine) from 2.5 to 100 MW: charge power, CO2 inventory and mass flows, and LCOS in EUR/MWh on the vendor's claimed CAPEX or a utility estimate, with the PNNL method.

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Open Jack

Founder · OpenJack

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  • CurrencyEUR 2024
  • Battery limitfully financed
  • 60 documented assumptions
  • Updated2 Nov 2026

Mass and energy balance

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

Reference case

Full discharges a year you expect to sell. 365 is PNNL's basis (one cycle a day). A cycle takes the charge time plus the discharge time, so above 12 h of duration fewer than 365 cycles fit in a year and the model caps them. The slider stops at 120, below which the LCOS leaves its sourced range at the worst corner.

Flows

  • In: Electricity for charging—

Asset

CO2 battery energy storage plant (Energy Dome type)

  • Out: Electricity discharged—

Annual quantities at the current usage.

Net electrical power delivered to the grid during discharge (MW). The catalogue binds co2_battery products here: SEC Latrobe Valley and NTPC Kudgi are 20 MW, County Offaly 23 MW. 2.5 MW is the Ottana demonstrator, 100 MW the largest plant announced on the same principle (Huadian Mulei). Sets the size in the CAPEX scale law.

Energy capacity
— MWh
Charge power
— MW
CO2 inventory
— t
CO2 mass flow, discharge
— t/h

CAPEX

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

Specific CAPEX at this size

—

Reference size 20 MW

PNNL-33283 §4.5.1, power-law form by OpenJack

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

CAPEX per kWh by rated discharge power

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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

Project figures

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

Concept sketch, not to scale · drag to rotate

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
30 years

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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—
  • Fixed O&M part of LCOS—
  • Charging part of LCOS—

Linked to the balance above

Full discharges a year you expect to sell. 365 is PNNL's basis (one cycle a day). A cycle takes the charge time plus the discharge time, so above 12 h of duration fewer than 365 cycles fit in a year and the model caps them. The slider stops at 120, below which the LCOS leaves its sourced range at the worst corner.

Hours of discharge at rated power. Energy Dome prints 8 to 24 h; its standard plant is 10 h (20 MW / 200 MWh). The vendor cost per kWh is quoted for that frame: outside 8-12 h the cost basis is extrapolated and a flag lights up. Energy capacity is held within 4-1,000 MWh.

AC-AC, MV-MV round-trip efficiency of the whole plant, including auxiliaries. 75 % is the figure in Energy Dome's 2024 decks; the 2026 product page states '70%+ net'; Politecnico di Milano reports about 77 % (± 2 %). No public source splits it by component, so it is an input, not derived. Sets the charging energy and the charge power.

Average price paid for the charging electricity. Default 26.3 = PNNL's 0.03 USD/kWh at the ECB 2020 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. The slider is held to 10-80 EUR/MWh so that every corner stays in the sourced LCOS range.

REAL rate, because every cost is in constant money without escalation. Default 6.52 % = PNNL real WACC. Never enter a nominal rate here. Kept narrow (6-8 %) so every corner of the inputs stays in the sourced LCOS range.

Period over which the CAPEX is annualised. 20 years is PNNL's economic-life convention; Energy Dome states a physical life of 30+ years with no degradation, shown separately as the LCOS at physical life.

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

87.55 PNNL-33283

131.3 US DOE CAES TSA 2023

525.3 US DOE CAES TSA 2023

Net round-trip efficiency, %

70 Energy Dome product page 2026

75 Energy Dome TMCES 2024 p.18

77 Astolfi et al. 2021

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.

59 outputs · 7 groups · 13 also shown above, dimmed

Levelised cost

7
Levelised cost of storage
ComputingEUR/MWh
Capital 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 30-year physical life
ComputingEUR/MWh
Total annual cost
ComputingEUR/year

Size and CAPEX

15
Discharge power
ComputingMW
Energy capacity
ComputingMWh
Charge power
ComputingMW
CAPEX per kWh
ComputingEUR/kWh
Total CAPEX
ComputingEUR
CAPEX per kW of discharge
ComputingEUR/kW
Reference CAPEX
ComputingUSD/kWh
Reference CAPEX at the 20 MW frame
ComputingEUR/kWh
Scaled CAPEX per kWh
ComputingEUR/kWh
CAPEX scale factor
Computingratio
Alliant estimate, low
ComputingUSD/kWh
Alliant estimate, high
ComputingUSD/kWh
Vendor-claimed CAPEX
Computingflag
Cost basis extrapolated
Computingflag
Below printed durations
Computingflag

CO2 loop

6
CO2 inventory
Computingt
CO2 inventory per MWh
Computingt/MWh
CO2 mass flow, discharge
Computingt/h
CO2 mass flow, charge
Computingt/h
CO2 cycled per year
Computingt/year
Implied net work per kg of CO2
ComputingkJ/kg

Energy balance

9
Net round-trip efficiency
Computing%
Charging energy per MWh returned
ComputingMWh/MWh
Charge duration
Computingh
Charge to discharge power ratio
Computingratio
Usable energy per cycle
ComputingMWh
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

7
Effective full cycles per year
Computingcycles/year
Cycles a year that fit in time
Computingcycles/year
Cycle time
Computingh
Cycles lost to cycle time
Computing%
Discharge hours per year
Computingh/year
Charging hours per year
Computingh/year
Discharge capacity factor
Computing%

Finance and yearly costs

6
Capital recovery factor
Computing1/year
Capital recovery factor at physical life
Computing1/year
Annualised CAPEX
ComputingEUR/year
Fixed O&M per kW
ComputingEUR/kW/year
Fixed O&M per year
ComputingEUR/year
Charging cost per year
ComputingEUR/year

Reference checks

9
Vendor frame compressor to turbine rating
Computingratio
Vendor frame turbine to compressor rating
Computing%
Gap to the vendor's 75 %
Computing%
Scale law vs PNNL 8 % per decade
Computingratio
Utility high to vendor CAPEX
Computingratio
PNNL charging price
ComputingEUR/MWh
Gap to PNNL real WACC
Computing%
Gap to PNNL economic life
Computingyears
Cycles vs PNNL baseline
Computing%

Sensitivities

6 charts
LCOS components vs full cycles per year

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LCOS components by CAPEX reference case

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CAPEX per kWh and total CAPEX vs rated power

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LCOS and achievable cycles vs storage duration

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CO2 inventory and discharge mass flow vs rated power

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LCOS vs charging price

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Sources

60 documented assumptions · 6 sources

About

Calculator context

A CO2 battery stores electricity by cycling carbon dioxide in a closed loop. Charging draws CO2 from a flexible dome at atmospheric pressure, compresses it, keeps the compression heat in a packed bed of inert particles, and condenses the gas into liquid held at about 70 bar and ambient temperature in steel vessels. Discharging evaporates the liquid, reheats it with the stored heat and expands it through a turbine back into the dome. This calculator is the whole-plant asset sheet of an Energy Dome type plant: it sizes the plant from its discharge power (the key co2_battery catalogue products bind to) and duration, and answers what a MWh returned to the grid costs.

Sizing. Energy capacity is power times duration; the reference is Energy Dome's standard 20 MW / 200 MWh / 10 h frame (SEC Latrobe Valley, Alliant Columbia; Kudgi is 8 h). Charge power is set so that charging takes as long as discharging, as in the vendor frame (24 MWe compressor, 18 MWe turbine over 10 h); those gross machine ratings are shown for reference and are not used to derive the efficiency. Round-trip efficiency is an input: 75 % net AC-AC in Energy Dome's 2024 decks, '70%+' on the 2026 product page, about 77 % ± 2 % from Politecnico di Milano. No public source splits it by component, so the model does not pretend to. There is no degradation and the depth of discharge is 100 % (vendor).

CO2 loop. The inventory is 10 t of CO2 per MWh of capacity: the one plant whose inventory is published holds 2,000 t for 200 MWh (IEEE Spectrum, 2025). That is a single-plant ratio, evidence medium, and it is the shared default of the whole CO2 Battery series so chained inventories agree. The implied net work, 360 kJ per kg cycled, is a coherence check against expansion from about 55 bar, not a validation. Mass flows through the compressor and turbine follow from the inventory and the charge and discharge times.

Cost. CAPEX is per kWh of capacity, from one of four cases: Energy Dome's own claim of 225 or 250 USD/kWh (2024 decks), which is a vendor figure and is flagged as such, or Alliant Energy's 60-90 M USD estimate for its 200 MWh Columbia plant (300-450 USD/kWh). Converted at the ECB 2024 rate and scaled with power by PNNL's 8 % drop per tenfold size for CAES, transposed. No source splits the cost into power and energy parts, so the cost per kW is the cost per kWh times the duration; outside 8-12 h the per-kWh basis is extrapolated and flagged. A Customized option takes your own quote. Fixed O&M is PNNL's CAES value of 16.12 USD/kW-year, transposed (no CO2-battery figure is published).

LCOS. The same method as the A-CAES calculator: PNNL-33283 Eq. 1 with a capital recovery factor at PNNL's real WACC of 6.52 % over 20 years, 365 cycles a year, and charging at 0.03 USD/kWh (26.3 EUR/MWh) divided by the efficiency. At the defaults (20 MW, 10 h, 75 %, vendor 250 USD/kWh) the LCOS is about 96.5 EUR/MWh, of which about 57.5 capital, 3.9 fixed O&M and 35.1 charging; on the Alliant high estimate it rises to about 142.5. Over the 30-year physical life it falls to about 87.5. A cycle takes twice the duration, so above about 12 h fewer than 365 cycles fit in a year and the model caps them. In project mode the charging electricity is the inlet and the discharged electricity the outlet, both in MW; the CO2 inventory is a one-off fill, not a flow.

Model

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

126 variables shown of 126
VariableValueUnitDepends on
20MW—
10h—
75%—
365cycles/year—
2——
0——
231EUR/kWh—
26.3EUR/MWh—
6.52%—
20years—
VariableFormulaUnitDepends on
if((<)+(>)+(<)+(>)+(*<)+(*>)+(<)+(>+)+(<=)+(>)+(<)+(>)+(<)+(>)+(<=)+(<)+(<)+(<)+(>)>0,1,0)bool
*ratio
*ratio
*ratio
VariableFormulaUnitDepends on
MW
*MWh
%
/max(,)MWh/MWh
*/max(,)MW
*/max(,)h
/max(,)ratio
/ratio
/*%
-%
*MWh
*(+)h
/max(,)cycles/year
min(,)cycles/year
(-/max(,))*%
**h/year
**h/year
/*%
*MWh/year
*MWh/year
-MWh/year
*MWh
/t/MWh
*t
*/max(,)t/h
*/max(,)t/h
**t/year
/max(*/,)kJ/kg
/(*)USD/kWh
/(*)USD/kWh
if(==,,if(==,,if(==,,)))USD/kWh
/EUR/kWh
(/)^(-)ratio
clamp(*(/)^(-),,)EUR/kWh
if(>=,,)EUR/kWh
**EUR
/max(*,)EUR/kW
(-^(-))/ratio
/ratio
if((<)*(<=)>0,1,0)flag
if((<)+(>)>0,1,0)flag
if(<,1,0)flag
if(<,/,(*(+)^)/max((+)^-,))1/year
*EUR/year
/EUR/kW/year
**EUR/year
*EUR/year
++EUR/year
/max(,)EUR/MWh
/max(,)EUR/MWh
*EUR/MWh
++EUR/MWh
/max(,)*%
if(<,/,(*(+)^)/max((+)^-,))1/year
(*+)/max(,)+EUR/MWh
/EUR/MWh
-%
-years
/*%

Assumptions

60 assumptions used in the calculations

  • Zero term in guards.

    Market range Exact, no range.

    0
    Unit conversion

  • Unit term in the CRF, guards and ratios.

    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.

    Market range Exact, no range.

    100%
    Unit conversion

  • MW to kW.

    Market range Exact, no range.

    1000kW/MW
    Unit conversion

  • Tonne to kilogram.

    Market range Exact, no range.

    1000kg/t
    Unit conversion

  • 1 kWh = 3,600 kJ; used to turn the CO2 inventory per kWh into an implied net specific work.

    Market range Exact, no range.

    3600kJ/kWh
    Unit conversion

  • Reference size of the CAPEX scale law: the frame the vendor cost per kWh is quoted for.

    20MW
    Energy Dome TMCES 2024

  • Energy of the standard plant; shown in the help and used for the reference frame.

    Market range 4 MWh (demo) to 1,000 MWh (Huadian Mulei).

    200MWh
    Energy Dome TMCES 2024

  • Duration of the standard frame the vendor cost is quoted for.

    10h
    Energy Dome / SEC

  • Compressor rating of the standard frame.

    Market range Single vendor value.

    24MW
    Energy Dome TMCES 2024 p.14

  • Turbine rating of the standard frame.

    Market range Single vendor value.

    18MW
    Energy Dome TMCES 2024 p.14

  • Default of the efficiency slider; the gap to it is an output.

    Market range 70 % (product page floor) to 77 % ± 2 % (Polimi).

    75%
    Energy Dome TMCES 2024 p.18

  • Lower guard of the round-trip efficiency.

    70%
    Energy Dome product page 2026

  • Upper reference of the efficiency band.

    77%
    Astolfi et al. 2021

  • Uncertainty band of the Polimi figure, used for the upper efficiency guard.

    Market range ± 2 points.

    2%
    Astolfi et al. 2021

  • Share of the energy capacity used every cycle.

    Market range Single vendor value.

    100%
    Energy Dome product page 2026

  • Physical service life of the plant.

    Market range 30+ years (vendor).

    30years
    Energy Dome product page 2026

  • CO2 held by the 200 MWh plant described by IEEE Spectrum.

    Market range Single reported value.

    2000t
    IEEE Spectrum 2025

  • Energy of the plant whose CO2 inventory is reported.

    Market range Single reported value.

    200MWh
    IEEE Spectrum 2025

  • Reference case 1.

    225USD/kWh
    Energy Dome TMCES 2024 p.18

  • Reference case 2 (default).

    250USD/kWh
    Energy Dome LDES 2024 p.12

  • Reference case 3.

    60000000USD
    Utility Dive 2024

  • Reference case 4.

    90000000USD
    Utility Dive 2024

  • Energy of the Alliant Columbia plant.

    Market range Single value.

    200MWh
    Utility Dive 2024

  • USD to EUR for the CAPEX.

    Market range Single annual average.

    1.0824USD/EUR
    ECB

  • USD to EUR for PNNL's O&M and charging price.

    Market range Single annual average.

    1.1422USD/EUR
    ECB

  • Fixed O&M per kW of discharge power.

    Market range No CO2-battery-specific range published.

    16.12USD/kW/year
    PNNL-33283 §4.5.2.1

  • Cost reduction per decade of power.

    Market range 8 % per 10x (CAES).

    0.08
    PNNL-33283 §4.5.1

  • Exponent of the CAPEX scale law on rated power, the size the catalogue binds to.

    Market range -8 % per decade of size (PNNL, CAES).

    0.963788
    PNNL-33283 §4.5.1, power-law form by OpenJack

  • Size ratio of one decade.

    Market range Exact.

    10
    Definition

  • Numerical guard of the scale law.

    Market range Not applicable.

    100EUR/kWh
    OpenJack

  • Numerical guard of the scale law.

    Market range Not applicable.

    1000EUR/kWh
    OpenJack

  • PNNL's real cost of capital.

    Market range Single PNNL value.

    6.52%
    PNNL-33283 Table 6.1

  • PNNL's economic life convention.

    Market range Single PNNL value.

    20years
    PNNL-33283 §6.1.1

  • PNNL's duty basis.

    Market range Single PNNL value.

    365cycles/year
    PNNL-33283 §6.1.3

  • PNNL's charging price.

    Market range Single PNNL value.

    30USD/MWh
    PNNL-33283 Table 6.1

  • Lower validity guard on power.

    2.5MW
    Energy Dome TMCES 2024 p.5

  • Upper validity guard on power.

    100MW
    Chain contract (Huadian Mulei)

  • Lower validity guard on energy capacity.

    4MWh
    Energy Dome TMCES 2024 p.5

  • Upper validity guard on energy capacity.

    1000MWh
    Chain contract (Huadian Mulei)

  • Lower validity guard on duration.

    4h
    Chain contract

  • Upper validity guard on duration.

    24h
    Energy Dome product page 2026

  • Shortest duration the vendor prints.

    8h
    Energy Dome product page 2026

  • Upper edge of the duration the cost per kWh is quoted for.

    12h
    Energy Dome TMCES 2024

  • Case identifier in the CAPEX selector.

    Market range Not applicable.

    1
    OpenJack

  • Case identifier in the CAPEX selector.

    Market range Not applicable.

    2
    OpenJack

  • Case identifier in the CAPEX selector.

    Market range Not applicable.

    3
    OpenJack

  • Case identifier in the CAPEX selector.

    Market range Not applicable.

    4
    OpenJack

  • External reference on the LCOS ruler.

    Market range 0.10 USD/kWh (CAES, 1,000 MW).

    87.55EUR/MWh
    PNNL-33283

  • External reference on the LCOS ruler (low).

    131.33EUR/MWh
    US DOE CAES TSA 2023

  • External reference on the LCOS ruler (high).

    525.3EUR/MWh
    US DOE CAES TSA 2023

  • Charge-side pressure ratio of the cycle.

    Market range About 55 bar charge; liquid storage about 70 bar at ambient (Energy Dome).

    55bar
    IEEE Spectrum 2025

  • 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 convention, stated once.

    Market range Not applicable.

    —
    PNNL-33283

  • Why no power/energy split is shown.

    Market range Not applicable.

    —
    Energy Dome TMCES 2024

  • Basis of the CO2 inventory and mass flows.

    Market range Single plant.

    —
    IEEE Spectrum 2025

  • Scope note on a source that looks related but is not.

    Market range Not applicable.

    —
    OpenJack review

  • Charge-side sizing rule.

    Market range Not applicable.

    —
    Energy Dome TMCES 2024 p.14

  • Variable O&M omitted.

    Market range Not applicable.

    —
    OpenJack