Equipment sizingCostingEnergy mass balanceStorage

Liquid CO2 storage vessels for a CO2 battery (ambient, ~70 bar): count, wall thickness, steel and cost per kWh

Carbon-steel bullets holding an Energy Dome-type CO2 battery's liquid CO2 at ambient temperature, 4 to 1,000 MWh. NIST densities, ASME UG-27 walls and the Seider vessel cost give vessel count, steel and installed EUR/kWh.

Open Jack

Founder · OpenJack

Add to project

CurrencyEUR 2023
Battery limitinstalled
67 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 cycles per year

Full discharges a year you expect to sell. 365 is one cycle a day, the usual basis for daily-cycling long-duration storage. Fewer cycles spread the same vessel cost over fewer MWh.

Flows

Annual quantities at the current usage. Band width: share of energy in; non-energy flows are not to scale.

Energy capacity

Electricity returned per full discharge of the CO2 battery. Sets the CO2 inventory the vessels must hold. 200 MWh is the Energy Dome standard plant (20 MW for 10 h, Sardinia and Latrobe Valley); the shared CO2 battery range runs from the 4 MWh Ottana demonstrator to 1,000 MWh.

CO2 inventory: — t
Liquid CO2 volume: — m3
Number of vessels: — vessels
Steel mass of the vessel bank: — t

CAPEX

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

Specific CAPEX at this size

—

Reference size 200 MWh

Seider 4th ed. / IEEE Spectrum 2025

CAPEX source

Model value: steel mass, Seider vessel price and installation factor. Customized: your own installed quote per kWh, used as is at every size; it is then no longer sourced.

Installed vessel CAPEX per kWh (applied) by energy capacity

Ex-factory
Installed· this figure
Fully financed

CAPEX at the battery limit—

Working capital, contingencyproject level

Included

Equipment
Installation, civil works and engineering

Not included

Working capital
Contingency

Added at project level

Working capital layer, from the project settings
Contingency, from the project settings

Project figures

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

Liquid CO2 storage vessels for a CO2 battery (ambient temperature, ~70 bar)Concept sketch, not to scale · drag to rotate

Liquid CO2 from the charge compression train in: —
Liquid CO2 to the discharge expansion train outMain product: —
CAPEX to the battery limit: —
Fixed O&M: 0 EUR/year
Variable O&M, excluding feedstocks: 0 EUR/year
Asset lifetime: 30 years

Vessel bank cost per MWh discharged

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

—

Vessel purchase part—
Installation part—

Linked to the balance above

Full cycles per year

Full discharges a year you expect to sell. 365 is one cycle a day, the usual basis for daily-cycling long-duration storage. Fewer cycles spread the same vessel cost over fewer MWh.

Storage duration

Hours of discharge at rated power. Sets the rated power and the CO2 flow leaving the vessels, not their size. A cycle also needs a charge: on the Energy Dome standard frame it takes about as long as the discharge, so cycles x (charge + discharge) must fit in a year.

CO2 inventory per MWh

Tonnes of CO2 cycled per MWh discharged. 10 t/MWh is printed for the 200 MWh Sardinia plant (2,000 t, IEEE Spectrum 2025). The Energy Dome 2022 deck implies about 11.5 t/MWh (66.7 kWh/m3 at 1.3 L/kg). The whole inventory is sized as liquid at full charge.

Liquid CO2 storage pressure

Absolute pressure in the vessels. Energy Dome's 2022 deck gives 70 bar at ambient temperature; IEEE Spectrum reports compression to about 55 bar. It must stay above the CO2 saturation pressure at the hottest ambient temperature, or the liquid cannot be held.

Maximum ambient temperature

Hottest temperature the uninsulated vessels reach. It sets the liquid density (NIST: 860 kg/m3 at 10 °C, 710 at 25 °C, 592 at 30 °C) and the saturation pressure. CO2 has no liquid above 31 °C; at 70 bar storage the limit is about 28.6 °C.

Vessel inner diameter

Inside diameter of each horizontal bullet, 12 m between tangents with 2:1 ellipsoidal heads. 3 m reflects the 'school bus' sized vessels reported at Sardinia. A larger diameter means fewer vessels but thicker walls.

Discount rate (real)

Real rate used to annualise the vessel CAPEX. Costs are in constant 2023 euros, so the rate must be real (after inflation).

Vessel service life

Service life of the vessel bank. Energy Dome states a 30+ year plant life with no degradation; static carbon-steel pressure vessels have no wear part to replace.

Vessel bank cost per MWh discharged by full cycles per year

Benchmarks

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

CO2 inventory per MWh, t/MWh

10 IEEE Spectrum 2025

11.53 Energy Dome NETL 2022 (derived)

Liquid specific volume, L/kg

1.3 Energy Dome NETL 2022

Liquid volume per MWh, m3/MWh

14.99 Energy Dome NETL 2022 (derived)

Reference cases at this size and usage

All results

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

55 outputs · 6 groups · 13 also shown above, dimmed

Storage cost

Vessel bank cost per MWh discharged: ComputingEUR/MWh
Vessel purchase part: ComputingEUR/MWh
Installation part: ComputingEUR/MWh
Annualised vessel CAPEX: ComputingEUR/year
Capital recovery factor: Computing1/year

CAPEX

Installed vessel bank CAPEX: ComputingEUR
Installed vessel CAPEX per kWh (applied): ComputingEUR/kWh
Installed vessel CAPEX per kWh, scale law: ComputingEUR/kWh
Installed vessel CAPEX per kWh (model): ComputingEUR/kWh
Purchased vessel cost per kWh: ComputingEUR/kWh
CAPEX per kWh as built: ComputingEUR/kWh
Whole-vessel rounding: Computingratio
Purchased vessels: ComputingEUR
Installation: ComputingEUR
CAPEX per tonne of CO2 stored: ComputingEUR/t
Purchased cost of one vessel, 2013: ComputingUSD
Purchased cost of one vessel, 2023 euros: ComputingEUR
Purchased cost per kg of steel: ComputingEUR/kg
Share of Energy Dome's whole-plant price: Computing%

CO2 inventory and liquid

CO2 inventory: Computingt
CO2 inventory per MWh: Computingt/MWh
Liquid CO2 density at the hottest day: Computingkg/m3
Liquid specific volume: ComputingL/kg
CO2 saturation pressure at the hottest day: Computingbar
Pressure margin above saturation: Computingbar
Margin to the critical temperature: Computing°C
Liquid CO2 volume: Computingm3
Liquid volume per MWh: Computingm3/MWh

Vessels and steel

Number of vessels: Computingvessels
Vessels needed (continuous): Computingvessels
Volume of one vessel: Computingm3
Required vessel volume: Computingm3
Vessel volume per MWh: Computingm3/MWh
Vessel volume per tonne of CO2: Computingm3/t
Vapour-space penalty: Computing%
Gauge pressure: Computingbar
Design pressure (gauge): Computingbar
Allowable stress: ComputingMPa
Shell wall thickness: Computingmm
Steel mass of one vessel: Computingt
Vessel weight for the cost law: Computinglb
Steel mass of the vessel bank: Computingt
Steel per MWh: Computingt/MWh

Code and correlation checks

Thickness to radius ratio: Computingratio
Pressure to stress ratio: Computingratio
Thin-wall formula out of range: Computingflag
Cost law out of range: Computingflag

Duty and chaining

Rated discharge power: ComputingMW
Discharge load hours: Computingh/year
Charge to discharge time ratio: Computingratio
Charge load hours: Computingh/year
Discharge capacity factor: Computing%
Energy discharged a year: ComputingMWh/year
CO2 cycled through the vessels a year: Computingt/year
CO2 flow leaving the vessels in discharge: Computingt/h

Sensitivities

5 charts

Vessel cost per MWh vs full cycles per year

Vessel count and CAPEX per kWh vs energy capacity

Wall thickness and steel per MWh vs vessel diameter

Vessel volume per MWh vs hottest ambient temperature

Installed vessel CAPEX per kWh vs storage pressure (25 °C hottest day)

Sources

67 documented assumptions · 11 sources

About

Calculator context

An Energy Dome CO2 battery keeps its charged state as liquid CO2 at ambient temperature, in carbon-steel pressure vessels at about 70 bar (Energy Dome, NETL 2022). This calculator sizes and prices that vessel bank. It takes the energy capacity (MWh, the key shared by the six CO2 battery calculators), the CO2 inventory per MWh, the storage pressure, the hottest ambient day and the vessel diameter. It returns the liquid volume, the number of vessels, their wall thickness and steel mass, the installed CAPEX per kWh, and the vessels' share of the plant LCOS.

Inventory. 10 t of CO2 per MWh discharged is the default: IEEE Spectrum (Dec 2025) prints 2,000 t for the 200 MWh Sardinia plant. Energy Dome's 2022 deck implies about 11.5 t/MWh (66.7 kWh/m3 at 1.3 L/kg). That is a derived cross-check, within 15 %. The slider runs from 9 to 12 t/MWh. The whole inventory is sized as liquid at full charge.

Liquid. The density is the NIST saturated-liquid value at the hottest ambient temperature, interpolated between NIST points at 10, 25 and 30 °C. The interpolation is a little low between the points, which is conservative. Liquid can only be held while the CO2 saturation pressure at that temperature stays below the storage pressure. The calculator refuses a design that breaks this rule, and any hottest day at or above the 31 °C critical point. At 70 bar the limit is about 28.6 °C. The vessels are filled to 95 % at most: the 49 CFR rule for pressure receptacles, transposed to stationary storage.

Vessels. Each vessel is a horizontal bullet, 12 m between tangents, with 2:1 ellipsoidal heads; about 3 m in diameter matches the 'few dozen' school-bus-sized vessels reported at Sardinia. The shell thickness follows ASME VIII Div. 1 UG-27. The design pressure is 10 % above gauge (Seider rule), the allowable stress is 15 ksi carbon steel by default or 20 ksi for SA-516 Gr 70, welds are fully radiographed, and 3.175 mm is added for corrosion. Steel mass uses the Seider weight formula. Per-MWh results use the continuous vessel count, so they do not jump with rounding. The vessel count, total steel and total CAPEX use whole vessels.

Cost. Each vessel is priced from its weight with the Seider et al. (4th ed.) horizontal-vessel correlation. That gives an f.o.b. price including nozzles, manholes and supports, escalated with CEPCI 2023 / 567 and converted at the ECB 2023 rate. It is then multiplied by the Towler & Sinnott fluids-processing installation factor of 3.2, which gives installed ISBL direct cost in constant 2023 euros. The vessel bank is a numbering-up of identical vessels, so no economy of scale is applied: the cost per kWh does not fall with plant size. The cost per MWh discharged annualises that CAPEX with a real capital recovery factor over the vessel service life (30 years by default, Energy Dome) and the cycles a year. It is the vessels' share of the plant LCOS only.

What to defend, and what not. The vessel-only CAPEX comes out high. On default settings it is a large share of the roughly EUR 220/kWh Energy Dome quotes for the whole 20 MW / 200 MWh plant (vendor claim, 2023 euros, the same year as this calculator). That share is shown as an output. Each modelling choice pushes the cost up: 15 ksi rather than 20 ksi steel, a generic fluids installation factor whose 0.8 piping term is large for simple storage bullets, and 70 bar where IEEE reports about 55 bar. At 55 bar the hottest day must stay below about 19 °C for liquid storage. Fixed O&M is not modelled, because no sourced figure was found. Engineering, offsites and the first CO2 fill are excluded.

Model

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

126 variables shown of 126

Value	Unit	Depends on
200	MWh	—
10	h	—
365	cycles/year	—
1	—	—
0	—	—
150	EUR/kWh	—
10	t/MWh	—
70	bar	—
25	°C	—
3	m	—
0.07	ratio	—
30	years	—

Variable	Formula	Unit	Depends on
	`if((<=)+(<=)+(<=)+(<=)+(<=)+(<=)+(<)+(>=)+((+(-)(-)/(-))>)+((+(/()))>)+(<)+(<)+(<)+(>)+(<)+(>)+(<=)>0,1,0)`	bool

Variable	Formula	Unit	Depends on
	`/max(,)`	MW
		t/MWh
	`*`	t
	`if(<=,+(-)(-)/(-),+(-)(-)/(-))`	kg/m3
	`/max(,)`	L/kg
	`+(-)*(-)/(-)`	bar
	`-`	bar
	`-`	°C
	`*/max(,)`	m3
	`/max(,)`	m3/MWh
	`(/-)*`	%
	`/max(*,)`	m3/t
	`*`	m3
	`/max(,)`	m3/MWh
	`^2(+)`	m3
	`/max(,)`	vessels
	`ceil()`	vessels
	`-`	bar
	`max(+,*)`	bar
	`if(==,,)`	MPa
	`*/max(-**,)+`	mm
	`(/)/max(/,)`	ratio
	`/max(,)`	ratio
	`if((>)+(>)>0,1,0)`	flag
	`(+/)(+)(/)*/`	t
	`*/`	lb
	`if((<)+(>)>0,1,0)`	flag
	`exp(+ln()+ln()^2)`	USD
	`*//`	EUR
	`/max(*,)`	EUR/kg
	`*`	t
	`*/max(,)`	t/MWh
	`/max(,)`	EUR/kWh
	`*`	EUR/kWh
	`clamp(*(/)^(-),,)`	EUR/kWh
	`if(>=,,)`	EUR/kWh
	`if(>=,,/max(,))`	ratio
	`***`	EUR
	`/max(*,)`	EUR/kWh
	`/`	EUR
	`-`	EUR
	`/max(,)`	EUR/t
	`/*`	%
	`*`	h/year
	`/(*)`	ratio
	`*`	h/year
	`/*`	%
	`*`	MWh/year
	`*`	t/year
	`/max(,)`	t/h
	`if(<,/,(*(+)^)/max((+)^-,))`	1/year
	`*`	EUR/year
	`*/max(,)`	EUR/MWh
	`*/max(,)`	EUR/MWh
	`+`	EUR/MWh

Assumptions

67 assumptions used in the calculations

Avoids a literal 0 in formulas.
Market range Not applicable.
0
OpenJack DSL convention
Avoids a literal 1 in formulas.
Market range Not applicable.
1
OpenJack DSL convention
Converts radius-based UG-27 to a diameter basis.
Market range Exact.
2
Geometry
Cross-section of the shell.
Market range Exact.
0.25
Geometry
Display in percent.
Market range Exact.
100%
Unit conversion
Mass conversion.
Market range Exact.
1000kg/t
Unit conversion
Volume conversion.
Market range Exact.
1000L/m3
Unit conversion
Length conversion.
Market range Exact.
1000mm/m
Unit conversion
Pressure conversion for UG-27.
Market range Exact.
0.1MPa/bar
Unit conversion
The Seider cost correlation takes the vessel weight in lb.
Market range Exact.
0.453592kg/lb
Unit conversion
Gauge pressure = absolute storage pressure minus one atmosphere.
Market range Exact.
1.01325bar
Standard atmosphere
Lower node of the density interpolation.
Market range Tabulated.
10.153°C
NIST WebBook
Liquid density at a cool site.
Market range Saturated liquid only; compressed liquid above saturation is a few percent denser (not credited).
859.99kg/m3
NIST WebBook
Middle node of the interpolation.
Market range Tabulated.
25.038°C
NIST WebBook
Default design density at a 25 °C maximum ambient.
Market range
709.92kg/m3
NIST WebBook
Lower node of the saturation-pressure line.
Market range Tabulated.
64.399bar
NIST WebBook
Upper node of the interpolation.
Market range Tabulated.
30.022°C
NIST WebBook
Liquid density 1 °C below the critical point.
Market range Tabulated.
592.32kg/m3
NIST WebBook
Highest ambient temperature at which 70 bar still holds liquid.
Market range Tabulated.
28.611°C
NIST WebBook
Upper node of the saturation-pressure line, extrapolated linearly below 25 °C (slightly low by under 1 bar at 20 °C).
Market range Tabulated.
69.886bar
NIST WebBook
No liquid CO2 can exist above it: the calculator refuses a maximum ambient at or above it.
Market range 30.98 °C (NIST).
31°C
Energy Dome NETL 2022
Leaves vapour space so thermal expansion of the liquid does not overfill the vessel.
Market range No independent range cited.
0.95ratio
49 CFR 173.304b
Design pressure margin above the operating gauge pressure.
Market range No independent range cited.
1.1ratio
BioSTEAM / Seider
Minimum design margin.
Market range No independent range cited.
2.068bar
BioSTEAM / Seider
Reference case 1 allowable stress.
Market range
103.4MPa
BioSTEAM / Seider
Reference case 2 allowable stress.
Market range No independent range cited.
137.9MPa
ASME II-D via secondary sources
Documents the source unit.
Market range Not applicable.
15000psi
BioSTEAM / Seider
A 70 bar vessel of this thickness is fully radiographed.
Market range 0.85 spot radiography, 0.70 none.
1ratio
ASME VIII Div. 1 UW-12 via CheCalc
Added to the pressure thickness.
Market range
3.175mm
BioSTEAM / CheCalc
Circumferential stress thickness.
Market range Exact.
1.2
ASME UG-27
Flags a design outside the thin-wall formula.
Market range Exact.
0.5ratio
ASME UG-27
Flags a design outside the thin-wall formula.
Market range Exact.
0.385ratio
ASME UG-27
Shell and heads mass.
Market range
7861kg/m3
IDAES / Seider
Adds the head steel to the shell.
Market range Exact within the method.
0.8ratio
IDAES / Seider
Unit vessel length.
Market range
12m
IEEE Spectrum 2025 (indicative)
Adds the head volume to the shell volume.
Market range Exact.
0.333333ratio
Geometry
Purchased cost of one vessel, incl. nozzles, manholes and supports.
Market range Valid 1,000-920,000 lb.
5.6336
Seider 4th ed.
Cost-weight elasticity.
Market range Exact within the method.
0.4599
Seider 4th ed.
Curvature of the cost-weight law.
Market range Exact within the method.
0.00582
Seider 4th ed.
Flags extrapolation.
Market range Exact.
1000lb
Seider 4th ed.
Flags extrapolation.
Market range Exact.
920000lb
Seider 4th ed.
Escalation base.
Market range Exact.
567
Seider 4th ed.
Escalates the 2013 correlation to 2023.
Market range Exact.
797.9
CEPCI 2023
Converts 2023 USD to 2023 EUR.
Market range Exact.
1.0813USD/EUR
ECB
Turns the f.o.b. vessel price into installed ISBL direct cost (erection, piping, instruments, electrical, civil, structures, lagging). Engineering, contingency and offsites are not included.
Market range No independent range cited.
3.2ratio
Towler & Sinnott 2022
Documents the largest term of the installation factor.
Market range No independent range cited.
0.8ratio
Towler & Sinnott 2022
Shows how the vessel bank compares with the whole-plant price: the model's vessel-only figure is already about 70 % of it, which says the conservative choices (S 15 ksi, generic factor 3.2, 70 bar) are high.
Market range No independent range cited.
220EUR/kWh
Energy-Storage.news 2023
Reference size of the scale law.
Market range
200MWh
IEEE Spectrum 2025
Numbering-up of identical vessels: the specific CAPEX per kWh does not change with plant size; whole-vessel rounding is shown separately.
Market range 1.0 for modular numbering-up; 0.6-0.7 only for a single larger vessel, which is outside this design.
1
Seider 4th ed. / IEEE Spectrum 2025
Prevents a degenerate value outside the domain.
Market range Not applicable.
10EUR/kWh
OpenJack DSL convention
Prevents a degenerate value outside the domain.
Market range Not applicable.
2000EUR/kWh
OpenJack DSL convention
Reference case 1: Seider/BioSTEAM carbon steel, S = 15 ksi.
Market range Not applicable.
1
OpenJack DSL convention
Reference case 2: SA-516 Gr 70 at 20 ksi.
Market range Not applicable.
2
OpenJack DSL convention
Charge power of the standard frame, used only to check that charge + discharge fit in the year.
Market range No independent range cited.
24MW
Energy Dome TMCES 2024
Discharge power of the standard frame.
Market range No independent range cited.
18MW
Energy Dome TMCES 2024
Charge energy = discharge / RTE; with 24/18 MW the charge then lasts 1.0 x the discharge.
Market range
0.75ratio
Energy Dome 2024
Default of the CO2 inventory slider (9-12 t/MWh).
Market range
10t/MWh
IEEE Spectrum 2025
Benchmark for the CO2 inventory per MWh.
Market range Single plant.
10t/MWh
IEEE Spectrum 2025
Second benchmark for the CO2 inventory per MWh.
Market range Not applicable.
11.53t/MWh
Energy Dome NETL 2022 (derived)
Inventory of the reference plant; the model returns 2,000 t at 200 MWh and 10 t/MWh by construction (not a validation).
Market range Single plant.
2000t
IEEE Spectrum 2025
Benchmark for the liquid specific volume.
Market range Not applicable.
1.3L/kg
Energy Dome NETL 2022
Basis of the 15.0 m3/MWh liquid-volume benchmark.
Market range Not applicable.
66.7kWh/m3
Energy Dome NETL 2022
Benchmark for the liquid volume per MWh.
Market range Not applicable.
14.99m3/MWh
Energy Dome NETL 2022 (derived)
Default of the storage pressure slider; a chain contract variable.
Market range
70bar
Energy Dome NETL 2022
Default of the diameter slider.
Market range
3m
IEEE Spectrum 2025 (indicative)
Scope: the liquid CO2 vessels only. The dome, compressor train, expander train and thermal storage are separate calculators. Chaining rule: the CO2 inlet comes from the charge compression train (upstream) and the CO2 outlet feeds the discharge expansion train (downstream) with the same yearly tonnage; link energy_capacity_mwh and co2_inventory_t one to one, never with a partial coefficient.
Market range Not applicable.
—
OpenJack chain contract
Fixed O&M (inspection, recertification) is not modelled and exported as zero; add a project-level line if needed.
Market range No independent range cited.
—
Research gap

Liquid CO2 storage vessels for a CO2 battery (ambient, ~70 bar): count, wall thickness, steel and cost per kWh

Mass and energy balance

CAPEX

Included

Not included

Added at project level

Project figures

Vessel bank cost per MWh discharged

Benchmarks

CO2 inventory per MWh, t/MWh

Liquid specific volume, L/kg

Liquid volume per MWh, m3/MWh

All results

Storage cost

CAPEX

CO2 inventory and liquid

Vessels and steel

Code and correlation checks

Duty and chaining

Sensitivities

Sources

About

Model

User inputs · 12

Constants · 58

Intermediate calcs · 1

Exposed outputs · 55

Assumptions