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Flywheel energy storage for frequency regulation: standby losses, cycling and cost per MW of reserve

Flywheel plant for frequency regulation: cost per MW of reserve and per MWh exchanged from the DOE/EPRI 2013 handbook (Table B-27) or Beacon Hazle costs, with standby losses drawn all year, round-trip losses, and a life set by 125,000 cycles or 20 years.

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Open Jack

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  • CurrencyEUR 2010
  • Battery limitfully financed
  • 55 documented assumptions
  • Updated27 Oct 2026

Mass and energy balance

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

Reference case

Full-depth equivalent discharges a year in frequency regulation. 5,000 is the DOE/EPRI 2013 life-cycle-cost basis (p.94); Beacon measured about 6,300 in the ISO-NE pilot; Table B-27 gives 15,000 as the vendor figure. With a 125,000-cycle life, above 6,250 cycles a year the cycle life, not the 20-year design life, sets the amortisation period. Charging plus discharging at rated power cannot exceed 8,760 h a year: at 0.5 h and 85 % efficiency the ceiling is about 8,050 cycles, and above it the inputs are flagged invalid.

Flows

  • In: Grid electricity drawn (charging + standby)—

Asset

Flywheel energy storage for frequency regulation

  • Out: Electricity discharged—

Annual quantities at the current usage.

Symmetric regulation capacity (+/- P) of the flywheel plant, in kW. The catalogue binds products here: Stornetic DuraStor 240 is 240 kW, DuraStor 1000 is 1,000 kW. Beacon's 20 MW plants are 200 flywheels of 100 kW in 1 MW blocks, so cost per kW does not change with size. Below 100 kW the model is extrapolated: Sandia says balance-of-system costs make small flywheels less competitive, so the constant cost per kW is probably too low there (see the 'outside sourced domain' flag).

Usable energy
— kWh
Standby power
— kW
Flywheels, Beacon 100 kW units
— units
Energy discharged
— MWh/year

CAPEX

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

Specific CAPEX at this size

—

Reference size 20,000 kW

Beacon 2010 slide 16 (200 x 100 kW flywheels, 1 MW blocks); DOE/EPRI 2013 p.91.

Model value: the selected cost reference, total plant cost per kW, constant across sizes (modular plant). Customized: your own all-in cost per kW, used as is at every size and duration; it is then no longer sourced.

CAPEX per kW used by rated 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.

Grid electricity drawn (charging + standby) in
—
Electricity discharged outMain product
—
CAPEX to the battery limit
—
Fixed O&M
—
Variable O&M, excluding feedstocks
—
Replacement provision
—
Replacement provision
—
Asset lifetime
20 years

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Cost per MW of reserve

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

—

  • Capital part—
  • Fixed O&M part—
  • Replacement part—
  • Variable O&M part—
  • Standby losses part—
  • Conversion losses part—

Linked to the balance above

Full-depth equivalent discharges a year in frequency regulation. 5,000 is the DOE/EPRI 2013 life-cycle-cost basis (p.94); Beacon measured about 6,300 in the ISO-NE pilot; Table B-27 gives 15,000 as the vendor figure. With a 125,000-cycle life, above 6,250 cycles a year the cycle life, not the 20-year design life, sets the amortisation period. Charging plus discharging at rated power cannot exceed 8,760 h a year: at 0.5 h and 85 % efficiency the ceiling is about 8,050 cycles, and above it the inputs are flagged invalid.

Hours of discharge at rated power, at 100 % depth of discharge; usable energy = power x duration. 0.25 h (15 minutes) is the DOE/EPRI 2013 Table B-27 plant and Beacon Stephentown. The handbook gives flywheels short durations of up to one hour; the slider stops at 0.5 h to stay close to the 15-minute regulation plants the costs come from. Each extra hour adds 5,168 USD2010 per kWh of storage.

Power drawn all year to keep the rotors spinning (bearings, vacuum, cooling, electronics), as a % of rated power. Manufacturers do not print it. DOE/EPRI 2013 p.90 gives one to two percent of rated output power; 1.5 % is the middle of that range, our choice. The same page gives less than 25 W per kWh of storage, which is lower at 15 minutes: the two figures do not agree, and the model keeps the rated-power range.

Charge-discharge conversion efficiency, excluding standby losses. 85 % is Table B-27; Pullen 2019 says 85-90 % is typically achievable.

Price of the electricity the operator buys back to cover standby and conversion losses. Default 117.8 EUR/MWh: Eurostat, EU27 non-household 20-70 GWh band, excluding taxes, 2025-S2. 2021-2026 Eurostat values for that band ran from about 67 to 186 EUR/MWh. This is 2025 money while CAPEX and O&M are 2010 money (no escalation).

Rate of the capital recovery factor over the effective life (design life or cycle life, whichever is shorter). Default 7.5 %, the rate Beacon used in its 2007 DOE review of the 20 MW plant. Costs are not escalated, so read it as a real rate.

Cost per MW of reserve by equivalent full cycles per year

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Benchmarks

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

CAPEX per kW, EUR/kW

1,629 2,159 USD2010/kW / 1.3257.

1,810 48 M USD / 20,000 kW / 1.3257.

2,602 69 M USD / 20,000 kW / 1.3257.

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.

73 outputs · 5 groups · 19 also shown above, dimmed

Cost of reserve

12
Cost per MW of reserve
ComputingEUR/MW/yr
Total CAPEX
ComputingEUR
Cost per MWh exchanged
ComputingEUR/MWh
Capital part
ComputingEUR/MW/yr
Fixed O&M part
ComputingEUR/MW/yr
Replacement part
ComputingEUR/MW/yr
Variable O&M part
ComputingEUR/MW/yr
Standby losses part
ComputingEUR/MW/yr
Conversion losses part
ComputingEUR/MW/yr
Capital share of cost
Computing%
Losses share of cost
Computing%
Cost per MW at the handbook's 15-year plant life
ComputingEUR/MW/yr

Size and CAPEX

15
Usable energy
ComputingkWh
Rated power
ComputingMW
CAPEX per kW
ComputingEUR/kW
CAPEX per kW used
ComputingEUR/kW
Model CAPEX in EUR
ComputingEUR/kW
Model CAPEX in USD2010
ComputingUSD/kW
Power part of CAPEX (selected reference)
ComputingUSD/kW
Hazle power part (implied)
ComputingUSD/kW
Power part of model CAPEX
Computing%
CAPEX per kWh stored
ComputingEUR/kWh
Size factor on CAPEX
Computingratio
Flywheels, Beacon 100 kW units
Computingunits
Beacon flywheel unit duration
Computingh
Systems of 1,650 kW in parallel
Computingsystems
Outside sourced domain (below 100 kW)
Computingbool

Duty and losses

18
Energy discharged
ComputingMWh/year
Energy discharged per MW
ComputingMWh/MW/yr
Equivalent full-load discharge hours
Computingh/year
Discharge capacity factor
Computing%
Hours at rated power, charge plus discharge
Computingh/year
Most cycles a year the plant can deliver
Computingcycles/year
Standby power
ComputingkW
Standby losses
ComputingMWh/year
Conversion losses
ComputingMWh/year
Charging energy
ComputingMWh/year
Electricity drawn from the grid
ComputingMWh/year
Heat and losses
ComputingMWh/year
Standby load penalty
Computingratio
Electricity in per MWh discharged
ComputingMWh/MWh
Effective round-trip efficiency
Computing%
Standby share of losses
Computing%
Standby loss per hour of stored energy
Computing%/h
Time to self-discharge
Computingh

Published references

14
DOE/EPRI 2013 total plant cost
ComputingEUR/kW
Two-part law / printed total plant cost
Computingratio
Beacon Hazle cost per kW
ComputingUSD/kW
Beacon Hazle cost per kW
ComputingEUR/kW
Beacon Stephentown cost per kW
ComputingEUR/kW
Thunder Said Energy cost per kW (2025 money)
ComputingEUR/kW
Schmidt et al. mean cost at this duration
ComputingUSD/kW
Cycles / ISO-NE measured
Computingratio
Standby from the 25 W/kWh figure
Computing%
Position in the 1-2 % range
Computing%
Standby / Soomro 3 %/h
Computingratio
Standby / IRENA 15 %/h
Computingratio
Efficiency gap to 90 %
Computing%
Efficiency vs Table B-27
Computing%

Life and finance

14
Effective life
Computingyears
Cycle-limited life
Computingyears
Life limited by cycles
Computingbool
Capital recovery factor
Computing1/year
Annualised CAPEX
ComputingEUR/year
Fixed O&M
ComputingEUR/year
Replacement, yearly average
ComputingEUR/year
Extra replacement when cycles wear the plant out early
ComputingEUR/year
Variable O&M
ComputingEUR/year
Standby electricity cost
ComputingEUR/year
Conversion loss cost
ComputingEUR/year
Total annual cost
ComputingEUR/year
Life with the handbook plant life
Computingyears
CRF at the handbook plant life
Computing1/year

Sensitivities

6 charts
Cost per MW of reserve by part vs cycles per year

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Cost per MWh exchanged and effective life vs cycles per year

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Cost per MW of reserve by part vs storage duration

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Cost per MW of reserve vs electricity price

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Standby loss per hour and effective round-trip efficiency vs standby losses

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CAPEX per kW and total CAPEX vs rated power

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Sources

55 documented assumptions · 11 sources

About

Calculator context

Flywheel storage plant for frequency regulation, of the Beacon Stephentown type: vacuum-housed rotors on magnetic bearings, grouped in 1 MW blocks, that absorb and return power within seconds, many thousand times a year. You set the rated power (50 to 20,000 kW), the duration (0.25 to 0.5 h), the equivalent full cycles a year, the standby losses, the round-trip efficiency, the cost reference and the electricity price.

The cost model is the DOE/EPRI 2013 Electricity Storage Handbook life-cycle method on its Table B-27 flywheel plant (20 MW, 15 minutes, 2010 dollars): 867 USD/kW for power plus 5,168 USD/kWh for storage, which rebuilds the printed total plant cost of 2,159 USD/kW. The second cost reference is Beacon's USD 48 M estimate for its Hazle plant. Costs are converted at the 2010 ECB rate and not escalated; the electricity price is 2025 Eurostat money. The plant is modular, so the cost per kW does not change with size; below 100 kW this is an extrapolation and a flag says so.

Standby losses are not printed by manufacturers. The handbook gives one to two percent of rated power, drawn all year because the rotors spin continuously; the default is the middle of that range. With the 85 % round-trip efficiency, the electricity bought back to cover standby and conversion losses is a cost line. The plant lasts the shorter of its 20-year design life and 125,000 cycles.

At 1,000 kW, 15 minutes and 5,000 cycles a year, the plant costs 1,629 EUR/kW, loses 131.4 MWh a year on standby, and needs about 249,600 EUR per MW of reserve a year, or 200 EUR per MWh exchanged. Capital is about 64 % of it. At 15,000 cycles a year the cycle life binds (about 8 years) and the cost per MW rises, while the cost per MWh falls. Charging plus discharging at rated power must fit in the 8,760 hours of a year, so above about 16,100 cycles at 0.25 h, or 8,050 at 0.5 h (85 % efficiency), the inputs are flagged invalid.

Outputs: cost per MW of reserve and its six parts, cost per MWh exchanged, CAPEX per kW, usable energy, standby and conversion losses, effective life, and published references (handbook, Beacon Stephentown and Hazle, Thunder Said Energy, Schmidt et al.). Value of the energy cycled, market revenue and taxes are left to project mode.

Model

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

137 variables shown of 137
VariableValueUnitDepends on
1000kW—
0.25h—
5000cycles/year—
1——
1.5%—
85%—
0——
2000EUR/kW—
117.8EUR/MWh—
7.5%—
VariableFormulaUnitDepends on
if((<=)+(<=)+(<=)+(<)+(>)+(<)+(>=)+(<=)+(>)+(<)+(>)+(<=)+(<)+(<)+(>=)+(**(+/max(*,))>)>,,)bool
*ratio
*ratio
VariableFormulaUnitDepends on
*MW
*kWh
ceil(/)units
/h
ceil(/)systems
if(<,,)bool
*h/year
/*%
**MWh/year
/max(,)MWh/MW/yr
/ratio
-%
*(+/max(,))h/year
/max(*(+/max(,)),)cycles/year
**kW
**MWh/year
*(/max(,)-)MWh/year
/max(,)MWh/year
+MWh/year
-MWh/year
/max(,)ratio
/max(,)MWh/MWh
/max(,)*%
/max(,)*%
/max(,)*%/h
/max(,)h
*/max(*,)*%
/max(,)years
min(,)years
if(<,,)bool
/USD/kW
-*USD/kW
if(==,,)USD/kW
+*USD/kW
/EUR/kW
(/)^(-)ratio
clamp(if(>=,,*(/)^(-)),,)EUR/kW
*EUR
*max(/max(,)-/,)EUR/year
/max(,)EUR/kW
/max(,)EUR/kWh
/max(,)*%
(+*)/ratio
if(<,/max(,),(*(+)^)/max((+)^-,))1/year
*EUR/year
/*EUR/year
//*EUR/year
/**EUR/year
*EUR/year
*EUR/year
+++++EUR/year
/max(,)EUR/MW/yr
/max(,)EUR/MW/yr
/max(,)EUR/MW/yr
/max(,)EUR/MW/yr
/max(,)EUR/MW/yr
/max(,)EUR/MW/yr
+++++EUR/MW/yr
/max(,)EUR/MWh
/max(,)*%
(+)/max(,)*%
min(,)years
if(<,/max(,),(*(+)^)/max((+)^-,))1/year
+(-)*/max(,)EUR/MW/yr
/EUR/kW
//EUR/kW
/EUR/kW
/EUR/kW
+*USD/kW
/ratio
/ratio
(-)/(-)*%
-%

Assumptions

55 assumptions used in the calculations

  • Unit constant used in ratios and in the CRF formula.

    Market range Exact.

    1
    Numerical or unit convention.

  • Zero used in guards and flags.

    Market range Exact.

    0
    Numerical or unit convention.

  • Converts percent inputs (0-100) into fractions.

    Market range Exact.

    0.011/%
    Numerical or unit convention.

  • Converts fractions into percent for display.

    Market range Exact.

    100%
    Numerical or unit convention.

  • Converts kW into MW for the per-MW indicators.

    Market range Exact.

    0.001MW/kW
    Numerical or unit convention.

  • Converts kW into W for the 25 W/kWh cross-check.

    Market range Exact.

    1000W/kW
    Numerical or unit convention.

  • Selector id of the DOE/EPRI 2013 Table B-27 cost reference.

    Market range Exact.

    1
    Numerical or unit convention.

  • Selector id of the Beacon Hazle cost reference.

    Market range Exact.

    2
    Numerical or unit convention.

  • Power-related part of the total plant cost of the handbook's 20 MW, 15-minute flywheel plant (vendor S5, survey year 2010). Used as the power part of the cost reference 'DOE/EPRI 2013'.

    Market range Schmidt et al. 2019 mean (via Pullen 2019): 641 USD/kW

    867USD/kW
    Table B-27, line 'Power - $/kW' = 867.

  • Storage-related part of the total plant cost, per kWh at rated depth of discharge. Multiplies the duration: each extra hour of storage adds this cost per kW. Also used as the storage part of the Hazle reference, whose split is not published.

    Market range Schmidt et al. 2019 mean (via Pullen 2019): 5,399 USD/kWh

    5168USD/kWh
    Table B-27, line 'Storage - $/kWh @ rated DOD' = 5,168.

  • Printed total plant cost per kW. Used only to check that the two-part law (867 + 5,168 x 0.25) rebuilds the printed total; the model computes CAPEX from the two printed parts, not from this total.

    Market range no independent range cited

    2159USD/kW
    Table B-27, 'TOTAL PLANT COST $/kW' = 2,159 (TPC 43,189,100 USD for 20,000 kW).

  • Duration of the costed handbook plant (0.25 h, 5,000 kWh for 20,000 kW). Used to split the Hazle total into a power part and the handbook storage part, and in the two-part check.

    Market range no independent range cited

    0.25h
    Table B-27, 'Hours of energy storage at rated capacity' = 0.25.

  • Size of the costed plant, used as the reference size of the CAPEX law. With an exponent of 1 the law returns the same cost per kW at every size.

    Market range no independent range cited

    20000kW
    20 MW plant, 200 flywheels of 100 kW / 25 kWh (Beacon 2010, slide 16); same size as Table B-27.

  • Fixed O&M per kW-year. The handbook calls flywheel O&M figures proxy estimates because credible O&M data is scarce, hence medium evidence. Exported undiscounted to the project.

    Market range no independent range cited

    5.8USD/kW/yr
    Table B-27, 'FIXED O&M - $/kW-yr' = 5.8.

  • Variable O&M per kWh discharged. Proxy estimate in the handbook; negligible in the total.

    Market range no independent range cited

    0.0003USD/kWh
    Table B-27, 'Variable O&M $/kWh' = 0.0003.

  • Replacement cost per kW, paid every 5 years. The handbook does not say which components are replaced. Spread linearly over the interval and undiscounted, a simplification; the project cashflow does not replace sub-components, so this part is shown as missing from the project figure.

    Market range no independent range cited

    290USD/kW
    Table B-27 'Replacement costs $/kW' = 290; p.94 '$290 per kW replacement costs every 5 years'.

  • Interval of the 290 USD/kW replacement.

    Market range no independent range cited

    5years
    DOE/EPRI 2013 p.94: 'every 5 years'.

  • Table B-27 AC/AC round-trip efficiency; default of the efficiency slider and baseline of the 'vs Table B-27' output.

    85%
    Table B-27 'Round Trip AC/AC Efficiency' = 85 %.

  • Top of the range of round-trip efficiency Pullen gives as typically achievable; upper end of the efficiency slider.

    90%
    Pullen 2019: 'Round trip efficiencies of 85-90% are typically achievable'.

  • Low end of standby losses as a share of rated power; lower end of the standby slider. Manufacturers do not print standby losses.

    1%
    DOE/EPRI 2013 p.90: standby losses 'in the range one to two percent of the rated output power'.

  • High end of standby losses as a share of rated power; upper end of the standby slider. The 1.5 % default is the middle of the range, our choice, not a printed figure.

    2%
    DOE/EPRI 2013 p.90: 'one to two percent of the rated output power'.

  • Second standby figure on the same page, per kWh of storage. At 15 minutes it is about 0.6 % of rated power, below the 1-2 % range printed alongside: the two figures do not agree at this duration. The model keeps the rated-power range (the higher losses) and shows this figure next to it.

    Market range no independent range cited

    25W/kWh
    DOE/EPRI 2013 p.90: 'typically less than 25 W DC per kWh of storage'.

  • Extreme self-discharge figure, as % of stored energy per hour; shown as a ceiling the model stays well under.

    Market range no independent range cited

    15%/h
    IRENA 2017: 'self-discharge of up to 15% an hour'.

  • Frictional losses of modern designs, as % of stored energy per hour; a lower reference than the handbook range at 15 minutes.

    Market range no independent range cited

    3%/h
    Soomro et al. 2019: 'frictional losses of less than 3% of energy per hour'.

  • Life-cycle-cost basis of the handbook for flywheels; default and lower end of the cycles slider.

    Market range 5,000 (handbook LCC) to 15,000 (vendor) a year

    5000cycles/year
    DOE/EPRI 2013 p.94: life-cycle cost metrics 'based on 5000 cycles per year'.

  • Vendor figure for cycles a year in Table B-27; upper end of the cycles slider.

    15000cycles/year
    Table B-27 'Number of cycles / year' = 15,000.

  • Measured regulation duty of a Beacon plant in the ISO-NE pilot, in 100 % depth-of-discharge equivalents; shown as a field reference for the cycles slider.

    Market range no independent range cited

    6300cycles/year
    Beacon 2010 slide 31: '6300 effective 100% Depth of Discharge cycles / year'.

  • Equivalent full cycles the flywheel is designed for. Divided by the cycles a year it gives the cycle-limited life, which binds above 6,250 cycles a year.

    Market range no independent range cited

    125000cycles
    Beacon 2010 slide 5: '20-year design life, 125,000 equivalent cycles'.

  • Physical design life of the plant; also exported as the asset lifetime. At more than 6,250 cycles a year the cycle life is shorter, and the project should use the effective life output instead.

    Market range 15 years in Table B-27

    20years
    AI

  • Plant life used in Table B-27. Shown as a sensitivity: the cost per MW of reserve is recomputed over 15 years.

    Market range no independent range cited

    15years
    Table B-27 'Plant Life, yrs' = 15.

  • Discount rate Beacon used for the net present value of its 20 MW plant; default of the discount-rate slider. Read as real because no cost is escalated.

    Market range slider 5-10 %, no independent range cited

    7.5%
    Rounds 2007, slide 8: 'Net Present Value with 7.5% discount rate'.

  • Converts every 2010-dollar cost (handbook, Beacon 10-K) into euros of the same year. No inflation escalation is applied, so CAPEX and O&M stay in 2010 money.

    Market range no independent range cited

    1.3257USD/EUR
    ECB annual average USD/EUR 2010 = 1.3257.

  • Converts the 2025 Thunder Said Energy cost into 2025 euros for display; not used in the cost model.

    Market range no independent range cited

    1.13USD/EUR
    ECB annual average USD/EUR 2025 = 1.1300.

  • Default of the electricity-price slider: the price of electricity bought back to cover losses. It is 2025 money while CAPEX and O&M are 2010 money.

    Market range about 67-186 EUR/MWh over 2021-2026 for this band

    117.8EUR/MWh
    Eurostat nrg_pc_205, EU27, non-household, band 20-70 GWh, excluding taxes and levies, 2025-S2 = 0.1178 EUR/kWh.

  • Total cost of Beacon's first 20 MW plant, including contingency, legal and DOE-loan costs (about USD 50 M of it is direct equipment and facility cost). Shown as a reference, not used in the cost model.

    Market range no independent range cited

    69000000USD
    10-K FY2009: 'The first 20 MW plant will cost approximately $69 million, of which approximately $50 million is direct equipment and facility costs'.

  • Estimated total cost of Beacon's second 20 MW plant; basis of the cost reference 'Beacon Hazle'. It is an estimate in the filing, not an as-built cost.

    Market range no independent range cited

    48000000USD
    10-K FY2009: second 20 MW plant 'At a total of approximately $48 million'.

  • Power of each Beacon plant, used to turn the 10-K totals into costs per kW.

    Market range no independent range cited

    20000kW
    Beacon 2010: 20 MW for 15 minutes.

  • Recent independent cost estimate for a 15-minute flywheel, in 2025 dollars. Shown as a reference in 2025 euros; not comparable one for one with the 2010 money of the model.

    Market range no independent range cited

    3000USD/kW
    Thunder Said Energy: '15-minutes of energy, for a capex cost of $3,000/kW and $10,000/kWh'.

  • Mean flywheel power cost from Schmidt et al. 2019 as quoted by Pullen; shown in USD as published, because its currency year is not established in our reading.

    Market range no independent range cited

    641USD/kW
    Pullen 2019 p.8 quoting Schmidt et al. 2019: '641 $/kW and 5399$/kWh'.

  • Mean flywheel energy cost from Schmidt et al. 2019 as quoted by Pullen; used with the power cost for a published cost at the selected duration.

    Market range no independent range cited

    5399USD/kWh
    Pullen 2019 p.8 quoting Schmidt et al. 2019: '641 $/kW and 5399$/kWh'.

  • Lower edge of the sourced domain. Below 100 kW the flag 'outside sourced domain' is raised: the constant cost per kW is extrapolated and probably too low.

    Market range no independent range cited

    100kW
    Bender 2015: 'Below 100 kW, balance of system costs make flywheels less cost competitive'; DOE/EPRI 2013 p.91: systems 'can be sized between 100 kW and 1650 kW'.

  • Largest single flywheel system in the handbook. Larger plants are several systems in parallel, as Beacon's 1 MW blocks are; the output counts them.

    Market range no independent range cited

    1650kW
    DOE/EPRI 2013 p.91: 'can be sized between 100 kW and 1650 kW, and may be used for short durations of up to one hour'.

  • Power of one Beacon flywheel; used to count flywheels for the rated power.

    Market range no independent range cited

    100kW
    Beacon 2010 slide 16: 200 x 25 kWh / 100 kW flywheels in a 20 MW plant.

  • Energy of one Beacon flywheel; with 100 kW it gives the 15-minute duration of the costed plants.

    Market range no independent range cited

    25kWh
    Beacon 2010 slide 16: 25 kWh / 100 kW flywheels.

  • Exponent 1: cost scales linearly with capacity because the plant is modular. Beacon's 20 MW plants are 200 identical 100 kW flywheels grouped in 1 MW blocks, and the handbook sizes single systems between 100 kW and 1,650 kW, so a larger plant adds modules (numbering-up) rather than bigger machines. No source we found gives an economy of scale for flywheel plants. Below 100 kW the linear law is an extrapolation and is flagged.

    Market range no independent flywheel scale exponent found

    1
    Beacon 2010 slide 16 (200 x 100 kW flywheels, 1 MW blocks); DOE/EPRI 2013 p.91.

  • Numerical guard of the CAPEX clamp. The model and customized values stay between 1,200 and 3,000 EUR/kW inside the sliders, so it never binds there.

    Market range Not applicable.

    500EUR/kW
    Model guard, checked at the slider corners.

  • Numerical guard of the CAPEX clamp; never binds inside the sliders (highest value 3,000 EUR/kW, customized).

    Market range Not applicable.

    6000EUR/kW
    Model guard, checked at the slider corners.

  • Handbook total plant cost at 15 minutes, converted at the 2010 ECB rate: the model value of the default reference at 0.25 h.

    Market range no independent range cited

    1,628.6EUR/kW
    2,159 USD2010/kW / 1.3257.

  • Beacon Hazle estimate per kW at 15 minutes, converted at the 2010 ECB rate (10-K filed in 2010; not deflated).

    Market range no independent range cited

    1,810.4EUR/kW
    48 M USD / 20,000 kW / 1.3257.

  • Beacon Stephentown total cost per kW at 15 minutes, including contingency, legal and DOE-loan costs, converted at the 2010 ECB rate. Higher than the model because it includes first-of-a-kind and financing costs.

    Market range no independent range cited

    2,602.4EUR/kW
    69 M USD / 20,000 kW / 1.3257.

  • Method: DOE/EPRI 2013 life-cycle cost (Appendix B). Annual cost = CRF x total plant cost + fixed O&M + replacement (290 USD/kW every 5 years, spread evenly) + variable O&M + electricity bought for standby and conversion losses. Cost per MW of reserve = annual cost / rated power in MW, the yearly revenue a MW of symmetric regulation capacity must earn. Cost per MWh exchanged = annual cost / energy discharged. CRF over the shorter of the 20-year design life and 125,000 cycles / cycles per year.

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  • CAPEX and O&M are 2010 dollars converted at the 2010 ECB rate, with no escalation; the electricity price is 2025 money. The sum is therefore a mixed-year figure that understates the capital part in today's money. For scale, Thunder Said Energy's 2025 figure for a 15-minute flywheel is shown in 2025 euros next to the model.

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  • The handbook figure is a total plant cost (TPC) and the Beacon figures are total project costs, so the CAPEX is all-in and is exported as fully_financed: project mode adds no further cost layers or contingency.

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  • Project mode chains the grid electricity drawn (inlet, charging plus standby) and the electricity discharged (outlet), both priced by the project; the loss electricity is therefore not booked again as O&M. Fixed and variable O&M are exported undiscounted. The 5-year replacement is a capital item the project cashflow does not schedule; the page shows it as missing from the project figure. Above 6,250 cycles a year set the project lifetime to the effective life output, not the 20-year design life.

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  • Sourced domain: 100 to 20,000 kW (single systems of 100-1,650 kW, plants built of 1 MW blocks), durations up to 0.5 h, 5,000-15,000 cycles a year. Below 100 kW the model is extrapolated and the flag is raised. Catalogue products Stornetic DuraStor 240 (240 kW) and DuraStor 1000 (1,000 kW) are inside it.

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