NREL is a national laboratory of the U, S, Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC, 

Energy Storage: Days of Service 

Sensitivity Analysis

Michael Penev, Neha Rustagi, Chad Hunter, Josh Eichman

National Renewable Energy Laboratory

Hydrogen and Fuel Cell Technical Advisory Committee 

March 19, 2019

This presentation does not contain any proprietary, confidential, or otherwise restricted information
Screening Analysis Motivation: 

Role of H2 in Energy Storage Market

National Renewable Energy Laboratory 2 Innovation for Our Energy Future

42%

37%

13%

5.6%

1%

1%

0.3%

0.09%

0 1,000 2,000 3,000

Thermal storage

Batteries

Flywheels

Compressed air w/ natural gas

Capacitors

Flow batteries

Hydrogen (power to gas)

Compressed air

Global operational capacity in 2018 (MW)

Source: DOE Global Energy Storage Database: https://www.energystorageexchange.org/

Global Energy Storage Inventory: 

• 95% is pumped hydro serving diurnal operation

• Batteries typically provide few hours of storage

• Thermal storage is predominantly molten salt for concentrated solar 

• Fly wheels provide very short duration storage (frequency regulation)

Pumped hydro

96%
Screening Analysis Scope

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System Energy storage options Performance & cost metrics

H2 & fuel cell Tank storage Salt domes Current status Future potential

Battery, lithium ion Battery Current status Future potential

Analyzed Components:

• Rectifier

• Electrolyzer

• Hydrogen compressors

• Hydrogen storage

• tank storage

• salt domes (geologic, 3 in USA)

• Batteries

• lithium ion

• Power generation

• fuel cell

• Inverter

Cost and performance parameters were 

extensively peer reviewed by battery and 

hydrogen technology experts.

Current timeframe assumes 6¢/kWh 

electricity cost for storage recharging.

Future timeframe assumes 3¢/kWh electricity 

cost for storage recharging.
Electrolyzer

Diagrams of Storage 

National Renewable Energy Laboratory 4 Innovation for Our Energy Future

DC Battery 

Storage

Power 

Conditioning 

System

Inverter

Rectifier

Hydrogen 

Storage

AC DC

AC DC

Power 

Conditioning 

System

Inverter

Rectifier

AC DC

AC DC

Fuel Cell

Compressor

H2 H2

H2

Battery Energy Storage

Round Trip Efficiency ~95%

Hydrogen Energy Storage

Round Trip Efficiency ~35%
Simple Benchmark Profile

National Renewable Energy Laboratory 5 Innovation for Our Energy Future

-10%

-8%

-6%

-4%

-2%

0%

2%

4%

6%

8%

10%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 24 48 72 96 120 144 168

Time (hours)

Discharging | charging (%/h)

State of charge (%)

Simple diurnal cycle:

 4 hours power generation 

 8 hours storage recharge

 12 hours stand-by 

Interest focus: long duration storage capability

Simple cycle provides a 

transparent and intuitive 

means of benchmarking 

energy storage systems.
Capital Cost Summary

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Technology Timeframe

Assumption

Charging

($/kW)

Storage

($/kWh)

Discharging

($/kW)

Battery Current 196 218 60

Battery Future Potential 183 80 60 

Hydrogen in tanks Current 942 35 574 

Hydrogen in tanks Future Potential 432 18 300

Hydrogen in salt domes Current 942 0.08 574

Hydrogen in salt domes Future Potential 432 0.08 300

Hydrogen storage provides: 

• lowest cost of stored energy

• more expensive charging and discharging capital

• lower round-trip efficiency

Charging capital: Rectifier, Electrolyzer, Compressor

Storage capital: Batteries, H2 storage tanks, salt dome

Discharging capital: Inverter, fuel cell 
H2FAST Model Used For Levelized Cost Analysis

National Renewable Energy Laboratory 7 Innovation for Our Energy Future

0.59 

0.17 

0.13 

0.03 

0.00 

0.21 

0.17 

0.12 

0.10 

0.09 

0.08 

0.04 

0.04 

0.03 

0.02 

0.01 

0.01 

0.00 

0.00 

0.00 

0.00 

Peak electricity sales

Inflow of equity

Inflow of debt

Monetized tax losses

Cash on hand recovery

Dividends paid

Off-peak electricity

Hydrogen storage

Planned & unplanned...

Repayment of debt

Interest expense

Income taxes payable

Electrolyzer

Installation cost

Fuel cell

Rectifier

Property insurance

Selling & administrative...

Cash on hand reserve

Inverter

Compressor

Operating revenue

Financing cash inflow

Operating expense

Financing cash outflow

Real levelized value breakdown of peak electricity ($/kWh)

-10%

-8%

-6%

-4%

-2%

0%

2%

4%

6%

8%

10%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 24 48 72 96 120 144 168

Time (hours)

Discharging | charging (%/h)

State of charge (%)

• Equipment sizing

• Cost estimation

• Efficiency estimation

• Energy Use

• Energy Costs

• Financial Assumptions

Techno-economic assessment is made based 

on minimal equipment sizing to achieve 

benchmark cycle. H2FAST model was used 

to evaluate levelized cost of peak power.

Preliminary

https://www.nrel.gov/hydrogen/h2fast.html
Levelized Cost of Energy vs. Duration of

Storage Li-Ion Battery

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0 1 2 3 4 5 6 7

Financing

Maintenance

Installation

Discharging capital

Storage capital

Charging capital

Operating cost

LCOE of peak power (2016$/kWh)

Storage duration (days)

Purchased electricity

Excellent round-trip efficiency (95%) minimizes operating costs (purchase of 

electricity @ 6¢/kWh). Capital intensity is dominated by battery module cost.

National Renewable Energy Laboratory 8 Innovation for Our Energy Future

Preliminary
Levelized Cost of Energy vs. Duration of 

H2 Storage (FC + Tanks)

National Renewable Energy Laboratory 9 Innovation for Our Energy Future

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0 1 2 3 4 5 6 7

Financing

Maintenance

Installation

Discharging capital

Storage capital

Charging capital

Operating cost

LCOE of peak power (2016$/kWh)

Storage duration (days)

Purchased electricity

Preliminary

Lower round-trip efficiency (35%) induces higher operating costs. Lower capital 

cost for storage reduces total cost escalation for long duration storage.
15h

24h

(1d)

48h

(2d)

72h

(3d)

96h

(4d)

120h

(5d)

144h

(6d)

168h

(7d)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4 Current.Battery

Current terrestrial H2

Storage duration

LCOE of peak power (2016$/kWh)

15h

15h

24h

(1d)

48h

(2d)

72h

(3d)

96h

(4d)

120h

(5d)

144h

(6d)

168h

(7d)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4 Current.Battery

Future.Battery

Current terrestrial H2

Future terrestrial H2

Storage duration

LCOE of peak power (2016$/kWh)

15h

15h

13h

12h

24h

(1d)

48h

(2d)

72h

(3d)

96h

(4d)

120h

(5d)

144h

(6d)

168h

(7d)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Current.Battery

Future.Battery

Current terrestrial H2

Future terrestrial H2

Current geologic H2

Current geologic H2

Storage duration

LCOE of peak power (2016$/kWh)

Fuel cells + geologic storage

• Below ~13h with current technology, batteries have economic advantage. 

• Durations over ~13h favor hydrogen technologies.

• Windows of cost use 6¢/kWh electricity for current timeframe and 3¢/kWh for future timeframe.

Economic Performance Benchmark Current 

& Future Hydrogen and Batteries

National Renewable Energy Laboratory 10 Innovation for Our Energy Future

Preliminary
-100%

0%

100%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 24 48 72 96 120 144 168

Time (hours)

Discharging |charging (%power) 

State of charge (%)

Hydrogen Co-Production Opportunity

Simple diurnal cycle:

 4 hours power generation 

 8 hours storage recharge

 12 hours stand-by

-100%

0%

100%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 24 48 72 96 120 144 168

Time (hours)

Discharging |charging (%power) |production

State of charge (%)

H2 co-production would improve 

economics if H2 price exceeds 

variable operating costs. 

O2 co-production may also bear 

value.

hydrogen co-production
Take-aways

National Renewable Energy Laboratory 12 Innovation for Our Energy Future

1. Hydrogen energy storage technologies have economic 

advantage for long-duration storage

 Above ~13h of storage with current tech

2. Round-trip efficiency disadvantage over batteries can 

be overcome for storage durations greater than ~12h

3. Additional work is needed to understand the potential 

revenue (avoided cost) of long-duration storage

4. Energy storage system economics can be improved 

with H2 co-production
Acknowledgements

National Renewable Energy Laboratory 13 Innovation for Our Energy Future

Peer review for this analysis has included representatives 

from:

• DOE, Office of Energy Efficiency and Renewable Energy 

(EERE), Fuel Cell Technologies Office

• DOE, EERE, Vehicle Technologies Office

• Xcel Energy

• Southern Company Services

• Argonne National Laboratory

• National Renewable Energy Laboratory

This work was authored by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, 

for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding provided by U.S. Department 

of Energy Office of Energy Efficiency and Renewable Energy Fuel Cell Technologies Office. The views expressed in the 

article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and the 

publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paidup, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for 

U.S. Government purposes.

NREL/PR-5400-73520
Backup Slides

National Renewable Energy Laboratory 14 Innovation for Our Energy Future
Parity Duration Sensitivity vs. Techno-Economic 

Parameters (Current, H2 vs. Batteries)

Round-trip efficiency improvements are most important

• Electrolyzer, compressor, fuel cell

• Above uses 6¢/kWh

12.0

11.9

13.7

14.5

14.6

15.1 20.1

18.3

16.4

15.6

15.6

11 12 13 14 15 16 17 18 19 20 21

Fuel cell

energy production

(24, 20, 16) kWh/kg

Electrolyzer

energy use

(43.4, 54.3, 65.2) kWh/kg

Electrolyzer

capital cost

(590, 737, 885) $/kW

Hydrogen storage

capital cost

(935, 1,168, 1,402) $/kg

Fuel cell

capital cost

(406, 507, 608) $/kW

Hydrogen-battery parity storage duration (h)

Preliminary
Means of Improving Round Trip Efficiency

Increased efficiency can be traded for capital 

expenses

1. Increase electrolysis & fuel cell active area

2. Consider solid oxide electrolysis (SOEC)

3. Consider SOEC with thermal storage (store waste heat from power 

generation and use for thermal needs in electrolysis)

4. Consider high pressure electrolysis (reduce compression needs)

5. Consider compression energy recovery with turbo expander

Round trip efficiency is more important than capital cost. 

Improving efficiency can be traded for increased capital cost.
NREL | 17

Technoeconomic Parameter Details

Techno-Economic Parameters Current status Future potential Reference

Rectifiers

Rectifier efficiency 98.4% 98.4% [2]

Rectifier cost ($/kW AC) $ 196 $ 183 [3]

Total installation cost factor (% of equipment capital) 57% 57% [3]

System O&M (% of capital cost) 1% 1% assumption

Electrolyzers

Electrolyzer power use (kWh DC/kg) 54.3 50.2 [3]

Electrolyzer cost ($/kW DC) $ 737 $ 232 [3]

System life (years) 20 20 [4]

System O&M (% of capital cost) 8% 9% [3]

Total installation cost factor (% of equipment capital) 57% 57% [3]

Compressors

Power use (kWh AC/kg) 1.42 1.42 [5]

Compressor cost factor A (equation form c=A*p^B; where p is power) 2290 2061 [5]

Compressor cost exponent B (equation form c=A*p^B; where p is power) 0.8225 0.8225 [5]

Total installation cost factor (% of equipment capital) 187% 187% [5]

System O&M (% of capital cost) 4% 4% [5]

Storage

Terrestrial storage installed cost ($/kg) 1,168 600 [5], [6]

Terrestrial storage installed cost ($/kWh LHV) 35 18 assumes 33 kWh/kg H2

Terrestrial storage O&M (% of capital cost) 1% 1% [5]

Geologic storage installed cost ($/kg) 2.69 2.69 [5]

Geologic storage installed cost ($/kWh LHV) 0.08 0.08 assumes 33 kWh/kg H2

Geologic storage O&M (% of capital cost) 4% 4% [5]

Cushion gas (%) 17.1% 17.1% [5]
NREL | 18

Technoeconomic Parameter Details

Techno-Economic Parameters Current status Future potential Reference

Fuel cells

Fuel cell power production (kWh DC/kg) 20.0 23.3 [7]

Fuel cell cost ($/kW DC) 507 237 [8]

Total installation cost factor (% of equipment capital) 20% 20% assumption

System O&M (% of capital cost) 6% 6% [8]

Inverters

Inverter efficiency (%) 98.6% 98.6% [9]

Inverter installed cost ($/kW) $ 60 $ 60 [10]

Total installation cost factor (% of equipment capital) 20% 20% assumption

System O&M (% of capital cost) 1% 1% assumption

Batteries

Charging efficiency 98.3% 99.4% [11]

Discharging efficiency 98.1% 99.4% [11]

Cost ($/kWh) 217.5 80 [12], [13]

System life (years) 10 10 [14]

System O&M (% of capital cost) 1.0% 1.0% assumption

Total installation cost factor (% of equipment capital) 20% 20% assumption

System O&M (% of capital cost) 1% 1% assumption

Feedstock

Electricity cost ($/kWh) 0.060 0.030 assumption
NREL | 19

Technoeconomic Parameter Details

Total tax rate (statefederallocal)

General inflation rate

Depreciation method

Depreciation period

Leveraged after-tax nominal discount rate

Debt/equity financing

Debt type

Debt interest rate (compounded monthly)

Cash on hand (% of monthly expenses)

21.00%

100%

3.70%

Revolving debt

 1.50

10.0%

 5 year

MACRS

1.90%
NREL | 20

References

[1] NREL, H2FAST, Spreadsheet version, Retrieved October 2018 from: https://www.nrel.gov/hydrogen/h2fast/

[2] ABB, 2014, High energy efficiency rectifier to power ETI Aluminyum's smelter in Turkey. Retrieved on July, 2018 from: 

http://www.abb.com/cawp/seitp202/2ea17550ae4cb481c1257b3b003a0515.aspx

[3] Hydrogen Production Analysis H2A, Central PEM Electrolysis, Retrieved October 2018 from: 

https://www.hydrogen.energy.gov/h2a_prod_studies.html

[4] NREL communications with electrolyzer manufacturing companies

[5] Argonne National Laboratory, Hydrogen Delivery Scenario Analysis Model (HDSAM) version 3.1. Retrieved on July, 2018 from: 

https://hdsam.es.anl.gov/index.php?content=hdsam

[6] Department of Energy. 2015. Multi-Year Research, Development, and Demonstration Plan, Hydrogen Delivery. Retrieved February, 2019 from: 

https://www.energy.gov/sites/prod/files/2015/08/f25/fcto_myrdd_delivery.pdf

[7] U.S. Department of Energy. 2016. Multi-Year Research, Development, and Demonstration Plan, Fuel Cell Section. Retrieved October, 2018 

from: https://www.energy.gov/eere/fuelcells/doe-technical-targets-fuel-cell-systems-and-stacks-transportation-applications

[8] Battelle Memorial Institute. 2016. Manufacturing Cost Analysis of 100 and 250 kW Fuel Cell Systems for Primary Power and Combined Heat 

and Power Applications. Retrieved on July, 2018 from: 

https://www.energy.gov/sites/prod/files/2016/07/f33/fcto_battelle_mfg_cost_analysis_pp_chp_fc_systems.pdf

[9] ABB. ABB central inverters. Retrieved on July, 2018 from: https://new.abb.com/docs/librariesprovider22/technical-documentation/pvs800-

central-inverters-flyer.pdf?sfvrsn=2

[10] Fu, Ran. Et. al. 2017. U.S. Sollar Photovotaic System Cost Benchmark: Q1 2017. Retrieved February, 2019 from: 

https://www.nrel.gov/docs/fy17osti/68925.pdf

[11] Apostolaki-Iosifidou E, Codani P, Kempton W, Measurement of power loss during electric vehicle charging and discharging, Energy (2017), doi: 

10.1016/j.energy.2017.03.015.

[12] InsideEVs. GM: Chevrolet Bolt Arrives In 2016, $145/kWh Cell Cost, Volt Margin Improves $3,500. Retrieved on July, 2018 from: 

https://insideevs.com/gm-chevrolet-bolt-for-2016-145kwh-cell-cost-volt-margin-improves-3500/

[13] Boyd, Steven. 2019. Batteries and Electrification R&D Overview. https://www.energy.gov/sites/prod/files/2018/06/f53/bat918_boyd_2018.pdf

[14] Smith, K., Saxon, A., Keyser, M., Lundstrom, B., 2017, Life Prediction Model for Grid Connected Li-ion Battery Energy Storage System, National 

Renewable Energy Laboratory, Retrieved October 2018 from: https://www.nrel.gov/docs/fy17osti/67102.pdf
Long duration storage benefit

• Present work shows likely cost advantage of long duration hydrogen storage 

compared to other storage technologies

• Additional cost advantages may include revenue from hydrogen and avoided 

costs.

To understand competitiveness of long duration storage, we can perform 

cost/benefit comparison using LCOE and avoided costs (LACE)

Preliminary Results – Do not cite

• Previous work has 

shown that market for 

multi-day storage is 

currently limited

• Using power system 

models, we can 

calculate the benefit 

(avoided cost) of 

operating the storage Preliminary results from the EPRI-DOE H2@Scale CRADA Project 

show how storage can be used as renewable penetration increases.