1. Opportunities for Hydrogen-Based Energy Storage for Electric Utilities
Todd Ramsden, Ben Kroposki, Johanna Levene
National Renewable Energy Laboratory
NHA Annual Conference 2008
March 31, 2008

2. Hydrogen Storage for Integrating Renewables
Concept: Use hydrogen as energy storage to better integrate renewable solar and wind resources into the electric grid
Analyze the cost of using hydrogen as an energy storage mechanism
System elements:
Electric Input
Grid, Renewables
Electrolyzer
Hydrogen storage
Tanks, geologic
H2 conversion
Fuel cells, H2 engine
March 31, 2008
NHA 2008

3. Study Background Value of Hydrogen for Energy Storage
Time shifting of available production capacity
Increased demand response (i.e., spinning reserves)
Time-shifting of wind energy to meet daily peak demand
Analysis intended as a scoping study to assess whether hydrogen might hold promise as a means to store energy for electric utilities
Not a cost study of a specific system design
Study analyzes the cost of individual subsystem elements
Cost projections based on DOE technology targets and DOE-sponsored models
Forecasted Load
Forecasted Wind
Actual Wind
March 31, 2008
NHA 2008

4. Study Framework
Study assesses the cost of producing 50MW of electricity via storage for 6 peak hours each weekday (300 MWh/day)
Study considers 3 basic storage system configurations, all using an electrolyzer system to produce hydrogen:
Case 1: Steel tank storage, H2 ICE
Case 2: Steel tank storage, fuel cell
Case 3: Geologic storage, fuel cell
3 Timeframes considered:
Near-term: Up to 2010
Mid-term:
Long-term:
Long-term case meant to represent best case scenario for hydrogen-based energy storage using stretch goals based on fully mature, optimized hydrogen technologies
March 31, 2008
NHA 2008

5. Analysis Approach
The study arrives at a $/kWh cost for using H2 for storage by analyzing a variety of costs including:
Capital costs • Replacement costs
O&M costs • Cost of input electricity
Cost of land and labor • Indirect costs (e.g., permitting, siting)
Cost and performance assumptions based on DOE’s technical targets for hydrogen and on major DOE hydrogen cost models, including:
H2A Production analysis model
H2A Delivery Components model
The DOE Hydrogen, Fuel Cells & Infrastructure Technologies Program’s Multi-Year Program Plan
DOE SECA program targets
The analysis uses a nominal cost of off-peak, input electricity of 3.8¢/kWh, but also analyzes cases using 2.5¢/kWh and 4.9¢/kWh
Analysis uses the HOMER model to evaluate possible system configurations and optimize system component selection to minimize resulting electricity price
March 31, 2008
NHA 2008

6. Economic Assumptions
10% real internal rate of return assumed for all investment costs
40 year lifetime modeled, with subsystem components replaced on a schedule determined by their operating life
Land costs of $50,000
Labor cost of $300,000 per year (not including maintenance labor, which is included as part of O&M for each subsystem component)
G&A cost of $75,000 per year (G&A rate of 25% of the labor cost)
Indirect capital costs of 25% of initial direct capital costs (representing costs for engineering design, permitting, site preparation, and project contingency)
March 31, 2008
NHA 2008

7. Electrolyzer Assumptions
Electrolyzer capital costs of $675/kW, $400/kW, and $300/kW in near-, mid-, and long-term (uninstalled)
Electrolyzer input electricity requirements of 53, 47 and 44 kWh electricity per kg of H2, in near-, mid-, and long-term (efficiencies of 62%, 70%, 75% LHV)
Lifetime is 10 years
Replacement costs equal the electrolyzer cell stack at 30% of system cost
Annual O&M costs equivalent to 3% of initial capital cost
March 31, 2008
NHA 2008

8. Fuel Cell Assumptions
Fuel cell capital costs of $750/kW, $400/kW, and $350/kW in near, mid and long term (uninstalled)
Overall fuel cell system efficiencies:
60%, 70% and 75% in the near-, mid-, and long-term
Stack lifetime is 10 years
Replacement costs for the cell stack assumed to be 30% of the total system cost
Annual O&M costs equivalent to 3% of initial capital cost
March 31, 2008
NHA 2008

9. Hydrogen Internal Combustion Generator Assumptions
Capital costs of $600/kW for the near- and mid-term, and $400/kW for the long-term (uninstalled)
Assumed lifetime: 16,000 hours in the near-term (approx. 10 years for this study); 40,000 hours in the mid-term; and, 60,000 hours in the long-term
Replacement cost = 100% of capital cost
Conversion efficiencies of 35%, 48%, and 50% in the near-, mid-, and long-terms
Annual O&M costs equivalent to 5% of the initial capital cost
March 31, 2008
NHA 2008

10. Steel Tank Storage Assumptions
Hydrogen is stored at 2,500 psi
Capital costs include both the storage tubes and the associated compressor system
Steel tanks have cost of $900/kg, $575/kg, and $345/kg in the near-, mid-, and long-term
Capital costs are not linear, due to the compressor system cost component
Cost curves for the Homer model were built using several storage sizes consistent with the storage needs for the three cases modeled
Total capital costs of $31M, $20M, and $12M for a 28,600kg storage system, for the near-, mid-, and long-term
Assumed lifetime of 10 years, after which the entire compressor subsystem is replaced
Compressor subsystem requires 1.2 kWh per kg of hydrogen stored
March 31, 2008
NHA 2008

11. Geologic Storage Assumptions
Capital costs include cost include both the cavern and the necessary compressor system
Maximum cavern pressure of 1,800 psi (125 atm)
Capital costs are not linear, due to the compressor system cost component
Cost curves for the Homer model were built using several storage sizes consistent with the storage needs for the three cases modeled
Total capital costs of $8M, $7M, and $6M for a 28,600kg storage system, for the near-, mid-, and long-term
Assumed lifetime of 10 years, after which the entire compressor subsystem is replaced
Compressor subsystem requires 1.1 kWh per kg of hydrogen stored
March 31, 2008
NHA 2008

12. Results - Overview
Lowest on-peak electricity costs are under Case 3 (geologic storage, fuel cell conversion)
Costs using steel tank storage with fuel cell conversion (Case 2) are similar to Case 3 in the mid- and long-term
Systems using H2 ICE generators do not appear to be competitive
On-peak electricity produced from fuel-cell based hydrogen storage systems may be cost competitive in the mid- and long-terms:
Near-term: $0.28/kWh
Mid-term: $0.19/kWh
Long-term: $0.16/kWh
March 31, 2008
NHA 2008

13. Details on Optimized Systems 3.8¢/kWh electricity input cost
Case
Description
Time-frame
Cost of Electricity
via stored Hydrogen ($/kWh)
Capital
Replace-ment
O&M
Round-trip Efficiency
Case 1
H2 ICE, steel tank storage
Near-Term
0.51
177 34 42
21%
Mid-Term
0.29 97 8 29
32%
Long-Term
0.23 68 4 24
36%
Case 2
H2 fuel cell, steel tank storage
0.33
131 13
0.22 75 9 19
44%
0.17 52 7 15
50%
Case 3
H2 fuel cell, geologic storage
0.28 95 27
0.19 56 18
0.16 43
Conventional NG Combustion Turbine
Advanced NG Combustion Turbine
Reciprocating Engine
0.150
0.200
0.165
Costs (Million $)
Based on an analysis of electricity production costs developed by Xcel Energy
March 31, 2008
NHA 2008

14. Cost of Hydrogen-Based Electricity Storage 3
Cost of Hydrogen-Based Electricity Storage 3.8¢/kWh electricity input cost
Typical current peak electricity production costs using natural gas combustion turbines
March 31, 2008
NHA 2008

15. Impact of Different Input Electricity Costs 3
Impact of Different Input Electricity Costs 3.8¢/kWh base electricity input cost, with range of 2.5¢/kWh to 4.9¢/kWh
March 31, 2008
NHA 2008

16. Effect of Input Electricity Costs on Case 3 Storage Costs (Input electricity costs of 3.8¢/kWh, 4.9¢/kWh, and 2.5¢/kWh)
March 31, 2008
NHA 2008

17. Capital Costs per Installed kW of Storage Capacity
March 31, 2008
NHA 2008

18. Summary of Findings
Fuel-cell based hydrogen energy storage systems appear to be the most promising, including systems using steel tanks for hydrogen storage and systems using geologic hydrogen storage
Fuel-cell based hydrogen energy storage systems can store electricity for 16¢/kWh in the long term
This appears competitive with current peak electricity production costs using NG gas turbines, at 15 to 20 ¢/kWh
Installed capital costs of hydrogen energy storage systems in the mid- and long-terms are in the range of $ per kW capacity
Round trip storage efficiencies of hydrogen systems are fairly low, ranging from 34% in the near-term to 50% in the long-term
March 31, 2008
NHA 2008

19. Conclusions
If the transportation market for hydrogen can drive down the cost of hydrogen technologies while improving performance, more market opportunities for hydrogen might be available
To fully compare hydrogen-based storage to other storage technologies and to other production technologies, analyses of these competing technologies will need to be performed, especially for the mid- and long-term when hydrogen-based storage appears most promising
March 31, 2008
NHA 2008

20. Acknowledgements Thank You! Any Questions?
We would like to thank the DOE Hydrogen, Fuel Cells, and Infrastructure Technologies Program, and in particular Roxanne Garland, Fred Joseck, and Jamie Holladay
Thank You!
Any Questions?
March 31, 2008
NHA 2008

21. Example System Optimization
Electrolyzer: 20,000 kW system
Fuel Cell: 55,000 kW system
Hydrogen Storage: 29,000 kg
March 31, 2008
NHA 2008