Energy Storage on the Grid: Informing Future Development Eric Hittinger Advisors: Jay Whitacre, Jay Apt Department of Engineering and Public Policy Carnegie Mellon University 1

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This study examines four energy storage technologies and four applications Energy Storage Technologies: – NaS Batteries – Li-Ion Batteries – Flywheels – Supercapacitors Applications: – Frequency regulation provided by energy storage – Peak shaving using energy storage – Wind Integration (Baseload) – Wind Integration (Load-following) 3

4 100 MW Natural Gas Turbine Charge/ Maintain Energy Curtailment “Flat Power” Output (within deadband) Wind Power vs. Time Wind + Gas Power vs. Time Wind + Gas + Battery Power vs. Time Wind Generation Sodium Sulfur (NaS) Battery A Co-located wind/natural gas turbine/energy storage system can deliver “baseload” power

Energy storage is used only to smooth the sharpest wind fluctuations 5 Wind Farm Output Output After Battery “Smoothing”

Cost-of-service is conceptually like a production function 6

Sensitivity plot for “Regulation” application using flywheels 7

Sensitivity of NaS battery properties 8

Sensitivity of flywheel properties 9

Sensitivity of Li-Ion battery properties 10

Sensitivity of supercapacitor properties 11

Capital cost improvements are still valuable even after current technology targets have been met Existing Targets US DOE’s Energy Storage Program: $250/kWh American Electric Power: $500/kWh ARPA-E GRIDS Program: $100/kWh Using $250/kWh: 12 Capital Cost Reduction Average Change in Sensitivity to Capital Cost Li-Ion Battery50%20% NaS Battery30%12% Flywheel50%*25%

Research Conclusions The relative importance of storage properties depends on storage type and application… …but certain properties, particularly capital cost, are consistently more valuable to improve. These results can help inform: – Energy Storage Development – Research Funding – Energy Storage Technology Targets 13

Questions! Support for this research has been provided by the EPA STAR Fellowship, the National Energy Technology Laboratory of the Department of Energy, and the Electric Power Research Institute under grants to the Carnegie Mellon Electricity Industry Center (CEIC). 14

15 In the Wind/Natural Gas/Storage systems, storage is used for intermittent sharp spikes Wind Natural Gas Storage 100 MW Gas Turbine 67 MW Wind Farm 0.7 MWh Battery 100 MW Target Power Output

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MW Natural Gas Turbine Charge/ Maintain Energy Curtailment “Flat Power” Output (within deadband) Wind Power vs. Time Wind + Gas Power vs. Time Wind + Gas + Battery Power vs. Time Wind Generation Sodium Sulfur (NaS) Battery The “load-following” application is very similar to the “baseload” application

NaS Battery Properties NaS Battery ParameterBase-Case Value Round-trip Efficiency80% Module Energy Capacity0.36 MWh Module Power Limit0.25 MW Module Maintenance (Heating) Power2.2 kW Module Capital Cost$240K ($670K / MWh) Module Fixed Operating Cost$8K / module - year ($22K / MWh-year) Length of Capital Investment20 years 18

Li-Ion Battery Properties Li-ion Battery ParameterBase-Case Value Round-trip Efficiency80% Capital Cost of Batteries$500K / MWh Capital Cost of Power Electronics$300K / MW Fixed Operating Cost$8K / MW - year Length of Capital Investment10 years 19

Flywheel Properties Flywheel Energy Storage Parameters Base-Case Value Round-trip Efficiency90% Module Energy Capacity0.025 MWh Module Power Limit0.1 MW Flywheel Friction Losses3% of max power (3 kW) Module Capital Cost$200K Fixed Operating Cost$5K / module - year Length of Capital Investment20 years 20

Supercapacitor Properties Supercapacitor ParametersBase-Case Values Round-trip Efficiency70% Capital Cost of Supercapacitors$143M / MWh Capital Cost of Power Electronics$60K / MW Fixed Operating Cost$13K / MW - year Length of Capital Investment20 years 21