1. Energy Storage for Renewables and MicroGrids John Pappas Center for Electromechanics The University of Texas at Austin

3. Power system protection

5. 15,000 rpmExamples of demonstrated systems

6. Utility Storage Flywheel Pendulum-mounted steel and reinforced flywheel Very large l/d Sited in ground No additional containment Vacuum barrier Surface mounted Motor/generator, bearings, gimbal Life cycle cost lower than batteries Initial cost competitive with batteries

7. Why CEM’s Focus on Utility Storage? Storage is widely recognized as critical in future power systems Storage enhances insertion of renewables Storage defers need for new transmission lines Storage is needed for stability Storage opens new opportunities for grid optimization

8. Today’s Technology In today’s grid Batteries CAES Flywheels Pumped hydro Thermal storage All work So, impediment is not solely lack of technology

9. Critical Questions Where to add storage to grid? Sources Does little for peak congestion Nodes Likely requires largest scale Loads Argument for PHEV’s May be better argument for stationary systems What are the real costs, who pays, who benefits? “Which is best technology?” is not a critical question

10. Technology Comparisons Given differing maturities, direct technology comparison misleading Level playing field by comparing energy lost Energy lost = Energy lost putting it into storage* plus Energy lost while in storage plus Energy lost retrieving from storage* * Includes opportunity loss if there is a mismatch with the power demand

11. Basic Efficiency - Data Summary CAES Tank Battery (Lead Acid) Battery (NiCad) Battery (Li lon) Super Capacitor Composite Flywheel Steel Flywheel 0.55 0.85 0.58 0.90 0.80 0.90 0.90 Turn around efficiency Charge time (hr) Self-discharge time (day) Operating Power (MW) Capital cost of stored Energy ($/Whr) Total stored energy Available (MWhr) Initial Cost of power ($/W) O&M , Installation, Space Total initial cost ($) Total initial cost ($/W) 4.0 4.0 4.0 4.0 4.0 4.0 4.0 2000 2000 33 2000 33 1 0.55 1 1 1 1 1 1 1 0.17 0.2 0.46 1.33 0.5 1.0 0.4 4 4 4 4 4 4 4 0.70 0.225 0.225 0.78 0.40 0.28 0.28 1,380,000 1,025,000 2,065,000 6,100,000 2,400,000 4,280,000 1,800,000 1.38 1.03 2.07 6.10 2.40 4.28 1.80 Too much uncertainty to predict ultimate best choice

12. Initial Cost of Delivered Energy 4.00 CAES Lead acid NiCad Li lon Super Cap Comp FW Steel FW 3.00 2.00 Cost per Watt-hr ($/Whr) 1.00 0.50 0.00 10 9 8 7 6 5 4 3 2 1 0 Hours Stored R&D moving flywheel cross-over to 10+ hours

13. Smart Grid Attributes Permit active participation by consumers Accommodate generation and storage options Enable new products, services, and markets Provide power quality Operate efficiently Reconfigure in response to system disturbances Technology Traditional power engineering Computing Telecommunications

14. Smart Grid is Growing in Two Directions Top down Large scale wind farms Smart meters Bottom up Microgrids Neighborhoods Industry Universities DoD facilities Urban environments

15. Microgrid Considerations Understanding source efficiency vs. power demand helps assess storage applicability Gas Turbine Performance 0.7 0.6 (P1,x1) 0.5 Specific Fuel Consumption (kg/KWHr) x 0.4 0.3 (P2,x2) 0.2 0 5 10 15 20 25 30 35 40 45 50 Power (MW)

16. Load Leveling Via Storage in Microgrid Load Leveling Analytical study comparing external storage vs. using microgrid as storage to achieve load leveling 0.3 0.2 Storage becomes economical Store Efficiency Function 0.1 Fuel consumption Function 0.0 0 10 20 30 40 50 60 70 Duty Cycle About the Mean Operating Point

17. Benefits From Point Design Analyses Analyses of specific technologies in a point application is the best way to make comparisons Choice among storage technologies and no explicit storage depends on temporal variations within a microgrid Operating economics can be properly compared to other technological imperatives Storage system response times Effect on operating cost of systems other than storage Cost of space used for storage and other systems Technology choices are driven by very specific needs

18. Summary Storage critical for “Smart Grid” Most agree, but assume different applications Excellent storage choices exist today With R&D, better choices will exist in the future Evolution of “Smart Grid” is a work in progress Storage can help shape the evolution