1. Rotating Machines as Energy Storage and Power Management Systems Mike Werst m.werst@cem.utexas.edu February 10, 2010

2. Topics About UT-Center for Electromechanics Flywheels as energy storage Kinetic energy storage Comparison to other forms of energy storage Peak power vs. peak energy Flywheel topologies Flywheel Energy Storage Examples

3. Areas of Technology VG 12983a Biotech Electric Power • Electromechanical cell manipulation • Advanced Generators • Electric Grid Control • Energy Storage • Distributed Generation Technology Defense • Missile and Aircraft Launcher • All Electric Ship • Advanced Wheeled and Tracked Vehicles • Electromagnetic Guns • Electromagnetic Armor Space • Space Power • Electromagnetic Launch • Satellite Attitude Control Transportation • Advanced Trains • Hybrid Vehicles • Active Suspension for Vehicles • Wheel Motors • Intelligent Highways Oil & Gas • Exploration • Transmission

4. Flywheel Energy Storage Wikipedia definition: “A flywheel is a mechanical device with a significant moment of inertia used as a storage device for rotational energy.” *Holm et. al., “A Comparison of Energy Storage Technologies as Energy Buffer in Renewable Energy Sources with respect to Power Capability.” Flywheels have a much broader range of usage than given credit for.

5. Kinetic Energy Specific Strength of Selected Materials *Burr, “Mechanical Analysis and Design, 1981 Flywheel energy storage efficiency is dependent on material and mass distribution

6. Flywheel Highlights VG 12973e Backup Bearings • Conducted flywheel tests, including – Flywheel only tests to identify failure modes and structural margins – Flywheel burst tests to test candidate containment designs • Demonstrated life of more than 110,000 cycles with a 50% DOD Magnetic Bearings Motor Generator Gimbal Shaft Composite Flywheel Containment System

7. Flywheel Challenges Losses Vacuum air gap significantly reduces windage losses at the price of vacuum pump auxiliary Bearings Roller bearing require lubrication Magnetic bearings expensive and require touch-down bearings Superconducting bearings need development Carbon fiber material and manufacturing cost Demand for high modulus/high strength carbon fiber Industrial participation/competitiveness will bring mfg cost down Flywheel safety Design margin Flywheel health monitors/fault protection Containment

8. VG 12973a Kinetic Energy Storage Application dictates flywheel topology that meets energy and power requirements Partially-Integrated Topology Non-Integrated Topology Fully-Integrated Topology

9. Flywheel Spin Tests VG 12973f • Flywheel tests to-date: – Numerous burst tests (modified design for containment proof tests) – Loss of vacuum test – Over-speed “As Built” Test - Preload loss - 1120 m/s - Benign and recoverable – Coupon/Fatigue tests Multi-ring preloaded flywheel Hydroburst test coupon High temperature & pressure autoclave 4-axis filament winder

10. Technical Successes - Flywheel VG 12973g • Record tip speed for composite flywheel/arbor assembly (1.34 km/s) • Key features – Composite structural arbor design – Detailed material andmanufacturing process QA

11. CEM Flywheel Comparison Designed Designed Built & tested Built & tested

12. Flywheel Energy Storage System for the International Space Station (FESS) • Operations advantages – Higher round trip efficiency – Known state-of-charge – Offer more flexibility in charge/discharge profiles – Doubled contingency power (energy) • Significant life cycle cost savings – Reduced logistics (up-mass & down-mass) – Reduced maintenance (EVA- IVA Hr/Yr) FW Battery (+ Electronics) (+ Electronics) Nominal Power 4.1 kW 4.1 kW Peak Power 6.6 kW 6.6 kW Energy Delivered 5.6 kW-hr 4.6 kW-hr Contingency Power 2 orbits 1 orbit Life Expectancy >15 years 5-6 years

13. Advanced Locomotive Propulsion (ALPS) Program Flywheel VG 12973h • electrical load leveling for hybrid electric locomotive • flywheel stores 480 MJ • @ 15,000 rpm • 2 MW motor/generator – ~3 min discharge • Testing with high input and output power

14. Backup Bearings Radial Bearing Stator Winding Permanent Magnet Rotor Composite Flywheel Materials Aluminum Ceramic Permanent Magnet Windings Titanium Inconel Composite Stainless Steel Steel Combo Bearing Transit Bus Flywheel Energy Storage: Power: 2 kWhr stored, 1 kWhr delivered 150 kW peak, 110 kW cont., Between 30,000 and 40,000 RPM Composite tip speed: Application: 930 m/s at 40,000 rpm Power averaging for 15 ton Hybrid Electric Bus

15. CEM Flywheel Energy Storage Systems for Military Applications VG 11536.ppt S 4101.0607 Composite Rotor Pulse Alternator 664 MW, 2.5 kW-h (1991) Iron Core Pulse Alternator 800 MW, 10.5 kW-h (1987) Composite Rotor Pulse Alternator 2.4 GW, 11 kW-h (1995) ? S 3010.1993 S 3910.1748 Composite Rotor & Stator Pulse Alternator 3 GW, 6.4 kW-h (1997) Current EM Gun Power Supply Research is Ongoing at CEM (2009) Electromagnetic Aircraft Launch System (EMALS) Energy Storage System (2006)

16. Homopolar Generator (HPG) Flywheels Faraday disks 1/10s to 10s of second discharge rates Very high current/low voltage machines CEM HPGs used for variety of applications Large x-section resistive welding—12” sch. 60 pipe welds Railguns—90mm, 9MJ muzzle energy High-field, single-turn magnets—9MA, 20T toroidal magnet All Iron Rotating (AIR) HPG 6.2 MJ, 50 V, 750 kA 60 MJ HPG Set—6 ea, 100V, 1.5MA/gen

17. Flywheel vs. Electrochemical Energy Storage 13 12 11 2 5 10 1 7 3 6 9 4 8 100,000 1,000,000

18. Summary Advanced carbon materials and manufacturing methods enable Energy densities comparable to chemical storage devices Extremely high power densities for pulsed power applications Flywheels capable of wide range of energy storage applications: .01s to 1800s Many challenges have been overcome: additional R&D could improve energy storage capacity, efficiency and usage