Kinetic into Potential Energy Flywheels: Kinetic into Potential Energy

Alternative Vehicle Energy Storage Ultracapacitors: Stores energy as a charge across two plates High power, low energy Flywheels: Energy stored in a high velocity composite wheel. When desired, energy is transferred to the axle via clutch Batteries: Electrochemical reaction creates electricity as long as reactants exist in closed containers (closed system) Fuel Cells: Electrochemical reaction creates electricity as long as fuel and oxidant are supplied (open system)

Vehicle Power Requirements Power (W,J/s) = Energy (mass*velocity2) (J, Ws) /Time (s) Small passenger vehicles = 70-90hp (50-65kW) SUV or truck = 120-180hp (90-135kW) Only 10-25hp when cruising (I.e. not accelerating) Electric Vehicles (EV’s) must store-release ALL this power/energy Hybrid Vehicles (HEV’s) only need recoup-release small portion of this power/energy to supplement IC engine

© on original matter only, Charles E. Bakis, 1999 Flywheels © on original matter only, Charles E. Bakis, 1999

Flywheel: Electromechanical System Motor/Generator Supply and remove energy via electricity Housing Containment (for safety in case of burst) Vacuum (prevent heating, reduce losses) Bearing(s) Allow free rotation of rotor Maintain orientation of rotor Rotor (complete rotating assy.) Rim (primary spinning mass) Hub (connects rim and shaft) Shaft (connects m/g to bearings, hub & rim) Suspension Shock & vibration isolation Anchorage

Rim/Hub/Shaft Assembly Designs Rim/Hub/Shaft Assembly “Cogged” Hub Design (GS Hub) Toray Composites (America)

Bearings Magnetic Bearings Ball Bearings Ball Groove Outer Race Inner Race Cage Groove Stator Rotor Source: The Barden Corp. Source: Revolve, Inc. http://www.revolve.com

Rotor Design Objective: Maximize energy per unit mass Assume: Thin rim flywheel of radius r and mass m Energy: K = ½ I2, where  = rotational velocity (rad/s) and polar moment of inertia I = mr2  K = ½ mv2 = ½ mr22 where rim velocity v = r Want high strength, low density & high velocity

Flywheel Pros & Cons Pros Cons High round-trip efficiency in short-term use (80-95%) Potentially long product life (measured in tens of years) Low toxicity of constituents High power per unit mass (fast, equal charge & discharge times) Easy to determine state of charge Cons Developing technology Currently expensive Potentially low energy per unit mass (due to bulky containment) Uncertain safety in a burst event: fragmentation & ejection of material sudden release of energy

Perspectives High speed flywheel must spin in vacuum Source: T. Michaelis, NASA GRC, 10/99

University of Texas Center for Electromechanics High speed fossil-fuel powered train w/ comparable acceleration as all-electric train 3 MW turbine-alternator to overcome rolling and aerodynamic losses at 150 mph 600 MJ (165 kWh) flywheel capable of delivering an additional 3 MW for acceleration, speed maintenance on grades, and recovery of braking energy