1. Kinetic into Potential Energy
Flywheels:
Kinetic into Potential Energy

2. 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)

3. Vehicle Power Requirements
Power (W,J/s) = Energy (mass*velocity2) (J, Ws) /Time (s)
Small passenger vehicles = 70-90hp (50-65kW)
SUV or truck = hp (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

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

5. 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

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

7. Bearings Magnetic Bearings Ball Bearings Ball Groove Outer Race
Inner Race
Cage
Groove
Stator
Rotor
Source: The Barden Corp.
Source: Revolve, Inc.

8. 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

9. 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

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

11. 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