Flywheels put a new spin on electric vehicles

This article describes advances in high-strength composite materials, frictionless magnetic bearings, high-efficiency motor/generators, and lower-cost miniaturized power conditioning and control electronics that have resurrected the possibility that the venerable flywheel could be used to power pollution-free electric and hybrid vehicles. Recently, many researchers have become convinced that modern flywheel energy storage (FES) systems, fiber-composite rotors spinning at many thousands of rpm on frictionless magnetic bearings, could drive generators that provide power for efficient nonpolluting EVs. Also known as inertial energy storage devices or electromechanical batteries (EMB), these systems could theoretically rival chemical batteries in terms of power, energy density, cycle life, charge time, operating temperature range, environmental friendliness, and maintenance needs. FES is now considered a viable technology for recovering braking energy (regenerative braking), averaging peak power demands, and storing energy for electric and hybrid vehicles. FES systems are also being developed for stationary applications such as utility loadleveling systems, uninterrupted power supplies, and storage capacity for solar and wind power systems.