ABSTRACT
Flywheel systems have been promoted as “mechanical” batteries and offered as energy storage systems (ESS) capable of high power and high cycle life. Operation of a flywheel ESS is basically the same as that for an ultracapacitor, only the energy is stored as kinetic rather than potential energy. Issues that plague flywheel systems parallel those of the ultracapacitor: A containment vessel to hold a vacuum for a long term and non-contacting bearings correspond to minimization of equivalent series resistance in an ultracapacitor. Most flywheels ESS operate in the angular speed regime of 50 to 90 krpm. With proper design and materials the flywheel is a feasible energy storage unit because it is inherently non-toxic, fully recyclable, and completely rechargeable. Flywheel polar moment of inertia is proportional to its rim radius squared. Energy storage capacity of the flywheel is dependent on the polar moment of inertia and on the speed ratio over which it can be operated.
