A flywheel, in essence is a mechanical battery - simply a mass rotating about an axis. Flywheels store energy mechanically in the form of kinetic energy. They take an electrical input to accelerate the rotor up to speed by using the built-in motor, and return the electrical energy by using this same motor as a generator. Flywheels are one of the oldest and most common mechanical devises in existence. They may still prove to serve us as an important component on tomorrow's vehicles and future energy needs. Flywheels are one of the most promising technologies for replacing conventional lead acid batteries as energy storage systems for a variety of applications, including automobiles, economical rural electrification systems, and stand-alone, remote power units commonly used in the telecommunications industry. Recent advances in the mechanical properties of composites has rekindled interest in using the inertia of a spinning wheel to store energy.