Flywheel energy storage (FES) works by accelerating a rotor (flywheel) to a very high speed and maintaining the energy in the system as rotational energy. When energy is extracted from the system, the flywheel's rotational speed is reduced as a consequence of the principle of conservation of energy; adding energy. A typical system consists of a flywheel supported by connected to a. The flywheel and sometimes motor–generator may be enclosed in a to reduce friction and. TransportationAutomotiveIn the 1950s, flywheel-powered buses, known as, were used in () and () and there is ongoing research to make flywheel systems that. • • • – Form of power supply• – High-capacity electrochemical capacitor • • • GeneralCompared with other ways to store electricity, FES systems have long lifetimes (lasting decades with little or no maintenance; full-cycle lifetimes quoted for flywheels range from in excess of 10, up to 10, cycles of use), high Flywheels are not as adversely affected by temperature changes, can operate at a much wider temperature range, and are not subject to many of the common failures of chemical. They are also less potentially damaging to the environment, being. • Beacon Power Applies for DOE Grants to Fund up to 50% of Two 20 MW Energy Storage Plants, Sep. 1, 2009 • Sheahen, Thomas P. (1994). New York: Plenum Press. pp. –78, 425–431.