Flywheel energy storage (FES) works by spinning a rotor (flywheel) 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 to the system correspondingly results in an increase in the speed of the flywheel. W. Main componentsA typical system consists of a flywheel supported by connected to a . The flywheel and sometimes motor–generator may be enclosed in a to reduce fricti. . Compared 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. . In the 1950s, flywheel-powered buses, known as, were used in () and () and there is ongoing research to make flywheel systems that are smaller, lighter, cheaper and have.
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