First-generation flywheel energy-storage systems use a large steel flywheel rotating on mechanical bearings. Newer systems use carbon-fiber composite rotors that have a higher tensile strength than steel and can store much more energy for the same mass.OverviewFlywheel energy storage (FES) works by spinning a rotor () and maintaining the energy in the system as . When energy is extracted from the system, the flywheel's rotational speed is reduced a. . 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 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.
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The (Zn–Br2) was the original flow battery. John Doyle file patent on September 29, 1879. Zn-Br2 batteries have relatively high specific energy, and were demonstrated in electric cars in the 1970s. Walther Kangro, an Estonian chemist working in Germany in the 1950s, was the first to demonstrate flow batteries based on dissolved transition metal ions: Ti.
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