A flywheel energy storage (FES) is a chemical-free mechanical battery that harnesses the energy of a rapidly spinning wheel and stores it as rotational energy. The energy is converted back by slowing down the flywheel. The flywheel system itself is a kinetic, or mechanical battery, spinning at very high speeds to store energy that is instantly available when needed.
Flywheels are not affected by temperature changes as are chemical rechargeable batteries, nor do they suffer from memory effect. They are also less potentially damaging to the environment, being made of largely inert or benign materials. Another advantage of flywheels is that by a simple measurement of the rotation speed it is possible to know the exact amount of energy stored. However, use of flywheel accumulators is currently hampered by the danger of explosive shattering of the massive wheel due to overload. (Blog)
Advanced FES systems have rotors made of high strength carbon filaments, suspended by magnetic bearings, and spinning at speeds from 20,000 to over 50,000 rpm in a vacuum enclosure. Such flywheels can come up to speed in a matter of minutes — much quicker than some other forms of energy storage. (Wikipedia)
There are now large scale FES build to support the grid and balance power supply. The flywheels store surplus energy that may otherwise be wasted and rapidly inject it back when there is an energy shortfall. Beacon Power, the world’s leading manufacturer of grid-scale flywheel energy storage systems, has begun commercial operation of its latest flywheel energy storage facility. The company operates the largest grid-tied flywheel facility in the world at 20 MW, located in Stephentown, New York.