Review of flywheel based energy storage systems

In flywheel based energy storage systems, a flywheel stores mechanical energy that interchanges in form of electrical energy by means of an electrical machine with a bidirectional power converter. Flywheel based energy storage systems are suitable whenever numerous charge and discharge cycles (hundred of thousands) are needed with medium to high power (kW to MW) during short periods (seconds). The materials for the flywheel, the type of electrical machine, the type of bearings and the confinement atmosphere determine the energy efficiency (>;85%) of the flywheel based energy storage systems. Monitoring of state of charge is simple and reliable as only spinning speed is needed. Flywheel based energy storage systems are commercially available with more than a dozen of manufacturers. Amongst the applications of flywheel based energy storage systems are: uninterruptible power supplies, hybrid power systems, power grids feeding trains, hybrid vehicles and space satellites.