The main components of the flywheel energy storage system are the composite rotor, motor/generator, magnetic bearings, touchdown bearings, and vacuum housing. The flywheel system is designed for 364 watt-hours of energy storage at 60,000 rpm and uses active magnetic bearings to provide a long-life, low-loss suspension of the rotating mass. The upper bearing of the unit is a combination magnetic bearing, providing suspension axially as well as radically. The lower magnetic bearing suspends the shaft in the radial direction only. At each end of the shaft there is also a touchdown bearing. This provides a back up bearing system should the magnetic bearings fail during testing.
The motor/generator unit is located at the lower end of the shaft. It consists of a two-pole rotor piece with surface mounted samarium cobalt magnets and a carbon fiber retaining wrap. On the stator side, there are three phase sinusoidally distributed windings in twelve slots. A water jacket around the stator provides cooling. Field orientation and a combination of mechanical sensor less techniques are used to control the motor from zero and low speed up to full speed operation. The self-sensing technique is used at zero and low speeds to start the machine, then the control is switched to a back-EMF based sensor less technique for the normal higher speed operating range of the machine.



A typical system consists of rotor suspended by bearings inside a vacuum chamber to reduce friction, connected to a combination electric motor/electric generator. On larger systems, the bearings are magnetic. The rotors are generally made of steel on smaller systems but large systems use high-tensile-strength fibers (such as carbon fibers) embedded in epoxy resins, or some other high-strength composite material. Energy is stored by using an electric motor to increase the speed of the spinning flywheel. The system releases its energy by using the momentum of the flywheel to power the motor/generator.