In a flywheel storage system, kinetic energy is stored in the form of a rotation mass, with the flywheel being the heart of such a system. A flywheel system may include either mechanical or magnetic bearings housed in a vacuum-tight chamber. The evacuation reduces friction and increases the roundtrip efficiency.
The bearings support the rotor, maintaining its position and allowing it to rotate at high speeds. The type of bearings used can be determined by the speed of the flywheel, power and potential maintenance problems. Mechanical bearings are subjected to a constant load and require maintenance at certain intervals. Often, expensive magnetic bearings are used in high-speed flywheel systems in order to bypass maintenance times and further reduce friction losses. However, magnetic bearings are relatively expensive compared to mechanical bearings and not always necessary, since, for example, friction losses in industrial applications are not decisive and maintenance times of other components are required anyhow. In addition to the bearings, a typical flywheel system also consists of an electric motor generator and a rotor. The design of the rotor is important for determining the effectiveness as well as the efficiency of the system. The shaft of the flywheel is connected to an electric motor generator.
Using the stored energy in the rotating mass unloads the energy stored in the flywheel. When the device functions as a motor, energy is supplied to the flywheel, and when the device functions as a generator, energy is stored. The present amount of energy and its duration is determined by the mass and speed of the flywheel. Such produce high power output for short periods of time, a typical time period is 1-30 seconds.