Flywheel energy storage technology is an energy storage technology that accelerates a flywheel (rotor) to very high speeds and stores the energy in the system as the rotor's rotational energy (angular kinetic energy). Due to the law of conservation of energy, when the speed of the flywheel (rotor) decreases, it releases its stored rotational energy, thus achieving the function of storing and releasing energy.
Most flywheel energy storage technologies use electricity to accelerate and decelerate the flywheel, but a small portion use mechanical energy directly.
The rotors of advanced flywheel energy storage systems are generally made of high-strength carbon fiber composite materials and use a magnetic bearing suspension system to allow the entire rotor to rotate at a high speed of 20,000 to 50,000 revolutions per minute in a vacuum.
The biggest advantage of flywheel energy storage systems is their extremely fast charging speed. They can increase the rotor speed to the maximum within minutes and reach their energy storage capacity limit.
I. Structure of Flywheel Energy Storage System
A typical flywheel energy storage system includes a flywheel that stores energy, supported by rolling bearings of an electric motor/generator. To reduce friction and energy loss, the flywheel and the electric motor/generator are usually enclosed in a vacuum chamber.
Because one of the design requirements for flywheels is to have very high tensile strength, the greater the tensile strength, the stronger the flywheel, the faster the flywheel rotates, and the faster the flywheel rotates, the more energy the entire flywheel energy storage system can store.
The rolling bearings in first-generation flywheel energy storage systems are generally mechanical bearings, which have the disadvantage of wear and tear and require more maintenance.
The rolling bearings in the new generation of flywheel energy storage systems use magnetic bearings, allowing the bearings to levitate and operate. In the future, room-temperature superconductors may also be used as rolling bearings, which would further reduce losses and improve performance.
II. Principle of Flywheel Energy Storage System
During energy storage, external electrical energy is converted by a power converter to drive a motor. The motor drives the flywheel rotor to accelerate until it reaches a set speed. During this acceleration, the flywheel stores energy in the form of kinetic energy, completing the energy storage process of converting electrical energy into mechanical kinetic energy. The energy is stored in the high-speed rotating flywheel. Afterward, the flywheel rotates at the set speed until it receives a control signal to release the energy.
During energy release, the motor functions as a generator. The high-speed rotating flywheel drives the motor to generate electricity, which is then converted into current and voltage suitable for the load via a power converter, completing the energy release process from mechanical kinetic energy to electrical energy. During energy release, the flywheel's rotational speed continuously decreases. The entire flywheel energy storage system realizes the input, storage, and output of electrical energy.
