
Flywheel energy storage (FES) works by accelerating a rotor () to a very high speed and maintaining the energy in the system as . When energy is extracted from the system, the flywheel's rotational speed is reduced as a consequence of the principle of ; adding energy to the system correspondingly results in an increase in the speed of th. The key advantages of flywheel-based UPS include high power quality, longer life cycles, and low maintenance requirements. Active power Inc. [78] has developed a series of flywheels capable of 2.8 kWh and 675 kW for UPS applications. The flywheel weighs 4976 kg and operates at 7700 RPM. [pdf]
The German company Piller has launched a flywheel energy storage unit for dynamic UPS power systems, with a power of 3 MW and energy storage of 60 MJ. It uses a high-quality metal flywheel and a high-power synchronous excitation motor.
Abstract - This study gives a critical review of flywheel energy storage systems and their feasibility in various applications. Flywheel energy storage systems have gained increased popularity as a method of environmentally friendly energy storage.
Flywheel energy storage (FES) works by accelerating a rotor (flywheel) to a very high speed and maintaining the energy in the system as rotational energy.
Indeed, the development of high strength, low-density carbon fiber composites (CFCs) in the 1970s generated renewed interest in flywheel energy storage. Based on design strengths typically used in commercial flywheels, σ max /ρ is around 600 kNm/kg for CFC, whereas for wrought flywheel steels, it is around 75 kNm/kg.
The superconducting flywheel energy storage system developed by the Japan Railway Technology Research Institute has a rotational speed of 6000 rpm and a single unit energy storage capacity of 100 kW·h. It is the largest energy storage composite flywheel developed in recent years .
In the future, the focus should be on how to improve the stability of the flywheel energy storage single machine operation and optimize the control strategy of the flywheel array. The design of composite rotors mainly optimizes the operating speed, the number of composite material wheels, and the selection of rotor materials.

Compared with other ways to store electricity, FES systems have long lifetimes (lasting decades with little or no maintenance; full-cycle lifetimes quoted for flywheels range from in excess of 10 , up to 10 , cycles of use), high (100–130 W·h/kg, or 360–500 kJ/kg), and large maximum power output. The (ratio of energy out per energy in) of flywheels, also known as round-trip efficiency, can be as high as 90%. Typical capacities range from 3 to 1. [pdf]
Flywheel Energy Storage Systems (FESS) play an important role in the energy storage business. Its ability to cycle and deliver high power, as well as, high power gradients makes them superior for storage applications such as frequency regulation, voltage support and power firming [, , ].
Among the different mechanical energy storage systems, the flywheel energy storage system (FESS) is considered suitable for commercial applications. An FESS, shown in Figure 1, is a spinning mass, composite or steel, secured within a vessel with very low ambient pressure.
The German company Piller has launched a flywheel energy storage unit for dynamic UPS power systems, with a power of 3 MW and energy storage of 60 MJ. It uses a high-quality metal flywheel and a high-power synchronous excitation motor.
Flywheel energy storage (FES) works by accelerating a rotor (flywheel) to a very high speed and maintaining the energy in the system as rotational energy.
The superconducting flywheel energy storage system developed by the Japan Railway Technology Research Institute has a rotational speed of 6000 rpm and a single unit energy storage capacity of 100 kW·h. It is the largest energy storage composite flywheel developed in recent years .
In 1999 , the University of Texas at Austin developed a 7-ring interference assembled composite material flywheel energy storage system and provided a stress distribution calculation method for the flywheel energy storage system.

Flywheel energy storage (FES) works by accelerating a rotor () to a very high speed and maintaining the energy in the system as . When energy is extracted from the system, the flywheel's rotational speed is reduced as a consequence of the principle of ; adding energy to the system correspondingly results in an increase in the speed of th. In this storage scheme, kinetic energy is stored by spinning a disk or rotor about its axis. Amount of energy stored in disk or rotor is directly proportional to the square of the wheel speed and rotor׳s mass moment of inertia. Whenever power is required, flywheel uses the rotor inertia and converts stored kinetic energy into electricity. [pdf]
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