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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 Systems (FESS) rely on a mechanical working principle: An electric motor is used to spin a rotor of high inertia up to 20,000-50,000 rpm. Electrical energy is thus converted to kinetic energy for storage. For discharging, the motor acts as a generator, braking the rotor to produce electricity.
The use of new materials and compact designs will increase the specific energy and energy density to make flywheels more competitive to batteries. Other opportunities are new applications in energy harvest, hybrid energy systems, and flywheel’s secondary functionality apart from energy storage.
While many papers compare different ESS technologies, only a few research , studies design and control flywheel-based hybrid energy storage systems. Recently, Zhang et al. present a hybrid energy storage system based on compressed air energy storage and FESS.
A typical system consists of a flywheel supported by rolling-element bearing connected to a motor–generator. The flywheel and sometimes motor–generator may be enclosed in a vacuum chamber to reduce friction and energy loss. First-generation flywheel energy-storage systems use a large steel flywheel rotating on mechanical bearings.
Power utilities need innovative ways to store renewable wind and solar energy, during low demand periods, so they can release it after sunset when demand is high. Several innovative power utilities already use flywheel storage systems to maintain power grid frequency. Renewable energy is knocking on flywheel energy’s door.
Anything to do with energy storage attracts us, although a flywheel energy storage system is very different from a battery. Flywheels can store grid energy up to several tens of megawatts. If we had enough of them, we could use them to stabilize power grids.
Because a flywheel must be accelerated by an external force before it will store energy, it is considered a “dynamic” storage system. The rate at which the flywheel spins remains nearly constant because of the vacuum-like container, which prevents friction from slowing the revolution.
Large scale lithium ion battery energy storage systems have emerged as a crucial solution for grid-scale energy storage. They offer numerous benefits and applications in the renewable energy sector, aiding in renewable energy integration and optimizing grid stability.
A large lithium battery energy storage system operated by Key Capture Energy that can power 15,000 homes for two hours during outages or high demand is shown in Blasdell, N.Y., Tuesday, Sept. 9, 2025. (AP Photo/Ted Shaffrey)
The Wilmot Energy Center uses lithium-ion batteries to store energy from the nearby Wilmot Solar Energy Center. The solar array has a capacity of 100 MW and generates enough electricity to power approximately 26,000 homes. The battery storage system can store up to 30 MW. 9. Blythe II Solar Energy Center, California
Since 2010, more and more utility-scale battery storage plants rely on lithium-ion batteries, as a result of the fast decrease in the cost of this technology, caused by the electric automotive industry. Lithium-ion batteries are mainly used. A 4-hour flow vanadium redox battery at 175 MW / 700 MWh opened in 2024.
In Ontario, Canada, Temporal Power Ltd. has operated a flywheel storage power plant since 2014. It consists of 10 flywheels made of steel. Each flywheel weighs four tons and is 2.5 meters high. The maximum rotational speed is 11,500 rpm. The maximum power is 2 MW. The system is used for frequency regulation.
The city of Fresno in California is running flywheel storage power plants built by Amber Kinetics to store solar energy, which is produced in excess quantity in the daytime, for consumption at night. Intermittent nature of variable renewable energy is another challenge.
Flywheel energy storage systems are suitable and economical when frequent charge and discharge cycles are required. Furthermore, flywheel batteries have high power density and a low environmental footprint. Various techniques are being employed to improve the efficiency of the flywheel, including the use of composite materials.
However, the high cost of purchase and maintenance of solar batteries has been a major hindrance. Flywheel energy storage systems are suitable and economical when frequent charge and discharge cycles are required. Furthermore, flywheel batteries have high power density and a low environmental footprint.
