a chemical battery is usually our first thought  when it comes to energy storage but another less  

known but promising solution and one that far  predates any modern battery is the flywheel  

this relatively simple mechanical battery with  high power density high efficiency low maintenance  

long life span and no carbon emissions is quite  exceptional but how does it compare to other  

energy storage technologies as the world shifts  from fossil fuels toward renewable energy sources  

such as solar and wind that aren't available  24 7 energy storage technologies play a vital  

role in balancing the supply and demand lithium  ion batteries are the front runner for consumer  

electronics evs and grid scale energy storage  with a global market of 46 billion us dollars  

expected to double by 2026 a dual function  electric motor is used to accelerate the  

flywheel which is a rotating mass that stores  kinetic energy and when the power supply is cut  

off and when energy is needed the motor operates  like a generator and the spinning flywheel force  

drives a device similar to a turbine to produce  electricity consequently slowing the rate of  

rotation a flywheel is recharged by using the  motor to increase its rotational speed once again  

the amount of energy that can be stored in a  rotational mass is directly proportional to the  

moment of inertia and the square of its angular  velocity the moment of inertia is dependent on the  

mass and diameter of the flywheel so to increase  the amount of energy stored in a flywheel its mass  

or size must be increased or the speed at which  it rotates must be increased the maximum operating  

speed of a flywheel is limited by the material  strength of the flywheel rotor since the late 20th  

century the modern flywheel developed expressly  for energy storage known as flywheel energy  

storage systems or fess has been mostly used  flywheel shapes that have been used range from  

the wagon wheel configuration found in stationary  steam engines to the mass produced discs found in  

internal combustion engines flywheels are  mostly designed in two shapes solid disks  

or long cylinders are usually constructed from  isotropic materials such as steel while hollow  

cylinders or tubes are constructed from carbon  and glass fiber reinforced composites bearings  

support the flywheel rotor while allowing it to  spin at high velocities ball bearings and active  

magnetic bearings are the two most common bearing  types used in flywheel systems ball bearings are a  

simple more common and less expensive alternative  to active magnetic bearings but are challenged  

by the life and load requirements due to the  gyroscopic forces and the friction it generates  

active magnetic bearings levitate and they  are free from contact therefore free from wear  

and also helps increase the efficiency due to  their minimal losses the flywheel is charged and  

discharged by a double function motor generator  which is usually attached to the rotor by a hub  

and a shaft a wide variety of motor types have  been deployed synchronous reluctance induction  

as well as many types of permanent magnet machines  avsas is housed in a vacuumed enclosure to reduce  

aerodynamic drag with an energy efficiency that  can be as high as 90 fps are especially attractive  

for applications requiring frequent cycling given  that they can undergo many charged discharge  

cycles with almost nowhere flywheels are used  to provide large electrical grids with an energy  

storage buffer for sudden changes in demand and  supply to prevent widespread power outages the  

electromagnetic aircraft launch system or emails  on aircraft carriers utilize flywheels to launch  

heavier aircraft by using much less energy the  system can fully charge in 45 seconds and can  

store 121 megajoules of extractable energy at full  charge large research facilities such as jet use  

fess to conduct fusion tests for plasma pulses of  up to a thousand megawatts fvss is also used in  

roller coaster launch systems flywheel systems are  most commonly used in providing temporary backup  

electrical power to support the load of a critical  facility such as a hospital or data center mobile  

applications of fvss are used as hybrid propulsion  systems in motorsport such as the audi r18 e-tron  

spacecraft such as the international space  station utilize flywheels as control moment  

gyros to stabilize and orientate the spacecraft  flywheels have been used for thousands of years  

and originated in the potter's wheel and water  wheels with the best known flywheels dating from  

the industrial revolution where it was used in  steam engines modern flywheels have been used in  

gyro buses since the 1950s where the flywheel  is mounted between the rear engine of the bus  

and the rear axle whenever the bus breaks  the flywheel works as a regenerative brake  

absorbing kinetic energy and slowing the vehicle  down in the last few years formula one race cars  

have been using flywheels to provide a power boost  via curse which is a flywheel spinning at 64 000  

rpm that absorbs energy that would be lost as  heat during braking when activated the flywheel  

temporarily engages with the car's drivetrain  and gives a brief speed boost flywheels still  

need to overcome a significant barrier before it  can solve the task of storing renewable energy  

although flywheels have a high efficiency and very  short start-up time they are still very expensive  

when compared to other alternatives  and lithium-ion batteries and with  

the continuous decline of lithium-ion battery  prices it will be difficult to utilize fess as  

a viable energy storage solution except for very  specific applications some developments that can  

significantly enhance flywheel performance  and make it more competitive with batteries  

are the development of new materials with high  strength and low density and superconducting  

bearings which can reduce the friction loss since  it enables increased rotating speeds and decreases  

self-discharge rates as electric connected  energy storage systems flywheels must compete  

with batteries and ultra capacitors on the  basis of cost for low cycle applications  

such as electric vehicles flywheels are unlikely  to achieve the already low incremental energy cost  

of batteries however applications requiring a  million cycles and a calendar life of decades  

may continue to be well served by flywheels as  battery lifespan remains much lower than this