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