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Flywheel as Energy Storage Device, Calculations and Rotor Requirements

Flywheel as energy storage device is an age old concept. Calculation of energy storage in Flywheel and its rotor requirement are discussed.

The technique of energy storage using Flywheel is thousands of years old. Just take an example of Potter’s wheel and think what it does. It just uses the inertia of wheel and keeps on rotating with minimum effort.  The concept of Flywheel to be used as a energy storing device is being used since 1950s. They could easily be sighted at bus-stops for charging the public transports. However, this idea could not be widely accepted view its bulkiness and excessive weight.

Fly wheel as energy storage device

Calculation of energy storage in Fly Wheel :

The storage of energy in Flywheel can be calculated as :

E = ½ Iω2


E = ½ (kMr 22


  • I stands for Fly wheel’s Moment of Inertia
  • ω stands for Rotating Velocity. It is measured as radians per second.
  • M stands for Flywheel’s Mass
  • R stands for Flywheel’s Radius, and
  • K stands for Inertial constant

Note: The value of ‘k’  depend on the Flywheel’s shape. For example – if the Flywheel is rotating on its axis (like a bicycle’s wheel or a hollow cylinder), the value of k will be 1. However, if the Fly wheel is having a solid cylindrical form, then the value of ‘k’ will be ½.

Rotor Requirement of Flywheel:

Gradually with advancing technology, the flywheels have become more sophisticated. Now a days, advanced Flywheels contain the kinetic energy in a fast moving rotary drum which acts as rotor of a generator. At the times when additional energy remains unconsumed , then it is used to boost the rotary drum’s speed. Whenever there is requirement of energy, then this drum drives the generator.

Sectional view of a flywheel rotor

The rotors of these super flywheels  are made up of very high strength:density ratio such as carbon fiber materials. A high strength material is required for the rotor as it generally spins at average speed of 100000 revolutions per minute and should be able to bear the high centrifugal force exertion. These rotors are mounted in a vacuum cavity to minimize the losses due to air friction.  This friction loss can further be nullified by the use of magnetic levitation bearings.

Read more about Alternative Energy Storage Methods

Ratna is a B.E (Computer Science) and has work experience in UK Mainframe IT industry. She is also an active Web Designer. She is an author, editor and core partner at Electricalfundablog.


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