Inertia Wheels 

Inertia wheels are a way to store electrical energy in the form of kinetic energy. They consist of a mass rotating around an axis connected to an electric motor.
 

Storage phase 

The motor converts incoming electrical energy into kinetic energy.
 

Stationary phase 

The rotation of the mass is maintained at a constant speed.
 

Release phase 

The generator converts the kinetic energy into electrical energy.