The flywheel principle

A flywheel is a kinetic battery that stores energy into movement. The acceleration of a rotor, or spinning wheel is used to store energy as rotational energy. Electricity is transferred to the rotor via a motor-generator, which transforms electrical energy into movement- a fast-spinning wheel.

The trick of a good flywheel is to keep this wheel spinning for as long and efficient as possible. This can be achieved by keeping friction to an absolute minimum. Energy can be taken out again by decelerating the rotor, transforming movement back into electricity. Flywheels are traditionally used for delivering or storing high power peaks for short periods of time (seconds to minutes). The inherent speed and robustness of flywheels make them perfect for absorbing frequent shocks in energy systems.

The energy stored in a flywheel can be calculated by Ek = ½ I * ω^2 . Here Ek is the energy stored as kinetic energy. ω is the angular velocity (rad/s). The I can be described as I = k * m * r2. I is the result of k, the inertia constant of the flywheel, m the mass (kg) and r the radius (m). This implies that the energy that can be stored in a flywheel is linearly related with the mass of the flywheel and quadratically depended on rim speed. This is why we go fast, not heavy. Making a small, compact flywheel that spins ultra-fast can easily match the energy stored of heavy flywheels, but can be far more efficient.

Fast-spinning flywheels need a solution for the losses that are being generated by friction of the rotor on the pin bearing. A light, compact high spinning flywheel without friction is the most advantageous way of designing flywheels since more energy can be stored in a small volume with less energy losses and more cycles.