Let explain the overall system. A mains motor of 240 Kilowatt capacity is used to drive a series of belts and pulleys which form a gear-motor which produces over twice the rotational speed at the shaft of an 10 MW electrical generator. Flywheel weight and the Diameter is calculated on the torque required (losses and back EMF drag) to rotate the rotor to achieve maximum power. Moreover the main internal PCB controls the EMF Drag Back accurately.