Flywheel power source with passive generator cooling

A process of storing and recovering energy in a flywheel power source, comprising:

• accelerating a flywheel inside an evacuated container with a brushless motor, for storing energy in the form of rotational inertia of said flywheel;
• decelerating said flywheel with said generator a rotor and a stator for retrieving said stored energy in the form of electrical energy, said generator having a rotor coupled to said flywheel and a stationary stator having coils made of multiple-strand individually insulated conductor wire;
• passively cooling said stator by heat transfer from said stator to a liquid coolant surrounding said coils, said coolant and said stator being contained in a stator coolant vessel partially filled with said coolant, and said coolant circulates in said coolant vessel solely by natural convection;
• whereby said liquid coolant limits the maximum temperature of said coils reached during discharging of said flywheel power source.