Abstract: A flywheel energy storage system includes a driving wheel rotatable relative to a first axis; an electric motor for driving the driving wheel; an electric generator; a driven wheel adapted to drive the electric generator; a flywheel rotatable relative to a second axis parallel to the first axis; a clutch assembly for engagement or disengagement of the flywheel and the driven wheel; and a transmission gear train assembly engagingly interposed between the flywheel and the driving wheel adapted for conveying kinetic energy from the driving wheel to the flywheel. The transmission gear assembly is provided for allowing the flywheel driven by a low-powered electric motor to drive a high-powered electric generator.