An inertial energy storage device includes a plurality of stationary electrical windings, a rotatable shaft, and a plurality of rotatable magnets coupled to the rotatable shaft. The plurality of stationary electrical windings extend about at least a portion of the plurality of rotatable magnets. The inertial energy storage device also includes a flywheel device that includes a substantially cylindrical hub rotatably coupled to the rotatable shaft. The flywheel device also includes a radially inner ring that includes a first material having a first density. The flywheel device further includes a radially outer ring that includes a second material having a second density. The first density is greater than the second density.