An example flywheel energy storage device includes a fiber-resin composite shell having an elliptical ovoid shape. The example device also includes an axially oriented internal compressive support between the axial walls of the shell. The example device also includes an inner boss plate and an outer boss plate on each side of the shell. The example device also includes a plurality of radially oriented, fiber-resin composite helical wraps forming the shell and coupling the shell to the inner and outer boss plates for co-rotation and torque transfer. The example device also includes boss plate attachments on internal boss plate supports to mount the shell for co-rotation and torque transfer via resin bonding, friction, and compression between the inner and outer boss plates.