composite thin cylindrical flywheels have great energy storage characteristics "greater than 400 Wh/kg can be achieved by certain composite materials" https://e

composite thin cylindrical flywheels have great energy storage characteristics "greater than 400 Wh/kg can be achieved by certain composite materials" https://en.m.wikipedia.org/wiki/Flywheel_energy_storage https://en.m.wikipedia.org/wiki/Flywheel_energy_storage -----