Flywheels are not silent and have unwanted gyroscopic effects. Getting even more impractical, you could store energy in a spring like a wind-up toy. A pure ele

Flywheels are not silent and have unwanted gyroscopic effects. Getting even more impractical, you could store energy in a spring like a wind-up toy. A pure electric system is much simpler as the motors are the regenerators and there is one energy store.