Oh, I can chip in here regarding big vs small flywheels.
If you look at the purpose of a flywheel - ie storing kinetic energy - a bigger/smaller wheel can serve the same purpose. The reason we don't have "large" flywheels is twofold:
1. size (obvious)
2. Torsional/shear stress - most materials are bad at tolerating shear stress. A bigger flywheel would require immense amounts of torque to get it moving. Generating a higher torque would impose huge amounts of torsional stress on the shaft driving the wheel.
1. size (obvious) 2. Torsional/shear stress - most materials are bad at tolerating shear stress. A bigger flywheel would require immense amounts of torque to get it moving. Generating a higher torque would impose huge amounts of torsional stress on the shaft driving the wheel.