Surly that's where we should be developing. Last I heard they're very efficient.
In theory it has no ceiling, storagewise. And it certainly isn't constrained by a chemical reaction.
The only downside is keeping it from blowing up. Right?
- They are VERY heavy. Typical energy density for flywheels is 10-40 kJ/kg (if you account for the whole flywheel), while Li-ion batteries and gasoline store 300-1000 kJ/kg and 46700 kJ/kg respectively (the latter does not account for ICE efficiency).
- They are relatively big, since you can store more energy with a bigger diameter (limited by material's strength-to-weight ratio).
- Flywheel is a big gyroscope. You do not want to rotate it around while it spins.
So back to my question.