Flywheel storage has allready been developed - magnetically levitated flywheels in a sealed vessel, using an inductive system, to charge or discharge the system.
As far as I recall, small ones can spin up to hundreds of thousands of RPM, and have a very high burst capacity.
For short term applications (many hours), they're apparantly quite efficient, the biggest issue is self discharge.
Slashdot Mirror
Flywheel storage has allready been developed - magnetically levitated flywheels in a sealed vessel, using an inductive system, to charge or discharge the system. As far as I recall, small ones can spin up to hundreds of thousands of RPM, and have a very high burst capacity. For short term applications (many hours), they're apparantly quite efficient, the biggest issue is self discharge.