Flywheel energy storage: Why not use room temperature diamagnets instead of superconductors? Flywheel energy storage has garnered some interest from academia and industry for its potential to store surplus electrical energy efficiently in kinetic form. 
Modern designs use magnetic bearings to minimize the drag that the rotating mass incurs by levitating it in its entirety within a vacuum chamber. Most serious research efforts seem to implement these bearings with superconducting magnets cooled to 50 K or lower, in order to take advantage of a phenomenon called flux pinning that apparently occurs under these conditions.
This flux pinning stabilizes the flywheel in a way that room temperature permanent ferromagnets alone (being a collection of point charges) are not able to, due to Earnshaw's theorem.
However, there also exist materials such as bismuth and pyrolytic carbon, which even at room temperature exert diamagnetic forces quite capable of stabilizing objects that are magnetically levitated by permanent ferromagnets.
Why not use these diamagnetic materials instead of the superconducting variety, and greatly reduce the complexity, cost and refrigeration losses of the flywheel design?
Here is an illustration I've made to demonstrate the kind of configuration I have in mind:
One possible reason for using superconductors could be that flux pinning might suffer less from eddy currents ("electromagnetic drag") than room temperature diamagnets, but I'm not sure how to evaluate the impact of this effect, if any; so an answer that attempts to shed some light on this aspect would be much appreciated.
 A: It's a good idea. The basic reason no one's done it is that diamagnets are 4-5 orders of magnitude smaller permeability.  Added to which, if you have a superconducting set up you can get a superconducting magnet which is multiples stronger than a permanent magnet. 
The set up you show would probably need to be ~1000 times higher to work. Maybe in space though. But then again spinning stuff in space might not be the best idea... 
A: Diamagnetic forces are too weak at room temperature to provide adequate levitation/stabilization of flywheels that weigh more than a few grams. Nice for demos of floating pyrolytic graphite flakes between bismuth blocks, but not interesting from the viewpoint of practical energy storage.
The only exception to this is superconductors, which are basically materials with infinite diamagnetic constants when in superconducting mode. Boeing has been doing flywheels with HTS bearings for over a decade. The news release on the RTRI 100kWhr/300kW flywheel is interesting. It, too, uses superconductive bearings. For installations that can afford the costs of continuously operated cryocoolers to keep the bearings in superconduction, the technology works well.
