AC energy storage 4 regen braking?

[mat h physics]

http://www.youtube.com/watch?v=3q3fdwaVIfE&feature=player_embedded

Think this is accomplished by using a ceramic flywheel for kinetic energy, and it buffers the power. Could regen braking use a similar concept?

 

[Rafabaca]

A small compactor bank could do the same thing. don't quote me on this but most regen controllers should stabilized the volts coming in.