He went through the entire vid without mentioning Williams Hybrid Power, the spin-off from the flywheel storage developed for the Williams F1 car in 2008/2009:



Unfortunately it couldn't be scaled up to the increased KERS output required for the 2011 season, at least not in a way that fit in an F1 car, so Williams now run the same electric KERS as everybody else. The flywheels are used in other racing series and in road cars though, as mentioned in their vid.

One very obvious difference between the prototype bicycle system in this vid and the WHP version is that they are using relatively lightweight composite flywheels and then spinning them to speeds that would tear apart the car flywheel from this vid, typically 20,000 to 50,000 rpm. This greatly increases the amount of energy storage available which increases linearly with mass, but with the square of rotational velocity.

http://rpm2.8k.com/basics.htm