Flywheels capable of competing with batteries, let alone gasoline, for energy density are waiting only for the invention of "Unobtanium."Electric cars will be worth buying ONLY when equipped with a superflywheel and ultracapacitors for extended range----see the sites williamshybridpower.com---vyconenergy.com---blueprintenergy.com. For hybrids, see the chinese BYD hopefully available in US soon
Can't get there from here.
Supercapacitors today have only the advantage of instantaneous discharge rate, but are otherwise less than 1/10th the energy density of batteries. The Tesla has proven beyond a shadow of a doubt that improving battery technology makes their use unnecessary, just another bulky pack of "stuff" to carry along adding weight, reducing cargo, and reducing maximum range between recharges. However, if EEStor should, on a long shot, prove to meet their claims - then perhaps they will have an advantage over batteries - for a while.