With the spec of the cars as shown , at racing speeds they will only run for about 12 minutes before needing charging .
One factor of racing is to spend as little time as possible on the brakes , so I doubt regenerative braking will ad even 1 minute to the run time .
If the format is to be 20 or 25 minute races with only 1 recharge , [ a 6 hr race would mean 2 hrs in the pits charging up ], then between 12 to 16 minutes into the race there would probably be no cars on the track .
To do a recharge in 5 or 6 minutes would need a generator truck
http://www.truckinchina.com/ISUZU-Em...d78980987.html
for each car .
So , although it ticks some boxes for the Greens , I cant see it being very exciting for the spectators or the teams who would have to spend well over £100,000 on a generator for each car .