Originally Posted by mattW
I typically hear that regen gives about a 10% increase in range, obviously that will vary with city/highway driving but 10% is the number that is always thrown around. And I think that the prius regen returned about 30%, so you would get 60A back. These aren't solid numbers from studies or anything, just what most people say when talking regen... hope that helps.
I suspect the Prius 30% figure is solely for optimistic regenerative cycle efficiency: how much of the power slowing down can be returned in later traction effort if everything is perfect.
A quick back-of-the-envelope calculation shows this to be likely. The motor and controller are each about 85% efficient. A very good battery is about 70% efficient at return charge energy. Multiplying these together, remembering that the power is making two trips through the motor and controller, gives you 0.85*0.85*0.70*0.85*0.85 = 36%. Factor in the drivetrain losses, at 90% efficient (although a dyno operator will give you a 130% factor for wheel-to-shaft horsepower) and you get very slightly under 30%.
Considering that each of these numbers is optimistic (e.g. a cold, loaded differential can absorb 10HP at highway speeds, the regenerated voltage will be far from optimal for charging), I suspect the 30% number is for the traction/power unit only, not as-installed: you won't be able to climb a 300ft hill from the power going down a 1000ft hill.
Consider regenerated power a tiny extra bump in efficiency, with a bigger bump in braking effectiveness. It's not a major win in range, despite what the press stories would have you believe.