I find it hard to believe you would get much energy recovery, given that even in hybrid cars the recovery rate is miniscule (6-7% at best). However, hybrid is becoming very popular in boats because of the flat torque curve of an electric motor. That means that a smaller engine can run at maximum performance/fuel efficiency rate, and that can be converted extremely easily to useful power.
I assume propellers share a certain level of physics with boat propellers, which are being redesigned to take maximum advantage of high torque engines
Any thoughts, anyone?