It makes little sense to use an alternator to generate electricity to power a motor, when you typically have a chain and gears that are DRAMATICALLY more efficient, and work in all conditions. He is probably using the alternator more as an intuitive throttle, rather than a generator. Most any e bike can accept a PAS sensor input for throttle.
Alternators are probably quite inefficient at those low speeds and loads, probably 40-60%? Then the drive system is likely 80-85% efficient. Making your mechanical energy electrical and back to mechanical is just silly if you want to pedal to assist the bike.
E-Bikes can be quite the efficient and economical mode of transportation. A well built model can be extremely reliable and nearly maintenance free. They're considerably less costly than an electric car conversion, and can easily be recharged off a standard outlet in reasonable times. I charge my bike off a regular 20A outlet at about 2kW in 30 minutes or so, depending on capacity used. It's quite impractical to travel by bike around here due to the lack of infrastructure, and it's cold most of the year. On a nice day, it can be quicker to take my bike than drive a car for shorter trips.
This is about the only EM friendly video I have of the newer setup. I'm on the right, a friend is on the left. This was at something like 9kW. At some point I will mount the bigger controller and do another run at 16kW.
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