Originally Posted by
atwl77
I've occasionally joked with my friends about having a dynamo hub charge a motor... but there's the issue with physics and all that. But still... if the motor's only working uphills, partially working on flats and not working downhills, there's surely *some* benefit, no? Only question then is how much, and whether that's significant or not.
The energy used to spin the dynamo hub will be greater than what the hub puts back into the battery. Where that energy comes from (motor, rider, gravity) will change based on going uphill or downhill, headwind or tailwind, etc, but the bottom line is that you can't convert one form of energy into another without losing some.