A look inside

There are three rotors. The inner and outer rotors turn in the same direction. The intermediate rotor turns in the opposite direction.

The inner rotor has a ring of rare earth magnets, these align with coils on the inner edge of the intermediate rotor. As they are travelling in opposite directions the amount of power generated is higher than with a static coil. The energy is passed to the outer edge of the intermediate rotor where it charges electromagnets. 

These in turn energize coils on the inner edge of the outer rotor, generating energy that is passed to a final set of electromagnets that energize coils in the outer hub.

From there the energy flows through the electronics and off to battery storage.