A question to you motor/generator mavens: a motor without permanent magnets can be quite efficient: the electric current is used to magnetize both the stator and the rotor. Why can't the same thing be done in reverse, in a generator? A small current from a battery or something could be used to get the magnetic field started, but once it's generating current, if that current were to be forced through both stator and rotor in the right orientation, wouldn't it be self-reinforcing? I.e., if the electromagnetic forces are such that it pushes back against the turning, then forcing it to turn (using the energy source that drives the whole thing, e.g., a wind turbine) would increase the current and the magnetic fields. This is basically done in a synchronous grid-tied generator, although it's tied to the grid, it generates a surplus, efficiently.
The catch is that you need to "commutate" it somehow if you're using DC. At least you'd need a way to commutate the initial excitation current, even if the generator then produces AC? What if the stator is driven with DC and the rotor has the old fashioned (brushed) commutation mechanism? A brushless design would last longer though.
