Generate Power off of several motors at once
Other things being equal, one 100 watt motor will have better efficiency, lower friction, better everything really, than 10 off 10 watt motors. Exactly the same goes for motors used as generators.

This is due to a larger motor having better geometry (tighter air-gap engineering) and better scaling (power handling and losses go up at different powers of the size). 

One big motor will use fewer mounting screws than a handful of small ones as well.

One word of warning, don't use a car alternator if you want an efficient generator. They are used in an application where spare power is 'free', cooling is plentiful, so are built small and cheap, at the cost of lousy efficiency.