A starter is a series wound motor, it is designed to generate the necessary field from the high current, perhaps 150 - 200 amperes, that flows while the engine is cranking. A conversion would be possible if the field were rewound with smaller wire and connected in parallel with the armature. Other considerations would be the fact that it is designed for intermittant use and would not dissipate the heat generated at a current much above what you could get out of an alternator. The bearings would also be short lived in continuous operation.
24V aircraft generators are available with ratings up to several hundred amperes, could generate 14.2V by simple reduction of the field voltage - and would be a good choice for a large wind generator. Generators, both aircraft and automotive have somewhat better efficiency than alternators but require more maintenance. Due to the requirement for (and losses of) electrical field power, automotive alternators are suitable for larger diameter wind turbines that can produce 14.2V and 30 AMPS in your average wind while exciting the field and supplying belt drive losses... this means around 600 watts of mechanical power.
I would forget the starter and look in the direction of big blades, like a gyrocopter rotor .... driving a 200 AMP large case marine alternator (or the aircraft generator) with a 20 to one belt ratio. You need serious power to make a real dent in your utility bill or run a normal residence and that means a 12 MPH or better average wind and a large diameter turbine.
