First of all, discard the idea of a car alternator. They are only about 55% efficient in converting mechanical power to electricity. They also require a high RPM. Your gearing losses will be tremendous. While junkyard alternators can be used when you have excess shaft hp available, I don’t think you don’t have any margin to spare.
As far as off the shelf items, your best bet would be a PM (permanent magnet) DC motor. Look for one with a low rpm rating. That will help keep your gearing losses down.
(from your limited description of your turbine, I suspect that you have a low RPM on the turbine shaft.)
Another course would be to build your own PM alternator. There are a number of examples on the fieldlines site that Thomas referenced. Another is Hugh Piggott’s site.
http://www.scoraigwind.com/Or, Google away.
While car batteries will work for the purpose of your thesis, they are not suitable for storing any significant amount of power for an alternative energy project. One of the biggest stumbling blocks is the cost of decent batteries. No matter how inexpensive a power source is, the cost of energy storage will usually kill it, when you are competing for those rare development dollars.
A diversion load does not generate any power. It burns excess power, to keep that excess from smoking the batteries. A diversion load would be a necessity, if your thesis ever moves into the real world.
You might consider modifying your project. If you designed an inexpensive positive displacement water pump, which could be powered by your turbine, it might have greater application. Moving water without an associated fuel cost, is one of the larger problems in many developing nations.
