Man, you guys really have me itching to do a system like this. I was really overthinking my system before, it's really quite simple. I could make an impeller, run up an externally regulated alternator to produce 36v, and just let it run to keep a 36v battery bank topped off. It doesn't have to make that much in the way of wattage, since it would run 24/7 aside from maintenance. Just enough to recharge the batteries while not in use.
Now I just need to find a place to do this-