Dave
I have had a look at this using the details you gave to Hugh. I don't think burn out is going to be an issue if you load it sensibly, your problem is going to be obtaining the power you want at the low speed of 200 rpm.
When you come to heating or mppt for battery charging you need an efficient alternator that means big and yours is relatively small for a 16ft prop. I assume you have chosen such a large prop to obtain more power in low winds. This works fine for battery charging, but for heating, the lower powers are of little use. 200W of battery charging is very useful, but 200W of heat will not do much.
If you want to keep the 16ft prop and also keep to the 200rpm top limit then I think you are looking at about 1500W and at an efficiency of probably 65% so stator heating is not going to be an issue. You could of course hold it into higher winds with a lower value of load resistance to drag the speed down into stall but then you would see much higher stator losses and still not see much over 1500W. It will be much better to furl at a low wind speed that gives 1500W at high efficiency than stall limit it to keep the speed down. This may mean that you will need a good alternator offset to make it furl properly, the offsets used for stall limited machines may not work with the prop tracking peak power.
All depends on your wind and how much heat you want and how often. If you came down to 12 ft and let the speed go up to 270 rpm ( same tip speed) , you could probably easily exceed 2kW for the same stator heating, but of course you would need higher winds to get it.
At present if you want to use 120v heaters then you will need to double your turns with a single wire for raw AC.
Whether you use ac or dc depends on your load control, switching dc is a major problem, I think you will be forced to use mosfets (or IGBTs) with pwm or use a phase controlled thyristor(scr) rectifier and solve the variable frequency firing circuit problem.
For 3 phase raw AC you can use mechanical contactors or triacs.
There is a strong case for considering single phase from the control point of view, but it means making the alternator 50% bigger for the same power out and it is already very small.
Flux