For a turbine prop to work effectively its speed needs to rise directly with wind speed, if you hold the prop speed constant it comes off the peak of its power curve very quickly, small deviations from the ideal speed don't badly affect the power out, but stall starts to affect things quite badly and when you hit hard stall the power falls drastically, in fact so drastically that you only get a tiny fraction of the power available, even though the theoretical power is rising as wind speed cubed. You can be forgiven for believing that in high winds there is so much power available that it ought to work well if it works ok in low winds.
The main trouble is direct battery charging where the alternator output is clamped to constant voltage. For an alternator to be efficient it needs to have low resistance, but a low resistance alternator clamped to a fixed voltage is forced to run at near constant speed.
In high winds the prop curve is fairly steep and is a good match to a reasonably efficient alternator. In low winds the power curve is very flat and is a poor match to a decent alternator. To get enough speed rise to avoid hard stall if you cut in at low wind speeds you have to use an inefficient alternator and this produces poor output and heating problems in high winds, but even then it gives better results than a highly efficient alternator causing hard stall.
It becomes a trade off between prop efficiency and electrical efficiency and the better the low wind performance you go for the worse the trade off. Unless it is a very poor wind site going for a low cut in speed to get results in very light winds will murder the high wind results and remember there is very little energy in low winds.
If you only get very low winds, then even this very low energy may be worth having and if you don't get many really windy days the trade off may work even if the top end performance is dreadful.
If you have a reasonable site you my do much better loosing a bit of low wind performance to have better output on the average days where most of your real energy comes from.
There are some tricks that help you get some of the best of both worlds but without some form of mppt you will need to make compromises.
I did a series of articles covering this problem years ago and I believe you can still find them in the FAQ section.
Flux