"not as common"
48 volt is much more efficient. Ames has one now that is the same price as it's 24v counterpart, but I have an Ames and wouldn't recommend it at all.
It doesn't handle overloads correctly. The voltage sags, but it doesn't trip offline.
The frequency is also off and can't be changed because it's crystal controlled.
Aviation batteries and telco equipment doesn't strike me as "home brew" If you have industrial grade equipment, why play with a homemade turbine? Valve regulated AGM's require TLC. If the batteries were flooded deep cycle, then that would be an ideal setup.
Converting down to 12v or 24v would be better/safer than just hooking it up to the turbine directly, unless the wind blows moderately steady all the time.
He needs a fail-safe dump load, too, without a self-regulating turbine.
If his batteries are new he has 20kwh of bank. That's going to hard to keep charged, again, unless the wind blows a lot, or he has a big generator to top it off during a calm couple of days.
If his batteries aren't new, then he needs to do a load test so he knows how far down a safe discharge is, and to plan for a proper recharge.
