Mack;
whereas the horizontal wind generator will not turn unless the wind is up to 8 MPH or more.
This fell out of the south end of a north bound bull!
It is simply NOT TRUE My 8 foot dual rotor vertical axis turbine spins in the slightest breeze. They all do.
Good luck building the turbine itself as you certainly will need it.
Just curious where you got that don't turn til 8 MPH bull?
3 KW at 10 MPH is going to take a massive machine of any style. Something on the order of 70 foot diameter horizontal at least after you figure in losses. Thats not much wind so it takes a huge swept area to get 3KW out from 10 MPH. Reality is not on your side regardless of the style turbine when hunting 3 KW in 10 MPH "wind". My numbers are from the IRC "bot" using 10 MPH and various rotor diameters until I exceeded 3KW the bot assumes 80% generator efficiency a Cp of 0.20 and air density of 1.225, I believe.
Sorry to inject this reality but thats how it is.
The good news is:
To answer your initial question. Yes, you could couple a dual rotor axial alternator to your VAWT would just need to follow the commonly used methods to find the right coil turns and wire size like any other machine once you know your RPM. Plus mechanical skills to do the connections, of course.
Seriously, good luck with it. We keep waiting for posts of success stories on VAWTS folks have built.
Tom