At 2000 rpm as you suggest, the blue alternator should be around 280vac. This at your 100w requirement will be only 3-400 milliamps.
Normal building wire will carry this the distance you need without too much trouble. Provided you transform at your battery end. This will keep the current in the three phase part to minimul levels, and match the high impedance to your battery bank. Without the transformers, transmission of the 280v (ac or dc) rectified and then tied to the battery will give poor performance
Microwave transformers with total rewind will do the transforming at the battery end. It will require three transformers. Probably at these modest power levels, you could build three out of two.
New primaries and new secondaries will be required. With this setup, it would probably match the system better than up close direct battery tie would do at these speeds. The data sheet claiming a 350v 2500rpm direct tied to a 12v battery for 15A is pretty sad. Even with all the losses of transmission and transforming, I think this would do better than up close direct battery tie in.
When working out your primary turns, my first guess would be about 1v per turn for around 3.5 to 4 square inches of of core cross section area. ( I'm guessing a 6 pole alternator @2000rpm.)
A second simpler way would be to rectify the 280vac to dc at the turbine end, with some capicitors to filter it, and the new voltage to transmit will be 280 X 1.414 = 395vDC. This will transmitt over your 700 feet with only 2 modest wires quite well.
At the battery end you can use a normal offline pwm to bring it back down to 12vdc, or modify a computer power supply to do the same thing. You should walk in your 100w this way.
The transmission loss in this case would be very small. (At 400vdc, the current to transmit is only 250ma for your 100w at the battery for conversion) Losses in the converter will probably be greater than the transmission losses.
The second version (DC transmission @400v) would be the best way to go, and you may find you have well over the power you wanted. Finding an off the shelf converter is easy now days as well, if modifying a psu is out of your interest.
.........oztules