lets say you wind mill at full rpm is 300
an altenater is most efficant from +3000 rpm
per 10 amps draw 1hp is required
30 amp alternator charging a empty battery will require 3hp to turn it
if at 300 rpm you wind mill prodces 30 hp at 3000 rpm you will have 3hp
so at full wind speed you will only just turn the alternator and we dont have many days where it will reach full wind speed.
the best way would be to turn the alternator into a permant motor, if you get some magnets to replace the outer coils, if the inner coil dose fail, then you can get a new alternator and just repace the outer coils onthat 1 with the magents from the old 1.#
or i might be able to make a motor for work disapeare (they do seem to have a trick of disapearing)
use some thig like these http://www.ebay.co.uk/itm/Super-Strong-Neodymium-block-magnets-F50mm-x-20mm-x-10mm-N35-grade-Rare-Earth-/370632703117?pt=LH_DefaultDomain_3&hash=item564b6e3c8d