I see this.
http://mwands.com/store/freedom-ii-hydro-pmg-permanent-magnet-generator?search=hydro900 rpms to charge at 48v and is rated for 2800 watts the electric 1/4 hp motor does 1750 rpms
I just so happen to have a 48v golf cart next to 4 mining rigs running on a 230v PDU consuming 13.3 amps (~3000 watts).. would be pretty easy to test this..
Planning on adding solar / wind eventually so will use components for that..
maybe there's too much resistance added though when there is a LOAD on these things.. .