Vital information missing - wind speed!.
A typical 8ft machine should do 50W in about a 10 mph wind so if that is a medium wind you are ok.
We have no idea how well matched your prop is to the alternator. To get a good idea try it temporally into 12v, 24v 36v and possibly 48v. One of those options will give most power out ( don't think amps, thinks Watts, amps x volts).
If you get a far better match then if you want to keep 24v then you may need to reconnect.
Flux
