I made a big study of wind gennys and the best ,and most powerful one is the Eclectic Energy D 400.I bought one 2nd hand but have not put it up yet as i do not think it will go on the mizzen mast because of its weight and size,with the turning circle of the fin and the blades.But there are many lighter ones like the LE series which are quite powerful.Some of the older types are just trickle chargers and not really worth the money.Trouble is they look quite attractive because of their light weight, and size. It is perhaps advisable to check the more modern firms ,like LE , to make sure they are still in business.Happy hunting and may all your voltages be big ones!!!!!