I took a look at this and as usual am awed by the simplicity. With wind levels as described by steve and a bit of experimenting a simple planetary gear design similar to those used in cordless drills, but based on small sealed ball bearings for long life should up the output speed into the direct charging area. This should simplify the overall design. If overvoltage/over speed is a problem just switch on a large enough load to power limit the turbine. This allows the turbine to work from very low wind levels to the maximum possible without damage. Since excess wind is free there is realy no efficiency penalty. Terry