Hugh Piggott's blog

Efficient wind turbine alternators connected directly to batteries do not have the right speed range to make the best use of the blades.  Adding a controller that converts the voltage between the windmill and the batteries can improve performance (rather in the way that grid-connect inverters do), but such controllers aren’t simple.  Outback Power Systems ‘Flexmax’ controllers have been used for this, but now the company is in new hands and this experimental application has been dropped.

Here are two companies that offer ‘market ready’ controllers for optimising the blade speed.  Finnprop specialise in heating controllers but they can do some battery chargers too.  Midnite offer their ‘Classic’ PV controller with an additional ‘Clipper’ box that adapts it to use with wind turbines (at a price).

“Finnprop is a company, which is solely dedicated to produce windmill´s power controllers. Our products make possible to utilisize electicity captured from wind to varied type of usage. FinnProp® windmill power controllers are designed to maximize windmill efficiency and allow propellers to rotate whenever the wind is blowing. We also produce fully tailor-made solutions.”

http://www.finnprop.fi/index6.html

“The Classic MPPT controller allows the wind turbine to operate at a much higher voltage
than has been possible in the past. The Classic is an extremely efficient DC to DC
converter that tracks the wind and transforms the DC voltage down to the battery voltage.
Preliminary testing shows 100% more power from some existing turbines.”

http://www.midnitewind.com/