As the rotation of the windmill varies with wind speed how is the output voltage and frequency maintained?
Can you only get electricity out if the wind speed falls within limits. Outside those limits is the windmill useless?
Wind turbines have variable pitch blades which change the angle of attack in different wind speeds. This means that the turbines 'on board computer' can keep the turbine at a constant rotational speed in different wind speeds. This, as such, is not new. Windmills with slatted sails (like this one) http://www.taphilo.com/photo/pictures/windmill s/Alford-windmill.jpg
used a governor on the main shaft to open up the slats if the wind got too strong to stop the windmill 'overspeedding'.
I don't know how they work, but it wouldn't take much for a mechanical engineer to design a variable gearbox to drive a generator at constant speed.
Alternatively an electrical engineer could easily adjust the output to whatever was needed.
If we can put a man on the moon nearly 40 years ago this should be a piece of ****.