Right, but I'd like some reference from the OP.
I'm extremely dubious a VAWT is going to be able to produce sufficient voltage at low wind speeds. That particular one you linked has a startup speed of 3m/s or 7mph.
Using this as an example:
.52m dia and 1.1m tall
At wind speeds of 15mph, it's only going to produce on the order of 27W.
Given the low wind speeds discussed, I'm dubious there has been enough wind to produce meaningful voltage. The "braking" observed may simply be the controller trying to extract power from it.