One more thing occurred to me. Although we know nothing about the whirligig you intend to employ…
I don’t think a wind charge controller for the inexpensive import windmill heads is that expensive. If it were me I’d probably just buy an appropriate wind charge controller and plumb it to the battery bank with a CT or shunt to track its Wh contribution. Then you won’t have any issues with the erratic output of wind, and you will also be able to observe its effectiveness at doing anything useful.