I have access to this decorative windmill. It’s been in place for decades, spins freely in the wind, and has made millions of revolutions in its lifetime. Its RPM’s are impressive even in relatively low wind.
What are your thoughts on how I should harness this energy?
Hook a small motor to it. Small is key, a bike light is too big. Those toy ‘stomper’ trucks that run on a single AA battery is about all I would hope for. Of you want useful power you need longer blades and less of them. These are designed to turn fast with very little wind without going to fast in big winds. It should be fun and you learn, but of you want useful it is a waste of time. You’re choice of goals.