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?
You can try just hooking on a chain and a dynamo.
But that entire blade mechanism looks way too heavy for its size. You won’t get much out of it without replacing it with something a lot lighter.