That is a long time. I guess it would be a legacy to your kids.
On different note what is the expected useful life of a windmill? In other words could you really have an expectation that it would ever pay for itself?
That should be the only real criteria for purchasing these things. One tax payer should not buying another a windmill.
The lifetime depends on who made it. Some of the original Jacobs machines are still in use today. Joeseph and Marcellus Jacobs were ranchers in Montana in the 1920’s and 30’s and developed a very reliable and cost-effective wind generator that powered many remote farms and ranches into the 1980’s, when the REA made great pains to make electrical service dirt-cheap for even some of the most remote customers.
Some of the older Jacobs machines are still sought by modern-day folks seeking to put up a home-scale wind generator for the quality of their construction.