Before you spend the ginormous amount of money to buy the land and build the windmills, you need to make sure you're building them in a place where the wind blows MOST of the time, and it's not too slow for the windmills, and it's not too fast for them either.
That's a special kind of place.
There are a lot of places where the wind doesn't blow enough of the time, and when it does, it's either too slow or too fast for windmills to operate safely and efficiently. In places like that, you could spend a fortune to build windmills, but they wouldn't produce enough energy to make it worth the money.