herdfan, these mid-to-small size systems are for one farmsite, and generally rely upon the electric coop (out here in rural MN all the power companies are actually REA coops originally started by the gov) as a 'battery' for the system. You buy power at retail, & sell power at wholesale to the power company. If you size the system about double - 3x what you use, I believe you get the quickest pay-back, as you can spread the fixed cost over more kwa's produced, but the tower doesn't grow too big (looks like beefy TV anntenna tower) to support an even bigger windmill.
This is different than people trying to produce their own power & be off-grid. You are trying to make a profit (tho small) from the tower, independent of your own power use. It's not a real profitable way to go, but if you have some cash to invest & want to feel Green it can work if you live close enough to the 'Buffalo Ridge' of SW Minnesota, where a lot of bonus wind sweeps down the long prairie from SD.
In the far west of SW Minnesota quite a few of the major wind towers (solid tube, like a new water tower) have sprung up. They are into full-scale power production. Much of the better sites already have leases signed, and there have been problems with companies going belly up & the lease & rights being in limbo....
--->Paul