Wind turbines are constantly getting taller because everyone knows
the higher you get off the ground, the better the wind speeds. But
building big towers is expensive, especially if you want one 15,000
feet tall. So why not ditch the tower and make the windmill fly?

Several people are trying to do that. They’ve been written about
before by others, but we’ve yet to tackle them, so here’s a little
round-up of the three most notable projects: Sky Windpower, Laddermill, and Magenn.
Each is a bit sketchy, but deserves to be given a shot. It seems
obvious that once someone creates a workable system, it will become a
huge winner, because of the sheer amount of power available up high: 1%
of the jetstream’s wind power could supply all US electrical demand.
Also, one of the main complaints about wind power is its
intermittency–the wind doesn’t blow all the time, and so (according to
Sky Windpower), most wind farms are only operating at their peak
capacity 19-35% of the time. The wind is much steadier at altitude, so
you get even more advantage over ground-based wind power. A final
advantage is ad-hoc generation: devices with a reasonably simple
tether-system do not have to be permanently installed in one place,
they could be trucked out to any location that needed them.

More here.