http://wired.com/news/planet/0,2782,67121,00.html
Roberts, a professor of engineering at the University of Technology, Sydney, believes there is enough energy in high-altitude winds to satisfy the world's demands. Wind-tunnel data suggests a cluster of 600 flying electric generators, or FEGs, could produce three times as much energy as the United States' most productive nuclear power plant.
At 15,000 feet, winds are strong and constant. On the ground, wind is often unreliable -- the biggest problem for ground-based wind turbines.
Of course, now the question is what would happen if that energy is harnessed on a wide scale? Will it be harmless, or will there be unpleasant changes in weather patterns?
The real question is how you get the power down from the windmill to the ground where people actually use it. Or maybe they intend to float giant chunks of rock up into the air using magic like in Chrono Trigger.
You'd need to tether whatever was floating up there anyway, so you just use a cable as the tether.
>>4
What about the standing wave vibrations which will arise from the cable being pushed around by the atmosphere, and being pulled by the windmill on top? How do you damp those to relieve the enormous strain and wear on the cable? And furthermore, what the heck do you anchor a 15,000 foot long cable to so that it won't break and cause enormous havoc and destruction?
Engineering something like this sounds simple enough as a proposal, but actually making it work would require some pretty extensive research. There're also a large number of worst case scenarios to deal with.
I think nuclear power would be much more sensible in the long run than trying to build something so fantastic as this. Also, spending the money on research into more efficient solar power would probably have much greater returns.