It's amazing how high birds can fly http://en.wikipedia.org/wiki/List_of_birds_by_flight_heights

Unfortunately it's likely that many many types of animals take advantage of low-altitude wind-streams, especially during migrations.

But maybe we could place several of them into the jet-stream (at 10-15 km) which is higher than all birds except one type of vulture.

Edit: Nevermind, Google is working on exactly that: http://www.gizmag.com/google-x-makani-power-airborne-wind-tu...

The cable seems to be the most difficult part: http://en.wikipedia.org/wiki/High-altitude_wind_power

The tethers wouldn't interfere with air travel?

Restrict airspace access for densely tethered wind-farms and if they are needed closer to cities then we can figure that out later.

I was thinking some sort of central tether connecting a large group of them then either directly beamed or daisy-chained balloons high up in the air. It would be an amazing technical and engineering accomplishment to do that but it might provide energy with minimal airspace disruption, though you wouldn't really want planes flying under them either, just in case.

Maintenance could involve having detachable cables (which would deploy a parachute and have bring lights in case a place was passing by at that time) so that the cable falls gently against the central tether and can be reattached using a heavy-lifting drone or blimp/drone hybrid.