Take a 2 MW single-tether kiteplane (like Joby's model) operating under a 2000 ft ceiling. To keep safely clear of neighbors it occupies a circular plot near a mile across. Presume a 3x3 array of nine kiteplanes for 18 MW from a 3 mile square kitefarm. The same land developed with conventional 5 MW HAWTs, spaced normally, could develop greater than 100 MW, presuming that better wind capacity-factor aloft roughly offsets the lowered system availability of complex delicate aircraft. Conventional HAWTs win overwhelmingly in raw land efficiency without even touching the upper-wind. However, the same land and airspace that the nine kiteplanes sparsely occupy can be densely packed with airborne turbines or wingmills, in string latticework based on classic kite methods, for over a rated gigawatt. AWE arrays of cross-linked semi-captive elements seem to have a fantastic advantage in space-efficiency, not just safety and control, over single-tether designs.

I used crude geometric methods to estimate these figures, so it will be fun to see how well someone else's calculations coincide. A suggestive guesstimate is that there is well over a gigawatt average in a tiny mid-lat crosswind patch of sky, just 100m across & 10km high.  Dave Santos, Nov. 10, 2010