The best known forms of Aerofoil is a plane wing, or a boat Sail. The basic point is that if you make something of the right shape, then it will convert wind motion into a force, which you can use for generating lift, or, in the case of a sail, horizontal motion.
It seems to me that you could us this to generate Energy. Imagine a large Aerofoil. You put this somewhere where it is windy, and the Aerofoil will lift upwards. If this is in a trade wind, it should be possible to keep such an Aerofoil aloft indefinately. If it's really high up, in the jet streams, then the amount of life would be pretty significant. I call these WindAerofoils.
If you have lift, then you can also generate Energy out. Basically in the middle of the wing you put an AirTurbine. which will produce Electricity either whenever the Aerofoil changes altitude. Of course, you have to get the Energy back to the ground. As with many of my systems, Hydrogen generation through Electrolysis seems to be the obvious solution.
Of course, eventually you get as high as you can go. It's easy to drop down again though. All you need to do it change the shape of the Aerofoil, either with flaps or, if the Aerofoil is made from flexible material, by letting in Wind into the structure.