There are two basic ways to use a kite to harness wind energy.
- Use a kite to carry turbines and generators up high and transmit the energy back electrically.
- Use a kite as a wing and harness the power transmitted mechanically to the machine that it's attached to.
Both are being pursued actively by numerous groups.The simpler solution seems to be the latter, if for no other reason than that the part that's flying around is commonly available (traction kites), and the fewer things you need to keep in flight, the simpler.
Within this approach, we need to decide what kind of work the linear force of the kite lines is going to perform. Again, numerous approaches have been and in some cases are still being pursued, from a laddermill, to a carousel, to other notions. Again, trying to keep things as simple as possible, we choose to emulate the well-proven interaction of kite surfers with large kites. One way to do this is to have the line(s) wind and unwind spool(s).
Our mechanical-force based approach is basically a long-stroke, reciprocating engine, driven by the tensile force on the kite lines. We steer the kite in a cyclic trajectory such that the lines reel out as there are large forces on them, and reel back in when there is a smaller force. As we do this, there's an energy surplus, as the force is greater when the wind is pulling the lines out.
We still need a means of temporarily storing the energy needed to reel the lines back in, and a means to harness the surplus.