A Breakdown of Kite Power

This explanation is from The Drachen Foundation - http://www.drachen.org.
The actual document is a PDF and can be downloaded from here http://www.drachen.org/journals/a16/Using-kites-to-generate-electricity.pdf

Ladder Mill

This is a continuously circulating loop of kites envisioned as flying up to altitudes of 30,000 feet. Kites on the up-bound or power side operate at full lift angle of attack creating high tension on the up-bound cable, kites on the down-bound or return side of the loop operate at near zero angle of attack, thus creating low tension on the retrieve cable. These tension differentials on the order of 10,000 pounds when applied to a capstan on the ground (like a belt around a pulley) can generate significant shaft torque to turn generating machinery. The cables would be made of carbon nanotube, which is on the order of 230 times stronger than steel on a strength per weight basis.

Reel

A plodding, low tech approach, this alternative envisions a stable kite with hard, steady pull. The kite is simply reeled out, then in, using a capstan connected to a generator. During the reel-out or power stroke, the kite pulls a maximum load. It is then depowered and reeled back. Power is harvested from the net energy gained during reel out, less than required to reel in. Electrical and mechanical components required are simple.

Fly Gen

This scheme harnesses the power experienced in traction kiting. It depends upon a maneuver common to traction kiting, the figure-8, in which the kite dives from high to low altitudes, trading potential energy (altitude) for kinetic energy (speed). The resulting increase in speed induces high relative winds at the kite and thus high
dynamic pressures which result in high lift on the kite, experienced as high tension in the kite lines. A kite with high lift-to-drag ratio is critical to the success of this technique. Scaling up power output will be possible only via increased kite size. Adding kites or stacking is not an option since the control system is not practically attainable. Note that this scheme is unique in the fact that it is the only one in which the generator goes aireborne (thus the name Fly Gen).