The PowerPlane Concept (VIDEO)
The PowerPlane system consists of a ground station containing an electric motor, that can also work as a generator, and an airplane.
During a power generating phase the plane flies patterns downwind of the ground station, while pulling with a high force on a cable connecting the ground station and the plane. Simultaneously the ground station is reeling out cable. Since power is force times speed, the high force times the reel out speed is generating power. When the maximum cable length is reached, the plane dives towards the ground station such that the force in the cable is low, simultaneously the ground station is reeling in the cable. Since the force is low, reeling in cable does consume less power than is produced in the reel out phase, resulting in net power at the end of each power cycle. When the cable is retrieved to its original condition, the process is repeated.