Airborne Wind Energy Systems (AWES) are a promising, new kind of technology to harvest wind energy. The expensive and immobile infrastructure of conventional wind turbines (tower and rotor) are replaced by an aircraft (giant kites or drones) and a tether. In some systems, the aircraft moves an electrical generator on the ground, whereas in other systems, electrical energy is produced by wind turbines onboard the aircraft and transmitted to the ground by a conductive tether. AWES systems operate at high altitude (over 500 metres) where winds are more intense and stable.