Reverse pumping: Theory and experimental validation on a multi-kites system

Most kite wind power systems have a great drawback that wind turbines do not have: they cannot stay in the air if the wind is not strong enough, [7-16]. As a consequence, most of the kite systems need to land when there is no wind, and to take-off once the wind is strong enough. These maneuvers are quite risky because generally the wind gets weak and turbulent close to the ground's surface. Moreover, as the wind can be strong enough at high altitude and weak close to the ground, it might lead to losses in energy production. From a material point of view, “classic” landings and takeoffs need a landing zone, ground handling or infrastructure (such as pylons) that reduces the advantages of kite systems. Some ideas, such as embedded motors or helium balloons, might solve this problem, but they have their own drawbacks such as the weight of the motor and its battery, the necessity of a conductive cable or the need to refill the balloons. The following paper studies a solution called “reverse pumping”. It basically consists of providing kinetic energy to the kite by pulling the kite with a rope. This kinetic energy is then transformed into potential energy by gaining altitude. This technique allows to keep the kite airborne in total absence of wind. This paper will study the reverse pumping principle, the constrains on the aerodynamical model, flight simulations and will present the experimental setup used to validate the theoretical study.