67 Rogelio Lozano Gipsa-lab/CNRS University of Grenoble Gipsa-lab, ENSEEE Domaine Universitaire - BP4611 rue des mathematiques 38400 Saint Martin d’Heres France jessica.reolon@gipsa-lab.fr www.gipsa-lab.grenoble-inp.fr
Reverse Pumping: Theory and Experimental
Validation on a Multi-kites System
R. Lozano Jr, M. Alamir, A.Hably, J. Dumon
Gipsa-lab/CNRS, University of Grenoble
Classic kite wind power systems have a great drawback that wind turbines do not have: they cannot stay in the air if there is no sufficient wind. Most of the kite systems need to land when there is no wind, and to take-off once there is enough wind. As these maneuvers happen close to the ground, where the wind is most turbulent, there is a great probability of crashing the kite. Also, ”classic” landings and takeoffs need a landing zone, ground handling or infrastructures such as pylons, thus reduce the advantages of kite systems. A first solution to over-come these drawbacks is to use helium balloons to make kites fly in still air, but balloons have leaks and need refilling solu-tions. Another solution is to add engines to our kites so that we transform them into vertical takeoff and landing tethered air-planes. There are two ways of supplying energy to the engines, the first is to use electric cables that transmit energy to the kite, and the other solution is to use an embedded battery. For the first solution, the electric cable is heavier than the classic ca-ble and limits the maximum reachaca-ble altitude, therefore lim-iting the maximum harvested energy. The problem of the bat-tery solution is that the vertical flight duration depends on the mass of the battery. In order to minimize the number of land-ings and takeoffs, we need to have enough energy to remain in flight during the period where there is no sufficient air, or to have enough energy to reach altitudes where the wind can lift the system’s weight. Reverse pumping brings a partial solution to these problems.
The proposed reverse pumping method can be decomposed in two phases, the kinetic charge and the potential transfer phas-es (Fig 2). During the kinetic charge phase, the amount of ener-gy ΔEt will be consumed on the ground by pulling the kite with
the rope. As a consequence, the kite will increase its kinetic energy by ΔEc. The gained energy will be transformed into
po-tential energy ΔEp by taking height during the potential
trans-fer phase. At the end of the cycle, the total energy of the kite should remain
great-er than or equal to its initial value, even in the presence of en-ergy losses ΔElost.
The kite’s energy variations obey the following equation, ΔEt =ΔEc +ΔEp +ΔElost
Using this method, the kite can stay in flight even in the ab-sence of wind. The reported study is composed of a the-oretical investiga-tion of the reverse pumping, the numer-ical simulations ap-plied to a twin kites system and finally, the validation of our simulations on our experimental setup (Fig 1).
Fig.1. The twin kite system used for the reverse pumping experiment.
Fig.2. Energy variations during the kinetic charge phase and the potential transfer phase. Note that the final height is greater than its initial value.
