Assessment of an Alternative Concept for a High-Altitude Wind-Power Generator

Abstract

To generate power from high-altitude winds, concepts using kites or planes linked to the ground with tether are in development. The most popular high-altitude wind generation concept is one using a flying wing attached to a single tether whose movement generates power by turning a winch. The usual trajectories for power generation consist of a period where the kite distance is increased, and the pulling force enlarged by figure-of- eight movements, interrupted by a pull-back phase where power is consumed. We compare that with a new concept we introduce here. It uses a triplet of tethers whose length sum is kept more or less constant using differential gears, resulting in a trajectory surface. It does not have a pull-back phase and allows to have similar power output in a closed trajectory. Moreover, starting and landing can be achieved without additional equipment when using a soft kite as wing, and keeping the wing flying without any wind is easier. Also the control can be easier, as one has more degrees of freedom in the force direction and the movement of the kite. Its disadvantages are an increased effort for the ground stations and more restrictions on the location. Also the tether’s air drag is increased. Optimal power generation is compared using an example configuration and state with given wind speed under the assumption of an optimal steering of the generators and the kites. This is done for state snapshots, for example trajectories, wind speeds, and kites.