Crosswind Kite Power

Research Foci

  • Kite power concepts.
  • Multidisciplinary modeling and optimization of power generating kites.
  • Control of power generating kites.

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Short Description

Kites, or tethered wings, are promising alternatives to harvest wind energy: As shown in Fig. 1, a (rigid) kite is flown in crosswind motions like figure eights (or alternatively circles). The kite has onboard turbines and generators to generate electrical power which is sent to the ground via electric cables integrated in the tether. Due to the high speed of the kite, the relative wind speed at the kite is about a magnitude higher than the actual wind speed, so that the onboard turbines can be small. This concept is called "drag power".

 

Fig.1: Illustration of "drag power"
Fig.1: Illustration of "drag power"

A second possibility for crosswind kite power is shown in Fig. 2: A kite (from soft materials like a paraglider or alternatively from rigid materials like a glider) is tethered to a winch on the ground which is connected to an electrical drive. The kite is flown in crosswind motions with a high lift force and pulls the tether from the winch. Energy is generated by operating the winch drive as generator (generative braking). When the maximum tether length is reached, the kite is flown to a low force position like the zenith, and/or pitched down, and reeled back in. A rigid kite can also dive towards the ground winch for minimal reel in time. During the reel-in phase, only a fraction of the generated energy is dissipated by operating the winch drive as motor. This concept is called “lift power”.

 

Fig. 2: Illustration of "lift power"
Fig. 2: Illustration of "lift power"

Both concepts can generate the same amount of power. Compared to conventional wind turbines, crosswind kite power promises to harvest wind energy at higher altitudes with stronger and steadier winds, but only by needing a fraction of the construction material. Hence, it promises to have a higher capacity factor, lower capital investments, and in the end a lower Levelized Cost Of Electricity (LCOE). Mechanical output powers of two megawatts were already achieved by a commercial soft kite by the company SkySails. A drag power rigid kite with a rated electrical power of 600 kW is currently under development by the company Makani Power/Google.

To contribute to solutions of the crosswind kite power challenges, research at TUM/EAL focuses on a number of aspects. Below is a list of our publications (most of them peer-reviewed). Small-scale demonstrators are beeing built to verify theories and concepts. Moreover, conceptual studies are performed. Fig. 3 shows a screenshot of the in-house developed simulation framework.

Fig. 3: Screenshot of a Kite Power Simulation
Fig. 3: Screenshot of a Kite Power Simulation

Publications