New philosophy for new technologyTo achieve change in energy policy, innovative technology for power generation is needed. Unfortunately, many alternative concepts are based on inventions that are more reminiscent of the steam engine era than of modern solutions. Without a doubt, this technology also works. However, like the steam locomotive, which is much more resource intensive than modern three-phase locomotives with respect to construction and operation, it rather contradicts an ecological approach. A great amount of material is needed to construct windmills, since the rotor and the heavy generator act on the tower with bending moments and with enormous static loads. Overload events complicate the dilemma: a tower cannot be simply retracted in the event of a hurricane. To safely dissipate the forces, massive concrete or pile foundations, which are a major cost factor and require a large amount of energy, are therefore needed. With respect to their size and expense, the subterranean structures look more like the 2 m thick steel domes of nuclear reactors than ecological structures. Off the coast, the manufacture of the foundations is particularly complex and expensive, and dismantling after use is rather doubtful.
While the kites likewise operate according to an ancient principle for utilizing the wind, the method is refined through the use of modern material and control technology. In order to produce power, a generator is needed in which a magnetic field rotates in a coil. Conventionally, the rotational movement is transferred via heavy, rigid rods and shafts. The developers from Berlin instead use lightweight, high-performance ropes made of heavy-duty fibres for power transmission. Peter Kövesdi, design engineer and specialist for wind systems at EnerKite, offers a visual comparison: "Just like you can use thin spokes placed under tension to make a wheel that uses much less material than one which is solid, ropes can be used to transfer large forces with very little material."
Focus on efficiencyWith the EnerKite, a flexible kite – a so-called parafoil – is brought to a height of approximately 150 m. There, unlike on the ground, the wind blows constantly, largely free of turbulence and at higher speed. One load rope and two control ropes transfer the pulling force of the kite to three generator drums. The kite is then "pulled" by the wind automatically from 100 m to 300 m, thereby generating the effective power. Once it has reached the maximum altitude, the kite is controlled in such a way so as to turn it out of the wind and the ropes are quickly drawn in. Very little energy is necessary for this purpose. Afterwards, the kite begins to climb, thereby generating power again.
Peter Kövesdi compares the good aerodynamic properties of the kite to the "down-to-earth" solutions as follows: "The advantage of the kite over windmills is the better utilization of the wind, as there is no turbulence caused by upwind rotor blades or by the tower. The kite is also always at an altitude in excess of 100 m and not, like the rotors, intermittently closer to the ground and intermittently higher than the tower. Thus, the technology can be designed for more uniform loading; in the event of a storm, the kite can be drawn in. This, too, reduces construction costs. The slow movement of the rope while the kite is close to the ground prevents collisions with birds, and the soft parafoil eliminates the risk of falling ice, as ice accumulations quickly flake off."
At sea, simple anchor buoys suffice for securing the generator pontoon; on land the turbine can be both stationary as well as mobile. Large access aisles for giant rotor blades and tower elements are not necessary. A kite can simply be rolled up like a tent; the same applies for the ropes.