B a c kg r o u n d
Energy
Kitepower sails toward energy transition As the energy transition gets wind beneath its wings, one Yes!Delft start-up is drawing inspiration from Dutch astronaut and professor, the late Wubbo Ockels. Its solution: fly kites in order to harness wind energy and convert it into usable power. Credit: Kitepower, CC BY-NC-ND
Collin Arocho
A
fter becoming the first Dutchman to go to space, Wubbo Ockels began working as a professor of aerospace engineering at Delft University of Technology (TU Delft). In 1997, inspired by a friction burn he received while flying his kite, O ckels applied for a patent on a technology that could harness the energy of the wind and convert it into usable power. Just a year later, he was awarded the first-ever patent on laddermill technology – a kite- controlled, airborne turbine that can collect and store energy from the blowing wind. In 2004, Ockels founded the kite power research group at TU Delft. The unit was designed to tackle scientific challenges like aerodynamics and automatic flight control of the tethered wing structure, as well as to design efficient generators to store the collected power. In 2016, after several years of technology development and product design, Kitepower was spun out of the university, lifting off with CEO Johannes Peschel holding the string. His goal: to bring this inexpensive and highly mobile system of clean energy generation to the market.
Pump action
Fundamentally, the Kitepower system is a relatively simple concept. A kite is attached to a long lead line made from dyneema – a lightweight, ultra-strong material. Ideally, this line will fly the kite a few hundred meters in the sky to catch the best wind. Going too high, however, would have a deleterious effect, as the increased drag on the line would hinder its performance. The dyneema lead is wound around and connected to a drum winch on the ground. 18
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The kites come in various sizes, 40, 60 and 100 m2, and are made from a super-light material, similar to that found in the sailing world.
When the sail takes off in the wind, the attached line is then pulled with it, turning the drum and driving a generator to create energy. Once deployed to a specified length, the kite is tilted out of the direct wind stream and reeled in by the turning winch. After being hauled in, the kite is tipped into the wind current and again pulled out by the force of the wind, completing this cycle repetitiously to create power. “It acts similar to a glider. We tip the kite and pull it back in very quickly. By doing this repeatedly, we’re actually creating energy through this pumping action,” explains Kitepower technical manager Joep Breuer. “While reeling back in, we’re using less than 10 percent of the energy that’s created from being pulled out. To be honest, the energy use is actually not the problem at all. The biggest obstacle is the time we use, because that’s time we’re not able to produce power, so we have to buffer.”
wind, in a cross wind, allowing it to go faster. As the speed of a kite increases, there’s a quadratic rise in the pulling force of the string, which yields more energy from the generator. To maintain this optimal path, Kitepower has developed a kite control unit, which utilizes motors to adjust the pitch and direction of the sail, maximizing efficiency and power production. “This kite control unit works much the same ways as a kitesurfer. It has two main motors, one to steer left and right and the other one to adjust the pitch to very quickly control the lift and drag on the kite,” describes Breuer. “We’ve also implemented GPS systems and a series of sensors to determine the position and orientation of the kite. This unit holds the intelligence of the system and can independently decide where the kite will fly, while we monitor on the ground through a wireless downlink.”
Kitesurfing
Despite the potential of this clean-energy solution, there’s still much to be determined. While the company’s first systems are being planned for deployment in Curacao in 2021, currently, the 20-man Kitepower team is
To generate maximum power, the engineers at Kitepower have adopted a specific flight path for the kite – a figure eight. This keeps the kite flying perpendicular to the
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