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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.
After 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, Ockels 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.
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.
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.”
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 wind, in a crosswind, 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.”
Replace mass with intelligence
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 still in the testing phase of its business development. But as engineers are out test-driving the system at the Valkenburg airfield, a growing number of the conventional wind turbines are popping up and spinning freely across the European landscape. Once installed, these massive fans can last for decades and are able to turn 24/7 in unmanned operation – a feat that will prove to be an uphill battle for the young company.
However, notwithstanding these obstacles the Yes!Delft start-up believes it has some very attractive and unique selling points. First, are the physical properties of the Kitepower system. The kites themselves 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. The only difference is the addition of an inflatable support structure to assist in taking off. This is a staggering 95 percent reduction in mass and materials, which equals a reduction in cost. Second, the entire system can be completely contained within a standard 20-foot shipping container, which allows for an unparalleled potential for mobility as the kite-powered solution can be loaded up on a truck and moved for deployment.
“I often say that we replace mass with intelligence. With our computer-optimized flight-path technology, we’re able to adjust and find the best wind in order to extract maximum energy – something a massive wind turbine will never be able to offer,” emphasizes Breuer. “Right now, we’re developing a 100-kilowatt version that should produce about 450 megawatt hours of electricity every year. That’s enough to power around 150 Dutch households on an annual basis.”