The flying power plant
The Empa spin-off TwingTec is working on small power plants in the form of kites. Last fall, TwingTec succeeded for the first time in taking off automatically, generating electrical energy while flying and landing again. Commercialization is thus within reach.
The TwingTec prototype T 28 - a power plant? Anyone who has ever steered a child's kite knows the feeling: the wind grabs the kite, pulling on the string. In a hurry, you slacken the rope, the pulley rotates, difficult to control, between your fingers. And the question arises: Could this wild energy be used not only to play, but also to generate electricity? Yes, you can. Rolf Luchsinger has proven it. He is CEO of Empa spin-off TwingTec, founded in 2013, making it one of the first companies to develop airborne wind turbines - and a nose ahead of some of its competitors. The young company employs nine people at its headquarters in Dübendorf.
Cycle climb
The idea behind the project is simple, but the practice is tricky: Meteorologists know that at 500 meters, the power of the wind is up to eight times stronger than at 120 meters - the hub height of modern wind turbines. A kite could take advantage of this strong wind by spiraling upward in circular paths and pulling a rope from a pulley. Connected to the axis of the pulley is a generator that produces electricity. Once the rope is unwound, the kite sinks back near the launch platform without propulsion; meanwhile, the rope is rewound, then the ascent begins again. "The big challenge is not the flying itself," Luchsinger says. "The problem is the automated launch and landing." After all, the kite power plant should be able to supply electricity without being controlled by humans.
Automated flight successful
In the fall of 2018, that's exactly what happened on the heights of the Chasseral in western Switzerland. The TwingTec prototype T 28, a device with a three-meter wingspan, took off from its base vehicle, spiraled upward, circled autonomously in the air for 30 minutes, produced electrical energy, and finally landed safely back on the launch platform. Now comes the next step: continuous power generation for customers. Luchsinger's team is currently working on the T 29 prototype, which is scheduled to make its first flights near Chasseral in the fall. T 29 will not only take off and land automatically, but also generate up to 10 kW of electrical power and feed it into the grid. Berner Kraftwerke BKW is taking care of the transmission of the experimental wind power to consumers.
However, the road from the first sketch to the first kilowatt-hour of grid power was long and winding. It started with the idea of using a stunt kite reinforced with compressed air, similar to kite surfing. Research on a series of prototypes then initially led away from sails to a structure with rigid wings. Steering by means of multiple ropes was also discarded in favor of control by flaps as in an airplane. For takeoff and landing, TwingTec used small rotors, similar to a drone. In 2014, TwingTec filed a groundbreaking patent for the energy kite's takeoff and landing technology, which has since been granted in several countries. A look at the numerous competitors shows how promising energy kites could soon be:
In Europe alone, ten start-ups and several teams from universities and technical colleges are developing solutions for this type of energy generation. They are all members of the "Airborne Wind Europe" association, which organizes a major conference every two years. The 8th Airborne Wind Energy Conference (AWEC 2019) will be held October 15-16, 2019, at the University of Strathclyde, Glasgow.
Commercialization in focus
So TwingTec cannot afford to take too much time and is preparing for the next step. The findings from the flight tests with the T 29 should soon lead to the first series product: the TT100, an energy kite with a 15-meter wingspan. Positioned on a standard shipping container, the kite is to take off and land autonomously and generate up to 100 kW of electrical power - that would be enough for 60 single-family homes. However, series production requires a lot of capital. The T 29 prototype, which is scheduled to fly at Chasseral in the fall, is supported by the Swiss Federal Office of Energy (SFOE). For the commercialization phase thereafter, however, private investors and partners from the energy industry are now being sought so that the enormous potential of wind power can finally be fully exploited.
