Anyone who has flown a kite in a windy breeze knows how powerful the wind can be. With this kid toy as a model, some companies want to generate power in the future: they plan to allow kites to spin through the air at several hundred meters in order to produce electricity. There, the wind blows much stronger and more evenly than on the lower layers. This is the reason why traditional wind turbines are launched into the sky. The average height of new turbines on Earth today is 200 meters, measured to the tip of the rotor blades. However, the scope for further growth is not so great. In turn, dragon power plants can go to a much higher level for them.
The forces are especially strong when the rockets are not standing in the wind, but swaying back and forth. says Florian Bauer, co-founder and managing director of Kitekraft from Oberpfaffenhofen. The spin-off of the Technical University of Munich has developed a kite made of aluminum and carbon, in which several small wind turbines are integrated. When the plant glides through the air, they generate electricity. Conductors in the guide rope transmit power to the ground. In order to get the kite airborne and land it again, Kitecraft designers designed the electrical unit of the system so that the rotors could also be used as propellers.
If possible this year, the company wants to operate the kite with a wingspan of 2.5 meters in continuous operation to demonstrate the robustness and safety of the concept. Within two years, a ten-meter system will be on the market that will produce an output of 100 kilowatts – forty the output of a typical wind turbine on Earth. “In the future, we’re aiming for distances of more than 20 metres. This would make power in the megawatt range possible,” says Bauer.
Electricity can be generated at height or on the ground
Kitecraft’s technology competes with another concept used by companies such as Hamburg’s Skysails, Enerkíte from Brandenburg and Kitepower from the Netherlands: Instead of generating electricity at high altitudes, they use a ground-mounted generator. It is propelled by the unwinding of the rope as the kite boards – which also moves in the form of eight lanes. Once the missile reaches its maximum flight altitude, it automatically assumes a position with low wind resistance, so that it can be towed close to the ground with little energy expended. Then the cycle can start again.
For Sarah Barber, head of the wind energy department at the Swiss Eastern University of Applied Sciences, kite power plants are particularly attractive because they allow the use of high wind speeds. “The output increases with speed to the power of three,” says the scientist. “A doubling of wind speed means eight times the output. That is why it is generally important to increase wind power.”
However, she is not sure that this concept will actually last – there are still several hurdles in the way. “Manufacturers must first demonstrate that the systems can withstand long-term variable mechanical loads,” Barber explains. There is still a lot to do with the controls. After all, keeping kites on course, launching and landing them safely isn’t a trivial thing, says Barber. According to the researcher, the biggest challenge is obtaining permits to operate the kites. To date, there are no regulations under which the authorities can give the green light.
If these tasks can be solved, the question remains: are paper power plants even necessary for the energy transition, given that wind turbines and solar parks already provide climate-neutral electricity at unbeatably low prices? Kitecraft chief Bauer is convinced that in the future systems with an output of 100 kilowatts will be able to generate power as cheaply as conventional wind turbines, in part due to lower material requirements. But they also have two unique features: “On the one hand, flying wind turbines are almost invisible,” says Bauer. “This makes it possible to use wind energy sites where conventional systems are out of the question for landscape protection reasons.” And secondly, it can be transported to the installation site without heavy transportation.
But it’s also possible without them, says Philip Bechtel, who researches kite power plants at the University of Bonn’s Institute of Physics, among other things. “We don’t necessarily need flight systems for power transmission, the necessary technologies have been around for a long time.” However, in some outlets, it can be a useful addition, says Bechtle. He cites the association with solar gardens as a potential application area. There they can generate electricity when the PV system is weakened by thick clouds or darkness.
“In this way, the connection to the power grid can be better used. This makes the whole system more economical,” says the scientist. In the short term, he sees potential where expensive and dirty diesel generators still generate electricity today, for example on islands or in remote locations. “This will be the entry market for system manufacturers,” says Bechtle. It should also be easier to get a permit to operate the power kites there.