Any Way the Wind Blows
Go fly a kite!
Well, don’t take this so seriously. We’re not trying to tell you off, but rather want you to think more about kites as an energy source. What? Kites? Well, yes. And one more thing: it’s about to get exciting.
The real idea: Flying power plants
Whether onshore or offshore, wind turbines belong to the energy mix in Germany. But they do have one drawback, which is that they are firmly anchored and depend on ground-level wind. So why don’t we set our wind turbines out to play? We think the time has come, and that’s where the kites come in.
Even in the Middle Ages, the force of the high-altitude winds helped to transport loads with kite power. With the invention of engines in the 19th century, however, this idea temporarily fell into oblivion. The decisive change brought a variety of developments that we now know from the aviation industry. But thanks to lightweight construction, autopilots and sensors, unmanned kites and gliders are back in the race - and the use of high wind speeds to generate electricity is again within reach.
Flying into the jet stream
Fixed wind turbines can reach a hub height of up to 200 meters. The rotor blade tips produce most of the energy because they rotate the most rapidly. The wind speed increases in higher air layers. There, the high altitude winds sweep over obstacles like trees and hills in the landscape with ease.
Flying kites can climb up to 800 meters to use these jet streams. Physics is on their side, because at twice the wind speed, the power contained in the wind multiplies by eight fold. Near the ground, the wind speed is about five meters per second. High altitude winds reach an average of forty meters per second. This means that the power included in the jet stream is not just eight times, but a whopping 512 times greater than at ground level. Just the decreasing air density reduces the usable power somewhat at higher altitudes.
Green, flexible & cost effective
In addition, one can use kites both very flexibly and precisely. Location and height are variable. Depending on weather conditions and wind speed, wind power can thus be used optimally and, above all, permanently - even at locations in inland areas, which have hitherto been unsuitable due to weak wind speeds for wind turbines.
Employing kites can even lead to improved utilization of facilities. And energy can also be generated directly on site - where it is needed. This considerably reduces the effort required for network expansion and the associated costs. It is estimated that the producer cost per kilowatt hour (kWh) is two cents. This would make electricity production by these flying power plants cheaper than all other renewable or fossil alternatives. However, potential impacts on air transport must also be considered. Similar to conventional power plants, no-fly zones would have to be defined in order to prevent collisions. And the fact that kites are mobile is both a blessing and a curse: when the location changes, the no-fly zones also have to be adjusted.
Flying wind turbines: complex technology, but in principle, simple
Airplanes are heavier than air. And yet they overcome great distances faster than other means of transport. What’s crucial is the boost. Flying wind turbine engines use the same principle. They convert some of the wind energy into buoyancy and hold themselves through sails in the air. But they don’t have to remain flying in just one area. The kite can also fly in circular movements to increase energy yields. Although these flight movements require the use of control systems, they have a further important advantage on top of better utilization: heavy and expensive components such as the hub, the mast or the center of the rotor blade are eliminated. These components normally reduce the wind efficiency by acting as a natural brake. Kites are thus lighter, cheaper and more effective, since they make the most of wind energy - just like the rotor blade tips of a conventional wind turbine. At the same time, the problem of surface sealing is also eliminated thanks to mobile design.
Energy producing kites are secured by a rope at the ground station, where the generator is also located.
The buoyancy puts tension on the rope. This creates mechanical energy that drives the generator and produces electricity.
Despite the simple principle, there’s a lot of technology in these flying power plants. For a safe flight and an optimal wind energy yield, sensors must permanently check a variety of parameters. These include, for example, data on the wind speed, wind direction, position and movement direction of the kite, as well as rope tension. Take-off and landing are fully automated and depend on the weather conditions. Above all, extreme weather conditions such as storm, cold or heavy rainfall will put the resilience of this still young technology to the test.
Just hot air?
The fact that flying wind power systems are not just science fiction, but already can contribute to energy demand, is shown by our current project in Ireland.
Together with Ampyx Power, a leading company in the aerospace energy industry, we are making this technology fit for the energy market. A team of fifty engineers is currently working on the construction of an offshore test center on the green island. The project, with a capacity of two megawatts, is intended to test the profitability of the flying wind energy systems and to pave the way for further sites.
Opportunities and challenges at a glance
- Very favorable production costs
- Lower costs thanks to 90% less material consumption from the lightweight design
- Less performance fluctuations due to constant wind speeds, resulting in higher capacity utilization
- At least 6000 full load hours per year - even in inland areas. Comparison: Offshore plants can have up to 4000 full load hours, onshore plants reach 2000 full load hours
- Increased mobility and flexible application possibilities, capable of changing flight altitude based on wind speed
- Reduced land use and less impact on the landscape, no dismantling required, fewer problems with bird protection
- The air density decreases at higher altitudes. This reduces usable power
- High wind speeds create greater load on the materials
- Possible problems due to material fatigue, icing or falling under extreme weather conditions
- High requirements for automated processes (permanent monitoring of flight parameters, autopilot, automatic take-off and landing operations)
- Possible impact on air traffic, definition of no-fly zones required