Wind energy (or wind energy) is among the cleanest and most renewable sources for producing electricity, but its maintenance costs, intermittency of winds and environmental impact are often an obstacle to building wind farms of big dimensions. The wind blows on average stronger at high altitudes, which in recent years has led to the construction of wind turbines on mountain and coastal reliefs, or on towers hundreds of meters high with a significant increase in construction costs. For some years now, a group of companies has been experimenting with an alternative deemed more efficient and cheaper: using large kites and exploiting their movement to produce electricity.
SkySails, for example, is a German company that is developing a system of large parachutes, similar to those used for paragliding, to be flown at 800 meters and anchored to the ground with a cable. The base, which can be a normal container on land or a floating system in the sea, has a winch that unrolls as the kite gains altitude thanks to the wind. The winch is connected to an electricity generator and, thanks to an automatic system, manages the departure of the kite so that it describes particular movements in the air, which contribute to the production of energy.
Once it reaches 800 meters, the kite is oriented so that it maintains an angle with which it offers less resistance to the wind. At this point, some of the energy produced is used to activate the winch motor, which brings the kite back, ending a cycle; subsequently, the system reactivates and starts all over again. According to SkySails, the recovery phase of the kite consumes 4 per cent of the electricity produced as a whole while taking altitude, describing various movements in the air: the process therefore maintains good energy efficiency.
The design phase of the kite system is almost complete and SkySails is confident of putting the first systems on sale starting next year. A single device will have a power of 200 kilowatts, enough to power a hundred homes. The installation and management of each system will cost an average of 300 thousand euros. At full capacity, SkySails says its solution will cost € 1,500 per kilowatt, roughly half the cost of a traditional wind turbine (which proportionally produces much more electricity).
As the Economist explains in a recent article, SkySails is not the only company experimenting with alternative systems to the classic ones with wind turbines. TwingTec of Switzerland has designed a system that uses some large drones like kites, instead of parachutes. The drone has electric motors to reach the service altitude and is connected with a cable to a winch, connected to an electric current generator. The movements of the drone, guided by the wind at high altitudes, cause the cable to be extended or partially rewound. When the wind at altitude drops below a certain limit, the drone automatically returns to base.
TwingTec's drone has a wingspan of 3 meters, but the company is working on a larger 5.5-meter version of it. The company already has an agreement with the Swiss electricity supplier BKW Energie, with which it will collaborate starting next October.
Ampyx Power, on the other hand, is Dutch and is working on a similar project, again with drones, which, however, are launched into the air via a sort of catapult. The version tested so far has a wingspan of 5.5 meters, but the company is working on much larger drones that can reach 12 meters, although an even more ambitious project aims to bring it to 36 meters by 2024. According to Ampyx Power, at full capacity will have a power of 2.36 megawatts and will cost 2.4 million euros, a price comparable to that of the classic turbines of wind farms.
Other companies believe that the production of electricity can take place directly at high altitude. Makani, recently acquired by Alphabet (the holding that controls Google), plans to use drones with a wingspan of 26 meters with 8 propeller motors used to take them off and take them to altitude. Once the right height is reached, the drone becomes a kind of glider and the propellers are transformed into small wind turbines to produce electricity, which is transported by cable from the drone to the base on the ground. The first tests on the system conducted in Hawaii have led to encouraging results, with an output of up to 600 kilowatts.
It is still not completely clear whether these alternatives can compete with traditional wind, but analysts say the new companies have good potential. Winds above 500 meters are sustained enough to make kites and drones usable in much of Europe. Below that quota, the possibilities of use are reduced and their yield remains sustainable only in coastal areas. The coasts are often heavily populated, which makes the installation of a traditional wind farm impractical or very expensive.
However, many doubts remain about these new technologies, starting with maintenance costs. Kites and cables would be subjected to greater wear than that suffered by traditional wind turbines. Flight safety authorities would also not be too happy to have hundreds of kites and drones in the air, which could interfere with air traffic activities. Their large-scale use would imply the identification of areas that cannot be flown over below a certain altitude. Further doubts are related to safety and systems to recover the drones, in the event of the breakage of the cables that keep them anchored to the ground.
