An Innovative Approach to Making Electricity From the Wind

By on June 9, 2019

From The Economist:  The wind blows more strongly at higher altitudes. That is why wind turbines have grown ever taller. The blade tips of today’s biggest now reach up a dizzying 260 metres, the height of the Transamerica building in San Francisco. Many dream of capturing stronger winds even higher up than that, but building taller turbine masts and constructing blades able to withstand the terrifying stresses involved in high-altitude wind gathering are costly. A number of firms are therefore developing a different and, they hope, ultimately cheaper approach to generating electricity at great heights. Their idea is to skip the mast altogether. Instead they propose to fly kites.

The kite developed by SkySails, a German firm, is a rectangular parachute-like structure attached to an 800-metre-long tether. This tether starts off coiled around a horizontal drum that is mounted on an axle which is anchored at each end in the shipping container in which the system’s generator is housed.

SkySails’ kite is launched, like a recreational kite, into the wind at ground level. Then, as the kite is pulled up by the wind while being manipulated to travel in a series of figures-of-eight in order to achieve a constant, optimal speed, the tether uncoils, spinning the drum. That powers a generator. Once the tether is fully extended, the kite is angled to catch less wind, reeled partway back in, and allowed to reel out again. In-reeling, according to SkySails’ boss, Stephan Wrage, consumes only 4% of the energy the kite generates on its way out, so the process is pretty efficient.

Let’s go fly a kite

The SkySails Power system, as it is called, goes on sale next year. A single unit will produce 200 kilowatts—enough to run about 100 homes. It will, Mr Wrage says, cost about €300,000 ($340,000). At $1,700 a kilowatt, that is half the cost of a conventional turbine of equivalent capacity, and is comparable with the cost per kilowatt of industrial-scale turbines that have outputs measured in megawatts. Nor is SkySails alone in designing a system that works with a simple, wind-launched kite of this type. Kitepower, a competitor in the Netherlands, has come up with a similar arrangement, albeit somewhat smaller, which it, too, expects to be on sale next year. Other firms, however, are working on kites that are launched actively from the ground, rather than relying on winds near the surface for their initial lift.

One such is TwingTec, a Swiss firm. Its prototype rises dronelike into the air, lifted by electrically driven propellers at the end of its wings (which have a combined span of three metres). The kite then stays aloft until its sensors indicate that the wind has died down, after which it lands itself automatically on a truck-top pad. TwingTec is now building a bigger version, with a wingspan of 5.5 metres, that will begin producing power for BKW Energie, a Swiss utility, in October.

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