22.04.21 Innovations: knowing which way the wind blows Author: Hans-Joachim Ziegler • Reading time: 3 min.

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Summary

Conventional wind turbines are getting taller, more powerful, more efficient, and cheaper. But there’s more to wind technology than incremental improvement. We present four unconventional approaches to transforming wind into energy.

1. For the benefit of Mr. Kite

Winds are stronger at higher altitudes, which is why wind turbines are getting taller. But their maximum height is limited by statics. Not surprisingly, dozens of companies worldwide are exploring high-flying, kite-like wind turbines secured to the ground by hundreds of meters of cable. These systems require around 90% less materials to build, deliver twice the energy yield, and, thanks to the steadier winds at their operating altitude, are more reliable than terrestrial wind turbines. The Fraunhofer Institute for Wind Energy Systems estimates that greater reliability could enable airborne wind turbines to produce electricity for two to four cents per kilowatt hour. These systems therefore have the promise of providing clean, affordable energy. So far, however, only prototypes exist.


2. Wind turbines without rotor blades

The rotor blades of wind turbines sometimes reflect light like a disco ball, much to the annoyance of nearby residents. Helpfully, Spanish startup Vortex Bladeless is doing exactly what its name suggests: developing wind power technology that doesn’t need rotor blades. The company’s system, which is only 2.75 meters in height, consists of a vertical cylinder connected by a rod to a stable base. Passing winds cause the cylinder to vibrate. An alternator converts this vibrational energy into electrical energy. The system has few moving parts, which minimizes maintenance costs. Another advantage is that it emits no audible sound. Its output, however, is modest: it would take several Vortex wind machines to power a single household. When (and whether) the system will enter mass production is uncertain.


3. Floating wind turbines

Nobody likes to look out the window at wind turbines. Offshore wind farms pollute the landscape less (unless you live on the coast), but are generally restricted to fairly shallow water since the tower foundations have to be firmly anchored to the seabed. Floating wind turbines, which are moored to the seabed with long cables, would make it possible to site wind farms in deeper water, where the wind yield is greater. Hywind Scotland, a five-turbine floating wind farm with an aggregate capacity of 30 MW, has been in operation since the fall of 2017. Semi-submersible tower-bearing structures provide enough buoyancy to support the weight of the turbine and to keep pitch and roll within acceptable limits. Other installations are planned for the coasts of Scotland, Norway, and France.


4. Vertical-axis turbines

Standard, horizontal-axis wind turbines make noise (“whump, whump, whump”), have to be placed fairly far apart to maximize wind yields, and pose a hazard to birds. Swiss startup Agile Wind Power has produced a three-blade vertical-axis turbine called Vertical Sky that it claims is three times quieter and can be grouped closer together. Not only that: thanks to its slow-rotation concept, Vertical Sky is much safer for birds. Although about 30% less efficient than a horizontal-axis turbine (because one of the three blades is always fighting the wind), vertical-axis turbines may be suitable for settings in which big, noisy conventional turbines wouldn’t be viable.

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