Vertical axis wind turbines for urban applications

As horizontal-shaft wind turbines (HAWTs) increase in size, they become more visually and audibly disturbing. This limits the use of the energy resource of wind in cities as even small turbines of a few tens of kW capacity require tall masts and are deemed visually unpleasant. The challenge to produce a wind turbine with the same capacity as rooftop solar has led to the development of a range of vertical-axis wind turbines (VAWT).

An advantage of wind over solar power is that it can blow continuously, and there is a distinct advantage in using wind as a power source for behind-the-meter applications. A wide range of different designs for VAWT have appeared, both in research fields and on the market, but few seem to have been successful, many simply being novelties. The most common are the rotating advertising signs at service stations. Many types have failed because the basic construction is visually unattractive. Nevertheless, VAWT offers a number of advantages.

Fig. 1: Savonius VAWT principle [1].

Advantages of VAWTs over HAWTs

Among the critical differences between VAWTs and HAWTs are the following:

  • VAWTs do not need control systems to point the rotors into the wind, they are able to rotate regardless of wind direction, giving a much simpler mounting design.
  • The noise level is much lower than that of HAWT.
  • Visual disturbance is lower (depending on the design).
  • The ability to operate in turbulent conditions.
  • VAWTs occupy a smaller footprint so they can be used in confined physical locations or can be positioned close together.
  • Savonius rotors are able to start rotating with slower wind speeds and can, consequently, generate power from these low wind speeds.
  • Savonius turbines rotate slower than aerodynamic driven rotors so they impart a different mechanical load to their support structure…(more)

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