Environmental Engineering Reference
In-Depth Information
The most intuitive method of harnessing wind power is with a turbine that turns like a
carousel on a vertical axis. The Finnish engineer Sigurd Savonius perfected this design in
the early twentieth century. Because the vanes are curved, one side catches more drag than
the other does. This causes it to turn, regardless of the wind's direction. The Savonius wind
turbine is used to this day, most commonly as part of a cooling device on the roofs of vans
and buses. Another relatively common type of vertical-axis wind turbine (VAWT) is the
Darrieus turbine, also named after its inventor. The Darrieus is more mysterious than the
Savonius; indeed, without an understanding of aerodynamics it's hard to understand how it
turns at all. VAWTs are mostly confined to small-scale applications, such as rooftops and
small concentrated wind farms.
Figure 4.10.
Savonius (left) and Darrieus (right) vertical-axis wind turbines.
Source:
aarchiba (left) and Toshihiro Oimatsu (right) at Wikimedia Commons.
Figure 4.11.
Horizontal-axis turbines. The famous Don Quixote-style windmill in
Spain, a small-scale turbine (1 kilowatt) for localized electricity production, and a modern
wind farm consisting of several wind turbines, each with a capacity of 1 megawatt.
Sources:
Jan Drewes at Wikimedia Commons (top left); Eclectic Energy Ltd. (top right);
Gian Andrea Pagnoni (bottom).
While the Savonius wind turbine relies largely on drag, and the Darrieus on lift, the
most commonly used type of wind turbine - the horizontal-axis wind turbine (HAWT)
- employs a combination of both forces. The HAWT is like an outsize version of the
pinwheel toys many of us played with as children. Commercial HAWTs vary in size from
the small turbines installed on sailing boats with a rotor diameter of less than 1 metre that
generate less than 1 kilowatt, to giant turbines more than 100 metres tall generating up to 7
megawatts of power.
When discussing the mechanics of wind turbines with my friends I've been amazed
to discover that many of them believed that they function in much the same way as a
waterwheel, with air substituted for water. They believed that the wind hit the rotors of the
