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Typically built with only two or three blades, a vertical axis wind turbine (VAWT) is a type of wind turbine in which the main rotor shaft runs vertically rather than horizontally. Though there are different styles of these types of turbines, one version looks much like an eggbeater. Its movement, on the other hand, is similar to a coin spinning on its edge.
When most people hear the phrase “wind turbine,” they visualize a horizontal axis wind turbine (HAWT). A HAWT looks very much like an airplane propeller. The reason people closely associate a HAWT with the wind turbine concept is simply because the vertical axis wind turbine is not as common as its horizontal counterpart. In fact, VAWTs are generally not used for commercial purposes, and they are rarely connected to electric power grids.
Of course, despite their differences in appearance and their distinct modes of operation, both the VAWT and the HAWT generate electricity by converting the wind’s energy into torque using a rotating shaft. That is, wind turns the blades of the wind turbine around the turbine's rotor. That rotor, in turn, is connected to the turbine's main shaft, and that main shaft powers a generator, which generates the electricity.
There are some benefits inherent in the vertical axis wind turbine’s design. The turbine’s generator and gearbox can be placed close to ground level, making maintenance easier and lowering initial construction costs. They also do not need to face the wind like HAWTs, which increases their ability to harness the wind’s power and thereby enhances their overall reliability. Manufacturers also argue the VAWT is less noisy than its HAWT counterpart.
The primary disadvantage associated with the vertical axis wind turbine, however, is that its efficiency is reduced because wind speeds are lower close to the ground. This type of turbine is generally not able to produce as much electricity as the HAWT design. VAWTs do not self-start either, which is a hindrance to power grid connectivity. For these reasons, the vertical axis wind turbine is often selected for installation when cost or reliability is the paramount concern. When total output and efficiency are the most important considerations, the horizontal axis wind turbine is typically used.
Research is being done on VAWTs in an effort to increase their energy output and minimize their mechanical and aerodynamic noise. Engineers hope to improve this type of wind turbine so that it can eventually be widely used in urban landscapes where space for wind farm installations is limited.
Of the many vertical axis wind turbine design types, the two most commonly constructed are the Savonious and the Darrieus turbines. A Finnish engineer named Sigurd J. Savonius invented the simple, drag-type turbine in 1922, and French engineer Georges Jean Marie Darrieus invented his more practical, lift-type turbine in 1927. Other vertical axis wind turbine design types include the turby, quietrevolution, aerotecture, giromill, and cycloturbine.
Detailed calculations regarding the vertical axis wind turbine’s rotor aerodynamics are available online.