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vertical-axis wind turbine (VAWT)
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A type of wind turbine in which the axis of rotation is perpendicular to the wind stream and the ground. VAWTs work somewhat like a classical water wheel in which water arrives at a right angle (perpendicular) to the rotational axis (shaft) of the water wheel. Vertical-axis wind turbines fall into two major categories: Darrieus turbines and Savonius turbines. Neither type is in wide use today.
The basic theoretical advantages of a vertical axis machine are:
The generator, gearbox etc. may be placed on the ground, and a tower is not essential for the machine
A yaw mechanism isn't needed to turn the rotor against the wind
Wind speeds are very low close to ground level, so although a tower isn't essential, the wind speeds will be very low on the lower part of the rotorSee also horizontal-axis wind turbine.
The overall efficiency of the vertical axis machines is not impressive
The machine is not self-starting, i.e. a Darrieus machine needs a "push" before it will start. This is only a minor inconvenience for a grid-connected turbine, however, since the generator may be used as a motor drawing current from the grid to to start the machine
The machine may need guy wires to hold it up, but guy wires are impractical in heavily farmed areas
Replacing the main bearing for the rotor necessitates removing the rotor on both a horizontal and a vertical axis machine. In the case of the latter, it means tearing the whole machine down
Related category
• WIND POWER
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