Vertical Axis Wind Turbines (VAWT) are less frequently used for wind power today than Horizontal Axis Wind Turbines (HAWT). The difference between these two designs is where the axis is located in relation to the blades.
VAWT are similar to how a "classic water wheel" operates. The water arrives at a perpendicular angle to the 'rotational' axis, which is the shaft of the water wheel.
There are 2 Vertical Axis Wind Turbines we see today..
1. Darrieus Wind Turbine
This Vertical Axis Wind Turbine's design was developed in the late 1920/early 1930 by French Engineer, Georges Darrieus. His machine has two to three C-shaped rotor blades that resemble hand held eggbeaters.
2. Savonius Wind Turbine
Savonius Wind Turbines was invented by Sigurd J. Savonius in 1922. He was a Finnish Engineer.
This drag based turbine can be designed in a variety of ways. The 'two' or 'three' scoop turbine can be made with buckets, steel drums, sails, and paddles....and when viewed from the top the rotor is 'S' shaped. The curvature of the scoops experience less drag when moving against the wind than when moving with it. This design is relatively easy to make but has it drawbacks as where its effectiveness to produce enough torque to turn the blades is very low.
Anton Flettner, a German aircraft Engineer developed what is known as the Flettner Ventilator in the 1920. This cooling device has been seen on the top of buses and vans. He used the Savonius turbine to drive the extractor fan in the ventilator.
Advantages and Disadvantage of VAWT
The controls and mechanics, ie: generator, gears, etc are located on the ground verses high on a tower.
As with a Horizontal Axis Wind Turbine, they do not require a tail or a 'yaw' mechanism to turn the rotor against the wind.
Some Disadvantages are:
Main disadvantage is the overall efficiency of VAWT. The speed of wind nearer to the ground is lower, therefore the low wind speeds will be low on the bottom half of the rotor.
Changing the main bearing in the rotor requires disassembling the whole turbine.
This machines needs a push to start. It does not start by itself. Other mechanical or electrical devices may be needed.
Guy Wires might be needed to hold turbine up which can be awkward in this particular design.