Residential Wind Power

As you will probably recall, classical water wheels let the water arrive at a right angle (perpendicular) to the rotational axis (shaft) of the water wheel. Among the Vertical wind turbines the Vertical axis wind turbines (VAWTs as some people call them) are a bit like water wheels in that sense. (Some vertical axis turbine types could actually work with a horizontal axis as well, but they would hardly be able to beat the efficiency of a propeller-type turbine).

The only vertical wind turbine which has ever been manufactured commercially at any volume is the Darrieus machine, named after the French engineer Georges Darrieus who patented the design in 1931.The Darrieus machine is characterized by its C-shaped rotor blades which make it look a bit like an eggbeater. It is normally built with two or three blades.

The basic theoretical advantages of a vertical axis machine are:
1) You may place the generator, gearbox etc. on the ground, and you may not need a tower for the machine.
2) You do not need a yaw mechanism to turn the rotor against the wind.
The basic disadvantages are:
1) Wind speeds are very low close to ground level, so although you may save a tower, your wind speeds will be very low on the lower part of your rotor.
2) The overall efficiency of the vertical axis machines is not impressive.
3) The machine is not self-starting (e.g. a Darrieus machine will need a “push” before it starts. This is only a minor inconvenience for a grid connected turbine, however, since you may use the generator as a motor drawing current from the grid to start the machine).
4) The machine may need guy wires to hold it up, but guy wires are impractical in heavily farmed areas.
5) 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. (That is why EOLE 4 in the picture is standing idle).

Vertical wind turbines have the main rotor shaft arranged vertically. Key advantages of this arrangement are that the turbine does not need to be pointed into the wind to be effective. This is an advantage on sites where the wind direction is highly variable. VAWTs can utilize winds from varying directions.
With a vertical axis, the generator and gearbox can be placed near the ground, so the tower doesn’t need to support it, and it is more accessible for maintenance. Drawbacks are that some designs produce pulsating torque. Drag may be created when the blade rotates into the wind.
It is difficult to mount vertical-axis turbines on towers, meaning they are often installed nearer to the base on which they rest, such as the ground or a building rooftop. The wind speed is slower at a lower altitude, so less wind energy is available for a given size turbine. Air flow near the ground and other objects can create turbulent flow, which can introduce issues of vibration, including noise and bearing wear which may increase the maintenance or shorten the service life. However, in the Vertical wind turbines when a turbine is mounted on a rooftop, the building generally redirects wind over the roof and these can double the wind speed at the turbine. If the height of the rooftop mounted turbine tower is approximately 50% of the building height, this is near the optimum for maximum wind energy and minimum wind turbulence.

If you are interested in building your own wind turbine you should have a look at the plans available here.  Many of our readers have built this do it yourself wind turbine for under $100 and are now living off the grid.