Vertical Axis Wind Turbines, no real alternative to horizontal axis turbines

Most people have never seen vertical axis wind turbines, also known as the “egg beaters” type windmills. These windmills have not in any way replaced the “traditional” horizontal axis wind turbine because they are simply not as efficient in turning wind power into energy. It says a lot that the great wind farms of the world, including offshore farms that generate electricity for the utility companies, make use of horizontal axis turbines.

Experimentation with vertical axis wind turbines has been under way for over a century, most recently in New Mexico, United States. In a sense they are not new innovations. Their scoop mechanism acts in much the same way as the topsails of huge sailing ships in the old days. Windmills of this configuration have historically been used to mill grains and draw water. They are not much good for generating electricity.

In wind turbine terms they are simply horizontal axis wind turbines lying down with their propellers facing the sky. A disadvantage of this style turbine is that it tends to be unsteady and needs guy ropes or wires to anchor it to the earth. Each blade sees maximum lift (torque) only twice per revolution, making for a huge torque (and power) -- just like cranking on a bicycle -- that is not present in horizontal axis wind turbines. They also require gears to help them overcome vibration and reach optimum speed, but torque is lost in this way.

There are two types of vertical axis wind turbines: the “drag” type and the “lift” type. Drag-based designs work like a paddle used to propel a canoe through the water. If you assume that the paddle used to propel your canoe does not slip, then your maximum speed is about the same speed you drag your paddle. The same is true for the wind.

The three-cup anemometers commonly used for measuring wind speed are drag-based vertical-axis wind turbines. If the velocity of the cups is exactly the same as the wind speed, we can say that the instrument is operating with a tip speed ratio (TSR) of 1. The ends of the cups can never go faster than the wind, so the TSR is always 1, or less.

Drag-based vertical axis wind turbines are useful in that hey can be made many different ways with buckets, paddles, sails, and oil drums.  A good turbine of this type might exceed a TSR of 1, but not by much. All of these designs turn relatively slowly, but yield a high torque.
The “lift” type vertical wind turbines look more like egg beaters. Their rotors are joined to the axis at two or more points, while the drag type is joined at only one place.

All vertical wind turbines are very difficult to mount high on a tower to capture the higher level winds. Because of this, they are usually forced to accept the lower, more turbulent winds and produce less in possibly more damaging winds.
Vertical axis wind turbines have not performed well in the commercial wind turbine market. The Darrieus Cylcoturbine was marketed commercially for several years. The Darrieus Giromill never progressed beyond the research stage. In the summer of 1997, the last U.S. Darrieus vertical axis wind turbine company went bankrupt

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