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Vertical Axis Wind Turbines

Vertical Wind Generators

Vertical axis wind turbines (Vawt's) are usually created from lift-based or drag based designs. Drag based vertical axis wind turbines work with something similar to the paddles utilized to push a canoe though the water. Assuming that the paddle used to push the canoe does not slip, your maximum speed will be similar to the drag of your paddle. This is similar with wind; the 3-cup anemometer for measuring wind speed is a drag based VAWT. If the cup’s velocity is similar to the wind speed, it can be said that the instrument is working with a tip speed ratio of 1. These cups cannot go faster than the wind, so TSR will always be 1 or less. Lift based models can provide more power and more efficiency than drag based turbines.

H-type vertical axis wind turbine

However, drag based VAWTs can still be useful as they can be created in different ways using paddles, sails, buckets, or oil drums. A Savonious rotor is an S-shaped turbine that can exceed a Tip speed ratio of 1, but may yield a higher torque. These are used for grinding grains and pumping water but they are not used for generating electricity. What is best for producing electricity is usually those that have a 1000 or above RPM, but drag based are usually at 100 RPM only. 

The eggbeater of the lift based VAWT has a maximum lift of blades at 2 per revolution. This makes a bigger torque output similar to that of a bicycle. Its long blades also produce unwanted natural vibration frequencies. VAWTs are also hard to put up high on towers to capture the higher levels of wind. These turbines are usually kept erect using guy cables, which compel a bigger thrust loading on the turbine bearings.

Another kind of VAWT is the cycloturbine, which is a kind of Giromill. This employs a wind vane to mechanically orient the blades pitch change utility. There are only a few references regarding vertical axis wind turbines, but there is alot of research currently underway on this technology. VAWT's have not been as popular as the horizontal variety in the commercial market for wind turbines. The cycloturbine was available on the market for many years, Giromill never come up from the research phase, and Darrieus went bankrupt. 

Darrieus Windmill

Vertical Axis Wind Turbines Today

Presently, vertical axis wind turbines are in the minority when they are compared with horizontal windmills. But people interested in VAWT's along with their new technologies are making them a more viable alternative. This variety of windmill and turbines are actually more for home as well as residential use as they are smaller and can be installed on a rooftop or in a backyard.

Some of the benefits of VAWT's are:

• They are bird-friendly

• Functions at lower wind speeds

• Can be mounted nearer to the ground

• Can operate in cross winds

• Quieter than other models

Quiet revolution Vawt

The company Bluenergy has recently created a solar-wind hybrid. It combines a VAWT with a sinosoidal blade design coated with flexible solar sheets. They look wonderful, are scalable, and combine the best of these new nechnologies into one. These types of turbines are fast becoming popular and many current VAWT's are aesthetically designed to be pleasant to homeowners.

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