Horizontal Wind Turbines

Wind Energy

Horizontal axis wind turbines

HAWT

Horizontal-axis wind turbines (HAWT) have the main rotor shaft and electrical generator at the top of a tower, and must be pointed into the wind. Small turbines are pointed by a simple wind vane, while large turbines generally use a wind sensor coupled with a servo motor. Most have a gearbox, which turns the slow rotation of the blades into a quicker rotation that is more suitable to drive a generator.

Since a tower produces turbulence behind it, the turbine is usually pointed upwind of the tower.

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Turbine blades are made stiff to prevent the blades from being pushed into the tower by high winds. Additionally, the blades are placed a considerable distance in front of the tower and are sometimes tilted up a small amount.

Downwind machines have been built, despite the problem of turbulence, because they don't need an additional mechanism for keeping them in line with the wind, and because in high winds, the blades can be allowed to bend which reduces their swept area and thus their wind resistance. Since turbulence leads to fatigue failures, and reliability is so important, most HAWTs are upwind machines.

wind farm turbines

Wind Farm

Turbines used in wind farms for commercial production of electric power are usually three-bladed and pointed into the wind by computer-controlled motors. These have high tip speeds of up to six times the wind speed, high efficiency, and low torque ripple which contribute to good reliability. The blades are usually colored light gray to blend in with the clouds and range in length from 20 to 40 meters (65 to 130 ft) or more. The tubular steel towers range from about 200 to 300 feet (60 to 90 meters) high. The blades rotate at 16-22 revolutions per minute, and a speed increaser gear box steps up the speed of the generator. Some models operate at constant speed, but more energy can be collected by variable-speed turbines which use a solid-state power converter to interface to the transmission system. Most turbines are equipped with high wind shut down features to avoid over speed damage.

Turbine assembly in Norway

Offshore wind farms are a promising area for new renewable power generation. Norway is home to key industrial wind power stakeholders, which build large wind turbines. Currently there are projects for a floating wind turbine technology.

| 01.01.2009 | Read more | Print |

advantages

Wind energy does not pollute the air like power plants that rely on combustion of fossil fuels, such as coal or natural gas. Wind turbines do not produce atmospheric CO2 emissions that cause acid rain or greenhouse gasses.
Wind energy is a domestic source of energy.
Wind energy relies on the renewable power of the wind, which cannot be used up.
Wind energy is one of the lowest-priced renewable energy technologies available today, costing between 4 and 6 cents per kilowatt-hour, depending upon the wind resource and project financing of the particular project.
Wind turbines can be built in farms and ranches, benefiting the economy in rural areas. Farmers and ranchers can continue to work the land because the wind turbines use only a fraction of the land. Wind power plant owners make rent payments to farmer or rancher for the use of the land.

disadvantages

Depending on the wind site, the wind farm may or may not be cost competitive. The wind power technology requires a higher initial investment than fossil-fueled generators.
The major challenge is that the wind is intermittent and it does not always blow when electricity is needed. Wind energy cannot be stored (unless batteries are used); and not all winds can be harnessed to meet the timing of electricity demands. Good wind sites are often located in remote locations or offshore, far from cities where the electricity is needed.
Wind resource development may compete with other uses for the land and those alternative uses may be more highly valued than electricity generation.
There are concerns over the noise produced by the rotor blades, aesthetic (visual) impacts, and sometimes birds have been killed by flying into the rotors. Most of these problems have been resolved or greatly reduced through technological development or by properly locating wind plants.