Wind energy is produced by the movement of air. This movement is converted into power for human use. Wind has been used as a source of energy for thousands of years but was replaced by coal, gas and oil for much of the 20th century. Today, wind is making a comeback as a source of electricity and power.
Horizontal-axis wind turbines (HAWTs) are the most familiar type of electricity-producing windmill. Most have three large blades that spin parallel to their towers, where the main rotor and generator are located.
Most HAWTs are painted white to help make them visible to low-flying aircraft. They stand about 61 to 91 meters (200 to 300 feet) tall, and the blades rotate at 10 to 20 rotations a minute.
The enormous, stiff blades on a HAWT usually face the wind. A wind vane or wind sensor determines which way the wind is blowing, and turns the turbine to face the oncoming wind.
Vertical-axis wind turbines (VAWTs) have varied, unusually shaped blades that rotate in complete circles around a tower. The main rotor and generator are located near the ground. VAWTs do not have to face the wind to generate electricity. Vertical-axis wind turbines can be much smaller than their horizontal counterparts. They are often installed on the roofs of buildings.
Turbines cannot operate at every wind speed. If winds are too strong, they can be damaged. Therefore, the turbine has an automatic controller that turns on when winds are blowing at ideal speeds for generating electricity. This speed is usually 13 to 88 kilometers per hour (8 to 55 miles per hour). If the winds become stronger than that, the controller turns the turbine off.
To generate a large amount of electricity, wind turbines are often constructed in large groups called wind farms. Wind farms are made up of hundreds of turbines, spaced out over often hundreds of acres.
Wind farms are often located in agricultural areas, where the land between the turbines can still be used for farming. Grazing animals are unaffected by the large, slow-moving turbines. In the United States, the "Corn Belt" overlaps with the "Wind Belt," an area across the Midwest that is ideal for harvesting crops and wind. Wind turbines tower over farmland in Iowa, Nebraska and Kansas.
Wind farms can also be located offshore. These turbines use the stronger, more predictable, and more frequent winds that develop above the ocean.
Technology is also being developed to create wind farms at extremely high altitudes. Jet streams are fast-moving winds that blow at elevations of 9753 meters (32,000 feet). Scientists are developing a wind turbine that would be tied to the ground like a kite, but float thousands of meters in the air to capture jet streams' energy for electricity.
Wind is inconsistent and can be difficult to predict. Its speed and direction change frequently, depending on other conditions, such as temperature, humidity and season. Today, this unpredictability makes wind power a poor candidate to be the primary source of energy. However, it can be an excellent addition to traditional power sources.
Windmills And The Evolution of Wind Energy
For thousands of years, people have harnessed the energy of the wind. They used wind to power boats and to cool homes. The ancient Greek engineer Heron of Alexandria designed the world's first windmill almost 2,000 years ago.
Windmills work similarly to wind turbines. In fact, the only difference between windmills and wind turbines is in how the energy they harness is used. Wind turbines generate electricity. Windmills were originally designed to grind grain and pump water.
In both ancient and modern windmills, a drive shaft connects the rotating blades to two large wheels, or millstones, on the floor of the windmill. The wind rotates the blades, the blades rotate the drive shaft, and the drive shaft rotates the millstones. Grain, such as barley, is poured into the hollow, rotating millstone and crushed into flour as the wheels grind together. Wind pumps, or water-pumping windmills, operate similarly.
Wind pumps have as many as a dozen rotating blades. Rotation of these blades causes a long rod to move up and down, and the motion of the rod raises and lowers a cylinder. During the down stroke the cylinder fills with water, and during the up stroke, the water is raised to a pipe or well. Wind pumps are still a familiar sight in many parts of the world.
Eventually, wind turbines were developed to generate electricity in Europe and North America. The first wind turbine generated electricity for the Maykirk, Scotland, home of inventor James Blyth in 1887.
However, wind energy fell out of favor in the 20th century. Fuels such as coal, oil and natural gas were seen as more reliable sources of electricity and energy. By the 1970s, though, the growing environmental movement had led people to seek less-polluting sources of energy. The world's first wind farm, a cluster of 20 turbines, was established during this time in New Hampshire.
Today, wind farms are constructed in many areas. The United States has the largest capacity for wind energy in the world and has developed wind farms in the Midwest, deserts and foothills. The largest wind farm in the United States is the Alta Wind Energy Center in Kern County, California, which consists of more than 300 turbines.
There are many advantages to using the wind's energy to create electricity.
- Wind occurs naturally and cannot be used up.
- Wind is a clean source of energy. Turbines have no emissions and do not pollute the air.
- Wind energy is cheap! In the United States, it costs between 4 cents and 6 cents per kilowatt-hour.
- Wind is generated all over the planet, and wind turbines can be installed economically almost everywhere.
There are also many challenges in using wind energy:
- Even though wind energy is cheap, the initial cost to build a wind farm is quite high.
- Wind farms require acres of land and must compete with other uses. When planning a wind farm in a hilly area, where winds are steady and strong, trees might need to be cut. This likely destroys habitats of dozens of species.
- Wind turbines can kill bats and birds.
- Offshore wind farms might damage the marine ecosystem. The seafloor must be disturbed and drilled to install a wind turbine.
- Some residents who live near wind farms complain about the noise or appearance of the machinery.
- Locations that produce great amounts of wind energy are often in remote areas, far away from the cities and people who could use it. Transmission lines have to be built to transfer the electricity to the cities.
The biggest problem with wind energy is, of course, the wind itself. When the wind is not blowing, electricity cannot be generated.
Anemometers are devices that measure wind speed and direction. They are used to show whether there is enough wind energy at a site to make a wind turbine economically practical.
Most windmills were used to process grain or pump water. Some also supplied power to mix pigments for paint and grind oil from such materials as peanuts or linseed.
land used for, or capable of, producing crops or raising livestock.
layers of gases surrounding a planet or other celestial body.
term for the rapidly developing economies of Brazil, Russia, India and China.
goods carried by a ship, plane, or other vehicle.
a barrier, usually a natural or artificial wall used to regulate water levels.
instrument or tool that transmits the movement of force (torque) to other pieces of connected machinery.
ability used by some animals to emit high-pitched sounds and determine an object's distance by the time it takes for those sounds to echo.
set of physical phenomena associated with the presence and flow of electric charge.
person who plans the building of things, such as structures (construction engineer) or substances (chemical engineer).
flat area alongside a stream or river that is subject to flooding.
coal, oil, or natural gas. Fossil fuels formed from the remains of ancient plants and animals.
machine that converts one type of energy to another, such as mechanical energy to electricity.
animal that feeds on grasses, trees, and shrubs.
gas in the atmosphere, such as carbon dioxide, methane, water vapor, and ozone, that absorbs solar heat reflected by the surface of the Earth, warming the atmosphere.
environment where an organism lives throughout the year or for shorter periods of time.
part of a body of water deep enough for ships to dock.
(horizontal-axis wind turbine) type of windmill where the rotor is arranged horizontally, the main components are in the tower, and the blades rotate when the device faces the wind.
amount of water vapor in the air.
change in economic and social activities, beginning in the 18th century, brought by the replacement of hand tools with machinery and mass production.
winds speeding through the upper atmosphere.
community of living and nonliving things in the ocean.
area of the United States consisting of the following states: Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, and Wisconsin.
one of a pair of large, flat, circular stones between which grain or other substances are ground.
energy released by reactions among the nuclei of atoms.
land reclaimed from a body of water by dikes and dams, and used for agriculture, housing, or industry.
network of cables or other devices through which electricity is delivered to consumers. Also called an electrical grid.
Canadian provinces of Alberta, Saskatchewan, and Manitoba. Also called the Prairies.
resource that can replenish itself at a similar rate to its use by people.
to turn around a center point or axis.
part of a machine that rotates around a fixed point (stator).
path in a body of water used for trade.
radiation from the sun.
knowledgeable or complex.
level of Earth's atmosphere, extending from 10 kilometers (6 miles) to 50 kilometers (31 miles) above the surface of the Earth.
to increase or add to.
the science of using tools and complex machines to make human life easier or more profitable.
to tie or fasten an object to something else by a long rope (tether).
powerful light waves that are too short for humans to see, but can penetrate Earth's atmosphere. Ultraviolet is often shortened to UV.
(vertical-axis wind turbine) type of windmill where the rotor is arranged vertically, the main components are at the base, and the blades are parallel to the tower, rotating around it.
movement or circulation of fresh air in a closed environment. Also called air circulation.
movement of air (from a high pressure zone to a low pressure zone) caused by the uneven heating of the Earth by the sun.
kinetic energy produced by the movement of air, able to be converted to mechanical power.
area with a large group of wind turbines, used to generate electric power.
instrument that generates power from the force of wind rotating large blades.
windmill used for pumping water from an aquifer or out of a flooded area.
machine that produces power using the motion of wind to turn blades.