Putting Wind to Work

Wind energy is produced by the movement of air (wind) and converted into power for human use. Wind has been used as a source of energy for more than a thousand years, but was largely replaced by fossil fuels for much of the 20th century. Today, wind is making a comeback as a source of electricity and power.

Wind energy is produced with Wind Turbines—tall, tubular towers with blades rotating at the top. When the wind turns the blades, the blades turn a generator and create electricity. Wind turbines can have a horizontal or vertical axis. The turbines do not actually produce wind energy, directly. The blades turn, convert the energy of wind into rotational energy, a form of mechanical energy, and this energy is in turn converted into electrical energy.

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 HAWT arrays are painted white, to promote visibility to low-flying aircraft. They stand about 60 to 90 meters (200 to 300 feet) tall, and the blades rotate at 10 to 20 rotations a minute.

The enormous, stiff blades on a horizontal-axis wind turbine usually face the wind (upwind). 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 their tower. The main rotor and generator are located near the ground, making maintenance easier and less expensive. VAWTs do not have to be upwind to generate electricity.

Vertical-axis wind turbines can be much smaller than their horizontal counterparts. Standing only five meters (15 feet) tall, these VAWTs can be 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 prime speed for generating electricity. This speed is usually 13 to 90 kilometers per hour (eight to 55 miles per hour). If the winds become stronger than that, the controller turns the turbine off.

Wind Farms
In order 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 hundreds of acres.

One of the largest wind farms in the world is Jaisalmer Wind Park, a series of connected facilities in the state of Rajasthan, India. In April 2012, Jaisalmer produced 1,064 megawatts of electricity, more than any other onshore wind farm in the world at the time.

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 U.S., 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 acres of corn, soy, and alfalfa in the states of Iowa, Nebraska, and Kansas. Some scientists suggest wind turbines may even improve the flow of carbon dioxide to surrounding crops.

Wind farms can also be located offshore. These turbines use the stronger, more predictable, and more frequent winds that develop as cool ocean breezes meet warmer continental winds.

The world’s most powerful offshore wind farms harvest the harsh winds off the coasts of Northern Europe. Walney Wind Farm, for example, is a farm of 102 turbines in the Irish Sea off the coast of Cumbria, England. Walney is the largest offshore wind farm in the world, generating 367 megawatts of power.

Technology is also being developed to create wind farms at extremely high altitudes. Jet streams are fast-moving winds that blow through the stratosphere at elevations of 9,754 meters (32,000 feet). Scientists and engineers are developing a wind turbine that would be tethered to the ground like a kite, but float thousands of meters in the air to capture jet streams’ energy for electricity.

Single wind turbines can be purchased by individuals to generate electricity for their home or business. Progressive Field, home of the Cleveland Guardians baseball team in Cleveland, Ohio, U.S., had an enormous vertical-axis wind turbine. The corkscrew-shaped turbine was expected to generate about 40,000 kilowatt-hours per year, roughly the amount of energy needed to power four homes. However, the turbine was removed in 2013 after being damaged.

Wind turbines depend on wind, which is inconsistent and can be difficult to predict. Although wind is a renewable resource, its speed and direction change frequently, depending on other conditions of the atmosphere, such as temperature, humidity, and season.

Today, this unpredictability makes it a poor substitute for fossil fuels or more powerful renewable energy sources, such as solar energy. Due to most nations' increasing demands on the power grid, wind can be an excellent supplement to traditional power, but not the dominant component in most regions.

Windmills and the Evolution of Wind Energy
For thousands of years, people have harnessed the energy of the wind. Five thousand years ago, wind-powered boats transported people and cargo along the Nile. Thousands of years before air conditioning, ancient engineers used a series of windows and thin slats—a process called natural ventilation—to provide cool breezes to people inside homes or other buildings. The ancient Greek engineer Heron of Alexandria is credited with designing the world’s first windmill.

Windmills function similarly to wind turbines, and ancient cultures had both horizontal-axis windmills and vertical-axis windmills. 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 (mill) grain and pump water.

In both ancient and modern windmills, a drive shaft connects the rotating blades to a series of two large wheels (millstones) on the floor of the windmill. (The housing for these wheels is why windmills have wide, conical shapes while turbines are tall, thin towers.) One millstone is parallel to the ground. The other sits on it, perpendicularly. 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.

Windpumps, or water-pumping windmills, operate similarly. Windpumps have as many as a dozen rotating blades (often called sails), sometimes in two bands. Rotation of the blades causes a rotor to move a long transmission rod up and down. The motion of the transmission rod raises and lowers a piston in a pump made up of a cylinder and two valves. During the downstroke the cylinder fills with water, and during the upstroke the water is raised to a pipe or well. The basic design of windpumps has not changed in more than a thousand years, and these structures are familiar sights across modern Australia, South Africa, Canada’s “Prairie Provinces,” and the American Midwest.

The earliest windmills that were used to grind grain were developed in Sistan, a region in what is today Iran and Afghanistan, in the 600s. The blades on these horizontal-axis windmills were made of sturdy reed mats.

By the 700s, windmills were grinding grain in the Middle East and pumping water in China. European merchants traveling to Asia brought the engineering technology back with them.

Perhaps the most familiar windmill arrays dot the nation of the Netherlands. Dutch windmills powered the massive engineering feat of draining the nation’s floodplains along the coast of the North Sea. As early as the 14th century, Dutch engineers and farmers used windpumps to drain low-lying valleys and erect dikes around the newly exposed land. These tracts, known as polders, were used to expand the Netherlands’ arable land.

Windmills lost some of their importance during the Industrial Revolution in the 1700s and 1800s. Windmills, relying on unpredictable and inconsistent wind, could not keep up with the increasing amount of energy needed to support new factories. New inventions such as the steam engine provided the strong and consistent energy required to operate large machinery and mass production.

Eventually, 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. The first wind turbine synched with a power grid sat atop a hill named Grandpa’s Knob in the U.S. state of Vermont, and only ran for about 1,100 hours in 1941.

Despite the relatively inexpensive and renewable source of energy, wind energy fell out of favor in the 20th century. Fossil fuels such as coal, oil, and natural gas were more reliable sources of electricity and energy.

The Oil Crisis of the 1970s, however, coincided with the growing environmental movement. People again began to seek cheaper, more sustainable sources of energy. The world’s first wind farm was established during this time: 20 turbines in the foothills of Crotched Mountain, New Hampshire, U.S.

Today, wind farms are constructed in many areas. The U.S. has developed wind farms in the Midwest (where wind turbines share space with agricultural fields), deserts, and foothills. The largest wind farm in the U.S. is the Alta Wind Energy Center in Kern County, California. The wind farm, consisting of more than 300 turbines, sits in the narrow, windy Tehachapi Pass, which connects the San Joaquin Valley to the Mojave Desert.

The quickly industrializing BRIC nations (Brazil, Russia, India, and China) are erecting wind farms across undeveloped land in deserts and the windy foothills of mountain ranges. The Gansu Wind Farm is in China’s Gansu province. The Gansu Wind Farm will be a connected series of wind farms capable of producing a whopping 20,000 megawatts of electricity upon completion.

Developing economies in Africa and Southeast Asia are also investing in wind farms. One of the biggest wind farms is the Lake Turkana Wind Power project, a series of 365 turbines near Lake Turkana, Kenya. The wind farm takes advantage of its site between two mountain systems, where winds are strong, steady, and predictable. When completed, the project will provide electricity to thousands of homes and businesses throughout northern Kenya.

Advantages

There are many advantages to using the wind’s energy to create electricity.

• Wind cannot be used up—it occurs naturally, whether we harness it for electricity or not.
• Wind is a clean source of fuel. Turbines have no emissions and do not pollute the air. This is globally important as more countries industrialize and increase their demand for electricity for homes, businesses, hospitals, and schools. Many schools in the U.S. state of Iowa, for example, have installed wind turbines. Initial investments in the machinery and equipment have been offset by savings of more than $100,000 a year. The schools also emit millions fewer kilograms of carbon dioxide.
• Wind energy is cheap! It is one of the lowest-priced renewable energy sources. In the U.S., it costs between four and six cents per kilowatt-hour. That is cheaper than natural gas, although still more expensive than nuclear energy or coal.
• Wind is generated all over the planet, and wind turbines can be installed economically almost everywhere. This makes it a key resource in developing economies. Nuclear energy, for instance, demands a workforce with substantial educational and engineering backgrounds, as well as an initial investment for nuclear power plants. Development of fossil fuel power plants relies on even more factors: the presence of coal, oil, or gas; the equipment and technology to refine it; and the finances to import or export the raw or refined goods. Nepal, for example, is a developing country with no fossil fuel resources, but it is rich in windy Himalayan mountain passes. Nepalese leaders are developing a policy to invest in wind farm projects using local materials. This would expand the nation’s power grid and allow for greater industrial development.

Challenges
There are also many challenges of using wind energy:

• Even though wind energy is cheap, the initial cost to build the wind farm or install a turbine still costs more than fossil-fuel generators. It may take years to offset the start-up cost.
• Onshore wind farms require acres of land and must compete with other uses. In the U.S. and Australia, the land between turbines is often used for agricultural purposes, and the farmer or rancher who owns the land is paid for renting out sections of his fields. When planning a wind farm in a hilly area, where winds are steady and strong, trees may need to be cut. This destroys habitats of dozens of species and may even impact the larger food web of an area. In Northern Europe, wind farms are often developed in bogs, which are reservoirs of the fossil fuel peat. Developing bogs for the installation of wind turbines may release many kilograms of carbon dioxide and other greenhouse gases.
• Wind turbines can kill bats and birds. Bats’ echolocation does not account for giant spinning blades, and they can be hit. The blades also hit birds and can scare certain species of birds away from their habitats. Potential solutions may not require sophisticated technology. A study that tracked bat deaths around turbines in the U.S. city of Somerset County, Pennsylvania, found that fatalities fell by more than half when turbines simply stopped operating during periods of very low wind activity. Other solutions include using ultraviolet (UV) light to improve the way bats perceive the moving blades, and designing a device that would imitate sounds that bats would avoid.
• Offshore wind farms may impact the marine ecosystem. The seafloor must be disturbed and drilled to establish a wind turbine . Although wind farms are carefully planned to avoid shipping routes and busy harbors, they may still pose a risk for vessels during violent storms.
• Some residents who live near wind farms complain about the noise or appearance of the machinery.
• Locations that produce great amounts of wind 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 most problematic asset of wind energy is, of course, the wind itself. When the wind is not blowing, electricity cannot be generated.