Energy from moving air
Wind is caused by uneven heating of the earth's surface by the sun. Because the earth's surface is made up of different types of land and water, it absorbs the sun's heat at different rates. One example of this uneven heating is the daily wind cycle.
The daily wind cycle
During the day, air above the land heats up faster than air over water. Warm air over land expands and rises, and heavier, cooler air rushes in to take its place, creating wind. At night, the winds are reversed because air cools more rapidly over land than it does over water.
In the same way, the atmospheric winds that circle the earth are created because the land near the earth's equator is hotter than the land near the North Pole and the South Pole.
Wind energy for electricity generation
Today, wind energy is mainly used to generate electricity. Water-pumping windmills were once used throughout the United States and some still operate on farms and ranches, mainly to supply water for livestock.
Electricity generation from wind
How wind turbines work
Wind turbines use blades to collect the wind’s kinetic energy. Wind flows over the blades creating lift (similar to the effect on airplane wings), which causes the blades to turn. The blades are connected to a drive shaft that turns an electric generator, which produces the electricity.
Electricity generation with wind
Total annual U.S. electricity generation from wind energy increased from about 6 billion kilowatthours (kWh) in 2000 to about 435 billion kWh in 2022. In 2022, wind turbines were the source of about 10.2% of total U.S. utility-scale electricity generation. Utility scale includes facilities with at least one megawatt (1,000 kilowatts) of electricity generation capacity
New technologies have decreased the cost of producing electricity from wind, and growth in wind power has been encouraged by government and industry incentives.
Where wind is harnessed
Wind power plants require careful planning
Operating a wind power plant is more complex than simply erecting wind turbines in a windy area. Wind power plant owners must carefully plan where to position wind turbines and must consider how fast and how often the wind blows at the site.
Good places for wind turbines are where the annual average wind speed is at least 9 miles per hour (mph)—or 4 meters per second (m/s)—for small wind turbines and 13 mph (5.8 m/s) for utility-scale turbines. Favorable sites include the tops of smooth, rounded hills; open plains and water; and mountain gaps that funnel and intensify wind. Wind resources are generally more favorable for electricity generation at higher elevations above the earth’s surface. Large wind turbines are placed on towers that range from about 500 feet to as much as 900 feet tall.
Wind speeds are not the same across the country
Wind energy resources vary hourly and seasonally throughout the United States. For example, in Tehachapi, California, where numerous wind turbines are located, the wind blows more frequently from April through October than it does in the winter, and the wind is usually strongest in the afternoon. These fluctuations are a result of the extreme heat of the Mojave Desert during summer months. As the hot air over the desert rises, the cooler, denser air above the Pacific Ocean rushes through the Tehachapi mountain pass to take its place. In Montana, strong winter winds channeled through Rocky Mountain valleys create more intense winds during the winter.
Fortunately, the seasonal variations in wind speeds in California and Montana match the electricity demands of consumers in those states. In California, people use more electricity in the afternoon and during the summer. In Montana, people use more electricity, in general, during the winter.
Locations of U.S. wind power projects
In 2022, 42 states had utility-scale wind power projects, which together produced about 10% (435 billion kilowatthours [kWh]) of total U.S. utility-scale electricity generation.1 The five states with the most electricity generation from wind in 2022 were Texas, Iowa, Oklahoma, Kansas, and Illinois. These states combined produced about 57% of total U.S. wind electricity generation in 2022
International wind power
World wind electricity generation has also increased substantially in recent years. In 1990, 16 countries generated a total of about 3.6 billion kWh of wind electricity. In 2010, 105 countries generated about 340 billion kWh, and in 2020, 129 countries (includes Puerto Rico) generated about 1,597 billion kWh of wind electricity
- The top five countries in wind electricity generation and their shares of world total wind electricity generation in 2021 were:
- United States21%
- United Kingdom4%
Offshore wind power
The waters off the coasts of the United States have significant potential for electricity generation from wind energy. There are currently two operating U.S. offshore wind energy projects: the Block Island wind farm off the coast of Rhode Island, with 30 megawatts (MW) of electricity generation capacity, and the Coastal Virginia Offshore Wind pilot project with 12 MW electricity generation capacity. As of December 2022, wind project developers reported plans for about 7,500 MW of nameplate wind electricity generation capacity in waters off the coasts of Maryland, Massachusetts, New Jersey, Rhode Island, and Virgina, and about 20 MW in Ohio state waters on Lake Erie. European countries and China lead the world in offshore wind electric generation capacity. Many other countries have and are developing offshore wind energy projects.
1Utility-scale includes facilities with a least one megawatt of electricity generation capacity.
Types of wind turbines
There are two basic types of wind turbines:
- Horizontal-axis turbines
- Vertical-axis turbines
The size of wind turbines varies widely. The length of the blades is the biggest factor in determining the amount of electricity a wind turbine can generate. Small wind turbines that can power a single home may have an electricity generating capacity of 10 kilowatts (kW). The largest wind turbines in operation have electricity generating capacities of around 15,000 kW, and larger turbines are in development. Large turbines are often grouped together to create wind power plants, or wind farms, that provide power to electricity grids.
Horizontal-axis turbines are similar to propeller airplane engines
Horizontal-axis turbines have blades like airplane propellers, and they commonly have three blades. The largest horizontal-axis turbines are as tall as 20-story buildings and have blades more than 100 feet long. Taller turbines with longer blades generate more electricity. Nearly all of the wind turbines currently in use are horizontal-axis turbines.
Vertical-axis turbines look like egg beaters
Vertical-axis turbines have blades that are attached to the top and the bottom of a vertical rotor. The most common type of vertical-axis turbine—the Darrieus wind turbine, named after the French engineer Georges Darrieus who patented the design in 1931—looks like a giant, two-bladed egg beater. Some versions of the vertical-axis turbine are 100 feet tall and 50 feet wide. Very few vertical-axis wind turbines are in use today because they do not perform as well as horizontal-axis turbines.
Wind power plants, or wind farms, produce electricity
Wind power plants, or wind farms, are clusters of wind turbines that produce large amounts of electricity. A wind farm usually has many turbines scattered over a large area. One of the United States' largest wind farms is the Horse Hollow Wind Energy Center in Texas, which at the end of 2021, had 422 wind turbines spread over about 47,000 acres. The project has a combined electricity generating capacity of about 735 megawatts (or 735,000 kilowatts).
History of wind power
People have been using wind energy for thousands of years
People used wind energy to propel boats along the Nile River as early as 5,000 BC. By 200 BC, simple wind-powered water pumps were used in China, and windmills with woven-reed blades were grinding grain in Persia and the Middle East.
New ways to use wind energy eventually spread around the world. By the 11th century, people in the Middle East were using windpumps and windmills extensively for food production. Merchants and the Crusaders brought wind technology to Europe. The Dutch developed large windpumps to drain lakes and marshes in the Rhine River Delta. Immigrants from Europe eventually took wind energy technology to the Western Hemisphere.
American colonists used windmills to grind grain, to pump water, and to cut wood at sawmills. Homesteaders and ranchers installed thousands of windpumps as they settled the western United States. In the late 1800s and early 1900s, small wind-electric generators (turbines) were also widely used.
When power lines were built to transmit electricity to rural areas in the 1930s, wind pump and small turbine use began to decline. However, some ranches still use windpumps to supply water for livestock. Small wind turbines are becoming more common again, mainly to supply electricity in remote and rural areas.
Wind energy use expanded in the wake of oil shortages and environmental concerns
The oil shortages of the 1970s changed the energy environment for the United States and the world. The oil shortages created an interest in developing ways to use alternative energy sources, such as wind energy, to generate electricity. The U.S. federal government supported research and development of large wind turbines. In the early 1980s, thousands of wind turbines were installed in California, largely because of federal and state policies that encouraged the use of renewable energy sources.
In the 1990s and 2000s, the U.S. federal government established incentives to use renewable energy sources in response to a renewed concern for the environment. The federal government also provided research and development funding to help reduce the cost of wind turbines and offered tax and investment incentives for wind power projects. In addition, state governments enacted new requirements for electricity generation from renewable sources, and electric power marketers and utilities began to offer electricity generated from wind and other renewable energy sources (sometimes called green power) to their customers. These policies and programs resulted in an increase in the number of wind turbines and in the amount of electricity generated from wind energy.
The share of total U.S. electricity generation from wind energy has grown from less than 1% in 1990 to about 10.2% in 2022. Financial and other incentives for electricity generation with wind energy have resulted in a large expansion of wind energy use in the United States and Europe. China has invested heavily in wind energy and is now the world's largest wind electricity generator. In 1990, 16 countries generated a total of about 3.6 billion kWh of wind electricity. In 2021, at least 128 countries (including Puerto Rico) generated about 1,808 billion kWh of wind electricity.
Wind energy & the environment
Wind is an emissions-free source of energy
Wind is a renewable energy source. Overall, using wind to produce energy has fewer effects on the environment than many other energy sources. Wind turbines do not release emissions that can pollute the air or water (with rare exceptions), and they do not require water for cooling. Wind turbines may also reduce the amount of electricity generation from fossil fuels, which results in lower total air pollution and carbon dioxide emissions.
An individual wind turbine has a relatively small physical footprint. Groups of wind turbines, sometimes called wind farms, are located on open land, on mountain ridges, or offshore in lakes or the ocean.
Wind turbines have effects on the environment
Modern wind turbines can be very large machines, and they may visually affect the landscape. A small number of wind turbines have also caught fire, and some have leaked lubricating fluids, but these occurrences are rare. Some people do not like the sound that wind turbine blades make as they turn in the wind. Some types of wind turbines and wind projects cause bird and bat deaths. These deaths may contribute to declines in the population of species also affected by other human-related impacts. The wind energy industry and the U.S. government are researching ways to reduce the effect of wind turbines on birds and bats.
Most wind power projects on land require service roads that add to the physical effects on the environment. Producing the metals and other materials used to make wind turbine components has impacts on the environment, and fossil fuels may have been used to produce the materials. Although most of the materials used to make wind turbines can be reused or recycled, turbine blades, as most are currently constructed, cannot be recycled. Researchers at the National Renewable Energy Laboratory (NREL) established an approach to manufacturing wind turbine blades, employing a thermoplastic resin system. These thermoplastic resins enable a manufacturing process that allows wind turbine blades to be recycled at their end of life and also reduces the energy required to manufacture blades.