The power of wind is undeniable. While a gentle wind ruffles leaves and a good breeze lifts kites, storm winds knock down trees and tear the roofs off houses. People have harnessed that power for centuries. It has been used to pump water, grind grain, and move ships across oceans.

The latest use for wind: to generate electricity. The means: a wind turbine, a special type of windmill used for this purpose. Wind energy has many advantages. It does not, for example, produce any carbon dioxide (CO2) emissions. It will not run out.

Traditional windmills, such as those with the wooden airfoil blades of the Netherlands, the cloth sails of Spain, or the lonely metal fans of the western United States, do not catch enough wind to make electricity. Instead, a wind turbine, much taller than a traditional windmill, does the job. A wind turbine looks like a gigantic pinwheel, with a towering post and huge propeller blades attached at the top. Why so tall? There is more wind higher up in the atmosphere!

The open blades of a traditional European windmill were covered with cloth sails during operation.	Metal fan windmill on a 1940s American farm.	Metal fan windmills are still used on modern farms.
Photo courtesy of Rochford District Council,	Both are used as water pumps or to provide electricity to the farm. Photos courtesy of NREL,

In remote locations around the world, rows of wind turbines dot the landscape, making electricity. Leading users of wind energy include Germany, the United States, Denmark, and Spain. India and China are building more of these facilities.

How It Works

Making electricity from wind is a very simple process. It starts with a very tall tower, one that can be as big as 67 m (220 ft), the height of a 21-story building, at the top. A special housing on top attaches the propeller blades to the tower, on a horizontal axis. The housing also contains a generator and a shaft. The wind turns the propeller blades, which then turn the shaft. The shaft connects to the generator, which makes electricity. Groups of turbines are usually set up over a large area to form a wind power plant, or wind farm.

Turbines and wind farms come in different generating sizes. For regional uses, power companies require that each turbine produce 100 kilowatts or more, up to megawatts, to provide for the power grid. The largest wind farms have up to 200 turbines, and even bigger ones are under consideration. Smaller wind farms and single windmills use turbines that each generate less than 100 kilowatts for smaller uses, such as power for homes, telecommunications dishes, and water pumps.

Where Are the Wind Farms?

Finding a location for a wind farm can be tricky. The first requirement: wind. A potential wind-farm site must have steady and sustained winds, to provide power on a regular basis. For a successful wind farm, a region’s wind speed should average 5.5 m/sec (12 mph).

Many places can meet the wind requirements, but a wind farm also needs a lot of open space. The turbines must be adequate distances from each other to operate properly. More open space as well as relatively flat land means greater wind speeds, since there are fewer buildings, trees, or hills to create friction for the wind as it passes over the land surface. Locations at higher altitudes also have greater wind speeds, which is why wind turbines are very tall. In addition, tall turbines take advantage of smoother air flow away from the ground. Wind turbines make noise, so the wind farm needs to be in an area where people won’t be bothered by the sound.

One solution to the location problem: offshore wind farms. Offshore wind farms have many advantages. The wind speeds over the ocean are higher and the winds blow more steadily. Offshore wind farms do not take land away from other uses, a big issue in densely populated countries. Also, the flat ocean offers even less friction to slow the wind. Many such farms are being built or planned in Europe, where the amount of available open land is limited. In addition, because the waters just offshore are relatively shallow, the cost of building the foundations and pilings required for the towers is reduced.

History

	above: Sketch of a Persian vertical axis windmill. Photo courtesy of Research Institute for Sustainable Energy,   left: 19th century American copy of a Persian style windmill, on a vertical axis. Photo courtesy of TelosNet,

The first record of a windmill comes from China in 200 b.c., one with a wind-driven water pump. Persians were using windmills to grind grain by the 5th century a.d. These early windmills differed from what we now think of as a windmill. They were built on a vertical axis with the sails or blades moving around a central post, like a carousel.

Windmills reached Europe by 12th century, with a big difference. European windmills were built on a horizontal axis. Why the change? Possibly, the Europeans applied the same approach to windmills that they were already using with the waterwheel. In any case, wind power spread quickly throughout Europe and the rest of the world. Windmills pumped water off the reclaimed land in Holland. In fact, the big towers with the wooden blades became the symbol of the Dutch. Countries such as Spain and Greece built windmills with cloth sails rather than wooden blades. In the United States, small steel-bladed windmills, used to pump water, dotted the West by the second half of the 19th century. Small windmills were common around the world until steam engines and later electricity replaced them.

The first person to use wind to generate electricity was Charles F. Brush. In 1888 he built the Brush postmill, in Cleveland, Ohio. It looked like a giant fan with a tail. The rotor was 17 m (56 ft) in diameter and had 144 cedar blades. The hinged tail could turn the rotor out of the wind. The postmill produced about 12 kilowatts, which charged batteries in Brush’s basement. The batteries powered lamps and small electric motors. Brush’s postmill operated for 20 years. But Brush abandoned his work with wind and moved on to other things.

Charles F. Brush postmill. Photo courtesy of TelosNet,

Poul la Cour wind turbines. Photo courtesy of Danish Wind Industry Association ,

Around the same time, Danish inventor Poul la Cour began working on making electricity from wind. La Cour developed his earliest wind turbines in the 1890s. He tested one in 1891, and he tried to set up a company to sell electricity. However, the business of power from wind never took off.

Periodically, interest in wind power resurfaced. In the 1920s propeller-style turbines were developed. At that time, in the western United States a number of these wind turbines operated for small uses. But the development of large power grids in the 1930s wiped out the young wind-energy business. Similarly, in Denmark small wind generators were part of the power picture from 1918 through the early 1930s. Interest faded until World War II, when there were limited fossil-fuel supplies.

During the 1940s, interest in wind turbines rose yet again. For a short time during World War II, a hilltop turbine operated in Vermont. Denmark remained a center of study for wind turbines. But the wind-power industry really began to develop only after oil prices climbed in the 1970s. By the early 1980s, the older ideas were revisited and refined to develop the modern turbine and the wind farm. By the 1980s, wind farms began to dot countrysides all over the world.

Issues

Wind, the energy source, also poses the biggest complication for wind-energy producers. Why? Because wind cannot be controlled or predicted very far in advance. Winds blow intermittently at times. The windiest times of the year are not always the times of the greatest electricity demand. Localized wind forecasting, the kind needed by wind farms, does not exist.

	Click for animation. Wind energy Towering wind turbines generate power from the steady higher-up winds. The winds make the large blades rotate. The blades are attached to a generator, which makes electricity.

All of this makes wind energy somewhat unpredictable: producers cannot guarantee the actual amount of electricity from wind at any given time. Because of this, wind-produced electricity suppliers often build fossil fuel-based electric plants along with the wind farm, to make sure that energy supply stays steady. Eventually, wind farms may be linked to the main power grid for a region.

Building a wind farm requires a large initial financial investment, one that does not necessarily pay off quickly. Wind farmers must plan to be in the business long-term. The tremendous turbines require a lot of open space. Wind farms are usually built in open, rural areas. However, if that area becomes more developed, the land under the wind farm may have more value for building than for producing energy.

Environmental issues also play a role in the wind-energy business. There is concern about the impact on wildlife of land-based wind farms. It is not clear whether the noise disturbs the animals in the region. There have been conflicting reports about the impact of the giant propellers on birds: some reports say that birds are at great risk of injury or death, while others say that most birds avoid the propellers. Offshore wind farms face similar concerns about birds, as well as the impact of the noise on undersea life.

Some people are bothered by the appearance of the wind farms and the giant turbines. However, land-based farms sit in isolated areas, and offshore farms are far enough from shore to be barely visible.

Down the Road

Wind-energy companies would like solve the problem of the unpredictability of wind-energy supply. One way to accomplish this: find a way to store the extra electricity generated by peak winds. Researchers in the United States are taking a number of different approaches. In one, the extra electricity would be used to create the fuel for hydrogen fuel cells.

Another approach has the wind suppliers working closely with hydroelectric power suppliers, since hydroelectric producers can control power production. At peak wind times, the wind-generated electricity would be used instead of electricity from a hydroelectric plant. When the wind quiets down in the summer, more hydroelectric power would be used.

Researchers are also working with a technique that uses the extra wind-generated electricity to create pressurized air. This compressed air would be stored in underground caverns. At peak hours the air would be sent to natural-gas plants, where it would cut natural-gas consumption by 40%.

Wind power will continue to be developed as a good source for clean energy.  Turbine makers are working on even bigger machines, ones that can generate even more power. The biggest turbines can produce 1.5 gigawatts, with even bigger ones still in the experimental stage.

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