Wind has been used to create energy for thousands of years. It can power boats and turn windmills. For much of the 20th century, however, wind power was largely replaced by coal, gas, and oil. These days, wind is making a comeback. It is increasingly being used to produce electricity.

In modern times, wind energy is produced with wind turbines. A wind turbine is a tall, tubelike tower with blades rotating at the top. When the wind turns the blades, the blades turn a generator. The generator then creates electricity.

Horizontal-axis wind turbines (HAWTs) are the most common type of wind turbine. Most have three large blades. These spin parallel to their towers. The generator is located in the tower.

Most HAWTs are about 61 to 91 meters (200 to 300 feet) tall. Their blades rotate 10 to 20 times a minute.

A HAWT's enormous blades usually face the wind. A wind sensor first detects which way the wind is blowing. It then turns the turbine to face the wind.

Vertical-axis wind turbines (VAWTs) have blades that rotate in complete circles around their tower. The generator is located near the ground. VAWTs do not have to face the wind to create electricity. They can be much smaller than HAWTs. Often, they are installed on the roofs of buildings.

If winds are too strong, turbines can be damaged. Therefore, every turbine has a controller. The controller turns the turbine on when winds are blowing between 13 and 88 kilometers (eight and 55 miles) per hour. If the winds become stronger than that, it turns the turbine off.

Wind Farms

To generate a large amount of electricity, wind turbines are often placed in large groups. These clusters are called wind farms. They are made up of hundreds of turbines. The turbines can be spaced out over hundreds of acres.

Wind farms are often located on farmland. In the United States, many are found on farmland in Iowa, Nebraska, and Kansas.

Wind farms can also be located offshore. These turbines use the stronger winds that develop above the ocean.

Wind is not steady or predictable. Both its speed and direction change often. So far, this has prevented wind power from becoming the main source of energy. However, it can be an excellent addition to traditional power sources.

Windmills and the Evolution of Wind Energy

Windmills are the ancestor of wind turbines. They have been around for almost 2,000 years.

Windmills work similarly to wind turbines. In fact, the only difference between windmills and wind turbines is what they are used for. Wind turbines generate electricity. Windmills were built to grind grain and pump water.

In windmills, a driveshaft connects the blades to two large wheels or millstones. These wheels are on the floor of the windmill. Wind rotates the blades. The blades then rotate the drive shaft, and the drive shaft rotates the millstones. Grain is poured into the hollow, rotating millstone. It is then crushed into flour as the wheels grind together.

Water-pumping windmills operate similarly. These are known as windpumps.

Windpumps have as many as 12 rotating blades. Rotation of these blades causes a long rod to move up and down. The motion of the rod raises and lowers a cylinder. During the down stroke, the cylinder fills with water. During the up stroke, the water is raised to a pipe or well. Today, wind pumps are still being used all around the world.

Wind turbines that generated electricity were first developed in the late 1800s. They were used in both Europe and North America.

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. Such fuels create a great deal of pollution, though. By the 1970s, many people had become interested in finding less-polluting sources of energy. The world's first wind farm was set up during this time. It was built in New Hampshire.

Today, there are wind farms in many parts of the world. The largest one in the United States is the Alta Wind Energy Center in Kern County, California. It has more than 300 turbines.

Advantages

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

• Wind cannot be used up.
• Wind is a clean source of energy. Turbines 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 found all over the planet. Turbines can be put up almost everywhere.

Challenges

Wind energy also has many problems:

• Wind energy is cheap to produce once a wind farm has been built. However, the cost to build a wind farm is quite high.
• Wind farms need acres of land. In hilly areas, trees might need to be cut. Many kinds of birds and animals depend on trees.
• Wind turbines can kill bats and birds.
• Offshore wind farms can damage the ocean. The seafloor has to be drilled into to keep turbines in place.
• Some people who live near wind farms complain about the noise. Others say the turbines are ugly.
• Locations that produce great amounts of wind energy are often far away from cities. Power lines have to be built to move the electricity long distances. This adds to the cost.

Of course, the biggest problem with wind energy is the wind itself. When the wind is not blowing, electricity cannot be generated.