Wind was used to create energy for thousands of years. It was used to power boats and turn windmills. It stopped being used for much of the 20th century. Now wind is making a comeback. Increasingly, it is being used to produce electricity.

Today, wind energy is produced with wind turbines. A wind turbine is a tall, tubelike tower. It has blades that rotate at the top. When the wind turns the blades, the blades turn a generator. The generator then creates electricity.

The Main Turbines

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

Most HAWTs are about 76 meters (250 feet) tall. Their blades rotate up to 20 times a minute.

A HAWT's huge blades 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) are the second kind of wind turbine. They have blades that rotate in complete circles around their tower. VAWTs do not have to face the wind. They can be much smaller than HAWTs. Often, they are put on the roofs of buildings.

Wind Farms

To produce more electricity, wind turbines are often set up in large groups. These groups 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 placed on farmland. In the United States, they are common in the states of Iowa, Nebraska, and Kansas.

Wind farms can also be set up offshore. These turbines use the ocean's strong winds.

Windmills and the History of Wind Energy

Windmills are an early form of wind turbine. They have been around for almost 2,000 years.

Windmills work much like wind turbines. The main difference between the two is what they are used for. Wind turbines produce electricity. Windmills were built to grind grain and pump water.

Wind turbines were first developed in the late 1800s. They were used to make electricity in Europe and North America.

This did not last long, though. Wind is unpredictable. It comes and goes. Sometimes there is almost no wind at all. In the 1900s, wind power was largely replaced by coal, oil, and gas. These fuels were seen as more dependable.

Such fuels cause pollution, though. By the 1970s, many people wanted cleaner ways to create energy. The world's first wind farm was set up during this time. It was built in the U.S. state of New Hampshire.

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

Advantages

Wind energy has many advantages.

• Wind cannot be used up.
• Wind is a clean source of energy. Turbines do not pollute the air.
• Wind energy is very cheap.
• 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 once wind farms are running. However, wind farms are expensive to set up.
• 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 birds. They can also kill bats.
• Offshore wind farms can damage the ocean.
• Some people who live near wind farms complain about the noise. Others say turbines are ugly.
• Wind farms are often set up far away from cities. Power lines have to be built to move the electricity over long distances. This adds to the cost.

The biggest problem with wind energy is the wind itself. When the wind is not blowing, electricity cannot be produced.