Energy Fact Sheet
WIND ENERGY
What Is Wind?
Wind is simply air in motion. It is caused by the uneven heating of the earth by the sun. Since the earth's surface is made up of land, desert, water, and forest areas, the surface absorbs the sun's heat differently.
During the day, the air above the land heats up more quickly than air above water. The warm air over the land expands and rises, and the heavier, cooler air rushes in to take its place, creating winds.
Likewise, the large atmospheric winds that circle the earth are created because the land near the earth's equator is heated more by the sun than land near the North and South Poles.
Today people can use wind energy to make electricity. Wind is called a renewable energy source because we will never run out of it.
The History of Wind
Machines
Since ancient times, people have harnessed the wind's energy. Over 5,000 years ago, the ancient Egyptians used the wind to sail ships on the Nile River. Later, people built windmills to grind wheat and other grains. The early windmills looked like paddle wheels.
Centuries later, the people in Holland improved the windmill. They gave it propeller-type blades. Holland is still famous for its windmills.
In this country, the colonists used windmills to grind wheat and corn, to pump water, and to cut wood at sawmills.
Today people still sometimes use windmills to grind grain and pump water, but they also use new wind machines to make electricity.
Today's Wind Machines
Like old-fashioned windmills, today's wind machines use blades to collect the wind's kinetic (motion) energy. Wind machines work because they slow down the speed of the wind. The wind flows over the blades causing lift, like the effect on airplane wings, causing them to turn. The blades are connected to a drive shaft that turns an electric generator to make electricity.
The new wind machines are still wrestling with the problem of what to do when the wind isn't blowing. They usually have a battery to store the extra energy they collect when the wind is blowing hard.
Types of Wind Machines
There are two types of wind machines commonly used today: horizontal-axis wind machines and vertical-axis wind machines.
Horizontal-axis wind machines have blades that go crosswise and look like airplane propellers. A typical horizontal wind machine stands as tall as a 10-story building and has two or three blades that span 60 feet across. The largest wind machines in the world have blades longer than a football field! Wind machines stand tall and wide to capture more wind. Vertical-axis wind machines have blades that go from top to bottom and look like giant egg beaters. The typical vertical wind machine stands about 100 feet tall and is about 50 feet wide.
Wind Power Plants
Wind power plants, or wind farms as they are sometimes called, are clusters of wind machines used to produce electricity. A wind farm usually has hundreds of wind machines in all shapes and sizes.
Unlike coal or nuclear electric power plants, most wind plants are not owned by public utility companies. Instead they are owned and operated by business people who sell the electricity produced on the wind farm to electric utility companies.
Operating a wind power plant is not as simple as plunking down machines on a grassy field. Wind plant owners must carefully plan where to locate their machines. One important thing to consider is how fast and how much the wind blows.
Scientists use an instrument called an anemometer to measure how fast the wind is blowing. An anemometer looks like a modern-style weather vane. It has three spokes with cups that spin on a revolving wheel when the wind blows. It is hooked up to a meter that tells the wind speed. (By the way, a weather vane tells you the direction of the wind, not the speed.)
As a rule, wind speed increases with height and over open areas with no wind breaks. Good sites for wind plants are the tops of smooth, rounded hills, open plains or shorelines, and mountain gaps where the wind is funneled. The three biggest wind plants in California are located at mountain gaps.
Wind speed varies throughout the country. It also varies from season to season. In Tehachapi, California, the wind blows more during the summer than in the winter. This is because of the extreme heating of the Mojave desert during the summer months. The hot desert air rises, and the cooler, denser air from the Pacific Ocean rushes through the Tehachapi mountain pass to take its place. In Montana, on the other hand, the wind blows more in the winter.
By happy coincidence, these seasonal variations perfectly match the electricity demands of the regions. In California, people use more electricity during the summer cooling months. In Montana, people use more electricity during the winter heating months.
How Much Energy Do We Get from the Wind?
Every year wind energy produces enough electricity to serve 300,000 households, as many as in a city the size of San Francisco or Washington, D.C. Still this is only a tiny amount of the electricity this country uses.
One reason wind plants don't produce more electricity is that they only run about 25 percent of the time. (That means they would run 25 hours in a 100 hour period—or six hours a day.) Wind machines only run when the wind is blowing around 14 mph or more. Coal plants, on the other hand, run 75 percent of the time because they I can run day or night, during any season of the year.
Wind machines do have some advantages over coal-fired power plants though. First, wind machines are clean. They do not cause air or water pollution because no fuel is burned to generate electricity. Second, we may run out of coal some day, but we won't run out of wind.
Pictures and Tables
Picture 1
Local winds caused by uneven heating of land and water
-Land heats up faster than water
-Warm air rises
-Cool sea breeze
-During the day, air over the ocean is cooler that air over the land.
Picture 2
Wind Machine-Converts the kinetic energy of wind into electricity
-Blades-"Catches" the wind
-Generator-Produces electricity
-Tower-To raise blades high where wind is steadier, harder
-Cable-Carries electricity down tower
-Electronic Control System-Hooked into computer to control machine
Picture 3
Production Capability of Wind Plants (How much they run.)
-25% is Production of Electricity
-75% is Non-production Time
