Wind

How does the sun create wind?
Wind is a result of solar energy. Wind is created when the sun unevenly heats up the atmosphere. The molecules in the warmer air move faster than the cooler air, causing the warmer air to rise away from the earth's surface. As the warmer air rises, the cooler air replaces it. In the process, energy from the sun is converted into kinetic energy (the energy of motion).

A cheap way to investigate this phenomenon is to observe a radiometer. A radiometer is a small, light bulb-shaped educational tool that can be used to show how light energy is transformed into mechanical energy. The opposing sides of each vane of the radiometer are alternately dark and light in color. As light (infrared radiation) hits the vanes, the lighter side reflects the light while the dark side absorbs it. As the dark side absorbs the radiant energy, a difference in temperature develops between the vanes. The freely moving air molecules bounce off the dark side with a great deal of energy. As the air molecules move away from the dark side of the vane, they form convection currents (wind) and momentum causes the vanes to spin. Image: Courtesy of NASCO

Radiometers can be found at many science and educational stores.

What are the differences between windmills and wind turbines?
Many people wonder what the difference is between a windmill and wind turbine. The differences are great and are explained in more detail here.

Windmills are much shorter than wind turbines, and usually have many blades. The blades catch more wind causing the windmill to be able to do more physical work. The propeller blades are connected to an axle with gears. The gears are connected to a vertical shaft that runs down the length of the tower and is connected to other mechanical equipment. Windmills do work such as pump water or grind grain, which is why they are a common site on farms where they are used in crop production. They are not built to produce electricity.

Photo by S. Lane (Spain windmill)

Wind Turbines harness the kinetic energy of the wind and convert it into electrical energy. This is accomplished by turning blades called aerofoils, which drive a shaft, which turns a motor (turbine), which is connected to a generator. Wind turbines need to be much higher than windmills (80-200 feet tall) and usually have 2-3 blades. Wind turbines can be used to provide electricity to single-family homes, especially in rural areas, businesses, or even many homes and businesses if owned by a utility company. The electricity produced can be stored in batteries for use when wind speeds are too low to produce electricity or when high winds could damage the turbine (in this case, the wind turbine can be turned off to prevent the generator from overheating).

Midwest Renewable Energy Association's Renew the Earth Institute, Custer, WI

Electric utilities use larger wind turbines. Often the utility will place many wind turbines together in what is called a wind farm. The largest wind farms in the world are in California, where they take advantage of fast, steady winds funneled through mountain passes.

Photos by M. Gransee-Bowmen

Please go to our Photos Page to view more photos of wind systems and other renewable energy applications.

How it Works
Wind turbines capture the wind's energy with two or three propeller-like blades, which are mounted on a rotor, to generate electricity. Depending on location and optimal wind speeds, blades can range from6-100 feet long. The turbines sit high atop towers, taking advantage of the stronger and less turbulent wind at 100 feet (30 meters) or more above the ground. Generators can produce 0.5 to 10 kilowatts of electrical power.

A blade acts much like an airplane wing:

When the wind blows, a pocket of low-pressure air forms on the downwind side of the blade.
The low-pressure air pocket then pulls the blade toward it, causing the rotor to turn. This is called lift.
The force of the lift is actually much stronger than the wind's force against the front side of the blade, which is called drag.
The combination of lift and drag causes the rotor to spin like a propeller, and the turning shaft spins a generator to make electricity.

Wind turbines can be:

connected to a utility power grid or
combined with a photovoltaic (solar cell) system (to create electricity).

There are two types of wind turbines: Horizontal axis and vertical axis (eggbeaters). Horizontal axis wind turbines are most commonly used today. Please review the drawing below and click the image to learn more.

1998 by the American Wind Energy Association

Vertical wind turbine article: Wisconsin State Journal - Give 'urban turbine' a whirl

Wind energy, used by civilizations for thousands of years to grind grain and pump water, was reborn during the energy crisis of the 1970's when improvements in materials and technology made wind turbines more common. Today, wind-generated electricity is helping to provide for U.S. electrical needs. Wind energy accounts for less than one percent of the electricity generated in the United States, but this number is growing. Worldwide, there are more than 25,000 wind turbines producing 5,000 megawatts of electrical power.

Locations
All markets for wind turbines require an estimate of how much wind energy is available at potential development sites. Correct estimation of the energy available in the wind can make or break the economics of a wind farm development. To provide the best information possible, National Renewable Energy Laboratory (NREL) researchers have been assembling data sets and refining modeling techniques for three decades.

Wind Energy Resource Atlas of the United States

http://rredc.nrel.gov/wind/pubs/atlas

Wind resources are plentiful in the United States. With average, reliable wind speeds of 15 miles per hour or more, Iowa, Nebraska, Minnesota, and North and South Dakota possess nearly half of the nation's wind potential. To supply the U.S. with one-third of its electrical needs would require covering one percent of the nation's land area with wind machines.

The best sites for wind potential in Wisconsin are found along Lake Michigan and Superior, where average wind speeds may reach 14 miles per hour. The U.S. National Renewable Energy Laboratory (NREL) estimates that Wisconsin has about 4,600 megawatts of potential wind power - an amount roughly equal to four-and-a-half times the electric power produced by Wisconsin's largest nuclear power plant (Point Beach Units 1 and 2). In 2003, Wisconsin utilities operated 55 large wind turbines at five sites in Wisconsin. These utility-scale wind turbines, along with smaller, individually owned wind turbines, generated 103.8 million kilowatt-hours. This amount is still small (less than one percent), but produces enough electricity to power over 11,000 Wisconsin households. Utility electricity generated by wind has increased 122 percent since 2000.

View Wisconsin Wind Farm Locations (.pdf)
View Wisconsin Wind Farm Locations (.pdf) with Utility names and number of wind turbines.
View Wind Energy Projects Throughout the United States

The Kewaunee County sites lie along the naturally windy Niagara Escarpment. Only 5% of Wisconsin's land area has enough wind to economically support electricity generation (MG&E).

View Wisconsin Wind Maps and Data
View U.S. Wind Resource Map (.pdf)

For more information on Wind Basics, please visit the American Wind Energy Association at www.awea.org/faq/wwt_basics.html or read Wind Outlook 2005 - their up-to-date assessment of the wind industry.

For more information on Vertical Axis Wind Turbines (VAWT's), visit the American Wind Energy Association at http://www.awea.org/faq/vawt.html.

Click here to learn more about wind (Northeast Sustainable Energy Association).

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