How Does the Wind Make Electricity?

How does the wind make electricity?

Modern wind turbines combine much more efficiently than old farm diameter and three feet thick. The other ancient knowledge with today’s high windmills, which use drag, the force of is a deeper cylinder, about 15 feet in tech know-how. From ancient Greek the wind pushing against the blades. diameter and 16 feet deep. sailboats to Dutch windmills, people The blades spin at a slow rate of about have used the energy in the wind for 20 revolutions per minute (RPM), thousands of years. American farmers although the speed at the blade tip can used millions of windmills to pump be over 150 miles per hour. water and to power radios and lights in the early part of the 20th century. With The Nacelle – The nacelle houses a modern aerospace designs and comput- generator and gearbox. The spinning Blades er-controlled operations, windmills are blades are attached to the once again cropping up in the generator through a American landscape. series of gears. The gears Nacelle . increase the rotational New utility-scale wind turbines are speed of the blades to the much larger than these familiar farm generator speed of over wind mills. These turbines are 20 sto- 1,500 RPM. As the genera- . ries tall, with blades 90 feet long, and tor spins, electricity is pro- produce enough power for 200 homes duced. Generators can be Gear Box or more. They are typically built in either variable or fixed speed. clusters, called "wind farms," though Variable speed generators pro- can also be built by themselves to sup- duce electricity at a varying ply a factory or small town. Wind tur- frequency, which must be cor- bines can also be very small, weighing rected to 60 cycles per second . as little as nine pounds, and producing before it is fed onto the grid. enough power for a sailboat. Fixed speed generators don’t . need to be corrected, but HOW DO THEY WORK? aren’t as able to take advan- There are four main parts to a wind tage of fluctuations in wind turbine: the base, tower, nacelle, and speed. blades. The blades capture the wind’s energy, spinning a generator in the The Tower- The most com- nacelle. The tower contains the electri- mon tower design is a white Generator cal conduits, supports the nacelle, and steel cylinder, about 150 to provides access to the nacelle for main- 200 feet tall and 10 feet in Tower tenance. The base, made of concrete diameter. Some turbines use a and steel, supports the whole structure. lattice tower, like the Eiffel Tower. Towers have a ladder The Blades – Designed like airplane running up the inside and a . wings, modern wind turbine blades use hoist for tools and equipment. ENERGY CENTER OF WISCONSIN lift to capture the wind’s energy. Because of the blade’s special shape, The Base – Bases are made of Base the wind creates a pocket of pressure concrete reinforced with steel 595 Science Drive as it passes behind the blade. This bars. There are two basic Madison, WI 53711 Phone: 608.238.4601 pressure pulls the blade, causing the designs. One is a Fax: 608.238.8733 turbine to rotate. This modern blade shallow flat disk, . www.ecw.org design captures the wind’s energy about 40 feet in WIND TURBINES IN THE MIX WIND RESOURCES IN WISCONSIN

As the speed of the wind changes, so too does the A good wind resource is one where wind speeds electrical output from a wind turbine. For off-grid average 16 mph or more over the course of a year. turbines, supplying power to a home or cabin, bat- Wind speeds are categorized by class, from a low teries are needed to store power and smooth out of class 1 to a high of class 7. Wind speeds of class fluctuations. But if a wind turbine or wind farm is 4 or greater are used for wind power production. part of the power grid, with dozens of power plants and millions of power-consuming appli- The power of the wind is measured in watts per ances, these fluctuations are typically not notice- square meter, and this increases by the cube of the able. Wisconsin’s use of wind power would have wind speed. For example, winds at 15 mph are to increase over 100 times for these fluctuations to almost twice as powerful as winds at 12 mph, become a problem in the electrical supply. doubling the output of a wind turbine. The densi- ty of the air also affects turbine output. Cold air The productivity of a wind turbine, or any kind at lower altitudes helps generate more electricity of power plant, is referred to as the capacity fac- Worker readies blade assembly for hoisting at Madison Gas than warm air at high altitudes. Height also tor. The capacity factor is the amount of power affects wind speed, since objects on the ground, and Electtric’s wind farm in Kewaunee County, Wisconsin. produced in a given time period compared to like trees and buildings, can reduce wind speed. what the generator could produce if it ran at full power of the generator, or have a 33 percent Therefore, taller turbines can capture higher wind capacity for that time period. If a generator ran capacity factor. This doesn’t mean it sits idle two- speeds and more energy than shorter turbines. full out all the time, it would have a capacity fac- thirds of the time; instead it produces lower lev- tor of 100 percent, but no power plant runs all els of power most of the time. Wind turbines can FOR MORE INFORMATION the time. In a good location, a wind turbine may produce power in winds as slow as 7 mph and as Brower, Michael, Brower & Co. Wind Energy produce on average a third of the maximum high as 45 mph. Resources. National Wind Coordinating Committee. 1997. Online at www.nationalwind.org.

Average Annual Wind Speeds Gipe, Paul. Wind Power for Home and Business. Extrapolated to a height of 110 feet Chelsea Green Press. 1993.

ENERGY CENTER OF WISCONSIN

Visit the Energy Center of Wisconsin’s wind power web site at www.wind.ecw.org or call 608.238.4601

ABOUT US The Energy Center of Wisconsin is a private nonprofit organization dedicated to improving Best - 13 to 14 mph energy efficiency and renewable energy in Good - 12 to 13 mph Wisconsin. Funded in part by Wisconsin utili- Fair - 11 to 12 mph ties, the Center invests $5 million annually in Poor - Less than 11 mph energy efficiency research, education and demonstrations aimed at residents, business and government.