Skip to main content


Wind: Classroom Activities

Harnessing Wind Energy


Goal

To develop a better understanding of how wind can be used as an energy resource.

Back to top

Background Information

Winds can be used to generate electricity. Using wind turbines, the kinetic energy of the wind is converted to mechanical energy, which is then used to produce electrical energy. Most turbines consist of a set of blades connected to a generator. The wind flows over the blades creating lift, like the effect on the wings of an airplane, which causes them to turn. The blades are connected to a drive shaft that turns an electric generator to produce electricity. The amount of electricity produced can vary greatly, from a few tens of watts to multiple megawatts of electricity. This depends on the length of the blades (some are as long as 30 meters) and the efficiency of the turbine. Another important factor is the speed and duration of the wind. The wind's capacity to generate electrical power increases with wind speed.

An anemometer is a common meteorological device for measuring wind speed. Most modern anemometers are cup anemometers, consisting of three or four hemispherical cups mounted on horizontal shanks that radiate from a vertical shaft. The cup assembly spins in the wind, because the force of the wind on the open side of the cup is greater than that on the rounded side of the cup. The speed of rotation is calibrated to the wind speed.

Back to top

Activity Overview

Students construct a simple anemometer, which they use to measure wind speeds at different locations.

Back to top

Materials and Equipment

Five paper cups, two drinking straws, pencil with eraser, push pin, tape, stapler, marker, stopwatch, calculator

Back to top

Activity

  1. Have students build an anemometer as shown in the following diagram. Tell students to color one of the cups with a marker to make it easier to count the revolutions.
    anemometer diagram
  2. Have students go to an outdoors location and calculate wind speed according to the following:
    1. Using a stopwatch, count the number of times the colored cup spins around in one minute. This is the number of revolutions per minute.
    2. Calculate the circumference of the circle (in feet) made by the middle of the rotating paper cups.
    3. Multiply the revolutions per minute by the circumference of the circle (in feet per revolution) to find the velocity of the wind in feet per minute.
      Note that this will be an underestimate, because the cups do not move quite at the same velocities the wind because of friction.
  3. Ask student to take their anemometers home during a weekend. Tell them to make measurements at different locations and different times of day over the two-day period. Have them make a map that shows the location of buildings, e.g. their house, and surrounding areas. Tell them to indicate on their maps the locations where they made their measurements of wind speed.
  4. Tell students to keep a record of the wind speeds they are measuring and the different times of day and locations of their measurements.
  5. Have students use their data to answer the following:
    1. Is the wind speed the same in the morning; the afternoon; the evening?
      Answers will vary. On average, wind speed is least in the morning and evening and greatest in the afternoon as the Earth's surface heats up, but there is much variability in that regard.
    2. How does location affect wind speed?
      Answers will vary. Wind speed is likely to vary somewhat from place to place, depending upon the geometry of the surroundings and their ability to impede or to channel wind.
    3. Do trees or buildings block the wind?
      Yes. Wind speed is especially reduced directly behind a large building, and especially when the walls of the building are nearly parallel and perpendicular to the wind direction.
    4. Where is the best location for a wind turbine at your home?
      Answers will vary. Students should support their answers with the data they have collected.
  6. Present the following calculation of wind power to your students:
    Wind power per square meter of turbine area is equal to 0.65 times the wind velocity cubed. For instance, if a wind turbine has a diameter of 2 meters, then the area that the turbine sweeps is π(1 m)2 = 3.14 m2.

    If a constant wind of 10 m/s (22 mi/h) is blowing, the power is equal to (103)(0.65)(3.14) = 2000 W. The efficiency of wind turbines is about 40 percent, so the actual power that can be produced is about 800 W. If the wind blew a constant 10 m/s every day of the year, this wind turbine could produce 7000 kWh of electricity.
  7. Have students use the example to complete the following:
    1. Calculate the electricity that can be produced at your home from a wind turbine with a diameter of 2 meters (the cost of this wind turbine is about $3,000).
      Answers will vary depending upon the wind speed determined in Step 5.
    2. What percentage of your household electricity needs does this represent?
      Answers will vary depending upon the wind speed determined in Step 5.
    3. How much wind power could be produced from a turbine with a diameter of 3 m? (Cost about $5,000.)
      Answers will vary depending upon the wind speed determined in Step 5.
  8. Discuss this activity with your class. Use the following prompts in your discussion.
    1. How do your calculations compare with those of other students?
    2. What are the characteristics of the locations of homes that have the highest wind velocities?
    3. What are the characteristics of those with the lowest wind velocities?
    4. Overall, how well suited is our community for wind power?
    5. Which locations in our community are optimally suited for placement of wind turbines?
    6. How realistic is the assumption that two days' worth of measurements can be extrapolated to use for yearly averages?
    7. For how long should measurements of wind velocity be taken to get an accurate measure of wind velocities in our community?

Back to top