# Hands-on Activity: Wind Power

### Summary

In this activity, students develop an understanding of how engineers use wind to generate electricity. They will build a model anemometer to better understand and measure wind speed.

### Engineering Connection

Engineers design and manufacturer machines that measure wind (anemometers) and convert wind into energy. They develop wind turbines that generate electricity by considering the Earth's surface, wind direction, average outside temperature, the impact by and on birds and insects, and the extreme forces on the turbine.

### Educational Standards

•   Common Core State Standards for Mathematics: Math
•   International Technology and Engineering Educators Association: Technology
•   Next Generation Science Standards: Science

### Learning Objectives

After this activity, students should be able to:
• Understand and explain how wind in used to generate energy.
• Explain how the use of anemometers is related to wind energy.
• Build and gather data from a model anemometer.
• Understand the relationship between changes in wind speed and changes in the rate of rotation of the anemometer.

### Materials List

Each group should have:
• 4 small paper cups (6 oz. or less)
• 1 push pin
• 1 sharpened pencil with an eraser on the end
• A stopwatch, wrist watch, clock or timer (with seconds)
• 1-2" diameter ball of modeling clay
• Stiff corrugated cardboard (2 pieces – 3" wide by 16" long)
• 1 pair of scissors
• 1 stapler
• Assortment of color markers
• 4 copies of the Power Math Worksheet

### Introduction/Motivation

What causes the wind? Most people do not know that wind is caused by the uneven heating of the atmosphere. Air is heated up by the sun which causes it to rise. This produces an area of low pressure. Cooler air produces an area of high pressure and moves in under the warm air. This movement creates wind. The direction and strength of the wind are changed by the Earth's environmental surface — meaning: trees and water can change the speed and direction of the wind. Some locations always have strong winds from a particular direction, while other locations have little wind or winds that change direction frequently.
How do we measure the speed of the wind? Well, wind speed is usually measured using a cup anemometer, which typically has three cups that capture the wind. The number of times that the cups spin in a full circle per minute is counted electronically. This type of anemometer is commonly seen on weather stations and is used for meteorological observations. Normally, the anemometer is fitted with a wind vane so that it can also detect the wind direction. We are going to make a type of anemometer today.
Did you know that we can generate energy from the wind? For thousands of years, people have converted wind into energy for various work-related reasons. Have you ever seen a windmill? Windmills have been used to convert wind energy into mechanical (movement) energy for farm tasks, such as pumping water or grinding grain. Have you ever seen a modern wind farm? Modern wind turbines have special generators that can convert mechanical energy (energy from movement) into electricity. Wind is a renewable resource, which means that there will always be wind; therefore, we will always have energy from that wind.
Engineers design and create anemometers for measuring wind and machines to convert wind into energy. Engineers also work to improve many wind-powered electricity-generating machines. Engineers need to think about things like the Earth's surface, outside temperature and wind direction when designing a wind turbine. They also think about what happens on very windy days and how insects and birds might be affected by wind machines.

### Procedure

Background

How can we get energy from the wind?
All electric-generating wind turbines, no matter what size, are comprised of a few basic components: a tower, a rotor (two or three blades mounted on a shaft, like a propeller), a speed-control system, and an electrical generator. In order to most effectively capture energy, the wind turbines are mounted on a tower at least 30 meters above ground. Often, these wind turbines are assembled in groups; these populations of turbines are known as wind farms.
Wind turbines turn the kinetic energy (the energy of motion) of the wind into mechanical or electrical power. The amount of power produced by a wind generator depends on elevation, wind speed and air temperature. Wind speeds of at least 14 miles per hour are required to generate electricity. Wind turbines are best located in areas where wind speeds are 16-20 mph and the rotor is placed 50 meters high. Since cold air is denser than hot air, turbines are able to generate about 50% more power in the winter than they do during the summer.
Engineers and wind
The anemometers that engineers design are critical instruments for determining the best locations for wind-power generators. The direction and strength of the wind is very dependent on local terrain, so measurements must be made to determine the best site for wind turbines. Also, wind speed changes with height, so anemometers are necessary to determine the best height for the tower. It is essential that these wind speed measurements be very accurate, because the power generated by a wind generator is related to the cube of the wind speed (if the wind speed doubles, the power available to a wind generator increases by a factor of eight). Therefore, any error in wind speed is greatly magnified. (For example, if your anemometer overestimates the wind speed by 10%, or 110% of the actual value, then you will overestimate the power generated by roughly 33%, or 1/3.) Professional, well-calibrated anemometers have a measurement error around 1%.
Engineers are also involved in the design, construction and maintenance of wind turbines. They study aerodynamics to learn more about the flow of air and other gases and the motion of objects through them. This knowledge is important to design wind turbine rotor blades for optimum performance and to determine aerodynamic loads for structural design of the entire wind turbine. Engineers must also design turbines to work in all types of weather conditions. For example, engineers designed a wind farm in Maine that works in the bitter cold of winter. The turbines include rotor blades with a slippery, black surface to minimize the buildup of ice and concentrate the Sun's energy to melt the ice.
In addition, there are several heaters and synthetic lubricants that enable the rotors to operate in temperatures as low as –40°C.
Another concern that engineers take into consideration is the fact that wind turbines kill thousands of insects, and dead bugs on the blades can significantly reduce the efficiency of the turbines. Occasionally, utilities must stop turbines and pressure-wash hundreds of blades, which only compounds the power losses already caused by the bugs. To reduce the problems caused by insects being beaten against the blades, engineers have designed bug-free turbines using nonstick surfaces and different blade angles.
An additional environmental design concern includes animal protection. For example, a large wind farm in California's Altamont Pass led to the significant loss of golden eagles during the early 1990s. However, the Migratory Bird Treaty Act and the Endangered Species Act prohibit the killing of a single bird from a protected species (such as the golden eagle). This situation raised concerns about building more wind farms and prompted some design changes.
Finally, wind machines can be very inefficient because distribution of wind energy is uneven and unpredictable since the wind does not blow strongly all of the time. Electrical engineers are devising strategies to ensure that electricity supply meets electricity demand. New technologies are being developed to store surplus energy generated during windy periods for use at a calmer time.

Before the Lesson

• Gather all necessary supplies ahead of time.
• Build and test a model anemometer before presenting this lesson to your class.
• Cut the cardboard strips to the appropriate lengths. (Note: You may need to adjust these a bit depending on the size of your cups).
• Make copies of the Power Math Worksheet.

With the Students

1. Brainstorm with students some advantages and disadvantages of using windpower. Write answers on the board. (Note: See Background information for examples.)
2. Distribute a set of supplies to each group.
3. Ask the students to cut off the rolled edges of the paper cups. This will make them lighter.
4. Ask one student in each group to color the outside of one of the cups with a marker.
5. Ask another student to form the two cardboard strips so they make a plus sign (+) and staple them together in the center where the two strips join.
6. Ask a third student to find the exact center of the cardboard cross. They can do this by simply using a ruler and pencil to draw lines connecting diagonal corners on the center (overlap) section of the cross. Where the pencil lines intersect will be the exact middle of the plus sign.
7. Ask the students to staple the side of the cups to the ends of the cardboard strips, making sure the cup openings all face the same direction, as shown in Figure 2.
1. Finally, have a student push the pin through the center of the cardboard (where the pencil lines intersect) and attach the cardboard plus sign to the eraser end of the pencil.
2. Ask the groups to gently blow on the cups to make sure the cardboard spins around freely on the pin. They may need to adjust their models slightly before proceeding.
3. Take the students outside with their partially constructed anemometers, their second-hand timer and their ball of clay.
4. Have each group choose a different spot where they would like to measure the wind speed.
5. Have the students place the modeling clay on a stable, horizontal surface (such as a wooden fence rail, picnic table, wall or flat rock). Ask them to stick the sharpened end of the pencil into the mound of clay so that the pencil stands vertically and the anemometer is free to spin.
6. Ask each of the groups to measure and record the wind speed by counting the number of times the anemometer spins around in one minute. (Note: to make this simple, they should watch the colored cup, and as it passes the pencil, they should count/add 1). Students should take at least three measurements of the wind speed at their location.
7. Have students calculate an average wind speed at their location. Consider calculating a class average as well. Discuss the minimum, maximum and average wind speed at the time of measurement.
8. Have students complete the Power Math Worksheet and check answers with another person in their group.
9. Run the "Toss a Question" Post-Assessment Activity.

### Safety Issues

Students should be careful not to lose the push pins; for this reason, only pass out one pin to each group of students.

### Troubleshooting Tips

Build and test a sample anemometer before trying this activity with your students.
Students will build a model anemometer in this activity that only provides an approximation of how fast the wind is blowing. A real anemometer will more accurately measure how fast the wind is blowing.
Make sure that students make an even plus sign from the cardboard strips — that is, each leg of the plus sign must be the same length. The axis of the anemometer needs to be placed precisely at the center of the cardboard plus sign. Some students may find determining the exact center of the cardboard plus sign difficult.

### Assessment

Pre-Activity Assessment

Activity Embedded Assessment

Data Recording: Ask each of the groups to measure and record the wind speed by counting the number of times the anemometer spins around in one minute. (Note: to make this simple, they should watch the colored cup, and as it passes the pencil, they should count/add 1). Students should take at least three measurements of the wind speed at their location.
Calculations: Have students calculate an average wind speed at their location. Consider calculating a class average as well. Discuss the minimum, maximum and average wind speed at the time of measurement.

Post-Activity Assessment

Power Math Worksheet: Have students complete the Power Math Worksheet and check answers with another person in their group.
Toss a Question: Give the students a list of the questions below without answers. Students should work in their teams and toss a ball or wad of paper back and forth. The student with the ball asks a question and then tosses the ball to someone for an answer. If a student does know the answer, he or she tosses the ball onward until someone gets it. Go over answers at the end.
• How does our model anemometer measure wind speed? (Answer: The wind hitting the cups of the anemometer causes the anemometer to rotate. The rate of the rotation of the anemometer is related to wind speed.)
• Why do engineers need to use anemometers in deciding where to put wind turbines? (Answer: Wind generators produce much more electricity where the wind speed is higher.)
• Where would an engineer locate a small wind turbine used for generating electricity for a single home? (Answer: On a hill by the house, on its roof, or someplace high by the house where the wind would not be blocked by the home, other structures or trees.)
• Where does wind come from? (Answer: Uneven heating of the atmosphere causes wind. Air is heated and its density decreases causing it to rise. This produces an area of low pressure. Cooler, denser, air produces an area of high pressure and moves in under the warm air. This movement creates wind.)
• Is wind a renewable or a non-renewable resource? Why? (Answer: Wind is a renewable resource, because it is formed naturally in the atmosphere. This means that there will always be wind from which energy can be harnessed.)

### Activity Extensions

• Arrange a field trip to a wind farm near you.
• Have students investigate the Bernoulli Effect.
• Have students build different wind vanes: http://sln.fi.edu/weather/todo/vane.html or http://www.energyquest.ca.gov/projects/windmeasure.html
• Have students use their anemometers to determine the speed of the air current produced by a fan.
• Investigate wind speed at different times of the day
• Have students keep a record of the wind speed over the weekend. They should measure the speed in the morning, the afternoon and the evening. Compare the students' measurements. Does wind speed vary much over the course of a day? Does wind speed vary much from place to place? What effects do structures have on the wind?
• Build a windmill and test a generator. See http://www.seco.cpa.state.tx.us/schools/infinitepower/docs/No17_96-817B.pdf for design/build instructions.

### Activity Scaling

For 3rd grade students, do the activity as is.
For 4th grade students, have build the anemometer as is and ask them to see how fast the wind is blowing in different places. Does the wind blow less when close to a building or blocked by a tree?
For 5th grade students, have the students calculate wind speed in miles per hour. Also, have them calculate the speed of the wind they measured. Remember to discuss the fact that these are not very accurate measurements, but this can give them an approximate value.
rotational rate of the anemometer - revolutions per minute (rpm).
wind speed (v) - inches/second or centimeters/second
diameter - length of cardboard strips in inches or centimeters.
*remember to check your units. You may want to have them convert this to miles per hour.
Also, for older students, have them calculate the kinetic energy of the wind they measured. Remember to discuss the fact that these are not very accurate measurements, especially since the error in their wind speed is now being squared.
mass of the moving air- m, in pounds or kg
wind speed –v, in miles/hour or meters/second
Have students complete the Power Math calculations. Discuss the results. Have students use their kinetic energy values (from above) to make power calculations based on their measurements from the activity (again with the understanding that they are quite inaccurate).
Have students brainstorm ideas for ways to improve the accuracy of their models. They may even want to redesign the anemometer model and repeat the experiment.

### References

Activity adapted from the California Energy Commission's website at: www.energyquest.ca.gov/projects/anemometer.html

The American Wind Association, www.awea.org

Hewitt, Paul G. Conceptual Physics, Boston, MA: Addison Wesley Publishing Company, 2004.

National Renewable Energy Laboratory, www.nrel.gov

US Department of Energy, "Wind Turbine Animation," www.energysavers.gov/your_home/electricity/index.cfm/consumer/your_home/electricity/index.cfm/mytopic=10501

USA Today, "Bugs can gum up wind-power turbines," www.usatoday.com/news/healthscience/science/enviro/2001-07-05-wind-power-bugs.htm Accessed July 2011

### Other Related Information

Search for photos of wind farms, wind turbines, and wind generators at: www.nrel.gov

### Contributors

Amy Kolenbrander, Jessica Todd, Malinda Schaefer Zarske, Janet Yowell

### Supporting Program

Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder

### Acknowledgements

The contents of this digital library curriculum were developed under a grant from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation GK-12 grant no. 0338326. However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.