Hands-on Activity Wind Power

Learning Objectives

After this activity, students should be able to:

• Explain how wind is used to generate energy.
• Explain how the use of anemometers is related to wind energy.
• Build and gather data from a model anemometer.
• Describe the relationship between changes in wind speed and changes in the rate of rotation of the anemometer.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

Common Core State Standards - Math

International Technology and Engineering Educators Association - Technology

State Standards

Materials List

Each group needs:

• 4 small paper cups, 6-ounce or smaller size
• 1 push pin
• 1 sharpened pencil with an eraser on the end
• stopwatch, watch, clock or timer (with seconds)
• 1-2" diameter ball of modeling clay
• 2 pieces of stiff corrugated cardboard, 3-inches wide x 16-inches long (~7.5 x 41 cm)
• 1 pair of scissors
• 1 stapler
• assortment of color markers
• Power Math Worksheet, one per student

Worksheets and Attachments

Introduction/Motivation

What causes 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 pattern of air movement creates wind. The direction and strength of the wind are changed by the Earth's environmental surface—which means that the existence of trees, water and various terrain can impact the speed and direction of 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 catch 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 indicate 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 convert mechanical energy (energy from movement) into electricity. Wind is a renewable resource, which means that more is always available, so 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 wind turbines. 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. To most effectively capture energy, the wind turbines are mounted on a tower that is at least 30 meters above the ground. Often, these wind turbines are assembled in groups and collectively called wind farms.

Wind turbines turn the kinetic energy (the energy of motion) of wind into mechanical or electrical power. The amount of power produced by a wind generator depends on elevation, wind speed and air temperature. For large turbines, wind speeds of at least 14 miles per hour are required to generate electricity; smaller turbines require 6-9 mph winds. 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 during the summer. However, this seasonal difference depends on location; for example, California's wind farms generate more electricity in the summer than in the winter. 

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). So, 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 about 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. They include special heaters and synthetic lubricants to 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 turbine efficiency. 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. Engineers are also developing new wind turbines that work without blades!

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. Since 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 the 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 calmer times.

Advantages and Disadvantages of Large-Scale Windpower

Before the Activity

• Gather supplies and make copies of the Power Math Worksheet.
• Build and test a model anemometer before presenting the activity to the class.
• Cut the cardboard strips to the appropriate lengths. Depending on the cup size, you may need to adjust the strip size a bit.
• Choose a day when this activity can be done outside—to catch the wind.

With the Students

1. Brainstorm with the class some advantages and disadvantages of using windpower. Write their answers on the board. (Note: See the Background section for examples.)
2. Divide the class into groups of four students each. Distribute a set of supplies to each group.
3. Direct students to cut off the rolled edges of the paper cups. This makes 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. An easy way to do this is by using a ruler and pencil to draw lines connecting the diagonal corners through the center (overlap) section of the cross. Where the pencil lines intersect is the exact middle of the plus sign.
7. Ask teams to staple the sides 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.

8. Next, 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.
9. Direct the teams to gently blow on the cups to make sure the cardboard structure spins freely around on the pin. They may need to adjust their models slightly before proceeding.
10. Take the students outside with their partially constructed anemometers, second-hand timer and clay balls.
11. Have each group choose a different spot where they want to measure the wind speed.
12. Have teams 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.
13. Direct the groups to measure and record the wind speed by counting the number of times the anemometer spins around in 1 minute. (Note: To make this simple, advise them to count one rotation each time the colored cup to passes by the pencil.) Require groups to take at least three wind speed measurements at their locations.
14. Have students calculate the average wind speed for their locations. Consider calculating a class average as well. Discuss the minimum, maximum and average wind speed at the time of measurement.
15. Have students complete the worksheet and check their answers with another person in their group.
16. Conduct the "toss a question" post-assessment activity, as described in the Assessment section.

Assessment

Pre-Activity Assessment

Brainstorming: Brainstorm with students some advantages and disadvantages of using windpower. Write their ideas on the classroom board.

Activity Embedded Assessment

Data Recording: Have groups measure and record the wind speed by counting the number of times the anemometer spins around in one minute, and doing this at least three times at each location. (Note: It helps to count how many times the colored cup passes the pencil.)

Calculations: Have students calculate an average wind speed for their locations. 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 individually complete the Power Math Worksheet and check their answers with another person in the group.

Toss a Question: Give students a list of the questions below without answers. Direct them to 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, they toss the ball onward until someone gets it. At the end, go over the answers.

• 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 engineers 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.)
• From where does wind come? (Answer: Uneven heating of the atmosphere causes wind. Air is heated and its density decreases causing it to rise. This produces a low-pressure area. 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 wind will always exist from which energy can be harnessed.)

Safety Issues

Advise students to be careful not to lose the push pins; it helps to just hand out one pin to each team.

Troubleshooting Tips

Build and test a sample anemometer before trying this activity with students.

The model anemometer that students build in this activity only provides an approximation of how fast the wind is blowing. A real anemometer more accurately measures how fast the wind is blowing.

Make sure that students make an even plus sign from the cardboard strips—that is, making each leg of the plus sign 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.

Activity Extensions

• Arrange a field trip to a wind farm near you.
• Have students investigate the Bernoulli effect.
• Have students build different wind vanes.
• 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, measuring in the morning, afternoon and evening. As a class, compare 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 the related activity Wind Power! Designing a Wind Turbine for design/build instructions.

Activity Scaling

For grade 4 students, have them build anemometers as described and challenge them to investigate how fast the wind is blowing in more than one location. Does the wind blow less when close to a building or blocked by a tree?

For grade 5 students, have 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

*remember to check your units

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

Other Related Information

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

Copyright

Contributors

Supporting Program

Acknowledgements

The contents of this digital library curriculum were developed under grants 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.