Vertical-Axis Wind Turbines (VAWTs) are very rare to find today. The most prevalent of this type of VAWT is the Darrieus turbine, which looks somewhat like an egg beater. To be a VAWT, the chief characteristic is that the blades spin a shaft that is aligned vertically (perpendicular) to the ground. Any turbine designed like this is a VAWT.

Two main disadvantages of VAWTs make HAWTs the more common design used today. One disadvantage is that commercial VAWTs cannot start spinning on their own; they require a little boost from an electrical system. Another disadvantage is that instead of being supported with a tower like HAWTs, VAWTs are held up with wires, which limits the height that they can reach, and thus limits the winds they can access (lower elevations means slower wind speeds). For these two reasons, commercial VAWTs are less efficient than HAWTs.

One advantage of using a VAWT over a HAWT is that the VAWT is always aligned with the wind. This means that even if the wind direction changes, the blades still rotate. (HAWTs must have additional equipment to align their blades with the wind direction.) Another VAWT characteristic is that all of the turbine equipment (the generator, gearbox, etc.) is located on the ground, which makes maintenance easier, but also takes up more ground space, which can be a disadvantage in certain locations.

Horizontal-Axis Wind Turbines (HAWTs) are often used for large-scale, utility electrical production using wind energy. HAWTs are more recognizable and better known than VAWTs. The optimal wind speed for these turbines is about 15 m/s. At this speed, most large turbines are able to produce their maximum power output. At about 20 m/s, most turbines shut down because of the danger to the structure due to wind speeds that high.

Several advantages suggest using a HAWT instead of a VAWT. First, HAWTs are more efficient than VAWTs, which means they generate more electricity if placed in the same spot as a VAWT. Another advantage is that they can reach much higher elevations because they use a tower to lift the turbine higher into the air where wind speeds are greater. They also generally have a smaller footprint (take up very little ground area), which is an important consideration in certain places.

HAWT disadvantages include the fact that all the turbine components are located hundreds of feet above the ground, making maintenance more difficult. HAWTs also must be adjusted to the direction of the wind; this requires designing a system that tracks the wind and automatically moves the blades into optimum position to catch the most wind.

• A few days before the activity, have students gather and bring from home a variety of plastic bottles, cardboard and other materials from which turbine blades can be made.
• Gather materials and make copies of the Wind Turbine Worksheet, one per group.
• Drill a hole on one end of each cylindrical block of wood equal in diameter to the diameter of the shaft of the hobby motor. Place the hole as close to the exact center of the wood as possible.
• Assemble the turbine testing device(s) using the wooden blocks, nails or screws, PVC pipe, DC motor, duct tape and alligator clip wires, as shown below.

  Assemble the class turbine testing device. Nail or screw together the two wooden blocks. Tape the PVC pipe and motor on top of the wooden block base. Connect the motor to a multimeter. click for copyright

• In this activity, each group creates a turbine on their own cylindrical block of wood and then takes turns placing their turbines on the class turbine testing device(s) to measure voltage.

1. Divide the class into groups of two or three students each.
2. Distribute the worksheets and blocks of wood.
3. In a class discussion, generate the problem that the students are trying to solve by designing wind turbines; this should include how to generate electricity for a house using a renewable energy source.
4. In groups, have students brainstorm designs for a vertical-axis turbine and a horizontal-axis turbine Possible questions to ask: How many blades? How to space them? From what material should we make the blades? What shape for the blades? Have students record all their brainstorm ideas on their worksheets.
5. From a review of their brainstorming exercise results, have each group choose one vertical and one horizontal design to build for their wind turbine models. Direct them to draw their designs on their worksheets and explain why they chose those designs.
6. Next, have each group build their turbines. Use the shorter cylindrical wood blocks for the horizontal-axis wind turbine. Use the longer cylindrical wood blocks for the vertical-axis turbine. Attach the turbine blades onto the side of the wood opposite the side with the hole drilled into it.

   Front and side view of activity set up with a hobby motor and multimeter connected to one team's block of wood and prototype wind turbine. click for copyright

7. Once a group has finished building their designs, have them test them. To do this, have them stick the end of the model turbine through the PVC pipe on the testing device and onto the shaft of the motor. You may want to tape the front end of the testing device to the surface it is sitting on in order to prevent movement during testing. Once the turbine is connected, have one student operate the fan at each speed setting.
8. Have each group take turns testing their turbine designs at three different fan speeds, recording the output data on their worksheets.
9. Repeat the testing procedure for the other turbines, again recording the data on their worksheets.

   A student team's prototype wind turbine design being tested and measured. click for copyright

10. Have students complete the calculations and analysis on their worksheets.
11. Conclude with a class discussion to review and compare the groups' findings. What improvements would they make? Where would they locate turbines near their energy-efficient houses? See additional post-activity discussion questions in the Assessment section.
12. Have student teams present their designs to the rest of the class, as described in the Assessment section.

Class Discussion: As a class discuss the following:

• Does anyone know what a windmill can be used for, or why people in the past built windmills? (Possible answers: For grinding corn, grain and other crops, for pumping water.)
• How are windmills able to do what they were built for? (Answer: They transfer the kinetic energy of the wind into rotational energy to be able to grind or pump.)
• In what other ways have people in the past used the wind for energy or power? (Possible answer: To move a boat by using a sail; the wind pushes against the boat's sails and transfers its energy into moving the boat.)

Worksheet: Have students complete the activity worksheet; review their answers to gauge their mastery of the subject.

Class Discussion: As a class, discuss the following:

• What parts of your designs seemed to result in greater efficiencies of converting the kinetic energy of the wind into electrical energy?
• In what ways could improvements be made to increase the efficiency of your turbines?
• What effect would incorporating aerodynamics into your designs have on the performance of your turbines?

Class Presentation: Have student groups present their designs to the rest of the class. Require them to include descriptions of how well the wind turbines worked, which type of turbine worked best, and what improvements they might make to their designs.