Abstract

Objective

The objective is to measure the current output of a small windmill generator and relate the power to the rate of rotation of the windmill's rotor.

Introduction

Wind is an alternative source of energy to petroleum-based fuels. A few reasons why include that energy from wind does not produce greenhouse gases, is widely available in many parts of the world, and is inexhaustible. Wind power is capable of becoming a major contributor to America's electricity supply in the future, according to a report by the U.S. Department of Energy. The report, referenced in the Bibliography, investigates the possibility of wind energy fulfilling up to 20 percent of the energy needs in the U.S. by the year 2030, up from about 2 percent in 2009.

Wind energy is converted to electrical energy by windmill generators. In this science fair project, your windmill generator will be a small electric motor. When wind makes the blades of the windmill spin, the motor acts as a generator. A generator uses the properties of electromagnetic induction to produce a voltage. This means that if you have a conductor surrounded by magnets, and one of those parts is rotating relative to the other, a voltage is produced in the conductor. Voltage is like electrical pressure—it is the force that moves electricity, also called electrical current, from one point to another. When there is a voltage present, electrical charges in a conductor will move, creating a current. In terms of a windmill, its generator has magnets and coiled wire. The shaft from the windmill rotor connects to an assembly of permanent magnets that surrounds the coil of wire. When the rotor spins the shaft, the shaft spins the assembly of magnets, generating voltage in the coil of wire. That voltage drives electrical current through wires attached to the motor.

The goal of this science fair project is to determine how the amount of current produced by a windmill generator depends on the rate at which the rotor is spinning. The speed at which the rotor is spinning will be measured using a laser photo tachometer. The tachometer reads the rate at which a beam of laser light is reflected back toward the tachometer from a piece of reflective tape attached to one of the blades of the windmill's rotor. You will then use a multimeter to measure the current produced by the windmill generator. Let's get started!

Terms, Concepts, and Questions to Start Background Research

• Greenhouse gas
• Windmill generator
• Electromagnetic induction
• Voltage
• Conductor
• Electrical current
• Permanent magnet
• Rotor
• Laser photo tachometer
• Multimeter
• Circuit
• Ohm's law
• Megawatts

Questions

• How does a windmill generator create an electrical current?
• Based on your research, what is the value that you get when you divide the voltage in a circuit by the amount of current produced by that voltage? Hint: look up Ohm's law.
• Based on your research, what do the letters P, I and V stand for in the equation P=IV?
• What are the units for power, current, and voltage?
• How does the United States compare (in megawatts) to other countries in its production of wind power?
• What is the power output of a modern full-sized windmill generator?

Bibliography

• U.S. Department of Energy. (2008). 20% Wind Energy by 2030. Retrieved July 29, 2009, from http://www.20percentwind.org/20percent_Summary_Presentation.pdf
• U.S. Department of Energy. (2006, November 30). How Wind Turbines Work. Retrieved July 31, 2009, from http://www1.eere.energy.gov/windandhydro/wind_how.html
• HowStuffWorks, Inc. (2009). How Wind Power Works. Retrieved July 31, 2009, from http://science.howstuffworks.com/wind-power.htm

Materials and Equipment

• Windmill generator; available from www.amazon.com
• Digital laser photo tachometer; available from online stores such as www.amazon.com
• Multimeter; available at any hardware or auto supply store, or from online stores such as Amazon.com
• Resistor, 1,000-ohm; available at any electronics supply store or from www.radioshack.com, part #: 271-004.
• Electric Fan
• Tape measure
• Lab notebook
• Water bottle
• Scissors
• Jumper wires with alligator clips; available from www.radioshack.com, part # 278-1157
• Phillips head screwdriver, small
• Helper

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Experimental Procedure

Assembling the Windmill

1. Open the box for the windmill generator and set out the parts.
2. You will only partially assemble the windmill.
1. It will only be partially assembled so that the wires from the motor can be attached to the multimeter. Usually, the motor is used to light up a light-emitting diode (LED).
2. The LED will be replaced by a 1-kilo ohm (kohm) resistor and the multimeter to read the current output.
3. Attach the rotor, front housing, back housing, half screw caps (2), rotor shaft, motor, and the gear with the metal shaft.
4. Do not attach the motor cover, the tail, or the LED lamp unit.
5. Secure the windmill assembly with the screws provided in the kit.
6. See Figure 1.

Figure 1. The windmill generator attached to a water bottle, multimeter, and laser tachometer. The resistor is attached to the left lead of the motor. The multimeter is set to read "current" (make sure you have the leads from the multimeter in the correct sockets [holes] to measure current). The short black and white wires are from the LED, which is not attached or used in the procedure.

Attaching the Resistor

1. Bend one of the wires from the resistor into a loop.
1. Bend the wire about 0.5 cm from the end.
2. Hook the bent loop of the resistor into the copper attachment point on the motor.
1. Attach the resistor to the left side of the motor, as seen when the motor is viewed from the side without the gear.
2. See Figure 1.
3. Gently twist the wire so that it stays attached to the motor.

Connecting the Multimeter

1. Using the wires with alligator clips, attach the positive (red) lead from the multimeter to the free lead of the resistor. If you need more help or information about multimeters, visit the Science Buddies page Electronics Primer: Using a Multimeter.
2. Attach the black lead from the multimeter to the other copper ring on the motor.
3. Set the multimeter to read "DC current."
4. Make sure the multimeter wires are in the correct sockets.

Setting Up the Tachometer

1. Read the directions that came with the laser tachometer.
2. Be careful not to shine the laser into your eyes or the eyes of anyone in the area.
3. Insert the batteries into the tachometer.
4. Cut a 1-cm piece of reflective tape (included in the tachometer box).
5. Attach the reflective tape to one of the rotor blades, on the side of the blade toward the motor (see Figure 1).

Attaching the Windmill to the Water Bottle

1. Fill a plastic water bottle about half full with water.
2. Screw the windmill assembly onto the water bottle.

Setting Up the Fan

1. Set the fan on a stable surface with at least 2 meters (m) of free space in front of it.
2. Set the fan speed to its highest level.
3. Place the windmill generator in front of the fan.
1. Initially, place the windmill 50 centimeters (cm) away from the front of the fan.
2. Hold the water bottle so that it does not fall over when the wind is blowing.

Taking Measurements

1. Turn the fan on.
2. Face the windmill into the wind so that the blades start to spin.
3. Measure the current that is generated, using the multimeter.
4. Measure the rate of rotation of the rotor, using the tachometer.
5. Shine the laser on the part of the blade that has the reflecting tape.
1. It will be easier to get the readings if you have a helper so that one person can manage the tachometer while the other manages the multimeter.
2. Record the rate of rotation and the corresponding current in a data table in your lab notebook.
3. Record the distance of the fan from the windmill. This will help you repeat a measurement, if needed.
4. The speed and current will fluctuate somewhat. Try to get the current reading and the rate of rotation at the same moment.
6. Move the windmill to various distances and repeat the measurements of the rate of rotation and the current.
1. The distances will depend on your particular fan. Try to get readings from very close to the fan (maximum rate of rotation), from a distance at which the fan is going as slow as possible (minimum rate of rotation), and from at least three distances in between.
7. Record the distance, current, and rate of rotation in your lab notebook.
8. Repeat the measurements at each position at least two more times so that you have three sets of data. This is done to show that your results are accurate and repeatable.

Analyzing Your Results

1. Graph the rate of rotation in revolutions per minute (RPMs) on the x-axis and the current (in milliamps or microamps) on the y-axis.
2. How does the current vary with changes in the speed of rotor rotation?

Variations

• Measure the voltage drop across the resistor at different rotor speeds. Graph the results.
• Calculate and graph the power output of the windmill. Do an online search for "Ohm's law power" to find the equation for calculating power when you know the current and the resistance (use 1,000 ohms). Hint: The power increases with the square of the current.
• Measure the wind speed for each reading. Use a handheld anemometer to measure wind speed, available from online stores, such as www.amazon.com. Graph wind speed vs. current, or wind speed vs. power.
• Investigate how different shapes and sizes of obstructions between the fan and the windmill impact the rate of rotation and the current generated.

• For more science project ideas in this area of science, see Energy & Power Project Ideas.

Credits

David Whyte, PhD, Science Buddies

Last edit date: 2011-11-04 11:00:00