Evaluation copy. Wind Power. Computer

Transcription

1 Wind Power Computer 26 Power from the wind has become an increasingly popular option for electricity generation. Unlike traditional energy sources such as coal, oil, and gas that contribute large quantities of carbon dioxide to the atmosphere, wind power relies on a non-polluting, renewable, ever-present resource the wind. In recent years, the cost of harnessing energy from the wind has become more affordable making it a viable alternative for many communities. A wind turbine generally consists of a two- or three-bladed propeller made of aluminum or fiberglass mounted on the top of a tall tower. It converts energy from the mechanical energy of moving air to electrical energy by means of a generator. The wind causes the shaft of the turbine to spin which in turn causes a generator to produce electricity. In this experiment, you will measure the power output of a wind turbine, investigate the relationship between power output and wind speed, and determine the relationship between power output and rotor shape. You will use a small motor as a generator and a pinwheel as the turbine. The power output of the pinwheel can be determined by measuring the current and voltage produced by the motor. Power is determined using the relationship Evaluation copy P = V I Power = voltage x current Agricultural Science with Vernier 26-1

2 Computer 26 OBJECTIVES In this experiment, you will Use a Current Probe to measure current output. Use a Voltage Probe to measure voltage output. Calculate power output. Determine the relationship between power output and wind speed. Determine the relationship between power output and rotor shape. MATERIALS computer Vernier computer interface Logger Pro Voltage Probe Current Probe ring stand utility clamp 3-speed fan pinwheel templates of each shape modeling clay 5 cm piece of drinking straw scissors 1-hole punch propeller shaft adapter 3 wire leads with alligator clips 1 resistor metric ruler 1.5 V DC motor plastic tubing clamps (optional) Figure 1 PRE-LAB QUESTIONS 1. In Part I of this experiment, you will increase the wind speed while keeping the rotor diameter constant. What effect do you think this will have on the power output of your wind turbine? 2. In Part II of this experiment, you will change the shape of your rotor while keeping the wind speed constant. What effect do you think this will have on the power output of your wind turbine? 26-2 Agricultural Science with Vernier

3 PROCEDURE Wind Power Part I Effect of Wind Speed 1. Cut out the square pinwheel design by cutting along all of the lines on the template. Cut out the hole in the center of the pinwheel and on the end of each of the blades using the 1-hole punch. Push the straw through the center of the pinwheel. Carefully bring each of the blades in toward the center of the pinwheel and thread the straw through each of the blades. Be careful not to tear the paper. Place a bit of clay on the end of the straw to keep the blades from spinning off the straw. Put a piece of tape or a plastic tubing clamp on the straw behind the pinwheel to keep the paper from sliding. 2. Measure the diameter of the pinwheel at its widest point and record it in the data table. 3. Put the propeller shaft adapter on the shaft of the motor. Insert the propeller shaft adapter into the end of the straw. You may wish to use a plastic tubing clamp to secure the straw to the shaft. Secure the motor to the ring stand using a utility clamp as shown in Figure Connect the Current Probe to Channel 1 and the Voltage Probe to Channel 2 of the Vernier computer interface. 5. Connect the motor, 1 resistor, wires, and clips as shown in Figure 2. Take care that the red lead from the motor and the red terminal of the Current Probe are connected 6. Prepare the computer for data collection by opening the file 26 Wind Power in the Agricultural Science with Vernier folder of Logger Pro. 7. Since the direction of spin of the pinwheel depends on its design, you will need to check to see that both the current and voltage readings are positive. a. Blow on the pinwheel. b. Look at the live readouts and note whether either reading is negative or zero. c. If the current reading is negative, disconnect the alligator clips from the wires on the motor and switch them. d. If the voltage reading is negative or zero, unclip the voltage probe clips and switch them. 8. Click. A dialog box will appear. Click to zero both sensors. This sets the zero for both probes with no current flowing and with no voltage applied. 9. Place the pinwheel about 15 cm in front of the fan. Turn on the fan to the high setting. Wait for 60 seconds until the fan reaches a constant velocity. 10. Click to begin data collection. 11. When data collection is complete turn the fan to the medium setting. Click anywhere on the Current graph. Select the Statistics button,, then click to display a Statistics box for the Current Probe data. The mean current value is displayed in the statistics box on the graph. Record the mean current value in the data table. - Black (-) M + 1 Red (+) Figure 2 I Agricultural Science with Vernier 26-3

4 Computer Click anywhere on the Voltage graph to select it and click the Statistics button,. Click to display a Statistics box for the Voltage Probe data. Record the mean voltage value in the data table. 13. Repeat Steps 9 12 with the fan on the medium setting and then again on the low setting. Be careful not to change the location of the pinwheel or fan between trials. Part II Effect of Rotor Shape 14. Cut out two of the rectangular pinwheel designs. Fold along the dotted lines and punch out the center holes. Put both pinwheel cutouts on the straw shaft and position them perpendicular to each other. Measure the diameter of the pinwheel and record it in the data table. 15. Place the pinwheel in front of the fan. Turn on the fan to the high setting. Wait for 60 seconds until the fan reaches a constant velocity. 16. Click to begin data collection. 17. When data collection is complete click anywhere on the Current graph to select it. Click the Statistics button,, then click to display a Statistics box for the Current Probe data. Record the mean current value in the data table. 18. Click anywhere on the Voltage graph to select it and click on the Statistics button,. Click to display a Statistics box for the Voltage Probe data. Record the mean voltage value in the data table. 19. Repeat Steps with the fan on the medium setting and then again on the low setting. Be careful not to change the location of the pinwheel or fan between trials. DATA Square Design Rectangular Design Rotor Diameter (cm) Current (A) Voltage (V) Power (W) Current (A) Voltage (V) Power (W) Low Speed Medium Speed High Speed PROCESSING THE DATA 1. In the space provided in the data table, multiply current and voltage to determine the power output of the turbine. 2. What is the relationship between power output and wind speed in Part 1? 3. What is the relationship between power output and rotor shape? 26-4 Agricultural Science with Vernier

5 Wind Power 4. What are some characteristics of an ideal location to build a wind farm, a grouping of many wind turbines? What make these characteristics ideal? 5. What are some advantages of using wind power over power from traditional means such as fossil fuels? What are some disadvantages? EXTENSIONS 1. Compare the power output of rotors made from materials of different stiffnesses. 2. Investigate the effect of rotor shape on power output of other rotor shapes of the same diameter as the ones in this experiment. 3. Investigate the relationship between rotor diameter and power output. 4. Use an anemometer to measure the wind speed in each of the trials in Part 1. Determine the mathematical relationship between wind speed and power output. Agricultural Science with Vernier 26-5

6 Vernier Lab Safety Instructions Disclaimer THIS IS AN EVALUATION COPY OF THE VERNIER STUDENT LAB. This copy does not include: Safety information Essential instructor background information Directions for preparing solutions Important tips for successfully doing these labs The complete Agricultural Science with Vernier lab manual includes 29 labs and essential teacher information. The full lab book is available for purchase at: Vernier Software & Technology S.W. Millikan Way Beaverton, OR Toll Free (888) (503) FAX (503)