Practical Investigation 9: the Power of Wind Turbines

PRACTICAL INVESTIGATION 9: THE POWER OF WIND TURBINES

NAME: ______CLASS: ______DATE: ______

Introduction In your previous investigations you learned how to measure electrical power. You also have learned about the scientific method and identifying and controlling variables.

Figure 1 The STELR wind turbine is a model turbine. The wind that drives it will be created by a fan.

The class will investigate the effect of the following variables on the electrical power delivered by the STELR wind turbine: • Blade angle • Blade number • Blade length

The investigation In this investigation you will work in a group to investigate the effect of blade angle and blade number for a given blade length. The group results will then be combined and discussed by the class.

Inquiry questions 1 What is the relationship between the number of blades on a wind turbine and the electrical power it delivers? Does this relationship depend on the angle of the blades and/or their length? 2 What is the relationship between the length of the blades on a wind turbine and the electrical power it delivers? Does this relationship depend on the angle of the blades and/or their number? 3 What is the relationship between the angle of the blades on a wind turbine and the electrical power it delivers? Does this relationship depend on the number of the blades and/or their length?

Materials • 12 blades of the same length (75 mm or 100 mm or 150 mm) • Turbine hub • DC motor • Two multimeters, or a suitable voltmeter and ammeter • 3-speed electric fan • Leads • STELR testing station • Safety glasses What to do

Figure 2

Step 1 Take the set of blades assigned to your group and insert the 12 blades into the turbine hub (Figure 2). Set them all at the same angle of 45°. Make sure the blades are tight in the hub and the hubs are tight on the motor drive shaft. Use the ungeared motor drive for the hub. Step 2 Place the fan 50 cm from the wind turbine and align the turbine hub with the hub of the fan, as shown in Figure 1. The fan must be kept at this distance for the whole experiment. (Think about why!) Do not turn on the fan yet! Step 3 As a group, predict what you think will be the answers to the inquiry questions. State your arguments. Step 4 Set up an electric circuit in which the wind turbine is in series with the globe on the testing station. Insert an ammeter and voltmeter into the circuit in appropriate position so you can measure the current flowing in the series circuit and the voltage across the wind turbine. Step 5 Have the teacher check your set-up. Put on your safety glasses in case the blades come loose. Step 6 Turn the fan on high and check whether you need to adjust the settings on the ammeter and voltmeter. Make these adjustments, and then, when the readings are steady, record them in your results table. Turn off the fan and the ammeter and voltmeter. Also record what blade length you are testing. Step 7 Change the angle of each blade to 22.5° (half of 45°), then repeat Step 6. Step 8 Change the angle of each blade to 11°, then repeat Step 6. Step 9 Remove every second blade from the hub so you now have six blades equally spaced set at 11°. Then repeat Step 6. Step 10 Change the angle of each blade to 22.5°, then repeat Step 6. Step 11 Change the angle of each blade to 45°, then repeat Step 6. Step 12 Continue testing so that you have tested 4 evenly spaced blades, 3 evenly spaced blades and 2 evenly spaced blades at 11°, 22.5° and 45°. Step 13 Pack up according to your teacher’s directions. You will then process your results and discuss them with the class.

Results Record all your results in Table 1 in the results sheet or in a spreadsheet.

Calculations 1 Calculate the electrical power delivered in each trial. Give your answer in mW. Your calculations should be placed in your table or spreadsheet. A sample calculation is shown in the table in the results sheet. 2 Plot the graph of electrical power against the number of blades for an angle of 11°. Use graph paper or a graphing program to produce the graph. Note:

• The number of blades is the independent variable and must be on the horizontal axis. The electrical power is the dependent variable and must be on the vertical axis. • Since you cannot have a fraction of a blade, the graph cannot be continuous. So it should be just a set of discrete points (points that are not joined by a line or curve). Ensure the points are clearly seen, without being too large.

3 On the same axes, using a second colour, plot the graph of electrical power against the number of blades for an angle of 45°. 4 For the set of 12 blades, plot the graph of electrical power against blade angle. Use graph paper or a graphing program to produce the graph. (This graph also will have electrical power on the vertical axis and consist of discrete points.) 5 On the same axes, using a second colour, plot the graph of electrical power against blade angle for 3 blades.

Conclusions Examine and compare and discuss the graphs produced by all the groups in the class. From these results, state your response to the inquiry questions.

Discussion questions 1 Were your predictions correct? Were you surprised by the results? Discuss. 2 Can you explain your experimental findings? 3 You tested three variables. What would be some other variables that would affect the electrical power delivered by a wind turbine? 4 Give reasons for the following: a The fan was set on high for each trial. b The fan was kept at a distance of 50 cm for each trial. c The blades on the fan had to be evenly spaced. d You did not test 1, 5 or 7 blades. 5 Identify some sources of error for this experiment that would affect the reliability of your results. 6 Suggest at least one way in which one or more of the sources of error you identified could be overcome if you were to repeat this experiment. 7 a Which combination of blade number, length and angle gave the highest power? b For this set of results, if the power could be delivered steadily for 1 hour, how much electrical energy would be delivered by the wind turbine? Give your answer in Wh. c Is it likely that the power could be delivered steadily over one hour? Discuss. PRACTICAL INVESTIGATION 9: THE POWER OF WIND TURBINES RESULT SHEET

NAME: ______CLASS: ______DATE: ______

Predictions

Inquiry question 1 What effect do you think increasing the number of blades will have on the electrical power delivered, and why?

______

Do you think that changing the angle or length of the blades will change the number of blades that deliver the greatest power? Why?

______

Inquiry question 2 What effect do you think increasing the length of blades will have on the electrical power delivered, and why?

______

Inquiry question 3 What effect do you think increasing the angle of blades will have on the electrical power delivered, and why?

______

Results State the length of the blades your group tested. ______Enter your results in Table 1. An example is shown to help you with the calculation of electrical power.

Table 1 Results

Number of Angle of blade Voltage V Current I Power P blades (degrees) (V) (mA) (mW)

P = V  I

12 22.5 0.58 15.6 0.58  15.6 = 9.0

45 Note: The value for P should not have more significant figures than the voltage or current. In the example, V has 2 significant figures and I has 3 significant figures, so P must be rounded off to 2 significant figures.

Calculations 1 Calculate the electrical power delivered in each trial. Place your calculations in Table 1. A sample calculation is shown to assist you. 2 Plot the graph of electrical power against the number of blades for an angle of 11°. Use graph paper or a graphing program to produce the graph. You may find it helpful to place the relevant figures from Table 1 into Table 2 to assist you.

Table 2 Table of values for blade angle of 11°

No. of blades 2 3 4 6 12

Power (mW)

3 On the same axes, and using a second colour, plot the graph of electrical power against the number of blades for an angle of 45°. You may find it helpful to place the relevant figures from Table 1 into Table 3 to assist you.

Table 3 Table of values for blade angle of 45°

No. of blades 2 3 4 6 12

Power (mW)

4 For the set of 12 blades, plot the graph of electrical power against blade angle. Use graph paper or a graphing program to produce the graph. You may find it helpful to place the relevant figures from Table 1 into Table 4 to assist you.

Table 4 Table of values for the set of 12 blades

Blade angle (degrees) 11 22.5 45

Power (mW)

5 On the same axes, using a second colour, plot the graph of electrical power against blade angle for 3 blades. You may find it helpful to place the relevant figures from Table 1 into Table 5 to assist you.

Table 5 Table of values for the set of 3 blades

Blade angle (degrees) 11 22.5 45

Power (mW)

Conclusions Examine, compare and discuss the graphs produced by all the groups in the class. From these results, state your response to the inquiry questions. 1 What is the relationship between the number of blades on a wind turbine and the electrical power it delivers? Does this depend on the angle of the blades and/or their length?

______

2 What is the relationship between the length of the blades on a wind turbine and the electrical power it delivers? Does this depend on the angle of the blades and/or their number?

______

3 What is the relationship between the angle of the blades on a wind turbine and the electrical power it delivers? Does this depend on the number of the blades and/or their length?

______

Discussion questions 1 Were your predictions correct? Were you surprised by the results? Discuss.

______

2 Can you explain your experimental findings?

______

3 You tested three variables. What would be some other variables that would affect the electrical power delivered by a wind turbine?

______

______4 Give reasons for the following: a The fan was set on high for each trial.

______

b The fan was kept at a distance of 50 cm for each trial.

______

c The blades on the fan had to be evenly spaced.

______

d You did not test 1, 5 or 7 blades.

______

5 Identify some sources of error for this experiment that would affect the reliability of your results.

______

6 Suggest at least one way in which one or more of the sources of error you identified could be overcome if you were to repeat this experiment.

______

7 a Which combination of blade number, length and angle gave the highest power?

______

b For this set of results, if the power could be delivered steadily for 1 hour, how much electrical energy would be delivered by the wind turbine? Give your answer in Wh.

______

c Is it likely that the power could be delivered steadily over one hour? Discuss.

______