A “How to” Handbook for Non-Technical Teachers Illinois Valley Community College Oglesby, IL 61348 www.ivcc.edu/wind www.ivcc.edu/nsf February 2013 Building a Mini Wind Farm: A “How to” Handbook for Non-Technical Teachers By Jim Gibson and Rose Marie Lynch Illinois Valley Community College 815 North Orlando Smith Road Oglesby, IL 61348 815-224-2720 www.ivcc.edu/wind www.ivcc.edu/nsf February 2013 Supported by National Science Foundation Grant #1003730 ii To Anyone Considering a Mini Wind Farm Project: This handbook is designed to provide instructions and resources to enable teachers, including those without a technical background, to guide students in building a wind farm. We encourage you to give your students first-hand experience with a renewable energy project that you can utilize to introduce or reinforce an unlimited number of concepts, at varying levels of expertise, in most subject areas. Jim Gibson Rose Marie Lynch Acknowledgements The authors wish to acknowledge the assistance of Illinois Valley Community College and the National Science Foundation. The material in this handbook is based upon work supported by the N.S.F. under grant #1003730 (“Preparing a New Workforce for a Sustainable Economy”) and the development of programs for wind energy technicians at IVCC. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. NSF Grant Principal Investigator: Jim Gibson, Program Coordinator of Electronics jim_gibson@ivcc.edu NSF Grant Co-PIs: Sue Isermann, Associate Vice President for Academic Affairs sue_isermann@ivcc.edu Jamie Gahm, Director of Business Training Center jamie_gahm@ivcc.edu Rose Marie Lynch, Communications Instructor rosemarie_lynch@ivcc.edu The authors also wish to acknowledge the assistance of Joe Tillman, Renewable Energy Instructor and Coordinator at Lake Land College, Mattoon, IL, for providing valuable suggestions on this handbook. The cover image is from the Image Gallery offered for free download, display, use and copy from the National Renewal Energy Lab (NREL), U.S. Department of Energy, at http://images.nrel.gov. Additional images from the NREL in this handbook are identified. iii Table of Contents Planning a Mini Wind Farm Project ................................................................................... 1 A Note About Safety................................................................................................... 2 Basics of Wind Turbine Design ...................................................................................... 3 Fun Facts ..................................................................................................................... 4 Materials Needed ................................................................................................................ 5 Tower Parts ..................................................................................................................... 5 Other Materials and Supplies for the Farm ..................................................................... 6 Instructions .......................................................................................................................... 8 Basics of Electricity for Building a Wind Farm ............................................................. 8 Source ......................................................................................................................... 8 Conductor.................................................................................................................... 9 Control ...................................................................................................................... 10 Load .......................................................................................................................... 11 Instructions for Assembling a Mini Wind Turbine ....................................................... 12 Instructions for Building a Mini Wind Farm ................................................................ 16 Assembling and Wiring the Load and Control ......................................................... 16 Connecting a Turbine ................................................................................................ 18 Connecting Substation to Load ................................................................................. 20 Connecting Turbine and Load Through Substation .................................................. 20 Testing the Circuit..................................................................................................... 21 Adding a Load........................................................................................................... 21 Adding Another Turbine ........................................................................................... 23 Testing the Circuit..................................................................................................... 25 Costs.................................................................................................................................. 26 Sources for Parts and Materials ................................................................................ 26 Additional Resources ........................................................................................................ 27 iv List of Figures Figure 1: Basic Components of a Wind Turbine ............................................................... 3 Figure 2: Tower Under Construction ................................................................................. 3 Figure 2: Technicians on Top of a Nacelle ........................................................................ 4 Figure 3: Turbine Generator .............................................................................................. 4 Figure 4: Components for a Mini Wind Turbine. .............................................................. 5 Figure 5: Terminal Strip...................................................................................................... 6 Figure 6: One-sixth of Terminal Strip ............................................................................... 6 Figure 7: LED .................................................................................................................... 7 Figure 8: Resistor Connected to LED ................................................................................ 7 Figure 9: Source in a Wind Turbine. ................................................................................. 8 Figure 10: Source in Classroom-size Mini Turbine ........................................................... 8 Figure 11: Conductor for a Wind Turbine ......................................................................... 9 . 9 Figure 12: Conductor for a Classroom-size Mini Turbine................................................. 9 Figure 13: Control for a Wind Turbine. .......................................................................... 10 Figure 14: Control for a Classroom-size Mini Turbine ................................................... 10 Figure 15: Load for a Wind Turbine ................................................................................ 11 Figure 16: Load for Classroom-size Mini Turbine .......................................................... 11 Figure 17: Tower Assembly............................................................................................. 12 Figure 18: Blade Attached to Source ............................................................................... 13 Figure 19: Electrical Tape on Motor Housing ................................................................. 13 Figure 20: Motor Inserted in Elbow................................................................................. 14 Figure 21: Blade and Motor Attached to Tower .............................................................. 14 Figure 22: Motor Wiring Threaded Through Turbine Tower .......................................... 14 Figure 23: Mini Turbine Side View ................................................................................. 15 Figure 24: Materials for Assembling and Wiring the Load and Control ......................... 16 Figure 25: Attaching Control to Wood Block.................................................................. 16 Figure 26: Load (LED) Wired to Control ........................................................................ 17 Figure 27: Top of LED Illustrating Flat Side................................................................... 17 Figure 28: LED with Flat Side on Right .......................................................................... 17 Figure 29: Load, Control, and Conductors Assembled.................................................... 17 Figure 30: Two Controls .................................................................................................. 18 Figure 31: Attaching Connecting Wires to Substation .................................................... 18 Figure 32: Wires from Bottom of Turbine ....................................................................... 19 Figure 33: Turbine Wiring Attached to Substation.......................................................... 19 Figure 34: Load Attached to Substation .......................................................................... 20 Figure 35: Substation Wires Twisted Together ............................................................... 21 Figure 36: Wire Nut Twisted Onto White Wires ............................................................. 21 Figure 37: First Load Connected to Second Load ........................................................... 22 Figure 38: Series of Loads Wired in Parallel ................................................................... 23 Figure 39: Connectors Added to Substation .................................................................... 24 Figure 40: Connectors from First Substation to Second ................................................. 24 Figure 41: Substation Wires Twisted Together ............................................................... 25 Figure 42: Wire Nut Twisted Onto White Wires ............................................................. 25 v vi Planning a Mini Wind Farm Project Building a wind farm can be the impetus to generate interest in and increase knowledge about global environmental issues, to introduce or reinforce concepts in diverse subject areas, and to practice and sharpen technical skills. A wind farm project is easily adaptable to many classroom settings, since farms can be constructed by students of varying ages and varying levels of expertise, guided by teachers with limited technical backgrounds, and utilizing readily available and relatively inexpensive materials STEM (science, technology, engineering and math) concepts and anything related to sustainability and innovation can be integrated into a mini wind farm projects. A wind farm, however, can be a part of a larger project, which can focus on a wide variety of subjects, for example: In business: The costs of wind energy In history or current affairs: Results of a “brown out” in a region In science: Using hand held test equipment In math: The relationship between force, magnetic field strength, and induced voltage In agriculture: The impact of wind energy on agriculture In government: The role of the state, or the Federal government, in encouraging wind energy In industrial technology: Building the tower and siting the turbine In electricity: Wiring and the importance of color coding. Electrical safety. Components of a circuit. In communication: Writing instructions for assembling a wind farm or delivering a persuasive pitch for wind energy In environmental studies: The impact of wind energy on endangered/threatened species In design/engineering: Effectiveness of varying blade designs The list above merely suggests the breadth of possibilities For younger students and those who have had little experience building things or using hand tools, constructing a farm requires the assembly of components for a wind tower/turbine and use of wire strippers and screwdrivers to wire the farm. For students of all ages and levels of expertise, this activity can be the impetus for career exploration, especially since expansion of renewable energy is creating new career needs and fields. Additionally, a mini wind farm project does benefit from and can build on media attention to renewable energy as well as the curiosity and interest generated by increasingly common and visible “green” structures such as wind turbines. 1 The following sections in this handbook provide detailed instructions for building a mini wind farm, including: 1. Understanding the basics of electricity, a circuit, 2. Constructing a circuit, including a mini turbine, 3. Assembling the system (making wire connections), 4. Testing (turning on wind source to activate mini turbine), 5. Adding additional load (emulating more houses connected to the grid), 6. Adding additional sources (connecting more turbines), 7. Testing again (turning on wind source to activate turbines). Materials needed, costs and sources for materials, and additional resources are also included. A Note About Safety A wind farm project is excellent for teaching or reinforcing electrical safety lessons. All connections should be made off line, when there is no possibility of power going through the line. For example, the instructions below indicate that the LED be attached to the control before wires are attached, and the loads are attached to the wind turbine when it is off. However, the small DC motors used as the source in this activity do not produce a dangerous level of power, no more dangerous than a flashlight. Source: NREL 2 Basics of Wind Turbine Design Wind turbines generate electricity by catching the energy of the wind with blades, the opposite of what a fan does. The basic components of a wind turbine are illustrated below. Photo Source: NREL Figure 1: Basic Components of a Wind Turbine The size of common commercial or large-scale wind turbines is illustrated in the photo below of a portion of a tower being assembled. Source: NREL Figure 2: Tower Under Construction 3 Sitting atop the tower, the nacelle houses the electrical and mechanical parts including such equipment as the generator and gearbox. In a commercial or large-scale turbine, the nacelle is the size of a railroad car. Some nacelles have landing pads for helicopters on top. Figure 2: Technicians on Top of a Nacelle Source: NREL The generator, at left, which will be installed in a wind turbine nacelle further illustrates the size of a large-scale turbine. Source: NREL Figure 3: Turbine Generator Fun Facts Many towers for commercial or large-scale turbines are over 300 feet tall, which is the length of a football field. Blades on large-scale turbines are typically 125 to 150 feet long. Blades on large-scale turbines appear to spin slowly, but the outside tip of the blades is traveling at 150 to 200 miles per hour. A wind farm requires one wind energy technician to maintain every 10 to 15 turbines. Wind energy is a form of solar energy. Wind is produced as a result of the sun heating the earth unevenly. Hot air rises and cold air rushes in to fill the void. 4 Materials Needed Building a wind farm requires a minimum of two mini wind turbines, so multiply the parts and supplies for the tower, the fan blade (propeller), and the motor listed below by two. Tower Parts A wind turbine tower is constructed from 1” PVC pipe and fittings, listed and illustrated below. Pipe: (1) 24” section (6) 6” sections Fittings (3) tees – one with a hole drilled in it, large enough for electric wiring to be threaded through it (5) 90-degree elbows Figure 4: Components for a Mini Wind Turbine. 5 Other parts and supplies required are: (1) propeller (bottom left in Figure 4), 4 ½” with 3 blades and 2 mm. hole (1) DC permanent magnet motor (bottom center in Figure 4, with red and black wire attached). Electrical tape Other Materials and Supplies for the Farm 1” by 4” by 6” wood blocks - 1 for each team of students plus 2 for each turbine. For eight teams and two turbines, a total of 12 wood blocks Wire: 20 or 22 gauge stranded, one roll of white and one roll of black. One piece of white and one of black for each team plus an additional piece of white and black for an added turbine, cut in three foot lengths. And one piece of white and one piece of black for each turbine (probably two turbines) cut in three inch lengths. Figure 5: Terminal Strip Terminal strips, also called terminal blocks, (Figures 5 and 6), for 20 gauge wire. The 12 section Euro Style Barrier Strip, in Figure 5, is economical since it can be cut into six sections, illustrated in Figure 6. Use diagonal cutters, a hack saw, knife or razor blade to cut the strips. Figure 6: One-sixth of Terminal Strip Wood screws, #4 by ¾” 6 LEDs (light emitting diodes), 6 mm. red or green – one for each team. Use LEDs that are the same color so the load is the same for each.* Wire nuts, 20 or 22 gauge (matching wire size) two for each turbine. Screw drivers, both flat head and Phillips. Figure 7: LED Wire strippers Diagonal cutters, a hack saw, knife or razor (to cut terminal strips). A high velocity floor fan or carpet fan (provides wind to activate turbine). Inexpensive box fans do not perform well with certain mini turbine blades. *TECHNICAL NOTE: Even if the LEDs are the same color ,if they aren’t from the same production lot, the load may not be exactly the same. If the already wired in LEDs dim when a new LED is added to the system but the new one is bright,, the LEDs are probably not from the same lot; therefore, not exactly the same load To keep all of the LEDs at the same light level, it may be necessary to add resistors. Suggested resistors are ¼ watt, 200 to 680 ohms, and use the same size on all LEDs. However, LEDs with different loads do not affect the overall outcome of this project . Figure 8: Resistor Connected to LED See section on Costs, which also suggests sources for these materials. 7 Instructions Basics of Electricity for Building a Wind Farm Building a mini wind farm requires an understanding of very basic electricity -- the components of a circuit: 1. 2. 3. 4. Source Conductor Control Load Source In a wind turbine, the source is a large motor or generator located behind and connected to the turbine blades. The source, and other mechanical and electrical equipment, is housed in a structure called a nacelle, which is approximately the size of a railroad car in large-scale turbines. Figure 9: Source in a Wind Turbine. In a classroom-size mini turbine, the source is a DC permanent magnet motor, approximately one inch in diameter, pictured at left with wiring attached. Figure 10: Source in Classroom-size Mini Turbine 8 Conductor For a wind turbine, the conductor is the transmissions wires illustrated below. Figure 11: Conductor for a Wind Turbine Source: NREL For a classroom-size mini turbine, the conductor is color-coded, small gauge wiring, pictured at right. . Figure 12: Conductor for a Classroom-size Mini Turbine 9 Control For a wind turbine, the control (substation or power bus) is illustrated at the right. Figure 13: Control for a Wind Turbine. Source: NREL For a classroom-size mini turbine, the control (substation or power bus) is a portion of a terminal strip (approximately 1” by 1 ½”). Figure 14: Control for a Classroom-size Mini Turbine 10 Load For a wind turbine, the load includes the houses, industries, businesses, all entities that draw on power. Source: NREL Figure 15: Load for a Wind Turbine For a classroom-size mini turbine, the load is one or more LEDs (light emitting diodes), illustrated below. Figure 16: Load for Classroom-size Mini Turbine 11 Instructions for Assembling a Mini Wind Turbine To build a mini wind turbine, begin by assembling the tower from the PVC pipe and fittings identified below. Figure 17: Tower Assembly As the figure above illustrates, the 6” pipe, four of the elbows, and the tees form the base for the tower, which is the 24” pipe. 12 Next, snap the back of the blade onto the source (DC motor) as illustrated below. Figure 18: Blade Attached to Source Wrap electrical tape around the housing of the motor, as illustrated below. The tape is to ensure a snug fit of the motor into the elbow, which mounts the motor and blade on the tower. Figure 19: Electrical Tape on Motor Housing 13 Thread the wiring attached to the motor through an elbow and insert the motor housing into the elbow, as illustrated below. If the motor does not fit securely into the elbow, wrap additional electrical tape around the motor housing. Figure 20: Motor Inserted in Elbow Thread the motor wiring into the 24” tower pipe and attach the elbow, as illustrated at the left below. Thread the motor wiring, which is now in the tower pipe, through the hole in the bottom of the tee, which attaches the tower to the base, as illustrated at the right below. Removing the tower pipe from the tee will simplify this process. Figure 21: Blade and Motor Attached to Tower Figure 22: Motor Wiring Threaded Through Turbine Tower 14 The mini turbine is now assembled. Figure 23: Mini Turbine Side View 15 Instructions for Building a Mini Wind Farm Assembling and Wiring the Load and Control After constructing a mini turbine, the next step is to assemble and wire the load (LED representing a house) and control (terminal strip), using half of a terminal strip, an LED, a wood screw, wood block, and a length of black wire and white wire as illustrated below. Figure 24: Materials for Assembling and Wiring the Load and Control 1. Strip both ends of a white wire and a black wire. 2. Using the wood screw, attach control (terminal strip) to wood block, locating the terminal approximately 1 inch from top of the wood block. Figure 25: Attaching Control to Wood Block 16 3. With control at top, wire the LED to the bottom of the control by inserting the LED wires into the slots in the control and tightening the screws. The flat side of the LED is wired on the right of the control (See Figures 26 through 28). The flat side, on right, is the cathode side (shorter wire); the other side is the anode (longer wire). Figure 26: Load (LED) Wired to Control Figure 27: Top of LED Illustrating Flat Side 4. Wire the conductors (a white and a black wire) to the top of the control by inserting the wires into the slots and tightening the screws. Wire the white wire to the right (the cathode or flat side of the LED) and the black wire to the left (the anode side). Wiring white to right and black to left makes it easier to keep track of polarity, which is commonly illustrated in the positive (+) and negative (-) ends on a battery; a battery has to be inserted correctly in order to work. White will be the common or negative wire and black the power or positive wire. Figure 29: Load, Control, and Conductors Assembled 17 Figure 28: LED with Flat Side on Right NOTE: See page7, Figure 8, if a resistor is needed. The load and control are now wired. Connecting a Turbine The first step in connecting a turbine to the system is to assemble a substation or power bus using a wood block, two pieces of terminal strips, two wood screws, and two threeinch pieces of black wire and two three-inch pieces of white wire. A substation is basically a separate connection between a turbine (source) and load (LEDs) or between one turbine and another. Using a substation makes it easier to connect and disconnect a turbine from the system, and also makes it easier to demonstrate the impact of adding extra turbines. 1. Create a substation or power bus: Attach two controls (pieces of terminal strip) on a wood block, mounting one near each end as illustrated below. Figure 30: Two Controls . Attach 3 inch pieces of black and white wire to the inside slots of the controls as illustrated below, keeping both pieces of black on one side and both pieces of white on the other side. Figure 31: Attaching Connecting Wires to Substation 18 The two black wires and two white wires between the controls will be connected later, using wire nuts. 2. Strip the end of the black and red wires coming from the bottom of the mini wind turbine. Figure 32: Wires from Bottom of Turbine 3. Attach the red and black wires from the turbine to the substation. To make it easier to keep track of polarity, before attaching the wires, rotate the substation so the black wires are on the left and white wires on the right. Insert the red wire from the turbine on the right so it will be attached to the white wire on the substation, and insert the black wire from the turbine on the left so it will be attached to the black substation wire, as illustrated below. The red is the common or negative wire and black is the power or positive wire. Figure 33: Turbine Wiring Attached to Substation 19 Connecting Substation to Load The next step is to connect the substation to the load (LED). Attach the black and white wires from the load into slots on one of the substation controls and illustrated to the left. Attach the black load wire to the black wire on the substation control and the white load wire to the white substation control wire. Figure 34: Load Attached to Substation Connecting Turbine and Load Through Substation The final step in completing the circuit is to connect the turbine and load through the substation, by connecting the short white and black wires on the substation. 1. Place the ends of the two white wires together and twist a wire nut on the ends of those wires, as illustrated in Figures 35 and 36. 20 Figure 35: Substation Wires Twisted Together Figure 36: Wire Nut Twisted Onto White Wires 2. Place the ends of the two black wires together and twist a wire nut tightly onto the ends of those wires. The circuit is now complete and ready for testing. Testing the Circuit 1. Place the fan (wind source) in front of the mini turbine and turn it on. 2. If the LED lights up, the circuit has been correctly completed; the turbine is providing electricity to the “house.” Adding a Load To simulate a more realistic scenario, connect additional LEDs (load) to simulate additional houses. 1. Turn the power off by shutting off the fan and waiting for the turbine blade to quit rotating. 2. Connect the conductors from one load to a second load. Loosen the screws holding the conductors (wires) in the control of the first load. Insert the loose end of the black wire from the second load into the same slot as the black wire on the first load and tighten the screw, connecting the two black wires. 21 Insert the loose end of the white wire from the second load into the same slot as the white wire on the first load and tighten the screw, connecting the two white wires. Figure 37: First Load Connected to Second Load The two loads (emulating two houses) are now wired in parallel. Both LEDs should light when the fan is turned on and the turbine blade begins turning. 3. Continue connecting conductors from additional loads the same way. Connect a third load to the second load, a fourth load to the third, and so forth. The entire series of loads should be connected as illustrated below. 22 Figure 38: Series of Loads Wired in Parallel 4. Test the connections several times as the loads are being wired together, by turning on the fan to activate the turbine. Be careful to turn the fan off and allow the turbine to stop before continuing with the wiring. The testing is partly to ensure that the connections are working (the LEDs are lighting), but also to check the strength of the signal. As the load increases, the LEDs will begin to dim and may even flicker. The next step in creating a wind farm, adding another turbine, is designed to boost the signal, brightening the LEDs. Adding Another Turbine To build a wind farm, add another turbine or source 23 1. Create a substation for the second turbine, following instructions above for creating the first substation. 2. Connect the wiring of the second turbine to the substation, following instructions above for connecting the first turbine to the substation. 3. Connect the substation of the first turbine to the substation of the second. On the substation of the first turbine, loosen the screws holding the black and white wires connected to the load. Add a 3-foot white wire and a 3-foot black wire to those slots the control, keeping the white wires together and the black wires together and tighten the screws on the two white wires and on the two black wires. Figure 39: Connectors Added to Substation Connect the loose ends of those 3-foot wires to the open slots on the control of the substation of the second turbine, as illustrated at the right. Figure 40: Connectors from First Substation to Second 24 4. The final step is to complete the circuit to the second turbine by connecting the short white and black wires on the substation for the second turbine, using the same method as for the first turbine substation. Place the ends of the two white wires together and twist a wire nut on the ends of those wires, as illustrated in Figures 41 and 42. Figure 41: Substation Wires Twisted Together Figure 42: Wire Nut Twisted Onto White Wires Place the ends of the two black wires together and twist a wire nut tightly onto the ends of those wires. The circuit is now complete and ready for testing. Testing the Circuit Arrange both turbines in front of the fan and turn it on to test the system. If the system is properly wired, the LEDs should light and be brighter with two turbines operating. You have successfully built and tested a wind farm. 25 Costs To build a wind farm with eight teams and two turbines, the total cost is approximately $48, as detailed below. Two turbines approximately $25 One turbine tower $5 1” PVC pipe – 5’ needed 3 tees 5 elbows $1.00 (20 cents a foot) $1.50 (50 cents each) $2.50 (50 cents each) Other parts for one turbine $7.50 DC motor Propeller $5.00 $2.50 Total for other supplies and parts approximately $23 1” X 4” wood Wire Terminal strips LEDs Wire nuts Wood screws Electrical tape $3.00 (need 12 6” pieces or 6’ for 8 teams) $10.00 for 100 feet – need one black and one white at $5 each $4.00 (need two 12-section units at $2 each) $2.00 (25 cents per unit - for 8 teams) $1.50 $1.50 $1.00 Sources for Parts and Materials Electronic stores Lumber yards Hardware stores Online The DC motor with wiring attached can be ordered from KidWind (a Wind Turbine Generator, SKU H0002) at http://learn.kidwind.org The propeller can be ordered from Kelvin Educational (Product # 851107) at http://www.kelvin.com 26 Additional Resources Illinois Valley Community College, Wind Energy Program Web Site Information on IVCC’s Wind Energy Technician Certificate programs and videos demonstrating the work of wind energy technicians http://www.ivcc.edu/wind Illinois Valley Community College, National Science Foundation Grant Web Site Information on wind energy careers, IVCC’s Wind Energy Technician Certificates, and NSF grant activities for the wind energy programs. http://www.ivcc.edu/nsf American Wind Energy Association http://www.awea.org Wind energy curriculum for K-12 http://www.awea.org/learnabout/education/Wind_Energy_Curriculum_for _K-12.cfm Engineering, Go For It http://www.egfi-k12.org Wind Power Lesson http://www.egfi-k12.org/lesson-wind-power James Madison University, Alternative Energy Educational Resources http://aeer.cisat.jmu.edu/activities.html Kelvin Educational http://kelvin.com KidWind Project Wind turbine kits http://learn.kidwind.org WindWise Education http://learn.kidwind.org/windwise Minnesota Energy Careers, Educators Resources in Energy http://www.iseek.org/industry/energy/education/curriculum.html National Energy Education Development Project http://www.need.org 27 National Renewable Energy Laboratory K-12 curriculum and photos for use free of charge www.nrel.gov National Science Foundation http://www.nsf.gov ScienceEducation.gov, Supporting Science, Technology, Engineering and Mathematics Education for America http://www.scienceeducation.gov U.S. Department of Energy – Energy Education & Workforce Development. K-12 lesson plans and activities http://www1.eere.energy.gov/education/lessonplans Instructions for building wind turbines from PVC pipe created by Kid Wind for the U.S. Department of Energy, available free of charge. www1.eere.energy.gov/education/pdfs/wind_basicpvcwindturbine.pdf Wind Powering America, U.S. DOE http://www.windpoweringamerica.gov Curriculum http://www.windpoweringamerica.gov/schools_teaching_materials.asp 28