Introducing Wind Power Essentials for Bringing It into the Classroom
By Andy Swapp, Paul Schreuders, and Edward Reeve
[email protected] HEN we think of wind power, we generaily think of sailboats, windmills, and wind turbines. Harnessing the wind dates back to the early Egyptians who used sails to propel ships across the water. The Persians buiit windmills on top of windy ridges to grind grain, and the Dutch built windmills to pump water. Wind has played a major role in America's history, from its discovery by sailing vessels, to its use of commercial wind farms to produce power for millions of homes. As a renewable source of energy, wind energy will play a significant role in our future. Public, commercial, and privately owned organizations are increasingly finding the value and profits in wind power. Initiatives to power 20% of the United
States by 2030 using wind power have spurred the creation of utilityscale wind farms from coast to coast. Including wind power in a technology and engineering education curriculum offers many benefits. Students can learn about an important technology that may effect their future as consumers of energy. They can also learn about careers in the renewable or "green jobs" market—a rapidly growing job category that offers a wide variety of options, including manufacturing, sales, research and development, installation, and maintenance.
Teaching Wind Technology
We encourage teachers who want to include wind Andy Swapp is technology and power in their curriculum engineering education teacher, Milford to get involved in local (UT) High School, and teaches wind community "wind" projtechnology at Southwest Applied Tech- ects taken on by individunology College. He is also a graduate als, businesses, or governstudent, Paul Schreuders is an assisment entities. Sponsors tant professor, and Edward Reeve is a typically welcome teachprofessor, all in the Engineering and ers, who become involved Technology Education Department, with local projects and Utah State University, Logan, UT. learn firsthand about wind
www.techdirections.com
power, gaining valuable knowledge that they can share with their students. Learning up close about wind power can foster motivation and excitement in teachers that they can share with their students. Opportunities for teachers can vary from observing the installa-
Photo 1—Andy Swapp working on wind turbine construction for a summer job
GREEN TECHNOLOGY / POWER & ENERGY
13
and the West depended solely on the charging at an auto repair shop. The charging process could take a couple wind for their electricity. of days, so families that could not The real push for wind power afford two batteries were frequently came after World War 1, with the airwithout radio reception. When farmplane and radio ers learned that they could charge driving innovabatteries with the wind, many investtions. Aircraft ed in radio chargers. A utility model development Windcharger cost farmers just $8, brought knowlwith the purchase of a Zenith radio. edge of the airfoil, not only for The 1920s and 1930s saw a boom wings, but also in wind generation. However, as the for propellers. federal government brought in rural Early innovators electrification starting in the 1930s, saw the airplane the wind industry all but died. A few propeller as an decades later, the energy crisis of the efficient way 1970s brought a major rebirth of reto capture the newable, sustainable, and affordable wind's energy energy, and some of the old Windfor conversion chargers were restored and operatto electrical ed. The 1980s saw some people tryPhoto 2—Students visiting a wind power installation power, and use ing to be more self-reliant, and major wind farm installations with updated of the airplane technology were implemented. When every teacher will have the time propeller increased the efficiency costs of fossil fuel dropped, attention or the desire to hire-on building 80 of wind electrical generators imto wind power diminished. meter (263') towers, but even a visit mensely. The earlier alternative was to a backyard residential wind sysSince the late 1990s, though, the an adaptation of the water-pumping tem will provide valuable real world wind industry has again been growwindmills that dot the West to pump experience. ing. In 2009, the U.S. wind industry water for livestock. These water pumpers turned slowly and had the installed 10,010 megawatts of generIn school, teachers should develhigh torque needed for pumping op wind power curricula that involve ating capacity, breaking U.S. instalwater from a well deep in the ground, a wide variety of experiences, ranglation records for the third year in but electricity production needed ing from field trips (both virtual and a row. Wind power represented 39% higher speeds. One early wind turin-person) to hands-on projects and of all U.S. electric generation capacbine was made from an airplane cross-curricular activities. There are ity additions for the year. According propeller and a 6 V generator. many resources for developing a to the American Wind Energy Ascurriculum on wind power, including In the early 20th century, crystal sociation, the wind capacity added wind energy associations, and eduradios were common appliances in 2009 generates enough electricity cational, government, and industry on farms and in rural communities. to power the equivalent of 2.4 milwebsites. They offer great informaThey would run up to a week on one lion homes, the generation capacity tion and activities that can be inbattery charge, and then the battery of three large nuclear power plants. corporated into the classroom. would have to be taken to town for According to the Department of En(For example, visit www.wind poweringamerica.gov/schools and learn.kidwind.org.) Terminology
tion of a residential wind turbine to getting a summer job installing multi-megawatt wind turbines for commercial power production. Not
Background on Wind Power Wind-powered generators have been around for a long time. Experimenters were converting wind into electricity in the late 1800s and significant use of wind-generated electricity in the United States dates to the early 1900s. Between World War I and the late 1930s, one wind turbine company alone sold approximately 750,000 wind generators. Half a century ago, millions of families across the Midwest, the Great Plains,
14 techdirections • SEPTEMBER 2011
Airfoil—For example, an airplane wing. An airfoil-shaped body moved through a fluid produces a force perpendicular to the motion called lift. Turbine—A rotary engine actuated by the reaction or impulse or both of a current of fluid (as water, steam, or air) subject to pressure and usually made with a series of curved vanes on a central rotating spindle. Yaw or yawing—To turn by angular motion about the vertical axis. Naceiie—A streamlined enclosure (as for an engine ) on an aircraft. In this case, an enclosure for the generator and gearbox of the wind turbine. Furi—To curl or fold.
ergy, the entire wind turbine fleet in place at the end of 2009—more than 35,000 MW—was enough to power the equivalent of nearly 10 miilion homes.
How Wind Turbines Work Whiie their size and shape may vary, aii wind turbines have some common components: a tower to hoid the turbine in the air, a body (or nacelle) containing the generator, and rotor biades attached to a hub to catch the wind. Today, wind power has become a viable option thanks to new biade design, smarter electronics and instrumentation, and utility companies wiiling to worli with wind power projects. Power generation from wind requires a machine that can handle varied conditions and forces. While they look slender and fragile from a distance, iarge-scaie wind towers must be constructed to withstand all the forces withstood by normal buildings and more. For example, the main rotor biades create gyroscopic forces that resist turning the turbine.
To counteract these forces, the nacelle must apply significant torque when rotating the turbine to face the wind, force that must be supported by the tower. Large wind turbines are a marvel of engineering design and construction. The recent incorporation of computer monitoring and turbine control units has increased turbine efficiencies greatly as compared with their 1980s counterparts. Wind turbines used for the generation of electricity are sized, rated, and referred to using a number of terms. Depending on their appiication, a manufacturer might describe a turbine as a "400 turbine," a "cabin-size turbine" (i.e., one providing enough power for a small cabin), a turbine with a rotor diameter of 1.0 m (-39 in.), or one with a swept area of 0.8 m^ (8.5 ft^. The early wind generators of the 1920s and 1930s were rated in voitage, but modern manufacturers usually rate turbines using power
Photo 3—Some of the major parts of a Clipper 2.5 MW wind turbine
output in watts. Since wind speed is variabie and the power produced by a turbine depends on the wind
iVIore than Fun Answers Green Technology Terms
1.C
8. T
15. P
2. E
9. A
16. H
3. M
10. S
17. D
4. L
11.1
18. J
5.0
12. B
19. N
6. K
13. F
20. G
7. Q
14. R
oming in October
New! all Produci Guide Don't miss it! (Advertisers, for details visit www.techdirections.com/ L TD_Product_Guide.pdf)
www.techdirections.com
Pitsco's activities, coordinating teacher guides, and supplemental materials cover a host of sustainable energy topics. From activity continuums for solar cars and wind energy to fuel cell, maglev, and more solar applications, educators won't waste energy finding the right activity.
Call 800-835-0686
PITSCO
Visit shop.pitsco.com
GREEN TECHNOLOGY/ POWER & ENERGY
15
Photo 4—A large horizontal shaft wind turbine
speed, this rating usually refers to the mciximum output rating. There appears to be no standard for rating the wind turbines used for home or light commercial power. One manufacturer will rate a turbine at 400 W in a 12.5 m/s (28 mph) wind, while another may rate a similar turbine
tend to consider any wind turbine with the rated output of 100 kW or less to be "small wind," and those over 100 kW as "large" or "commercial" wind turbines. Unlike the smaller turbines, large, commercial turbines follow a self-imposed industry standard of rating. The large wind turbines are generally of the megawatt (MW) class. To understand what can be done with a megawatt of electrical power, picture a 100 W light bulb. Now picture 10 of these light bulbs. It takes 1,000 W or 1 kW of electricity to illuminate the 10 bulbs. If you gathered 10,000 100 W light bulbs, they would use one MW. Alternatively, 1 MW will power roughly 650 homes in the United States. While students often think that wind power is unique, it actually has many similarities to other forms of electricity generation. The turbineto-electricity conversion process is common throughout the electricity production field. Heat from burning coal, oil, natural gas, or nuclear reactions is used to boil water and the resulting steam rotates a turbine that
Photo 5-A comparison of the old water pumping windmill with high solidity and the electricity producing wind turbine with low solidity
at 300 W based on a different wind speed. Ian Woofenden, a wind power workshop instructor, has suggested that an appropriate rating method for small wind turbines would be by their use, such as cabin size, home size, and small community size. Planning and zoning regulators
16 tochdirections • SEPTEMBER 2011
shaft turbine. The horizontal shaft turbine has been, by far, the most popular. The vertical shaft turbine is usually associated with ancient grain mills and experimental turbines that resemble eggbeaters, called Darrieus turbines. Another conformation, called a Savonius rotor, uses a vertical shaft to support dish-shaped rotor blades or sails, often made from 55-gallon drums cut in half length-
Photo 6—A small wind turbine suitable for use in the technology classroom
turns a generator for the production of electricity. A wind turbine converts wind power into mechanical power when its blades catch the wind and rotate. There are two main configurations of the turbine body and blades: the horizontal shaft turbine and the vertical
wise. Thus far, vertical turbines have proven to be inefficient for electricity production, but designers regularly come up with new prototypes with increased efficiencies. A typical water-pumping windmill has multiple blades that almost fill the swept area of the rotor, which is called "high solidity." A wind turbine for electric power generation generally has three blades and has very little solidity. You can compare the two turbines in Photo 5. Each captures the wind and converts it to a useful form of energy. However, a higher solidity allows the windmill to turn with higher torque, where a low solidity allows the wind turbine to turn at a higher speed.
Controlling the Direction on of the Turbine Photo 7-A permanent magnet alternator made by students for use on a homebuiit wind turbine
Unfortunately, it is impossible to gather all of the power available in the wind. In 1919, the German physicist Albert Betz tried to improve the performance of windmills. As part of the process, he performed a series of mass and energy balances assuming a perfect turbine and found that the maximum efficiency for capturing the wind's power was 59%. The rotational power captured from the wind is converted to electrical power by turning a generator. A gearbox is usually used ¡n commercial turbines to connect the generator to the rotor, while direct drive is usually found in smaller, home-size turbines. Recently, however, some manufacturers have been experimenting with megawatt-size turbines without a gearbox. There are differences between brands of turbines and their configurations, but the concept of converting wind energy into electrical energy is very much the same. Most teachers lack access to a large commercial wind turbine, so small wind turbines are far more common for educational use. Small wind turbines, ciassified as 100 kW or iess, are typically found on a ranch, farm, or rural setting, where electricity for one home or smaii business is needed and transmission lines are not ciose enough to warrant the cost of connection to the grid. Smaller turbines are also used in locations that have grid power when people want to reduce electricity costs or become more self-reliant. Small wind turbines usually use a permanent magnet alternator type of generator. These generators are available commercially, and teach-
wvflw.techdirections.com
ers and students can also build one. Photo 7 shows homebuiit windings and rotor. There are several manufacturers and you can choose from a variety of sizes. Small 300 W to 400 W turbines serve as basic battery chargers for mountain cabins or remote meteoroiogicai sensors. Some of these turbines also have special seals and coatings to withstand a marine environment for use in coastal locations or mounted on sailboats. Some cattle ranchers in the West are replacing old water pumping windmilis with smaller more efficient electricity producing wind turbines and submerslbie pumps. Combined with a soiar panel, these small wind turbines can easily out produce an antiquated water-pumping windmiii. Today's small wind turbine is made up of some very basic parts (Photo 8). The nose cone is made of injection-molded plastic or composite material. Materials used ¡n the blades include wood, wood laminates, fiberglass, carbon fiber composites, and injection moided plastic. A few prototype blades use metal or cloth. The rotor blades are connected to a hub that turns a main shaft that enters the body, or nacelle, of the turbine. Inside the body, the main shaft turns a magnet rotor. The magnet rotor contains powerful rare earth magnets called neodymium-iron-boron. The magnets are mounted with alternating north and south poles. When the magnet rotor spins, it passes by the stator (windings of copper wire) creating a magnetic flux that excites electrons in the coils, thus producing electricity.
A key factor that must be considered in designing and piacing a wind turbine is wind direction. Many turbines are configured so that the rotor blades are kept on the downwind side of the tower. Yaw is the motion made by a turbine as it pivots around the tower to keep the blades directed into the wind. There are three different types of yaw configurations, in the first, a fixed yaw holds the turbine ¡n a fixed position and is used in an area where the wind predominantly blows in one direction, such as a beach where the wind comes off the ocean. The second configuration is free
Photo 8—A smaii wind turbine with a cutaway housing that can be used for ciassroom demonstrations
yaw turbine, which has no yaw controls, allowing the turbine to turn freely as the wind changes direction. The upwind turbine has a tail that keeps the rotor assembly pointed directly at the wind. in the third configuration, an active yaw system keeps the rotor assembly directed toward the wind. An active yaw system has computercontrolled drive motors connected to Instrumentation that moves the turbine Into the wind and locks ¡t in place using a breaking system. While some small wind turbines have active yaw control, this configuration is usually seen in large turbines. While increasing wind speed increases the power output from the turbine, too high a wind speed can damage it. Consequently, turbines are built with a mechanism that lim-
GREEN TECHNOLOGY / POWER & ENERGY
17
^
wind direotlon
Pivot
Small wind turbine In normal operating position
In normal winds, the turbine Is oriented to expose a maximum of the rotor's swept area to the wind.
8mall wind turbine In the furled position
In high winds, the turbine Is reoriented to expose a muoh smaller portion of the rotor's swept area to the wind,
Fig. 1—Comparison of a small wind turbine in normal operating posture and furled due to high winds its their rotational speed. Small wind turbines are generally designed with one of three forms of speed protection: an electric break, a furling system, or pitch control. In an electric breaking system, a signal shunts the output wires of the turbine, forcing the generator to act as a break. The owner or a maintenance person can adjust the electric break to occur at different wind speeds. In a furling system, the rotor blades are moved to expose less cross-sectional area to the flow of the wind (Fig. 1). Using the tail vane as a counter balance, the turbine's alignment is offset from that of the tail. A pivot point allows a strong wind to push the rotor blades parallel with the tail vane, allowing dangerously high wind to pass. When the wind re-
18
techdirections • SEPTEMBER 2011
turns to operating speed, the weight of the tail pushes the rotor back into an upwind position. Blade pitch speed control is a mechanical system that controls rotor speed using counter weights attached to the rotor blades or hub assembly. When the rotor blades spin at a certain speed, centrifugal force moves the counter weights, which, in turn, alter the pitch of the rotor blades to allow a majority of the wind to pass. When the rotor slows, the counter weights seek their original position and the blades pitch normally.
Instructional Strategies Wind power in the classroom can be taught with multiple strategies: • Problem solving—Students
might work on engineering design to get the best results from their own turbine blades. • Inquiry-based—Students can gather information and conduct experiments to improve blade design. • Cooperative learning—Students can work together to accomplish a goal, such as designing a wind turbine or tower. • Interdisciplinary learning—Students can use mathematics, hand tools, or simple machines to assemble a small wind turbine, or test output with a multimeter. Another approach is to run a mini wind turbine blade design contest that turns your classroom into a design competition. The Kidwind project's blade design challenge Is very adaptable to any classroom. With it, students design wind turbine blades that will be attached to a small dc motor/generator mounted in a PVC pipe tower. A box fan provides the wind source and voltage is measured coming out of the turbine. This is a great introductory project that stresses the importance of good blade design. Teacher Geek (www.teachergeek. com) offers a wind turbine model for the ciassroom that can increase in complexity by winding your own Stator and then adding a gearbox, all while designing blades to optimize output. A small, 400 W turbine with the side of the housing cut away will allow students to see the internal workings of the turbine (Photo 8). Students at Milford High School develop a pair of briefs, each containing 23 points of interest including an introduction, wind turbine nomenclature, and a description of the processes used in harvesting wind energy. Once a student knows the parts of a turbine, he or she must then explain the purpose of the individual parts. Students who master the small turbine brief move on to a briefing based on a picture or diagram of a large commercial turbine and predict the function and major parts of the turbine. Students learn the similarities of small turbines and large turbines. This helps them become familiar with the names and
Table 1— Briefing assessment rubric Strong—5 points
Competent—4 points
Emerging—3 points
Needs Work—2 points
The five W's were covered, but not in a confident manner.
One of the W's was not covered.
Two or more of the W's were not covered.
Three or more W's not covered.
Presenter knows each of the parts of the turbine and can point to them with confidence.
Presenter knows each of the parts of the turbine.
Presenter knows some of the parts of the turbine.
Presenter struggles with naming any of the parts of the turbine.
Presenter has a good understanding of the processes that convert mechanical energy from the wind into electrical energy that may be stored or used.
Presenter has a fair understanding of the processes that convert mechanical energy from the wind into electrical energy that may be stored or used.
Presenter has a poor understanding of the processes that convert mechanical energy from the wind into electrical energy that may be stored or used.
Presenter has no understanding of the processes that convert mechanical energy from the wind into electrical energy that may be stored or used.
Poor—1 point
Introduction The five W's were covered. The audience has a strong understanding of (1) who is presenting, (2) what the turbine is, (3) vKhere it is manufactured, and (4) where it may be used, (5) why and how we use this turbine.
Nomenclature Presenter knows each of the parts of the turbine and can point to them with confidence. Presenter can stop and converse about a part of the turbine and carry on without missing the next step. Processes Presenter has a strong understanding of the processes that convert mechanical energy from the wind into electrical energy that may be stored or used.
functions of the basic wind turbine and helps them to generalize the knowledge.
Table 2—Student briefing compietenesü checkiist Nomenclature & Knowledge items
1st Brief
Additional Resources Most states have an energy office that will have much information and many resources of use to educators. Those who want to leeirn more about local resources and the availability of grants should contact that office. The U.S. Department of Energy also works with state energy offices to promote advocacy of wind power with a wind working group, and its Wind Powering America Schools program that has some funding for wind turbines at schools. You might also contact your local power company. Many can provide additional teaching resources and some also have funds available to provide green power sites at schools.
Final Thoughts Wind power is important because it offers one route to a more sustainable future. And an introduction to wind power can introduce students to many career options. By giving students a way to experiment with creating energy, even if it is on the test bench with a mini wind turbine, we give them vaiuable information— and a bit of excitement! ®
www.techdirectlons.com
Knowledge Evaluation 2nd Brief
Presentation Evaluation 1st Brief
2nd Brief
Introduction Modei Company Name Company Location Use/Rating Why/How Used Nomenclature Nose Blades Hub Main Shaft Magnet Rotor Magnets Fiux Stator 3-phase AC Controller Rectified DC Slip rings Body Powder coat Pot LED Taii Upwind Processes Survival wind speed Classroom cut-away
GREEN TECHNOLOGY/ POWER & ENERGY
19
Copyright of Tech Directions is the property of Prakken Publications and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
