Prospecting for wind: a gold prospector would set out with a pack mule, provisions, a pickaxe, and a shovel, whereas today's wind prospector is armed with a computer, the Internet, Google maps, and a host of meteorological tools.
Many people use wind to help meet their needs. To a sailor on a sailboat, the wind is necessary. To the cattle rancher in the southwest, a windmill may be a good method to provide water to livestock and wildlife. Over the years, people have been able to harness or capture the wind in many different ways. More recently, we have seen the rebirth of electricity-generating wind turbines. Thus, the age-old argument about technology being either good or bad can also be applied to the wind. The wind can be a hazard or an asset. One situation where the wind is viewed as an asset is when it serves as a free energy resource, but to take advantage of this, there is some basic information that must be known about the wind and how to prospect for it.
What is prospecting for wind? It is helpful to start by breaking this question down:
* What is prospecting? The Oxford English Dictionary (2010) defines "prospect" as: "To conduct a survey or examination of; to evaluate in terms of future prospects"
* What is wind? In his book Power from the Wind, Dan Chiras (2009) describes the wind as follows: Wind is air in horizontal motion across the Earth's surface. All winds are produced by differences in air pressure between two adjoining regions. Differences in pressure result from differential heating of the surface of the Earth. Heating is of course the work of the sun (p. 26).
According to Chiras, there are different types of winds that can be used to drive wind turbines, including offshore, onshore, mountain/valley, global air circulation, and winds caused by storms (Chiras, 2009, pp. 26-34). Each type of wind has individual characteristics that need to be considered when looking for wind to develop into an energy-producing site.
Searching for a good site for a wind farm is much like searching for gold. Prospecting is the first step in finding a wind site to develop for energy production. In the past, a gold prospector would set out with a pack mule, provisions, a pickaxe, and a shovel, whereas today's wind prospector is armed with a computer, the Internet, Google maps, and a host of meteorological tools. Once gold was located and the samples assayed, the feasibility or profitability to mine was determined. In addition, further exploration might have been needed to determine the amount of gold. Wind prospecting is similar to this.
What may seem to be a "good" wind site, as indicated by a picnic being ruined due to a sudden gust of wind or by slower than average times at a track meet, might not be as good as it seems. The wind could be due to infrequent events, such as wind from a passing storm, which would make for a poor choice to install a multimillion-dollar wind farm. Wind is somewhat hard to pin down, since human senses tend to exaggerate the amount of wind present. However, human observation is a way that many "wind sites" are discovered.
What constitutes a "good" wind site? Many factors must be considered when selecting a site. The answer to this question must focus on the ability of the wind energy to do something useful for human beings, animals, and/or the environment. Thus, the main factor in choosing a good wind site is the amount of wind the site has to offer. If there is little or no wind, there is little or no energy to use.
There are many ways to prospect for wind. Looking at the surrounding terrain in the area is a good place to start. The surrounding terrain may show evidence of wind as indicated by such things as exposed rocks, sand dunes, and drifted topsoil. Talking to long-time residents of the area may reveal a long history of wind. Buildings may have wind damage like shingles blown off the roof and paint sandblasted from the sides. Vegetation is another indicator of high and consistent wind. Plants that are significantly shorter than those in other areas, and trees that are flagged or have more limbs on one side than the other are reliable signs of consistent wind. Shown in Figure 1 is the Griggs-Putnam Index that links tree flagging to average wind speeds (Woofenden, 2009). These are good indications that the wind has been at work and there may be enough wind to justify installing a small wind turbine at a cabin or home.
Using Meteorology to Measure the Wind
Once a potential wind site has been identified, the prospector will determine the value of the wind. Since weather has a lot to do with finding a good wind site, the science of meteorology is used. Homeowners, ranchers, and farmers may choose to do their own meteorology. Assessing the wind is usually performed using a meteorological tower. However, in the case of the small turbines used by a single individual or family, it may be more cost-effective to put up a wind turbine and measure the power output than spend almost the same amount of money to buy a meteorological tower.
Commercial wind developers will usually hire a meteorologist or a meteorological firm to do the testing. These firms will install a meteorological tower and report on the value of the wind. Wind velocity is measured using an anemometer. These instruments are often seen on weather stations, near airports, and on home-hobby weather units. Anemometers are not only used in weather recording and forecasting, but also in mines, tunnels, and ventilation systems; in aircraft testing and other experimental work; and in aerial navigation.
Meteorological towers (or "met towers") often have anemometers affixed at multiple places on the tower, allowing meteorologists to measure wind speed and direction at various heights (see Figure 2). A 60-meter met tower might measure the wind speed and direction from 10 to 60 meters off the ground, using instruments placed every 10 meters. To reduce the amount of data collected and analyzed, the measurements are usually averaged over a period of 10 minutes.
While there are several different kinds of anemometers, the basic cup anemometer (see Figure 3) is a standard fixture in the industry. It consists of several plastic or metal cups (usually three) attached to the ends of horizontal arms mounted on a vertical shaft. Wind catches in the cups and causes them to revolve. This action turns the shaft. In one common type of cup anemometer, the shaft is connected to an electrical generator. The amount of current produced by the generator varies with the speed of the wind (Howstuffworks, 2009) and is connected to a device that reads the wind speed in miles per hour, kilometers per hour, or knots.
If the funds for purchasing an anemometer are unavailable (or if you are interested in a more hands-on project), you and your students can make your own anemometer using a small DC motor. DC motors are inexpensive, readily available, and by turning their shaft using either a propeller or the cup/shaft arrangement found on commercial anemometers, can act as generators. Just as you can control the speed of the DC motor by controlling the voltage, when you use the motor as a generator, the voltage it creates will be proportional to the speed that the shaft rotates. The voltage can be measured using a standard voltmeter. The resulting combination should be sufficient for identifying areas of high and low wind velocity. If you can access a commercial anemometer to calibrate your unit, it can give you actual wind velocities.
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There are other devices that measure the wind speed and direction, such as sonic detection and ranging (SODAR) and light detection and ranging (LIDAR) units. SODAR is a device that bounces sound off of particles in the air, creating data that allows a computer to calculate the wind speed and direction (see Figure 4). LIDAR uses laser technology to track objects in the air, from very small particles to a balloon moving through the air. Tracking this movement in the air allows the LIDAR unit to calculate the wind speed and direction. Unfortunately, SODAR and LIDAR units are very expensive and are primarily used in commercial ventures. All of these devices are designed to help the meteorologist gain understanding of the wind patterns and currents.
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One year's data is the minimum amount required for viable decision-making, since wind patterns are often seasonal. In an ideal situation, the meteorologists would continue monitoring the site, since collecting more data at each location further increases the strength of an evaluation. Financiers rely on high-quality data provided by the meteorologist. Data quality is especially important when planning a commercial wind farm, where millions of dollars will be spent.
Assessing Meteorological Results
Once the meteorological data has been gathered, it must be evaluated. In a best-case scenario, the data indicates a steady increase in wind speed as the tower gets higher, and the wind has a prevailing direction throughout the seasons. Another desirable feature in a wind site is wind that naturally increases in velocity during peak power demand times and slows as the demand drops. Velocity is one of the main factors in appraising the wind's value, and sometimes the most misunderstood.
In a worst-case scenario, the wind direction changes 180[degrees] halfway up the tower. This condition is known as wind shear and would be detrimental to a wind turbine's blades, as they will sweep through opposing wind forces. The power of wind shear is apparent when one considers that it has been a primary cause of aircraft crashes occurring immediately after takeoff.
Appraising the Energy Available from the Wind
The amount of energy available from the wind has several components. One component is velocity, measured either in meters per second (m/s) or miles per hour (mph). Another component is the distribution of the wind--in other words, how often the wind blows at a given velocity and direction and for how long the wind blows, or the duration of a given velocity. Air density also plays a role. Lower elevations have thicker, denser air, and higher elevations have thinner, less dense air. If a wind turbine was put on the top of Mount Everest (8850m/29,035 ft) and the same kind of turbine on the beach near sea level, when both turbines experience a consistent 9 m/s (20 mph) wind, the turbine on the beach would produce more power because of the greater air density. Even if you do not have beachfront property, wind power may still be feasible.
Another factor to consider is the power output of a wind turbine, which is directly related to the area swept by the blades. Swept area refers to area in square feet of the rotor and is determined by using the formula pi (3.14159265) x radius squared. For example, a 30-foot diameter turbine would have a 15-foot radius and a 706.5 square-foot swept area. Also important is the diameter of the blades. The larger the diameter of a wind turbine's blades, the more power it is capable of extracting from the wind. According to the American Wind Energy Association (n.d.), the available power in the area swept by a wind turbine rotor is:
P = 0.5 * [rho] * A * [V.sup.3]
where: P = power in watts (746 watts = 1 hp) (1,000 watts = 1 kilowatt)
p = air density (about 1.225 kg/[m.sup.3] at sea level, less higher up)
A = rotor-swept area, exposed to the wind ([m.sup.2])
V = wind speed in meters/sec (9 m/s = 20 mph) (2.24 m/s = mph)
Paul Gipe (2004) notes that an important feature of this formula is that the velocity term is cubed. Thus, doubling the wind velocity does not just double the available power. It increases by a factor of eight. So a gain of even lm/s in wind speed by building a taller tower or by moving the tower a little to the right or left to gain the small increase in wind speed may be worth the effort.
Other Considerations in Appraising a Wind Turbine Site
Wind velocity and distribution are not the only factors in choosing the site for a wind turbine or a commercial wind farm. Many areas have building codes and minimum set-back requirements for the turbines. Most building codes state that, if the tower falls over, it must land on your own property with some room to spare. For example, in our region of the country (Utah), the setback from the property line to the base of your tower must be at least the tower height times 1.2. Thus, a 25 m (82 foot) tall tower requires a setback from the property line of 30m (1.2 x 25 m). Typically, this requires that a good wind site be situated on a property with lots of room.
There are also environmental factors that need to be considered, including the impacts on local wildlife habitats, indigenous plants, aquifers, archeologically important sites, and scenic views. Keeping your neighbors happy is also a good idea, since public protests can kill or significantly delay a project. Transmission of the electrical power generated by the wind turbines is a problem with some good wind sites. If a transmission line must be built to get the electricity to a buyer, the costs may be prohibitive.
All of these costs and benefits need to be weighed, and compromises must often be made. A good wind site is convenient, takes the above factors into consideration, minimizes the social and environmental impact of the turbines, and maximizes the power output and the profit from the turbine(s).
Why Should We Teach About Wind Power?
There is a diverse array of opportunities for employment in the green energy field. Developing a wind-power site is a source of jobs for our graduates. At one end of the job scale are the engineers who design the towers and electrical systems for manufacturers or power companies. On the other end of the scale are the technicians who build and/or maintain the site.
An educated landowner might be informed enough to know the risks, evaluate local weather data, and find information sources on which to base the purchase decision. However, landowners are far more likely to rely on the contractor selling the turbine to provide the meteorological data, or purchase a turbine without proper consideration of wind speeds and distribution challenges. Thus, there are jobs for local contractors, their personnel, and consultants to provide an independent opinion.
In the green job market, one of the more overlooked jobs is prospecting or site selection. Wind prospecting teams play a pivotal role in the wind industry. Personal observation and experience in the wind-prospecting field have suggested that the wind industry will need one highly skilled technician and three to four laborers to erect each meteorological tower. These teams travel to remote locations all over the world and construct, relocate, or repair met towers. Without the crucial data provided by these teams, obtaining the financing for multimegawatt wind farms would be unlikely. Currently, most of these employees are given on-the-job training, and a need exists to develop formal educational opportunities in this area.
Teaching About Wind Prospecting
There are many different strategies and activities that can be incorporated into the technology and engineering education classroom to teach about prospecting for wind. For example, to teach about wind prospecting, teachers are encouraged to use instructional strategies that:
* Develop problem-solving activities in which students use engineering design to solve the challenge of placing instruments into the airflow.
* Use inquiry-based instruction where students are encouraged to find information in order to design and conduct experiments.
* Set up cooperative learning groups where students learn to work together to accomplish a goal.
* Use interdisciplinary learning where students use math calculations, simple machines, and their skills in electronics to install a simple data logger to collect data.
Teachers can develop a variety of student activities related to prospecting for wind. A simple activity can begin with looking at local weather data and determining if further study would be warranted. Students can be given an activity where they try to estimate the wind using the Griggs-Putnam index (see Figure 1). This index can be used to perform a basic field study. For example, if there is a windy bluff or a beach nearby with vegetation, such as trees and bushes, the teacher may want to take a field trip to one of these sites and ask the students to use the Griggs-Putnam Index to rate the amount of flagging on a few different trees or shrubs (see Figure 5). In this exercise, students will be required to determine the class of flagging (I - VII) and then find the average wind speed on the chart. Also, virtual tours to sites such as Yosemite National Park (www.nps. gov/yose/naturescience/panoramic.htm) or Cedar Breaks National Monument (www.nps.gov/cebr/) can be used to allow students to see examples of flagging. A species of tree that is often flagged or even carpeted is the Bristlecone Pine. An online image search using Bing or Google will allow students plenty of opportunity to judge and classify vegetation and the amount of flagging.
Another activity students could be given to learn about the wind involves using handheld anemometers. Given "low-cost" handheld anemometers, students could work individually or in teams to take various wind measurements around the school campus or at other designated sites. The purpose of this activity would be to try to locate the "windiest spot," and wind measurements could be taken over a specified period of time. In addition, data collected using the handheld anemometer could be logged and analyzed using appropriate spreadsheet software (e.g., Excel) to teach students about how data collection and analysis can be used in a decision-making process. Furthermore, around the county there are many commercial meteorological towers that are equipped with communication devices that automatically transfer data from the site to a remote location. Many of these sites make their data available to the public, and teachers are encouraged to try to find a "met tower" in their area that could be used for wind-data analysis.
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Most states have an energy office that provides citizens with valuable information and resources related to energy, and teachers are encouraged to visit these sites to find helpful resources that can be used in the classroom. For example, in Utah, the energy office (www.energy.utah.gov) has lots of good information related to energy, including many wind resources. A notable program under this office is an "anemometer loan program" that provides an anemometer and the necessary equipment needed to measure wind resources to individuals who are interested in installing a wind turbine on their property.
Wind prospecting is the first step in determining if wind could be used to provide power to build wind turbines. After students have completed wind-prospecting activities, teachers are encouraged to develop engineering-design problems that challenge students to design and build wind turbines.
Teaching about prospecting for wind and building wind turbines can help teachers address many of the standards and related benchmarks stated in Standards for Technological Literacy: Content for the Study of Technology (ITEEA, 2000/2002/2007). For example, teaching about the wind and other alternative energies is covered in many of the benchmarks stated in Standard 16 (Energy and Power Technologies). Standard 7 addresses the History of Technology, and teachers could teach about the windmill and its many uses throughout time. Developing an in-depth "standards-based" unit on windmills could show the broad impacts of technology on society and address many of the benchmarks identified in Standards 4-6. Furthermore, those teachers who choose to use problem-solving activities that involve building and testing wind turbines will address many of the benchmarks identified in Standards 8-13.
Technology and engineering education teachers are encouraged to teach about wind prospecting--the first step in deciding if "wind" can be used to build wind turbines. Prospecting for wind and harvesting the wind to build wind turbines is becoming very popular today in the U.S. as the country continues to look to alternative energy sources. The purpose of this article is to introduce the concept of wind prospecting and to present ideas on how it could be taught in the technology and engineering classroom.
Anemometer: An instrument for measuring wind speed.
Meteorology: A science that deals with the atmosphere and its phenomena and especially with weather and weather forecasting.
SODAR: SOnic Detection And Ranging
LIDAR: Light Detection And Ranging Wind Shear: A difference in wind speed and direction over a relatively short distance.
American Wind Energy Association. (n.d.). Wind Energy FAQ. Retrieved from www.awea.org/faq/windpower.html
Chiras, D. (2009). Power from the wind. Gabriola Island: New Society Publishers.
Gipe, P. (2004). Wind power: Renewable energy for home, farm, and business. (Revised ed.). White River Junction: Chelsea Green Publishing Company.
Howstuffworks. (2009, 15-September). Retrieved from Anemometer: http://science.howstuffworks.com/anemometer-info.htm
International Technology Education Association (ITEA/ ITEEA). (2000/2002/2007). Standards for technological literacy: Content for the study of technology. Reston, VA: Author.
Oxford University Press. (2010). Oxford English Dictionary (2nd ed.), Prospect. Retrieved from http://dictionary.oed.com
Woofenden, I. (2009). Wind-electricity user, consultant, and instructor. In I. Woofenden, Wind power for dummies (p. 364). Hoboken: Wiley Publishing, Inc.
Andy Swapp is a graduate student at Utah State University and a teacher of Engineering and Technology at Milford High School. He is also an adjunct professor at the Southwest Utah Renewable Energy Center. He can be reached via email at andy. email@example.com.
Paul D. Schreuders, Ph.D. is a bioengineer and an Assistant Professor of Engineering and Technology Education at Utah State University. He can be reached via email at firstname.lastname@example.org.
Edward Reeve, Ph.D., DTE is a Professor of Engineering and Technology Education at Utah State University. He can be reached via email at email@example.com.
This is a refereed article.
By Andy Swapp, Paul Schreders, and Edward Reeve, DTE
Figure 1. This figure shows the Griggs-Putnam index that links tree flagging to average wind speeds (Woofenden, 2009). Average Wind I II III IV V VI VII Speed mph 7-9 9-11 11-13 13-16 16-18 18-21 22+ m/s 3-4 4-5 5-6 6-7 7-8 8-9 10+ km/h 11-14 14-18 18-21 21-25 25-29 29-32 32+
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|Author:||Swapp, Andy; Schreuders, Paul; Reeve, Edward|
|Publication:||Technology and Engineering Teacher|
|Date:||May 1, 2011|
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