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techdirections September 2013 : Page 14

Provide Endless Learning Opportunities Build a Solar and Wind Power Trainer for the Classroom By R. Gene Turchin gene.turchin@gmail.com; rturchin@fairmontstate.edu S HRINKING budgets often make it hard to incorpo-rate alternative energy training into technology or career and technical edu-cation programs. Inexpensive desktop units can demonstrate photovoltaic sources and virtually any small dc motor can have blades added to make it into a small wind generator, but real-world units are prohibitively expensive for most schools. In the course of looking into alternative energy education, my colleagues at Fairmont State Univer-sity and I saw value in bringing an engineering perspective to looking at the “free energy” websites and adver-tisements. Many legitimate suppliers of wind and photovoltaic products exist, but in many cases the expected outputs are overinflated. We thought that constructing and evaluating a low-cost unit would provide students with good experience and realistic expectations about alternative sourc-es of electric power. Sunforce products (www.sun forceproducts.com) produces a line of inexpensive photovoltaic panels and wind generators that can easily be converted into a robust trainer for students. Amazon bundles a package that includes four 15 W solar panels, an inverter, a battery charger, and a 400 W wind generator in a pack-age for around $900. Add a battery, a couple of light fixtures, a duplex receptacle, and a few other goodies R. Gene Turchin is an assistant professor, Department of Technology, College of Science and Technology, Fairmont (WV) State University. and you will have a very respectable training unit. When we decided to add an alter-native energy section to our STEM summer camp, the search began for a hands-on unit that was much more than a desktop demonstration unit. The Sunforce products are designed simply enough that the construction of the unit can be part of the student learning activity or instructors can pre-construct the units and focus on the measurement of parameters and capa-bilities of wind and solar generators. cell will provide 12 V at about 1.25 A to charge a 12 V battery. A regulated battery charger is supplied to pre-vent overcharging the batteries. We constructed a control and distribution panel on a 1/8" alumi-num plate that was lying around the shop, but 1/4" plywood or Plexiglas The Photovoltaic Cells Each solar panel measures 13" × 38" and is supplied with an automo-tive type connector (Photo 1) that allows the panels to be connected with two-pole dc trailer-type connec-tors available from Radio Shack or any automotive store. The panels are connected in parallel through a four-to-one connector and then attached to the battery charger module. Each Photo 1—Male and female photovoltaic connectors Photo 2—Panels mounted on PVC frame and cart 14 tech directions X SEPTEMBER 2013

Provide Endless Learning Opportunities Build a Solar and Wind Power Trainer for the Classroom

R. Gene Turchin

<br /> SHRINKING budgets often make it hard to incorporate alternative energy training into technology or career and technical education programs. Inexpensive desktop units can demonstrate photovoltaic sources and virtually any small dc motor can have blades added to make it into a small wind generator, but real-world units are prohibitively expensive for most schools.<br /> <br /> In the course of looking into alternative energy education, my colleagues at Fairmont State University and I saw value in bringing an engineering perspective to looking at the “free energy” websites and advertisements. Many legitimate suppliers of wind and photovoltaic products exist, but in many cases the expected outputs are overinflated. We thought that constructing and evaluating a low-cost unit would provide students with good experience and realistic expectations about alternative sources of electric power.<br /> <br /> Sunforce products (www.sunforceproducts.com) produces a line of inexpensive photovoltaic panels and wind generators that can easily be converted into a robust trainer for students. Amazon bundles a package that includes four 15 W solar panels, an inverter, a battery charger, and a 400 W wind generator in a package for around $900. Add a battery, a couple of light fixtures, a duplex receptacle, and a few other goodies and you will have a very respectable training unit.<br /> <br /> When we decided to add an alternative energy section to our STEM summer camp, the search began for a hands-on unit that was much more than a desktop demonstration unit. The Sunforce products are designed simply enough that the construction of the unit can be part of the student learning activity or instructors can preconstruct the units and focus on the measurement of parameters and capabilities of wind and solar generators.<br /> <br /> The Photovoltaic Cells<br /> Each solar panel measures 13" × 38" and is supplied with an automotive type connector (Photo 1) that allows the panels to be connected with two-pole dc trailer-type connectors available from Radio Shack or any automotive store. The panels are connected in parallel through a four-to- one connector and then attached to the battery charger module. Each cell will provide 12 V at about 1.25 A to charge a 12 V battery. A regulated battery charger is supplied to prevent overcharging the batteries.<br /> <br /> We constructed a control and distribution panel on a 1/8" aluminum plate that was lying around the shop, but 1/4" plywood or Plexiglas will work as well. The Sunforce 15 W solar cells are shipped with a predrilled frame made of PVC pipe. Wing nuts are provided with the frame, so assembly is very simple. The frame is designed to allow for two different tilt angles (summer and winter) by selecting a set of holes in the top of the frame, and we drilled an extra set to mount the panels on a four-wheel utility cart so we could move it to different classrooms (Photo 2). A four-page pamphlet is provided to illustrate wiring and frame construction, but the procedure is very straight forward and many tech educators won’t need to use the directions.<br /> <br /> The frame and connections can easily be put together by students, if you want to include construction as part of the lesson. We saved the boxes and packing because they provide good compact storage if you don’t want to have the trainer out during the entire school year.<br /> <br /> The output of each cell depends on how much light it receives. In a classroom or lab with windows and fluorescent lighting, it can vary from about 11 V to 15 V with no load.<br /> <br /> The Control and Distribution Panel<br /> The control and distribution panel can be wired to suit your needs. Our panel was wired to provide two separate paths for charging the battery: one from the photovoltaic cells and a separate one from the wind generator. The documentation supplied with the units hints that there could be some interference or “backfeed” between the two charging sources. This problem can be reduced or eliminated by the addition of a simple silicon diode in the output from the solar collectors and the wind generator.<br /> <br /> We used standard surface-mount metal boxes to give a feel for a real installation. The layout of the boxes was done to illustrate the paths of the system (Fig. 1). The block diagram was used for the basic design and then the boxes moved around on the panel for practical layout.<br /> <br /> The Inverter<br /> A device called an inverter is used to change direct current into alternating current. The default unit is listed as 200 W, but I suspect from the look of the components that 200 W is very optimistic for a continuous load. There is no way to be certain short of a load test, but the unit will probably supply 50 W to 75 W continuously. Our initial inverter smoked when it was first fired up, probably because of a grounding error, so we purchased a 275 W unit at a local auto parts store. It had a substantial heat sink, so we were much more comfortable with it.<br /> <br /> Output<br /> The 110 Vac is supplied via two standard ac receptacles on one end. For the trainer unit, we used a computer power cable and plugged it into the receptacle on the inverter and then hardwired it to the distribution panel box through the top. On the plug, the longer blade is the electrical neutral and is usually a white wire. The black wire is connected to the circuit breaker distribution buss, while the white wire is connected to the ground buss. You can choose to hardwire to the inside of the inverter and remove the outlets, but that may have been the cause of our meltdown on the initial inverter, and using a cable with a plug makes for easier disconnect for teaching purposes. (See Fig. 2.)<br /> <br /> Input<br /> The inverter is supplied with 12 Vdc from the battery, and the original unit was equipped with an automotive cigarette lighter plug. The wires from the plug terminated in large alligator clips, which were intended to clip to the battery terminals. In the interest of student safety and the possibility of the clips coming loose, we terminated the wires with circular solder-less connectors that fit securely over the battery terminals for a more solid connection.<br /> <br /> To do this, cut the auto accessory plug from the end of the inverter input cable. The black zip cord is ribbed on one side to indicate the negative wire. It is connected to the spring clips on the side of the connector. Leave a small piece of the wire attached to the plug so that you can be sure of the polarity. Connect directly to the battery negative terminal. A junction box is useful for these connections.<br /> <br /> Wiring<br /> Separate fuses and switches are used for the wind generator and the solar panels so that only one unit is supplying charging to the battery. We did this for teaching purposes. When the lesson discussion is about photovoltaic cells, the wind generator is switched off (disconnected from the charging circuit) so that the students can measure the output of the solar cells. If only the wind generator is being discussed, the solar panels are switched out of the charging circuit. (See Fig. 3 and Photo 3.)<br /> <br /> The Wind Generator<br /> Testing the wind generator proved a little more difficult than solar panels. It is important that the wind generator be mounted on a stable steel pipe and anchored securely. We mounted ours on the end of a wooden pushcart so it could easily be moved outside or into a classroom. The specifications for the generator say it that it needs about a 20 mph wind to generate 12 V. A steady 15- to 20-mph wind is actually a fairly hefty breeze.<br /> <br /> Non-engineers often neglect research before taking on an alternative energy project. If your school is considering teaching wind energy, it would be wise and good design practice to see if it is viable for your location. The federal government furnishes wind resource maps and charts, which can be found at the U.S. Department of Energy site at www.windpoweringamerica.gov/ wind_maps.asp. The maps list the average wind at 80 meters (262.5 feet). Wind speeds are given on a color-coded map for each state and are listed in meters per second. The potential for learning opportunities here is enormous, such as working with metric-to-English conversions.<br /> <br /> Here in West Virginia, the potential for small wind generators appears to be limited, since our average speed throughout most of the state is between 4 and 4.5 m/s. The average looks to be about 10.1 mph with a few exceptions statewide. Since our generator requires a 15-20 mph wind, it doesn’t bode well for small generators. A 20 mph wind translates to a generator shaft speed of about 500 rpm for this particular generator (from the manufacturer’s spec sheet).<br /> <br /> To show that the generator actually outputs a dc voltage, you can connect an electric drill to the shaft with an allen wrench and give it a spin. A typical battery-powered electric drill will run in the neighborhood of 300 rpm to 500 rpm. AC-powered drills usually run at higher speed, so your choice boils down to ease of demonstration. The small 3/8" drill that I used produced about 6 Vdc at its top speed without a battery connected. It turns out that many wind generators use microprocessors for voltage regulation so that the generator must actually be connected to a battery to produce the proper output voltage.<br /> <br /> Connecting Alternative Energy and Conservation<br /> To tie the concepts of alternative energy source and conservation together, you can either create your own lessons or use one from these sites, which offer some nice sample lessons:<br /> <br /> www.clarkson.edu/highschool/k12/project/documents/energysystems/7-Household- Conservation-Efficiency.pdf<br /> www1.eere.energy.gov/education/lessonplans/<br /> <br /> You might also challenge your students to design an off-grid alternative energy system for a small house or apartment. Suggest required minimum appliances such as a refrigerator, lighting, and other bare-bones items that a house might need. The power usage of various appliances can be determined from the appliance label or by means of inexpensive power measuring devices such as the Kill-A-Watt, which gives the appliance’s wattage usage and additional parameters.<br /> <br /> Students can also use a Kill-A-Watt to compare electrical power consumption of appliances like a hair dryer on high and low settings or compare compact fluorescent lights with conventional incandescent lamps.<br /> <br /> By requiring students to perform and record measurements of the outputs of various components, the concepts of Ohm’s law and power usage can be reinforced. Here are some suggested parameters to test:<br /> <br /> -Measure the dc output of each solar cell.<br /> -Measure the combined parallel output of the solar cells.<br /> -Measure the charging current of the solar cells between the charger and the battery.<br /> -Measure the solar cell voltage output under room lighting conditions and compare to outside light.<br /> -Measure the current to the input of the charger.<br /> -Switch the solar cells out of the charging circuit and measure the output of the wind generator when driven at various speeds with a drill.<br /> -Perform blade tip speed calculations on the wind generator.<br /> -Use the concept of energy to perform calculations on how energy can be extracted from the wind.<br /> <br /> Final Thoughts<br /> During and after the construction of our trainers, we came up with many ideas. There are so many possibilities to introduce physics and engineering principles with the trainers that it was difficult to limit our focus. You may find yourself wanting to add more lessons as both teacher and student explore the concepts and principles involved in alternative energy.<br /> <br /> R. Gene Turchin is an assistant professor, Department of Technology, College of Science and Technology, Fairmont (WV) State University.<br /> <br /> Additional Resources<br /> <br /> http://learn.kidwind.org<br /> <br /> www.eia.doe.gov/kids/energy.cfm?page=wind_home-basics<br /> <br /> www.p3international.com/index.html

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