U.S. DEPARTMENT OF Energy Efficiency & ENERGY EDUCATION AND WORKFORCE DEVELOPMENT ENERGY Renewable Energy Utilizing Photovoltaic Cells and Systems (Nine Activities) Grades: 5-8 Topic: Solar Owner: National Renewable Energy Laboratory This educational material is brought to you by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy. This lesson plan may contain links to other resources, including suggestions as to where to purchase materials. These links, product descriptions, and prices may change over time. Utilizing Photovoltaic Cells and Systems For the Teacher As teachers, we want students to learn about energyy, how we use it, and where it comes from. It is important that students become aware of both renewable and nonrenewable forms of energy resources so that as they grow into adults they can be informed citizens and can make goood choices about the resources they use. One renewable resource that many of us u se today is solar energy. Solar energy is used in residential homes, industrial applications, central power semiconductors on the surface of stations, commercial buildingss, and more. photovoltaic cells) to find the Students may know a little about solar best possible materials for harnessing the energy, as some of their homes may use sun’s energy. solar panels for heating or coolinng purposes. The following projects allow National Science Education students to set up their own Standards by the National investigaations and manipulate variables Academy of Sciences surrounding photovoltaic cells. These projects can be easily integrated into a Science Content Standards: 5-8 normal science classroom curriculum, or Science As Inquiry can be completed by students individually – Content Standard A: for science fair projects. “Abilities necessary to do scientific All of the projects listed will fit inquiry” easily into classroom lessons surroundinng “Understandings about scientific scientific inquiry and the scientific inquiry” method. The projects will also help Physical Science illustrate concepts about electricity, lighht – Content Standard B: and color, velocity and gravity, chemistry “Transfer of energy” and polarity, and could even lead to Earth and Sp ace Science social studies or social action projects. – Content Standard D: At NREL scientists are researching “Earth in the solar system” ways to make solar energy easier and Science and Technology less expensive to use. The authors of – Content Standard E: this section are studying diffe rent “Abilities of technoloogical design” transparent conducting oxides (the 73 This lesson plan may contain links to other resources, including suggestions as to where to purchase materials. These links, product descriptions, and prices may change over time. “Understandings about science and cells were not produced until the mid technology” 1950s. In 1954, the first crystalline silicon Science in Personal and Social cell was created in Bell Laboratories in Perspectives the United States. This cell was 4.5% – Content Standard F: efficient, which means that it only turned “Science and technology in 4.5% of the sun’s energy into electricity. society” Today’s PV cells are made of several layers of semiconductor material. On the bottom of the cell is a layer of a conductive metal and on the top is an additional conductive film. When sunlight strikes the upper semiconductor layer, photons excite electrons in the semiconductor, causing them to migrate to the next layer. As you probably know, electrons have a negative charge. When they move to the next layer, they leave a positively charged hole behind. When the Technology Description excited electrons reach the surface of the cell, it moves through the external circuit In 1839, at age nineteen, French and returns to the opposite layer to fill in scientist Edmund Becquerel was the first the positively charged hole. This creates person to observe an extraordinary and electricity. very useful phenomenon called the You may have seen photovoltaic photovoltaic effect. The photovoltaic cells and modules on people’s homes and effect is the process that occurs when businesses. These cells are capturing the photons, or the particles of energy in a sun’s energy and changing it into beam of sunlight, hit atoms in electricity for us to use. Buildings are not semiconductors and knock electrons the only place where photovoltaic cells loose, which makes electrical current are used. The sun powers illuminated possible. warning signs on many highways and Semiconductors are materials that almost every American space satellite allow electric currents to flow through uses PV for its electric power! them under certain conditions. You may be asking yourself why Semiconductors are neither excellent we would want to use the sun’s light for conductors (like copper wiring) nor are electricity when we have so many other they excellent insulators (like glass or energy resources. The answer is that plastic), but have properties somewhere every day more solar energy falls to the in the middle. Semiconductors are used in Earth than the total amount of energy the photovoltaic cells (sometimes referred to planet’s 6.1 billion inhabitants could as PV cells or solar cells), computers, consume in 27 years. In other words, windows, and more. there is plenty of sunlight to go around Although Becquerel discovered the and we won’t run out of it until the sun photovoltaic effect in the 1800s, solar dies (which is not expected to happen for 74 This lesson plan may contain links to other resources, including suggestions as to where to purchase materials. These links, product descriptions, and prices may change over time. SunWind http://sunwindsolar.com/ Resources for the following projects: PV and Electrical Measuring Supplies PV cells: (Please note that when searching for PV cells on the internet, use key words “solar cells.”) www.scientificsonline.com (Click on the solar energy tab, then click on solar cells. (Contains low-cost solar cells to another 4.5 billion years). This makes the be assembled.)) sun a renewable resource. Today's scientists continue the http://www.solarnature.com/educationa quest for an economical system for l.html (Many choices at many prices) converting sunlight to electricity. Scientists want to make energy from the Radio Shack stores or sun cheaper for us to use in our homes www.radioshack.com and businesses so that we can decrease our usage of non-renewable energy. http://www.solar­ world.com/default.htm Resources: (Many choices – prices range from $8.00-$16.00) U.S. Department of Energy PV Home Page Resistors (1 ohm to 1 megaohm): http://www1.eere.energy.gov/solar/photo voltaics.html Radio Shack stores or www.radioshack.com - Be sure to get a How Stuff Works low watt resistor for safety purposes. www.howstuffworks.com/solar-cell.htm (Cat#’s 271-1116 and 271-1108 are fine - they are $0.99 Florida Solar Energy Center each) www.fsec.ucf.edu/pvt/ Voltmeters: Roofus’ Solar Home http://www1.eere.energy.gov/kids/roofus/ www.nebraskascientific.com (Use the site search option and type voltmeter - Solar Energy $15.95) http://www.eia.doe.gov/kids/energyfacts/s ources/renewable/solar.html 75 This lesson plan may contain links to other resources, including suggestions as to where to purchase materials. These links, product descriptions, and prices may change over time. Multimeters: Resistors (1 ohm to 1 megaohm): (See resource section.) www.nebraskascientific.com (Use the site search option and type multimeter - 25W-100W Light bulbbs: $33.50) Grocery store ($0.75-$1.00 each) www.cs-sales.com (Do a search on the Vololtmeter: site. Options rang e from $7.95-59.95) (See resource section.) Multimeter: Projeect Ideas (See resource section. Thhis equipment is not absolutely necessary for this project, but it allows you to measure 1 What is the output of a both voltage and current.) photovoltaic (PV) cell? Safety and Environmental Learninng Objective: You will be able to Requirements: Even if you wear measure and find out for yourself just sungllasses, do not look directly at the how much energy (voltage) a reflected image of the sun. Bulbs can get photovoltaic cell can create simply by hot! The PV cell is most likely brittle; placing it in front of a light so urce! handle it with care. Also, be sure to follow all instructions on the voltmeter or multimeter carefully because you are dealinng with electricity. Sugggestions: Connect the resistor and voltmeter (or multimeter) to PV cell leads (leads may have to be soldered on with low-temperature solder.) Try 25W, 40W, etc., bulbs at a fixed distance from the PV cell and record the voltagees of each bulb. Controls and Variables: Light intensity, Then try one bulb at several distances. distance from PV cell to light source, load Also, try a fixed distance with one bulb, (resistor or light bulb) but hook up a load to be powered by the PV cell. Measure the voltaage drop across Materials and Equipment: the load and the current to the load. Calculate the power geenerated with: PV cells: power = current X voltage (or power = 2 (See resource section.) voltage /resistance). 76 This lesson plan may contain links to other resources, including suggestions as to where to purchase materials. These links, product descriptions, and prices may change over time. Flashlight bulbs: Hardware store (Prices vary.) Fresnel Lens: www.sciplus.com (Do a search for Fresnel lenses. A variety of lenses exist between $0.75 and $1.25.) Safety and Environmental 2 How does concentrating the Requirements: Concentrated sunlight sunlight affect the output from can be extremely dangerous to the naked a solar cell? eye. Even if you wear sunglasses, do not look directly at the reflected image of the Learning Objective: You will be able to sun. Also, light bulbs can get hot! The determine for yourself whether PV cell is most likely brittle; handle it with concentrating light with mirrors and/or care.