Activity 1: Build a Model of a Solar Cell
Duration: One-45 minute period
Teacher Background:
Operation of a solar cell is very abstract. To help students better understand the process of converting sunlight into electricity students will construct a nonworking model of layered solar cell. The cell will be loosely held together by toothpicks so that they can take it apart throughout the lecture.
Purpose: Create a model of a solar cell.
Materials per cell:
Foam sheets, 4 x 5 inches
Clear plastic sheet, 4 x 5 inches
Toothpicks
Scissors
Pen/pencil
Glue
2 small nuts
2 alligator clips
Mini-lamp assembly
Ruler
Procedure:
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1. Create a 3D model based on the image below. Using the foam sheets create the layers in the same proportion as you see in the image
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2. Use the clear plastic sheet to simulate the top protective layer.
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3. Glue the nuts to the bottom of the cell, at about 1 inch apart. These will simulate the wire connectors that hookup the solar cell to a circuit.
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4. Insert a toothpick in the corner through all layers. This will allow you to separate the cell at will.
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5. Connect one end of the alligator clips to the nuts, one on each. Connect the other ends of the clips to the mini-lamp.
Activity 2: Factors Affecting PV Cell Performance
Duration: Two-45 minute periods (and homework time)
Teacher Background:
The amount of sunlight of the total amount that shines down on a cell that is converted into electricity is called the cell's conversion efficiency. The efficiency rating is different for all the different types of solar cells and can be affected by various factors such as wavelength, temperature, intensity of light, angle of incidence, and distance. In this activity students will test cells to determine how various factors affect cell performance.
Purpose: To determine how various factors affect solar cell performance.
Part 1: Wavelength
Visible light is made up of a rainbow of colors from red to violet with various wavelengths of radiation from 400nm to 780nm. Each wavelength carries with it a certain amount of energy. Solar cells are designed to take advantage of certain wavelengths. In this section, you will determine how wavelength affects solar cell performance.
Materials Per Group:
Ring stand
Meter stick
1 sheet of red film 20 x 26 cm
1 sheet of yellow film 20 x 26 cm
1 sheet of green film 20 x 26 cm
1 sheet of blue film 20 x 26 cm
Lamp with 100 watt light bulb
Multimeter
Crystalline silicon solar cell
Procedure:
Record all data in the data table
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1. Set up the lamp on a ring stand at 30 cm away from the solar cell.
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2. Set up the solar cell with the multimeter set to measure volts.
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3. Turn on light and measure voltage.
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4. Turn lamp off and set multimeter to amps.
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5. Turn lamp on and measure current.
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6. Turn lamp off and set multimeter to measure volts.
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7. Position the red colored film 15 cm from light.
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8. Turn on the lamp and measure the voltage.
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9. Turn off the lamp and switch multimeter to amps.
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10. Turn on lamp and measure the current.
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11. Repeat this for the other colors.
Questions:
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1. What is the independent variable?
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2. What is the dependent variable?
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3. Write a hypothesis for this experiment.
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4. Graph the data.
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5. Analyze the data by writing a conclusion. Make sure that you include references to the data in your conclusion.
Part 2: Temperature
PV cells work more efficiently at cooler temperatures. The exact temperatures are dependent on the type of material used. So, when planning to install solar cells the ambient temperature must be taken into consideration so that the correct type of PV cell can be chosen. If controlling for temperature is not an option than a system can be designed to cool the cells.
Materials Per Group:
Ring stand
Meter stick
Fan
Thermometer
Lamp with 100 watt light bulb
Multimeter
Crystalline silicon solar cell
Procedure:
Record all data in the data table
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1. Set up the lamp on a ring stand at 30 cm away from the solar cell.
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2. Set up the solar cell with the multimeter set to measure volts.
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3. Place a small thermometer near the cell. Wait two minutes and record temperature.
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4. Turn lamp on and measure voltage.
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5. Turn lamp off and set multimeter to amps.
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6. Turn lamp on and measure current.
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7. Turn lamp off.
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8. Set up a fan 15 cm perpendicular to the solar cell.
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9. Repeat steps 1-7.
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10. Repeat steps 1-9 two more times.
Questions:
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1. What is the independent variable?
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2. What is the dependent variable?
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3. Write a hypothesis for this experiment.
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4. Graph the data.
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5. Analyze the data by writing a conclusion. Make sure that you include references to the data in your conclusion.
Part 3: Intensity of Light
PV cells work differently under different lighting conditions. Some cells work best under bright lighting conditions and others under diffuse lighting conditions. In this section you will determine which lighting condition is ideal for the PV cell. First you will test the cell under direct lighting and then under diffuse lighting.
Materials Per Group:
Ring stand
Meter stick
1 sheet of mesh, 20 x 26 cm
Lamp with 100 watt light bulb
Multimeter
Crystalline silicon solar cell
Procedure:
Record all data in the data table
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1. Set up the lamp on a ring stand at 30 cm away from the solar cell.
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2. Set up the solar cell with the multimeter set to measure volts.
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3. Turn lamp on and measure voltage.
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4. Turn lamp off and set multimeter to amps.
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5. Turn lamp on and measure current.
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6. Turn lamp off.
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7. Place a piece of mesh 15 cm below lamp.
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8. Repeat steps 1-6.
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9. Repeat steps 1-8 two more times.
Questions:
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1. What is the independent variable?
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2. What is the dependent variable?
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3. Write a hypothesis for this experiment.
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4. Graph the data.
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5. Analyze the data by writing a conclusion. Make sure that you include references to the data in your conclusion.
Part 4: Angle of Incidence
The output of a PV cell is largely dependent on the amount of light that hits the surface, so by changing the angle at which the sun's rays hit the cell, the amount of light can be changed. The closer it is to a 90 degree angle the more light it receives and the higher the output.
Materials Per Group:
Ring stand
Meter stick
Protractor
Lamp with 100 watt light bulb
Multimeter
Crystalline silicon solar cell
Procedure:
Record all data in the data table
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1. Set up the lamp at a 90 degree angle to the solar cell on a ring stand. Maintain a 30 cm distance.
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2. Set up the solar cell with the multimeter set to measure volts.
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3. Turn lamp on and measure voltage.
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4. Turn lamp off and set multimeter to amps.
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5. Turn lamp on and measure current.
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6. Turn lamp off.
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7. Set up the lamp at a 60 degree angle to the solar cell on a ring stand. Maintain a 30 cm distance.
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8. Repeat steps 2-6.
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9. Set up the lamp at a 45 degree angle to the solar cell on a ring stand. Maintain a 30 cm distance.
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10. Repeat step 2-6.
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11. Set up the lamp at a 25 degree angle to the solar cell on a ring stand. Maintain a 30 cm distance.
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12. Repeat step 2-6.
Questions:
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1. What is the independent variable?
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2. What is the dependent variable?
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3. Write a hypothesis for this experiment.
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4. Graph the data.
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5. Analyze the data by writing a conclusion. Make sure that you include references to the data in your conclusion.
Part 5: Distance
Distance also plays a part in performance of the cell. The closer the cell is to the Sun the higher the performance. This is because the Sun's rays spread out. Think of a flashlight. The closer you hold it to a wall the more intense the light, but if you move further away the light isn't as bright. In New England this distance might be a factor worth considering as we are closer to the Sun in the winter time and further from it in the summer. In this section you will determine whether the distance between the cell and the light source affect performance.
Materials Per Group:
Ring stand
Meter stick
Lamp with 100 watt light bulb
Multimeter
Crystalline silicon solar cell
Procedure:
Record all data in the data table
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1. Set up the lamp on a ring stand at 60 cm away from the solar cell.
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2. Set up the solar cell with the multimeter set to measure volts.
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3. Turn lamp on and measure voltage.
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4. Turn lamp off and set multimeter to amps.
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5. Turn lamp on and measure current.
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6. Turn lamp off.
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7. Set up the lamp on a ring stand at 45 cm away from the solar cell.
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8. Repeat steps 2-6.
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9. Set up the lamp on a ring stand at 30 cm away from the solar cell.
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10. Repeat steps 2-6.
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11. Set up the lamp on a ring stand at 15 cm away from the solar cell.
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12. Repeat steps 2-6.
Questions:
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1. What is the independent variable?
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2. What is the dependent variable?
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3. Write a hypothesis for this experiment.
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4. Graph the data.
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5. Analyze the data by writing a conclusion. Make sure that you include references to the data in your conclusion.
Activity 3: Are Photovoltaics the Most Cost Efficient Choice for Your Home?
Duration: Two - 45 minute period
Teacher Background:
In order to determine how many solar cells are needed to power all the electricity needs a home has you need to know the home's average energy consumption, the amount of solar radiation the home's geographic area receives, and the size of the solar module.
To tailor this lesson to your geographic area, use the following sources: Average energy consumption and cost per household by state: http://www.eia.gov/tools/faqs/faq.cfm?id=97&t=3. Average solar radiation: http://rredc.nrel.gov/solar/old_data/nsrdb/1961-1990/redbook/atlas/serve.cgi
Purpose: In this activity you will determine where in the United States photovoltaic systems are the most cost efficient source of energy.
Materials:
Pen/pencil
Calculator
Data table
Procedure:
Using the data table below calculate how many years it would take for a photovoltaic module system to pay for itself. Use the following table to record your calculations.
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1. Calculate the, kWh/day, usage by dividing, kWh/month, by 30 days.
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2. Convert, kWh/day, to watt-hours /day, by multiplying by 1000.
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3. Calculate, watts from module/day, by multiplying number of, peak hours of sunlight, by, solar module wattage.
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4. Calculate, modules needed, by dividing, watt-hours /day, by, watts from module/day.
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5. Determine the, cost for all modules, needed by multiplying the number of, modules needed, by $400 (average cost).
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6. Calculate each household's, current electricity cost/year, by multiplying, kWh/month, by, cost of electricity/kWh, and then by 12 months.
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7. Determine, years to pay off solar modules, by dividing the, cost of all modules, by the current electricity cost/year. Round to the higher whole number.
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Questions:
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1. In which state would the photovoltaic system pay itself off the quickest?
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2. If the electricity consumption and cost per kWh were equal which state would find photovoltaics the best option?
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3. Why do you suppose that Hawaii's electricity cost is so high?
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4. Did any of these results surprise you? Why?
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5. For the states where photovoltaic systems are not as cost effective, what other renewable energy sources might they use? Explain your answer.