A Cool Way to Make Electricity: Solar Cell Power Output vs. Temperature
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Project Summary
| Difficulty | 5 |
| Time required | Short (several days) |
| Prerequisites | You must know or must learn how to use a voltmeter or multimeter. |
| Material Availability | Specialty item: digital thermometer with probe |
| Cost | Average ($50–$100) |
| Safety | No issues |
Sponsor
| Sponsored by generous support from AMD |
|
Objective
The goal of this project is to measure how the power output of a solar cell varies with ambient temperature.
Introduction
Solar cells (or photovoltaic cells) are devices that can generate electricity directly from sunlight. You may have seen arrays of solar cells on a roof in your neighborhood, or perhaps a much smaller array powering an emergency phone along a highway. In this project you will investigate how power output from a solar cell changes with temperature.
Terms, Concepts and Questions to Start Background Research
To do this project, you should do research that enables you to understand the following terms and concepts:
- solar (or photovoltaic) cell,
- Ohm's law (V = IR, I = V/R, R = V/I)
- load resistor,
- current,
- power.
- Given a simple circuit with a battery of known voltage connected to a resistor of known value, how do you calculate the current flowing through the resistor?
- Given the circuit described above, how do you calculate the power dissipated by the resistor?
Bibliography
- This ThinkQuest website built by students at Miramar High School, Miramar, FL, has information on how solar cells work, including an interactive presentation:
Barron, J. and students, 2004. "Solar Cells." Miramar High School, Miramar, FL. [accessed January 9, 2006] http://library.thinkquest.org/04apr/00215/energy/solar/solar_cells.htm - On this page you can build virtual circuits with batteries and resistors, then test your circuit by throwing a switch to light up a bulb. If there's too much current, the virtual light bulb blows up, too little current, and the bulb won't light. When you get the current right, the bulb glows brightly.
Unknown, 1999. "Ohm's Law." Physics Department, University of Oregon. [accessed January 9, 2006] http://zebu.uoregon.edu/nsf/circuit.html#Ohm - This link may give you more ideas on how to go about doing this project:
Smith, M., 2002. "How temperature affects a solar cell." MadSci Network [accessed January 9, 2006] http://www.madsci.org/posts/archives/jan2002/1011551989.Ph.r.html
Materials and Equipment
The basic materials and equipment needed for this project are:
- small solar cell,
- voltmeter or multimeter (check the solar cell's output voltage and current ratings and choose a meter that will accurately measure the voltage of your circuit),
- digital thermometer (can be purchased for around $20 from specialty electronics dealers),
- load resistor (use Ohm's Law and the solar cell's output voltage and current ratings to calculate the correct value for the load resistor),
- wire clip leads to connect load resistor to solar cell,
- light source.
You will also need both to cool and to warm the solar cell. It might be a good idea to keep the load resistor at a constant temperature, to make sure its resistance does not vary. (Many multimeters will also read resistance values, so you could check to see if the resistance varies with temperature. How would your results change if the resistance increases as temperature increases?)
- For cooling, use an ice bath with a piece of angled aluminum bar (available at the hardware store) to conduct heat from the solar cell. Aluminum is a good heat conductor. You can use the following:
- small plastic container,
- ice,
- water,
- small piece of angled aluminum bar,
- packing tape.
- To build the ice bath:
- Fasten the aluminum bar at the top of the plastic container, so that one angle makes a platform and the other extends into the container.
- Fill the container with ice and some water so that the angled aluminum that extends into the container is in contact with ice.
- Place the solar cell against the top surface of the aluminum bar to cool the solar cell.
- Be careful not to get your solar cell or other circuit elements wet!
- For warming to different temperatures, use a hair dryer and capture more or less of the hot air it produces by changing the position of your tubing. You can use the following:
- hair dryer,
- 2 paper towel tubes,
- aluminum foil, and
- packing tape for making connections.
- For keeping the two parts of your setup isolated, use two cardboard boxes:
- one to hold the solar cell, with enough room beneath it for the ice bath or the inlet tube from the hair dryer, and
- another box to hold the resistor and some insulation (to keep it isolated at constant temperature).
- Make your electrical connections from the solar cell to the resistor long enough so that you can separate the boxes. You want to be sure that the hair dryer warms only the solar cell, not the resistor.
Experimental Procedure
- Do your background research and make sure that you understand the terms and concepts and can answer the questions above.
- Construct your experimental setup, following the suggestions above.
- Connect your voltmeter or multimeter to read the voltage across the resistor.
- Set up your light source at a fixed distance from the solar cell, making sure that you can measure a constant voltage across the resistor when conditions are not changing.
- Take at least five voltage readings at room temperature and record the values in your lab notebook. Be sure to the note the temperature.
- Warming the solar cell:
- Set up the hair dryer and tubes so that you capture only part of the dryer output to flow over the solar cell.
- As a control, use the digital thermometer to verify that the temperature remains constant in the resistor compartment when you warm the solar cell compartment with the hair dryer setup. Arrange your two compartments so that the air from the hair dryer does not flow over the load resistor compartment.
- Next attach the temperature probe of the digital thermometer to the solar cell.
- When the temperature is stable, take at least five voltage readings and record them in your notebook.
- Adjust your tubes to capture more of the hair dryer's output, wait for the temperature to stabilize again, and take at least five voltage readings.
- Try to adjust your setup so that you can get readings from at least three different elevated temperatures.
- Cooling the solar cell:
- Set up the ice bath as described above. Place the ice bath so that the back of the solar cell is in contact with the aluminum bar.
- Wait for the temperature to stabilize.
- Take at least five voltage readings.
- Calculate the average the voltage reading at each temperature.
- More advanced students should also calculate the standard deviation of the voltage readings. Examine your measurements to see if they fall in the expected range around the average value. (Hint: how can the standard deviation help you with this?) If you have anomalous readings in your sample, you may want to exclude or repeat them.
- Calculate the power at each temperature.
- Make a graph of the solar cell power output vs. temperature.
Variations
- Test solar cell power output as a function of the angle of the incoming light. Keep the distance and brightness of the light source constant, but vary the angle of the incoming light. Make a graph of your results (power vs. angle). If you've taken trigonometry, see if you can figure out the mathematical function that explains the results. Explain why.
- Another variation would be to measure the power output of the solar cell as a function of the intensity of the incoming light (see the Science Buddies project: How Does the Intensity of Light Affect the Power Output of Solar Cells?. To vary the intensity of the light, you could use light bulbs of the same size and shape, but different wattage. For a more advanced project, you could do background research to learn how to measure the intensity of the incoming light, perhaps using a photographic light meter.
- A more advanced project idea would be to measure the power output of the solar cell as a function of the color of the incoming light. You should do background research to learn how light energy varies with wavelength. You will also need to know the spectral characteristics of your light source. For this reason, it would be a good idea to use sunlight for this project. You can get a booklet with 100 color filters for about $10 plus shipping. A search on "color filter booklet" should turn up multiple sources.
- For more science project ideas in this area of science, see Electricity & Electronics Project Ideas
Credits
Andrew Olson, Ph.D., Science Buddies
Last edit date: 2006-06-01 09:30:00
