AbstractSolar power is hot these days. Gleaming, black solar panels soak up rays on more and more rooftops of homes and businesses providing a clean, alternative source of heat and electricity. You might guess that different times of the day yield different levels of solar power. But just how much does the sun's position in the sky affect the power that solar cells and panels can generate? That's the question this project is all about.
Darlene Jenkins, Ph.D.
The idea for this project came from this DragonflyTV episode:
- TPT, 2006. Solar Car by Isaac and Anjali, Twin Cities Public Television. Retrieved on April 22, 2007.
The goal of this project is use a solar car to discover if the position of the sun affects the power generated by solar panels.
Check out the video to see how two clever students, Anjali and Issac, designed an easy experiment to measure how solar power changes over the course of the day. They started with a toy car powered completely by sunlight and set up their own mini race track to test how much the angle of the sun affected the speed of the car. You might find their results surprising. And if you feel the need for speed, you might want to set up your own race track and try a few solar runs of your own.
How do the panels on the solar car actually work? Solar panels are sometimes called photovoltaic cells (photo = light, voltaic = electricity) because they absorb photons of light to create an electrical voltage. Most panels are specialized arrays of semiconductors like silicon mixed with other elements that together use the sun's energy to jostle free electrons residing within the molecular complex of the panels. The freed electrons begin to flow in a united and directed fashion due to positive and negative charges set up within the panels. This, in turn, creates the electrical current that can be tapped to provide power to homes and businesses, or in the case of this project, to solar cars.
How much power is generated by a solar panel depends on its size and composition as well as its exposure to the sun. Even small changes in sunlight can reduce power production by 50% or more, so installers placing panels on rooftops must pay close attention to the roof's position and angle to the sun. In the video above, Anjali and Issac had the same idea when they set up their tests with their solar car.
In Anjali's and Issac's experiment, the car picked up speed as the angle of the sun increased after 8 a.m. But the car seemed to reach its top speed as early as 10 a.m. even though the sun continued to climb higher in the sky up until noon. If you were to try a similar experiment, do you think your results would be the same? Would using different cars make a difference? Would collecting more data each hour change the results? Perhaps you can think of additional questions to ask or different ways to run your solar car tests in your experiment.
In the next sections, we've provided directions for Anjali's and Issac's experiment as well as some suggestions for additional things to try. You can repeat their experiment exactly as they did or make modifications of your own. You'll also want do some background research to learn more about the science that links the powerful light from our nearest star to the electrical current in our cars and homes.
Drivers, start your engines— or rather, power them up, and let the sun shine on!
Terms and Concepts
- Solar cells (photovoltaic cells)
- Solar panels
- Silicon semiconductors
- How does the angle of the sun with respect to the ground change during the day?
- How does the angle of the sun relate to the sun's intensity?
- What are solar panels made of and why?
- How do solar cells (photovoltaic cells) collect light energy and convert it to electricity?
- What factors make solar panels better (more efficient) at collecting light and producing energy? What are some limitations to using solar cells and panels?
- Why are solar panels relatively expensive right now, and how are scientists trying to make them more affordable?
- Solar Action Alliance. (n.d.). Solar 101/Basics. Retrieved August 10, 2016.
- Aldous, S. and Toothman, J. (2000, April 1). How Solar Cells Work. Retrieved on August 10, 2016.
- Pollick, M. (n.d.). How Do Solar Panels Work? WiseGeek. Retrieved August 10, 2016.
- The idea for this project came from this DragonflyTV podcast:
Twin Cities Public Television. (n.d.). Solar Car by Isaac and Anjali. PBS Kids Go!. Retrieved August 10, 2016.
Materials and Equipment
- Toy solar car, for example:
- Solar Car Book (and mini solar car kit) available from Amazon.com
- An outside area free of shadows (throughout your test period) for making your test track
- Masking tape (to mark off your track start and finish lines)
- Meter/yard stick
- Large chalkboard protractor to measure the angle of the sun (available online, search for "chalkboard protractor")
- Clock or watch to track time of day
- Stop watch or timer that measures seconds
- Lab notebook
- Pen or pencil
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To repeat Anjali's and Issac's experiment:
- Review the video once more to see how Anjali and Issac set up their experiment.
- Mark off your race track on a smooth, flat sidewalk or driveway that is at least 12 meters (about 40 feet) long.
- Mark both the "start" and "finish" lines with a piece of tape.
- It is important that your test track be free of shadows for the entire duration of your test.
- Plan to run your car races on the hour, starting at 8 a.m. and continuing until noon. (Time points should be 08:00, 09:00, 10:00, 11:00, and 12:00 noon.)
- Measure of the angle of the sun in the sky right before each test:
- Tie a string to a meter stick. Hold the stick straight up on the sidewalk.
- Pull the string tight until it reaches the end of the stick's shadow.
- Use the protractor to measure the angle of the string from the surface of the ground. (Watch the video again to see how this is done, if necessary).
- Record the angle of the sun at each time point of the experiment.
- At each time point, use your stop watch to determine the time it takes your car to travel the distance of your track. Test your car twice for each hourly time point.
- Record the car's times in seconds for all races in your notebook.
- At each hour time point, be sure to wipe the surface of the solar panels with a clean cloth so there is no dirt to interfere with light absorption.
- If your car completes the course quickly enough, try increasing the test runs to three to five runs per hour. This will give you more data per hour to calculate your average speeds.
Analyzing Your Data
- Calculate the average start-to-finish time for each hourly time point.
- Calcuate the average speed, in meters per second, of your car at each hourly time point. Average speed is equal to the distance of the test track (in meters) divided by the average time (in seconds) it took the car to reach the finish line. For example, a 10 second time for a 40 meter distance would mean 40 meters /10 seconds or 4 meters per second.
- Make a table that shows the time of each race, the average speed of your solar car (in meters per second), and the angle of the sun at each time point.
- Did your car's speed change over time?
- When did you observe the top speed of your car? What was the angle of the sun at that time point?
- Graph your data to show the average speed of your car (in meters per second, y-axis) vs. the angle of the sun with respect to the ground (in degrees, x-axis). Did your car's speed change as the angle of the sun increased?
Ask an Expert
- Run tests past noon to include the afternoon hours. Do you see a change in speed as the afternoon progresses? Remember that your test track needs to remain shadow-free for the entire duration of the experiment.
- What do you predict your results would be if you ran this experiment in the winter versus the summer, or in spring or fall? Explain your predictions and if possible, try to do an experiment in at least two seasons of the year. Compare your results from both experiments and explain why there are changes or not.
- If your car has panels that can be tilted, see what happens when you first test with the panels in the flat position, then immediately retest with the panels tilted more directly toward the sun. Can you figure out how to measure the angle between the sun and the car's solar panels if the panels are not parallel to the ground?
- Do different colors of light influence how much power can be generated by your solar panels? Try covering your solar panel with colored cellophane paper and repeating the experiment at high noon to get the maximum light. Use different colors for each test (i.e., red, yellow, green, blue, violet). Explain why we see different colors of light and how the different wavelengths affect solar panels.
- Apply your knowledge— taking into account what you have learned about solar panels and solar power:
- What advice would you give your family about the best place to install solar panels in your home? How about at your school? Why?
- Find out what your typical electric bill is at home per month, and figure out the ideal size of solar panel setup needed for your home. (You'll have to do a little research to see what voltage/current is available on various types of solar cells/panels).
If you like this project, you might enjoy exploring these related careers: