How Efficient is a Solar Panel?
Comparison of energy input to the energy output of a photovoltaic cell determines its effectiveness.
A photovoltaic cell, also known as a solar panel, converts solar energy into electrical energy. Solar panels are composed of thin layers containing semiconductors such as silicon. When light strikes these panels, the absorbed energy excites the electrons in the semiconductive material, causing them to move from their original location and generate electricity (Figure 1).
Solar panels were first invented to harness solar energy in the late 1800s. However, the first photovoltaic cells were only about 1 percent efficient. In the mid-1950s, scientists began using silicon in solar panels, which improved the efficiency to about 6 percent. Today’s advanced photovoltaic cells operate with an efficiency of about 20 percent. In this laboratory, you will design an experiment to determine the efficiency of a photovoltaic cell.
- solar lamp
- ring stand
- utility clamp
- photovoltaic cell (solar panel)
- insulated wire leads with alligator clamps
- lightbulb with connector wires
- science notebook
- Your job is to design and perform an experiment to determine the efficiency of a solar panel.Page 29 | Top of Article
- You can use any of the supplies provided by your teacher, but you will not need to use all of them.
- Before you conduct your experiment, decide exactly what you are going to do. Write the steps you plan to take (your experimental procedure) and the materials you plan to use (materials list) on the data table. Show your procedure and materials list to the teacher. If you get teacher approval, proceed with your experiment. If not, modify your work and show it to your teacher again.
- Once you have teacher approval, assemble the materials you need and begin your procedure.
- Collect your results on a data table of your own design.
|Your experimental procedure|
|Your materials list|
1. Pyranometers measure solar power in watts, while the output of the photovoltaic cell can only be measured in reference to amperage or voltage. So that values can be compared, convert the photovoltaic cell output into watts using the following equation:
watts = amps × volts
2. What is the difference between voltage, amperage, and power?
4. How efficient was the solar panel you tested?
5. What are the benefits of using solar energy as a power source? What are the disadvantages?
6. How do you think the efficiency of solar panels in converting solar energy to electricity might be improved?
What’s Going on?
Photovoltaic cells, or solar panels, are devices that capture energy from the Sun in order to convert it to electrical energy that can be used as a power source. Solar panels contain collections of semiconductive plates that can absorb a certain wavelength of sunlight. As solar energy hits these panels, it excites the electrons in the plates, causing them to move from their original locations. As electrons begin to flow, they are collected and moved out of the solar panel to be utilized as electricity. Solar panels are often used to power calculators and generate electricity within homes. They are also commonly used to power space probes.
Although the efficiency of photovoltaic cells has improved greatly since they were first designed in the 1800s, a great deal of energy is still lost during the conversion from solar energy to electrical energy. Some of the sunlight that hits a solar cell is reflected, returning to the atmosphere instead of being converted into usable energy. Additionally, a portion of the electricity generated from the movement of electrons is lost as heat or is reduced due to resistance or recombination. Although the efficiency Page 31 | Top of Articleof solar panels is generally only around 20 percent, in some cases solar energy can be much more cost-efficient than traditional electrical energy. Depending on the location of the panels, the type of electricity that must be generated, and the amount of sunlight that can be absorbed, the overall benefits of having solar power often outweigh the costs.
Since 1998, scientists from all over the world have been assembling the International Space Station. Even as the assembly continues, scientists on the space station are able to perform experiments and tests for weeks at a time. The electricity required by astronauts and scientists aboard the space station is provided by very large solar panels. (Figure 2). The solar panels on the International Space Station are designed so that they will tilt toward the Sun, maximizing their efficiency.
Want to Know More?
See appendix for Our Findings.
Energy Information Administration. “Energy Kids Page,” November 2007. Available online. URL: http://www.eia.doe.gov/kids/energyfacts/sources/renewable/solar.html . Accessed March 25, 2009. Sponsored by the Department of Energy, the Kids Page provides easy-to-understand information and diagrams on solar panels.
Knier, Gail. “How Do Photovoltaics Work?” Science at NASA. Available online. URL: http://science.nasa.gov/headlines/y2002/solarcells.htm . Accessed March 25, 2009. On this Web page, Knier explains how light energy is converted to electricity.
National Renewable Energy Laboratory. “Solar Energy Basics,” November 6, 2008. Available online. URL: http://www.nrel.gov/learning/re_solar.html . Accessed March 25, 2009. This Web site describes applications of solar energy.
Tabak, John. Solar and Geothermal Energy. New York: Facts On File, 2009. An excellent overview of both solar and geothermal energy and the prcesses by which they can be harnessed.