Standards

Mid-continent Research for Education and Learning
Earth and space sciences, Level 4 (grades nine -12)
High school students should know the major external and internal sources of energy on Earth (e.g., the Sun is the major external source of energy; the decay of radioactive isotopes and gravitational energy from the Earth's original formation are primary sources of internal energy)

Materials

CNNfyi.com article "Solar power takes root in California"
Internet access
small DC electric motor
solar panel
string
mass set
stop watch
meter stick
ring stand and clamps
multimeter
strong light source

Suggested time

One class period

Procedures

1.Review the recent energy problems occurring around the United States, including rising utility prices. Ask students for suggestions on ways to get additional energy.

2. Have students read the CNNfyi.com article "Solar power takes root in California" and ask the following:

• According to the article, why has California earned a reputation as being "power savvy"? What is renewable energy? Why do you think it is important to use renewable energy? What is Sacramento Municipal Utility District (SMUD)'s solar energy program?
• What did Nick Ray have installed on his roof? How much of a difference does Nick Ray expect to see on his electricity bill? How much will his system cost? How much of a discount was Mr. Ray offered? Why? About how much money does the solar cell industry make per year? What is expected to happen to that figure between now and 2005?
• How has California's energy crunch affected interest in solar power alternatives? Explain. What do people in the industry believe will happen soon to revolutionize the solar power industry? What do you think this technology might look like? What do you think is preventing wider use of solar power today?

3. Inform students that one of the main obstacles to overcome in the effort to increase photovoltaic technology use is low efficiency. Have your students use a solar-powered motor to help determine the efficiency of a small photovoltaic cell. 1. Divide the class into small groups and provide each group with the following: small DC electric motor, solar panel, string, mass set, stop watch, meter stick, ring stand and clamps, multimeter, strong light source.

2. Clamp the electric motor to the ring stand and position the motor so the shaft extends out over the edge of the table.

3. Attach the string to the shaft of the electric motor so that when the motor runs the string will wind up around the shaft.

4. Fix the solar panel to the table, wire it to the motor, and check its polarity.

5. Shine a bright light on the solar panel and watch for the motor shaft to begin turning. If it fails to turn, use the multimeter to check for output from the solar panel and input to the motor. Change connections as needed.

6. Attach a known mass to the loose end of the string, so that as the shaft of the motor turns, the mass is lifted from the floor.

7. Choose a light source and place it at a set distance from the cell so that most of the light hits the solar panel. Connect the panel to start the motor turning.

8. As the mass is raised, use the stopwatch to measure how long it takes it to reach the top of the ring stand. Record the data.

9. Repeat, this time using the multimeter to measure current flowing to the motor and the motor's resistance. Record the data.

10. Have students calculate the efficiency of the solar cell by comparing output power to input power using the following equation: current (amps measured by the multimeter) squared x resistance (ohms) x time needed to raise the weight (sec) = power input (watts). Determine the output power (put out by the machine) using this equation: the product of mass of the weight (kg) x gravity (9.8 m/s/s) x height (distance mass was raised), divided by time needed to raise the mass (sec) = power output (watts). Determine the efficiency by dividing the output power by the input power and multiplying the result by 100%.

Assessment

Have students share how accurately they think this experiment simulates how the sun could be used to reduce power needs. Have students suggest refinements to solar technology that they think could increase solar power efficiency.

Accommodations

Logical/mathematical
Students can develop a list of renewable energy sources and determine the benefits of using each source.

Challenge

Students can use Riverdeep.com's Build a Solar Energy Collector to create their own collector. Have students explain to the class how a solar energy collector works using their own as an example.

Rivers feel heat as U.S. energy demand rises
April 11, 2001
Lesson plan: Power crisis in California
January 24, 2001
Lesson plan: Impact of California's power crisis
January 4, 2001

Blackout
ENERGY FACTS: PHOTOVOLTAIC CELLS
SOLAR ENERGY
PV Power:PV Frequently Asked Questions

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