Hands-on Activity Photovoltaics & Temperature:
Ice, Ice, PV!

Learning Objectives

After this activity, students should be able to:

• Describe the effects of temperature on the efficiency of a PV system.
• Explain the temperature coefficient and how it is calculated.
• Explain the importance of understanding how PV panels react to different weather conditions when designing a solar power plant for a specific location.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

Common Core State Standards - Math

International Technology and Engineering Educators Association - Technology

State Standards

Materials List

Each group needs:

• mini PV panel ($10-30; available online; do a product search for "small solar panel" or see the Solar Panel Source Information attachment in the Photovoltaic Efficiency unit)
• multimeter ($10; available online; see the Solar Multimeter Source Information attachment in the Photovoltaic Efficiency unit)
• 2 wires with alligator clips
• clamp or desk lamp with 100-watt incandescent bulb (~$8; best for each group to have their own, but teams can share if necessary)
• stop watch
• calculator
• Student Investigation Guide, one per group
• Investigation Worksheet, one per person

Note: The non-expendable items (mini PV panels, multimeters, wires with alligator clamps, lamp and light bulb) are reusable for the entire four-lesson unit, as well as other projects.

For the entire class to share:

• a bucket of ice water, large enough to submerge three-quarters of the PV panel
• a bucket of ice water, large enough to submerge three-quarters of the PV panel
• towel or paper towels
• (optional) thermometer, to measure the room temperature

Worksheets and Attachments

Pre-Req Knowledge

A basic understanding of an electrical circuit, including voltage, current, power and resistance.

Introduction/Motivation

When designing a solar PV power plant, engineers determine the expected power output of the entire plant. To do this, they must take into account all the factors that affect the efficiency of the PV panels and electrical equipment over the life of the power plant. Let's explore some of those factors.

If engineers installed the exact same power plant in Las Vegas, NV, and Fargo, ND, do you think it would produce the exact same amount of power over the course of a year? (Answer: No) Would it produce more or less power and what are some of the factors that would influence the power generation of the PV plants?

Well, for starters the collector slopes would be different for each latitude. If not set correctly, the panels would lose efficiency because they would not be facing the optimal direction. Another factor is the weather. The weather in Fargo is extremely different than the weather in Las Vegas. Las Vegas is in a hot and sunny, desert climate while Fargo is covered in snow many months of the year. It is obvious that snowy and cloudy days result in the PV panels producing less power, but what about a sunny day in Fargo vs. a sunny day in Las Vegas? How do you think the ambient temperature (surrounding environmental temperature) of the air would affect the efficiency of the solar panels?

The temperature of a PV cell is directly influenced by both the ambient temperature and amount of solar radiation hitting the panel. The same PV panels installed in Fargo will be colder then the panels in Las Vegas, but is this a good or bad thing? Let's do an experiment to find out!

Procedure

Before the Activity

• Gather materials and make copies of the Student Investigation Guide (one per group) and Investigation Worksheet (one per student).
• Practice setting up the experiment. Tip: It is best to set up the experiment far from a window to prevent errors due to additional incoming sunlight.
• Place a bucket of ice water at the front of the room.
• Measure and write the room temperature on the board.
• Write on the board the equations found in the associated lesson and on the worksheet.
• (optional) Write the symbols for AC (~) and DC (—) on the board and explain what they mean. (This information can be found in the multimeter manual or online.)
• Divide the class into groups of two or three students each.
• Show an example set-up of what will be done in the activity (see Figure 1).

With the Students

1. Give each group an investigation guide and each student a worksheet.
2. Direct students to gather each item on their materials list (in the guide).
3. Have students set up the 100-watt lamp in a stable position at a desk or lab station. (It is critical that the lamp does not move during the experiment.) Position the lamp about 1 foot (31 cm) from the flat surface where the PV panel will be placed.
4. Mark the exact placement of the top corner of the PV panel throughout the experiment. To do this, have students place two pieces of tape at a 90° angle from each other at a location where the PV panel will be positioned directly under the lamp.
5. Have students assemble the experimental set-up following instructions on the guide (see Figure 1).

   

6. Turn the multimeter to measure volts.
7. Designate one person in each group to be the recorder for the first experiment.
8. Have each group place its panel under the lamp, its corner lined up with the tape marks.
9. Record and calculate the Ambient Conditions on page 1 of the worksheet:

• Measure and record the room temperature.
• Turn the lamp on, set the multimeter to read milliamps and record the current. (Make sure the leads are plugged into the correct sockets.)
• Switch the multimeter to voltage and have one team member read and record the voltage. (Make sure the multimeter is turned to the voltage setting; the leads may need to be switched, depending on the multimeter used.)
• Calculate the power by multiplying I x V, being sure to convert from milliamps to amps before using Equation 1.

10. Remove the PV panel from under the lamp, being careful not to touch the lamp.
11. Detach the leads from the panel and have one student bring it to the bucket of ice water. Make sure students leave the multimeter at their desks to avoid contact between electrical parts and water.
12. Submerge the PV panel about three-quarters of the way into the bucket of ice water for one minute. Tips: Do not hold the panel by the wires. Do not hold the panel by the wires. Do not let the wires get wet! Hold the panel by its edges and not by its leads, because the leads will pull out!
13. While the students are cooling the panels, ask them to predict what might happen to the voltage and current of the panels at a lower temperature, based on the equations on the board (and on the worksheet). Record their predictions on the board.
14. After 1 minute in the ice water, have students remove the panel and quickly dry it with a towel. Return to the desk and quickly attach the leads of the (now cooler) PV panel to the multimeter.
15. When the leads are in place and the multimeter is set to measure voltage (the 20V DCV setting), have students place the panel back under the lamp in the same position as before. Immediately record the voltage. Since a direct temperature measurement cannot be made of the panel, assume the first voltage value to be taken at 0°C.
16. At 30-second intervals, record the voltage (power will be calculated later). Continue to do this for 15 minutes or until the voltage stops significantly changing. The voltage should increase as the panel warms up, with the rate being dependent on the light used and the ambient temperature.
17. Calculate the power output of the panel at each of the time intervals. Graph power output vs. time.
18. Have students complete the questions on their worksheets.
19. Conclude with an informal discussion covering worksheet predictions and questions, as described in the Assessment section.

Vocabulary/Definitions

ambient: Surrounding environmental conditions.

open circuit voltage: Voltage available from a power source in an open circuit.

photovoltaic cell: A cell of silicone that produces a current when exposed to light.

photovoltaic thermal (PVT): A system of pipes that run a fluid behind the PV panels to simultaneously cool the panels and heat the fluid.

short circuit current: Current drawn from a power source if no load is present in the circuit.

Assessment

Pre-Activity Assessment

Prediction: Before beginning the activity, ask the students to predict:

• If engineers installed the exact same power plant that exists in Las Vegas, NV, in Fargo, ND, would it produce more or less power over a year? Record predictions on the board.

Class Discussion: Discuss as a class the engineering challenges to design a PV power plant. (Possible factors to consider: Optimal panel angle placement [unique at every latitude], climate and weather conditions [sunny days, cloud cover, snow cover, length of days, ambient temperature, etc.], PV panel material composition, etc.)

Activity Embedded Assessment

Worksheet: Have students record measurements and follow along with the activity on their Investigation Worksheets. After they have finished their worksheets, have them compare answers with their peers. Walk around the class as the students are conducting the investigations and be sure that they are recording correct values and using all equipment correctly. A quick comparison to other groups and the data in the Investigate Worksheet Answers shows whether they understand the procedure and are collecting good data.

Post-Activity Assessment

Prediction Analysis: Have students compare their initial predictions with their test results, as recorded on the worksheets. Ask them to explain why their predictions were correct or incorrect.

Informal Discussion: Solicit, integrate and summarize student responses.

• (Question from worksheet) Explain what the temperature coefficient means and how it can be used to predict the power output of the panel at any temperature? (Answer: The temperature coefficient tells us how much the voltage changes for a 1º change in panel temperature. Knowing this, we can calculate the voltage output of the panel at any temperature.)
• What would an engineer need to consider when designing an array of solar panels in your area? (Answer: Weather conditions such as cloud cover, length of days, and temperature; shading from trees or nearby buildings; the amount of energy used by the building, school or home, and when it will be used.)
• Engineers can design ways to improve the efficiency of solar panels that must operate in non-optimal temperature conditions, including cooling systems that use outside air, fans and pumps. How might this affect the cost of the solar panel? (Answers should consider increased costs for complex technologies or fewer costs for more passive approaches that require no added power. See Lesson Background for Teachers in the associated lesson.)

Investigating Questions

From the Investigation Worksheet:

1. Is the panel more efficient when it is colder or hotter?
2. Predict the power output of the panel if left in these experimental conditions indefinitely.
3. Describe the shape of the curve in the graph and why it looks this way.

Safety Issues

• Be aware that 100-watt lamps get hot!
• If using a thermometer, give a brief safety talk; thermometers are very delicate and if broken, can be dangerously sharp.
• Keep ice water away from all electrical equipment.

Troubleshooting Tips

The wire connections are very important. Make sure the connections are tight throughout. If you do not get a reading on the multimeter, look for a bad connection or alligator clamp somewhere in the circuit.

Be sure that the conductive pieces, especially the ends of the leads of both the PV panel and the multimeter, are not touching any other conductive materials, such as a metal table.

Be sure you understand how to use the multimeters, take measurements in the correct setting, and convert the units as necessary (for example, 78.9 mA read from the multimeter equals .0789 A).

Activity Extensions

Design for Cooling Panels: Have students conceptually design creative ways to keep the solar panels in a power plant cool. Choose a hot location, such as a Nevada desert, and ask students to consider the real weather conditions for this site in their design. Have students draw their designs on paper or computer, and arrange for them to present and/or discuss their designs with the class.

Activity Scaling

• For lower grades, set up a demonstration of the activity, asking students to guess the voltage before and after placing the panel in ice water. Or, place a panel under the lamp for a few minutes and have them guess what the voltage will be after it heats up.
• For upper grades, have students look up the temperature coefficients of different PV panels on manufacturer specification sheets. Also have them look up the range of temperature coefficients for different types of PV materials and draw a graph comparing the different materials.

Copyright

Contributors

Supporting Program

Acknowledgements

The contents of these digital library curricula were developed by the Integrated Teaching and Learning Program under National Science Foundation GK-12 grant no. 0338326. However, these contents do not necessarily represent the policies of the National Science Foundation, and you should not assume endorsement by the federal government.