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After watching a NewsHour video on college students’ innovations that includes a thermoelectric phone charger, students will be challenged to design a sustainable light source using hot and cold temperatures. If time allows and resources are available, students will test their ideas using a thermoelectric generator (TEG). TEGs produce electric power through extreme differences in temperature, which have the potential to provide electricity in remote areas. A successful prototype that lights up an LED will need several TEGs in a circuit and some creativity in maintaining hot and cold sources in contact with each side of the TEG.
How can we invent a clean energy and affordable device to produce light using extreme temperatures?
One or two 50-minute class periods (Note: If you have limited time and resources, you can work through the sketch/design phase only).
Science, engineering, technology
New inventions have the power to change the world and are a natural fit for the United Nations’ Sustainable Development Goals (SDGs). The goals challenge communities to find local solutions to 17 major problems facing our world. The goal of “Affordable and Clean Energy,” SDG #7, requires creative approaches to producing electricity. Some researchers have proposed using existing hot and cold sources to create local lighting in remote places. Our invention challenge is to create a light source that runs on electricity produced from temperature differences.
- Pen, paper or other art materials
- Various sources of hot and cold, such as hand warmers, body heat, ice, ice gel packs, water, sun (you can be creative and think of any safe heat or cooling source!)
- Conductors and insulators for maximizing temperature differences (aluminum foil, hot pads or other cloth, cardboard, Styrofoam, conductive paste, etc)
- Alligator clips (several per group)
- If available: Thermoelectric Generators (Heat Sinks) (several per group)
- If available: LEDs
- If available: Multimeter (note: if electric supplies are not available, you could use a specification sheet for a thermoelectric generator and two thermometers instead of above materials)
TEGs generate electricity through temperature extremes: the greater the difference in temperature, the more power produced. There are many naturally occurring hot and cold temperatures we could use to produce power this way; the challenge is maintaining that power, as heat always moves to colder temperatures towards equilibrium. However, with some creative thinking, you can apply your knowledge of circuits, conductors and insulators to harness temperature differences as an energy source! Let’s see one team of high school inventors’ approach to applying this technology:
- How does their thermoelectric generator work?
- What challenges might a user of their TEG face?
- What was the highest voltage you observed with your TEG? Do you think you could achieve 3 Volts to light an LED?
Only if TEGs and other materials available, otherwise skip to main activity: Take one TEG and connect it to the multimeter leads as shown. Turn the dial to DC Voltage (2 V is recommended) and hold the TEG in your hand to see what happens. What can you do to increase the voltage potential? What happens to the voltage when you put your hands on both sides of the TEG?
Try out a few items at your station and see what happens to the voltage when the TEG touches different temperatures. Does the voltage stay the same over time, or does it change? Why do you think that is?
For single day, design only:
- Brainstorm and list sustainable sources of hot and cold that are readily available to you and that could be brought close to each other.
- Sketch a device that would bring your most sustainable hot and cold sources near each other. Consider: How would you keep the two sources of hot and cold insulated from each other?
- Share designs in class. What are some practical considerations for maintaining heat levels necessary to sustain and power your device?
- Revise sketch based on class discussion and feedback.
If time and materials available for build and experimentation:
Part 1: Creating a series circuit
- Take your TEG from the warm-up activity and record the highest voltage potential and current. How might you increase the voltage potential by connecting multiple TEGs in a circuit?
- Try creating a series circuit with two or more TEGs by connecting the positive (red) lead of one to the negative (black) lead of another as shown in image 3. What happens to the voltage potential?
- How else can you increase the voltage potential? Try placing more of your TEGs in the series (connecting) positive to negative, and then experimenting with different temperatures on each side. The Seebeck Effect states that the voltage potential is proportional to the temperature difference. Most LEDs require 3 Volts or more; what can you do to make the LED light up? (Teacher note: you can ask students to create a sketch of their prototype to test the next day, or simply let them experiment with materials to learn about conductors and insulators.)
Part 2: Sustaining Power (Day 2)
Producing enough power to light an LED is just the first step; can you make this energy source sustainable for more than a few seconds? You may have noticed that the voltage slowly decreases as the temperature difference decreases. How could you take advantage of conductors and insulators to invent a prototype that keeps the hot side hot and the cold side cold?
- Experiment with the materials available to you and divide into conductors and insulators. As you design your prototype, think about where you want to conduct heat, and where you want to prevent heat from transferring to your cold materials.
- Build your prototype and test with your TEG and best hot and cold temperature sources. How long can you keep the LED lit?
- What can you do to improve your original design? What can you add to sustain the light, or to make your design more practical to use?
Think back to UN SDG 7:
- Where could this energy source be introduced (think extreme temperatures)?
- What challenges might you face using this energy source?
- What other low-voltage applications might be able to take advantage of a TEG?
Want to learn more about SDGs? Check out this NewsHour EXTRA lesson here.
Here’s a fun graphic from the Smithsonian’s Lemelson Center breaking down the steps of the invention process!
Kirstin Bullington teaches at Richland Two Institute (R2i2) of Innovation in Columbia, South Carolina. Kirstin served in the Peace Corps as a health specialist volunteer in Togo (West Africa) to work on the HIV/AIDS epidemic. After returning to the U.S., Kirstin joined Teach for America and taught high school biology in Newark, N.J. As a robotics coach, she was introduced to the field of engineering, and immediately sought opportunities to teach those courses at the high school level. She joined the R2i2 in 2016, because of its “endless possibilities” to make high school education meaningful and relevant. In 2019, Kirstin’s students received a Lemelson-MIT InvenTeam grant for their solar hybrid device which they worked on with a school in Senegal.
To explore the rest of Classroom’s Invention Education lesson series, click here. We’re always looking for ways to make our invention resources stronger. If you completed part or all of this lesson, we would appreciate it if you filled out this feedback form.