Hands-on Activity: Cooking with the Sun
Educational Standards :
Learning Objectives (Return to Contents)
After this activity, students should be able to:
Materials List (Return to Contents)
Each team needs the following plus the materials for one type of solar cooker:
For a shade area control station:
Each team needs the materials to build one of the four types of solar cookers.
Cooker #1 (Box Panel Cooker)
Cooker #2 (Modified Box Panel Cooker)
Cooker #3 (Simple Cone Cooker)
Cooker #4 (Parabolic Solar Cooker)
Introduction/Motivation (Return to Contents)
Who likes to cook? Who likes to eat? How do you think you could heat water or cook food without a stove, oven or microwave? How did people cook before such appliances? People have been able to cook food over open fires, but have you ever heard of cooking with the sun? Although people have used the sun to dry foods for centuries, solar cooking (cooking with the sun) is a more recent technology. There are several reasons to use the sun to cook as much as possible. Regular cooking techniques require burning wood, other fibrous plant remains or fossil fuels (indirectly, if electricity made from burning fossil fuel is used in cooking). Energy from the sun is free — you only need to build a device to capture it. Most solar cookers are easy to build, and solar cooking reduces fossil fuel and electricity consumption.
In areas without electricity or gas for energy, people often do not have ovens or stoves for cooking, so engineers design inexpensive solar cookers to help them. Usually, the people in these areas use wood to cook, so the use of solar cookers also saves trees, which reduces deforestation. Deforestation is a big contributor to global warming, habitat destruction and erosion of soil (which leads to flooding and landslides). Solar cookers can also be used to purify water without using wood or fossil fuel resources. Using solar cookers reduces pollution and the emission of greenhouse gases. Using a solar cooker, rather than an oven or stove, does not heat up the house in summer and is inexpensive to build. These are all good reasons to use a solar cooker! See http://solarcooking.org/ for photographs of solar cookers being used in places all over the world.
Cooking food with the sun is basically the same as regular oven or stove cooking (not microwave cooking). However, there are three principles of solar cooking that engineers must consider: directing the maximum possible amount of sunlight to the food by reflection, converting sunlight into thermal energy, and holding on to solar heat by using insulation. Also, all solar cookers must be able to absorb as much sunlight as possible. Black pots, pans and dishes are all used in solar cookers to maximize the absorption of light. Some solar cookers have black interior surfaces to maximize conversion of sunlight into thermal energy.
Insulation minimizes how fast heat is lost from the solar cooker. Some models also use a glass or plastic lid to trap the heat inside. Cooking times are decreased if insulation is included, such as cardboard, wood, plastic, glass, a layer of air or commercially-produced, high-temperature resistant foam. Box cookers are the most efficient because they retain more heat than other models through the use of insulation on the sides of the box.
Review the ways heat moves:
Which method of heat transfer delivers heat from the Sun to the Earth? (Answer: Radiation) Radiation is how the heat is going to get into our solar oven. So, how are we going to keep the heat in the oven? How does your house keep heat in during the winter, or keep heat out in the summer? (Answer: Insulation) Insulation is any material that slows down heat transfer. For our solar ovens, we are going to use cardboard as insulation. While cardboard is not the best insulator, it will work well-enough for our solar oven. (What might be a better insulator?)
Can you think of any ways to get more heat into our oven? Can we reflect heat? We can reflect heat just like we can reflect light. This means that if we use something reflective, such as aluminum foil, we can bounce more heat into our oven.
Placing a brick or other high heat capacity object in a solar cooker increases its ability to use solar energy. Although the solar cooker takes longer to heat up, the thermal mass (an object that stores the heat from the sun) stores energy that can be used to cook food after the sun sets. Using thicker pots increases solar cooker efficiency for the same reason.
Today, we are going to become engineers and design our own solar cooker. Do you think you will be able to heat water (and make some food)? Once we learn about the design of solar cookers, we can help people who do not have ovens or stoves. Let's get cooking!
Vocabulary/Definitions (Return to Contents)
Procedure (Return to Contents)
In this two-day activity, student teams build and compare several different solar cooker designs as they heat water. This activity requires one class period on Day 1 to build the solar cookers, and another class period on Day 2 to measure and graph the temperature increases of water positioned in the cookers that are placed outside in the sun. Students also really enjoy using the solar cookers to heat or cook quick-cooking foods. See the Activity Extensions section for food ideas.
Solar cooker design considerations: Since the sun's position in the sky varies throughout the day, reflectors and reflecting surfaces are used on most solar cookers to allow them to capture enough light. Reflectors direct light onto the pot. Parabolic reflectors can have either a point or a line focus. The parabolic cooker in this activity directs light to the axis. The cone cooker in this activity works similarly. Parabolic reflectors with a point focus maximally heat one spot so the pan is placed at that spot. Panel cookers are more efficient than parabolic cookers because the panels reflect light toward the middle of the cooker and can be adjusted as needed. Box cookers usually have adjustable reflectors and reflective lining, so they are the least affected by variation in the direction of sunlight. However, if cookers are too deep, the resulting shadows in the cooker reduce its efficiency.
Before the Activity
Day 1 — Building the Solar Cookers
Construction of Cooker #1: Box Panel Cooker
Construction of Cooker #2: Modified Box Panel Cooker
Construction of Cooker #3: Simple Cone Cooker
Construction of Cooker #4: Parabolic Solar Cooker
Day 2 — Testing the Solar Cookers
Safety Issues (Return to Contents)
Troubleshooting Tips (Return to Contents)
Do this activity on a warm, sunny day. Or, use heat lamps if the Sun is not shining.
It is best to paint the boxes a day before you construct the ovens so the paint has time to dry.
Advise the students testing the simplified cone cooker to be careful in setting the beaker of water in the collector. Shorter jars work better in this collector, but that affects the rate of heat transfer to the water somewhat. They may need to remove the jar briefly while they measure the temperature, replacing it as quickly and carefully as possible.
It helps heat up the water if the teacher places the ovens/water in a sunny spot in advance of when the students start to measure the water temperature.
Plan for other activities or classroom projects for students to work on between measurement times when they are waiting for their oven temperatures to rise. This might include conducting the Post-Activity Assessment activities or Activity Extensions.
Assessment (Return to Contents)
Discussion Questions/Review: Solicit, integrate and summarize student responses.
Brainstorming: In small groups, have the students engage in open discussion. Remind students that no idea or suggestion is "silly." All ideas should be respectfully heard. Ask the students:
Activity Embedded Assessment
Worksheet: Have students record the activity measurements and graph the data on their worksheets. After students have finished their worksheets, have them compare results with their peers. Review the worksheets to gauge their mastery of the subject.
Re-Engineering: Ask the students how they could improve their solar cooker and have them sketch or test their ideas.
Discussion Questions: Ask the students and discuss as a class:
Pro & Con: Ask students to list on the board all the advantages and disadvantages they can think of for using solar cookers. Possible advantages: Uses a free and renewable energy resource that does not emit greenhouse gases (that contribute to pollution and global warming); reduces need for fossil fuels and electricity; reduces need for wood to burn fires (saves trees and reduces deforestation, habitat destruction, soil erosion, etc.); helpful in areas without electricity, gas or appliances [ovens, stoves] that use them; does not heat up the house in the summer; inexpensive to build; can be used to purify water, too.) Possible disadvantages: Depends on having a sunny day, must cook outside, etc.
Activity Extensions (Return to Contents)
Cook a snack: Have the students use their solar cookers to make a fast-cooking food, such as hot dogs (pre-cooked, so only re-warming required), sliced frozen cookie dough, s'mores, brownies or nachos. Compared to cooking with a conventional oven or stove, the cooking times need to be adjusted. For example, these cookers only reach about 250 ºF (121 ºC) in direct sunlight, therefore cooking times will be longer than in commercial solar cookers or conventional ovens, which reach 450 ºF (232 ºC). If cooking food, alter the activity by having teams measure the air temperature inside their cookers every 2 minutes for 20 minutes and record these temperatures on their worksheets. Also see the Florida Solar Energy Center's What's Cooking Recipes (for s'mores, s'mores with peanut butter, banana boats and baked beans) at: http://www.fsec.ucf.edu/en/education/k-12/curricula/sm1/documents/SM1_whats-cooking-recipes.pdf.
Have students brainstorm different materials and different designs of solar cookers. If possible, have them construct their own solar cooker, evaluate their design and defend their ideas. Students can research information at the Solar Cooking Archive and Solar Cooking Plans by the Solar Cookers International, http://www.solarcooking.org and http://www.solarcooking.org/plans.htm (for photographs of many solar cooker designs); and Solar Cooking by the El Paso Solar Energy Association, http://www.epsea.org/cook.html.
Sunny Side Up Lunch: On a really hot day, put an oiled, cast iron frying pan on the hot sidewalk in direct sunlight. Break an egg into it and cover the pan with a sheet of glass or plastic. Cook and enjoy!
Have students take temperature measurements in different parts of their oven? Is the temperature the same everywhere? Why might it be warmer or cooler in certain areas?
Thinking like engineers, have students reflect upon how their solar ovens worked, and draw a labeled sketch and instructions for how they would re-design it to make a better solar oven.
How is capturing energy through solar cells like what plants do in photosynthesis? In what other ways do engineers mimic designs seen in nature? Explore this idea with the students. For reference, see the grade 5 (3-6) Biomimicry: Natural Designs activity at TeachEngineering.org.
See many other hands-on activities about the Sun's energy in the grade 4 (3-5) Energy lesson, Let the Sun Shine! activity at TeachEngineering.org.
Activity Scaling (Return to Contents)
References (Return to Contents)
Catching Sunshine. Developed by Online Science-athon. Energy Science Projects and Activities. Energy Education and Training, Energy Efficiency and Renewable Energy, U.S. Department of Energy. Accessed November 28, 2005. (For grades 4-8, an activity to construct a solar collector, determining how to maximize the amount of sunshine it collects.) http://scithon.terc.edu/CatchingSunshine/
Constructing and Testing Solar Cookers. Renewable Energy Lesson Plans, Texas State Energy Conservation Office. Accessed November 28, 2005. (Activity adapted from this middle school lesson plan, click on #12 Cooking with the Sun) http://www.infinitepower.org/lessonplans.htm
Cooking with the Sun. Last Updated September 6, 2005. NASA. Accessed November 28, 2005. (Great instructions and photos for making a pizza box solar oven to cook a snack.) http://www.nasa.gov/audience/forkids/activities/A_Cooking_with_the_Sun.html
Dictionary.com. Lexico Publishing Group, LLC. Accessed December 20, 2005. (Source of vocabulary definitions, with some adaptation.) http://www.dictionary.com
Lindo, Natasha and Lerios, Toli. Physics of Solar Cooking. Engineering Group, Stanford Youth Environmental Science, Stanford University, CA. Found at Outdoors Physics, Umeå University, Sweden. Accessed November 30, 2005. (Source of background information) http://www.ccathsu.com/files/handouts/Parabolic%20Solar%20Cookers.pdf
Schleith, Susan and Sheinkopf, Blanche. Solar Matters III. Florida Solar Energy Center, University of Central Florida. Accessed September 18, 2006. (A solar energy science unit for grades 6-8). http://www.fsec.ucf.edu/en/education/k-12/curricula/sm3/
Solar Energy, Dr. E's Energy Lab, EERE Kids. Updated November 7, 2005. Energy Efficiency and Renewable Energy, U.S. Department of Energy. Accessed November 28, 2005. http://www.eere.energy.gov/kids/solar.html
Solar Energy Basics. Learning About Renewable Energy & Energy Efficiency, National Renewable Energy Laboratory. Accessed November 28, 2005. (Source of background information) http://www.nrel.gov/learning/re_solar.html
The Solar Cooking Archive. Solar Cookers International. Accessed March 26 2007. http://solarcooking.org
Student Resources on Solar Energy. Learning About Renewable Energy & Energy Efficiency, National Renewable Energy Laboratory. Accessed November 28, 2005. http://www.nrel.gov/learning/sr_solar.html
What's Cooking Teacher Information, Solar Matters III. Florida Solar Energy Center, University of Central Florida. Accessed September 18, 2006. http://www.fsec.ucf.edu/en/education/k-12/curricula/sm3/documents/SM3_WhatsCooking2.pdf
ContributorsXochitl Zamora-Thompson, Sabre Duren, Jeff Lyng, Jessica Todd, Geoffrey Hill, Jessica Butterfield, Malinda Schaefer Zarske, Denise Carlson
Copyright© 2005 by Regents of the University of Colorado.
Supporting Program (Return to Contents)Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder
Acknowledgements (Return to Contents)
The contents of this digital library curriculum were developed under a grant from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation GK-12 grant no. 0338326. However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.