Solar cooker
A cardboard box, foil and plastic wrap trap the Sun's heat. Melt chocolate, warm water or cook rice.
The big idea
Sunlight carries heat. A box that catches it and keeps it in can get hot enough to cook. No fuel and no smoke.
You will need
Tick things off as you gather them.
Step by step
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Step 1: Cut a flap in the lid
Draw a square on the lid, leaving a border of about 3 cm. Cut along three sides only, so the fourth side becomes a hinge you can fold up.
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Step 2: Cover the flap with foil
Glue foil to the inside of the flap with the shiny side out. Keep it as smooth as you can. This is your mirror.
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Step 3: Line the box with black
Stick black paper on the bottom and inside the box. Dark surfaces soak up heat. Light ones bounce it away.
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Step 4: Seal the opening
Stretch plastic wrap over the hole in the lid and tape it down tight. Add a second layer a little apart from the first. The air gap between them keeps the heat in.
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Step 5: Aim at the Sun
Take the cooker into full sun. Prop the flap so it bounces sunlight into the box. Turn the box so it faces the Sun.
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Step 6: Load it and measure
Put the thermometer and your dark tin (with chocolate or water) inside. Close the lid. Read the temperature every 10 minutes for the first hour, then every 30 minutes.
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Step 7: Compare with a plain box
Do the same with a second box that has no foil and no plastic. Which one gets hotter? Plot both on one graph.
What to look for
- The cooker gets much hotter than the plain box.
- Chocolate melts within an hour or so in strong sun. Rice takes a few hours.
- Clouds or a shadow slow everything down.
An example of the pattern you should see, not measured data. Your numbers will differ, and that is fine.
Why it works
The black surface turns sunlight into heat. The foil mirror sends extra sunlight into the box. The plastic wrap lets light in but stops hot air getting out, the same trick a greenhouse uses. Because heat cannot escape quickly, the inside warms far above the air outside.
Try this next
- Add a second foil flap on another side and measure the change.
- Try a glass lid instead of plastic wrap.
- Work out how long it takes to heat 200 ml of water by 30 degrees.
Stay safe
The pot and the inside of the box get hot. Use a cloth or a glove. Foil can bounce glare into eyes, so do not look at the mirror.
Link to the grid
Solar cookers use heat directly. Solar power plants use panels instead, but the lesson is the same: the Sun delivers energy for free, and what matters is how well you catch it and keep it.
Learn how the grid worksMore sun power experiments
Mini solar panel circuit
A small solar panel lights an LED or spins a toy motor. Test it in sun, in shade and at different angles.
Solar water heater
Black-painted bottles or pipe in the Sun heat water. Measure the temperature as it rises.
Shadow-tracking solar map
Track shadows on the school roof through the day to find the best place for solar panels.