It’s so hot, you can fry an egg on the sidewalk!  Even for those of you living in the deserts of Arizona, a fried egg is probably a bit of a stretch…but with DIY solar ovens you can at least roast a s’more!  This easy project made of household materials teaches kids about solar energy while they cook with the heat from the sun.  It’s also a good way to see the Greenhouse Effect in action!  This is a great hands-on activity for kids 4 and up, with plenty of ways for older kids to change the experiment and test hypotheses. (I speak from experience when I say that the 3-and-under crowd may not be too engaged until it’s time to eat.)  Special thanks to my local chapter of the MOMS Club for coming out and cooking with me on this hot day!

LEARN SCIENCE VOCABULARY:

Solar Energy – energy obtained from the sun.  There are really 2 kinds: Active Solar Energy, which uses solar panels to collect sunlight and turn it into electricity, and Passive Solar Energy, which uses the sun’s heat to warm something directly.  Our oven will use Passive Solar Energy.

Thermal – a term used to describe anything having to do with heat.  It is from the same root word as thermometer (an instrument used to measure heat) and thermal underwear (long-johns used to keep a person warm)!

Greenhouse Effect – the rays from the sun hit the earth and much of the thermal energy (heat!) remains trapped by the gasses in the earth’s atmosphere, the same way that the clear walls of a greenhouse trap in heat.  This effect also happens inside a car on a sunny day (even in the winter, the interior of the car will be much warmer than the air outside).

MATERIALS NEEDED:

• Cleaned out pizza box (The pizza box shape is the best, but other boxes will work also. Box size and shape is a great variable kids can change to test out the efficacy of your oven!)
• Black construction paper
• Aluminum foil
• Plastic wrap
• Masking tape and/or glue
• Large scissors
• Pencil or stick
• Optional: thermometer 
• Something to cook! (We made s’mores, but you could also try ‘grilled’ cheese, Lunchable-type pizzas, or basically anything melty that your adventurous child wants to put in there. Note of caution: the temperature will not get high enough to cook off bacteria, so if you do try to fry an egg, please don’t eat it!)

HOW TO MAKE IT:

1. Have a grown-up use the large scissors to cut a flap out of the top of the pizza box.

   

2. Glue black construction paper to the bottom of the box.  It doesn’t have to cover the whole area.  (Dark colors absorb THERMAL energy and get warm quickly, as you probably noticed if you have stepped on asphalt in bare feet during the summer, or if you have dark hair and stand out in the sun too long!)

   

3. Wrap the flap you cut out with aluminum foil.  Use tape or glue to hold it in place.  (The foil will reflect some of the sun’s rays down into the box to help maximize the heat trapped in your oven.)
   

   
4. Tape plastic wrap across the lid of the box, covering the opening created by the flap.    (The plastic wrap creates the GREENHOUSE EFFECT…it will let the sun’s rays come in, but prevents heat from escaping!)

   

5. Place the food items in the ‘oven’ on top of the black paper and close the pizza box. Prop up the foil-covered flap using the pencil or stick. You may have to use a bit of masking tape to hold it in place.

   

6. Put the oven in a sunny location, making sure that the opening is facing the direction of the sun so you can maximize the amount of SOLAR ENERGY entering the box.  If you have a thermometer, measure the temperature outside in the sun and then place the thermometer inside the box to record the changes as the oven heats up. Ours was in the sun for just 10 minutes and the temperature inside the box went up almost 30°F!

   

    

7. You can let your food “cook” as long as you’d like, but don’t open the oven until you are ready to eat or you will let out the heat.  When your food is done “cooking,” just lift the lid and enjoy!  (Since we had a bunch of hangry toddlers at a MOMS Club playdate, we took our s’mores out after 10 minutes.)
   

   

Extend the experiment for older kids!

1. DATA COLLECTION: Data is simply the information collected during an experiment.  Use a thermometer to measure the temperature change each minute.  Make a simple Data Table to record your measurements.
2. CHANGE A VARIABLE: There are so many things that kids can change in this experiment to determine the effect on the efficiency of their solar ovens (this is best demonstrated by recording the temperature change inside the oven, but even without a thermometer kids can observe which method melts their food the quickest).  Make a hypothesis before you test each new variable!
   • size or shape of box
   • color of paper inside the oven
   • foil-covered flap open versus flap closed
   • placement of oven in full sun versus in full shade
   • removing the plastic wrap

THE SCIENCE BEHIND IT:

Your homemade solar oven works in much the same way as the GREENHOUSE EFFECT caused by Earth’s atmosphere.  Light and heat from the sun pass through the plastic wrap and enter the oven.  Some of this SOLAR ENERGY is reflected back into space, but some is trapped inside the box (just like the gasses in Earth’s atmosphere trap heat), causing the temperature inside to rise.   The black paper helps to increase the internal temperature because the color black absorbs all wavelengths of light and converts that energy to heat.  If you were to line your oven with white paper, you will see that the temperature will not rise as quickly because white reflects all wavelengths of light back out to space.

An increase in the GREENHOUSE EFFECT leads to an increase in the average surface temperature on earth (a phenomenon commonly referred to as Global Warming).  The GREENHOUSE EFFECT in itself is not a bad thing…without it our planet would not be able to hold  heat at all and the surface would be a frozen wasteland like Mars!  But since the GREENHOUSE EFFECT is caused by the gasses in our atmosphere (carbon dioxide is the most abundant greenhouse gas), surface temperature increases when there are more of these gasses released into the atmosphere through human activities.  Burning fossil fuels, like gasoline and coal, or cutting down forests (because trees, like all plants, soak up carbon dioxide in their leaves) are major contributors to increasing the earth’s GREENHOUSE EFFECT.