Solar Ovens Are Totally Hot!

By Science Buddies on November 13, 2014 11:49 AM

Can you harness the sun to cook your dinner? A solar oven skeptic is converted.

By Kim Mullin

Solar oven science project success story

My 6th-grader loves to build things, so when he needed an energy-related project for his science class, constructing a solar oven was right up his alley. He looked online for kid-friendly solar oven designs, many of which involve pizza boxes, and was skeptical. "I don't think this is really going to work," he announced.

After weighing the pros and cons of different designs, he decided go for Science Buddies' double-box solar oven, outlined in the Now You're Cooking! Building a Simple Solar Oven project. Spurred on by visions of roasted marshmallows, he was ready to start building!

Cardboard, Tinfoil, Black Paint, Glue, and a Turkey Bag

Perhaps my son was skeptical about a homemade solar oven because the required materials are so low-tech. Instead of making a trip to a hardware or electronics store, we picked up black paint and a turkey bag at the grocery store, and found everything else in the house.

The toughest part of the construction phase was adjusting the boxes so they were the right dimensions. My son calculated the required box height, which is based on the cooking pot size, and then measured and drew the lines. After one hairy attempt at cutting the heavy cardboard, dad took over use of the utility knife.

Attaching tinfoil to the cardboard surfaces of the oven was a different sort of sticky situation. After using lots of white glue to secure the foil to the oven's flat "heat shelf," my son decided that a glue stick was probably sufficient for attaching foil to the vertical interior sides of the boxes and would also be a lot less messy! As it turns out, the glue stick worked just fine. The final steps, gluing in the turkey bag "window" and bending a coat hanger to prop open the reflector panel, were a snap for him.

Time to Cook!

Construction was finished by half past three on a Saturday afternoon, and we were all excited to see the solar oven in action. My son measured one cup of water into the cooking pot, grabbed the oven thermometer, and carried it all out to the sidewalk. The goal was to get the water to boil. Would it work? Would the skeptics be proven wrong?!?

Dad and son played catch and peeked through the turkey bag window every five minutes (without blocking the sun!) to record the temperature. The oven heated up to 170 degrees Fahrenheit pretty fast, but then it seemed to stall out. We live on a hill, there are lots of trees, and the shadows were starting to get long in the late afternoon, given the time of year. The project was put on hold for the day, a pretty big disappointment.

Take Two

The next day, my son took his oven to the big, flat school parking lot at 11 a.m. It was windy, and the night had been cool, so again the skeptics wondered if it would work. At 11:12 a.m., the starting temperature in the oven was 65 degrees. In ten minutes, it was up to 145 degrees. Slowly, slowly, the temperature climbed, and the water was boiling an hour later. Success!

Part of the assignment was to make a change to the oven and then test it out again. My son constructed an additional reflector with yet more cardboard, tinfoil, and glue. Now it was my turn to be the skeptic. How could one extra flimsy tinfoil panel make a difference?

After letting the oven cool down, my son put the extra reflector in place and began recording the time and temperature again. Within 20 minutes, the difference was clear. (You will have to try it yourself to see what happens!) Excited by the results of his test, we continued to monitor the oven. As we were wondering how hot the oven could get, a strong gust of wind ripped the lid off, ending the experiment for that day.

Solar Cooking? S'more Please!

Yet a third trial on a later date provided mixed results. Not long after setting up the oven, cloud cover began to form in the sky. As we scanned the horizon, hoping to see a break in the clouds, the oven heated up enough to melt the chocolate in the "victory s'mores" that were cooking, but it was nowhere close to the high temperature it had reached on a sunny day.

Nonetheless, the success of the project turned my son and I from solar oven skeptics to true believers! Sitting in the parking lot, we licked dripping chocolate from our fingers, talked about the advantages and limitations of solar ovens, and plotted our next solar-cooked meal!