Summer fun with kids: How to build a solar oven

I was recently putting together treat bags for my daughter’s birthday and trying to minimize the cost to create the 25 or so bags. One of my ideas to stay within budget was to melt old crayons in a mold to make new marbled crayons to share. To make the process fun (and keep the house cooler on a hot day), we decided to experiment with using a homemade solar oven to melt the old crayons in our mold!

A solar oven uses the sun’s energy to heat food or other items, reducing the need for conventional energy sources. Building a solar oven out of a cardboard box turned out to be a great way to learn about solar energy and sustainability while giving our old crayons new life! Here’s a step-by-step guide to creating your own beautiful marbled crayons with a homemade solar oven.

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Materials You’ll Need:

Crayons

• A good quantity of old crayons – ask friends, daycare, school or somewhere else where they run programs with kids if you can take their old broken crayons off of their hands.
• Some kind of mold – you can use a muffin tray with liners, a silicone mold (I used one I had on hand from making bath bombs), or anything else that can be pulled away from the wax once it has re-solidified

Solar oven

• A cardboard box (a pizza box or a larger box, depending on your preference)
• Aluminum foil
• Plastic wrap or a large plastic bag
• Black construction paper
• Tape (duct tape or masking tape)
• Scissors or a utility knife
• Ruler
• Wooden skewer or a stick (to prop open the lid)
• Glue (optional, for added durability)

Steps to prepare crayons:

• Peel the crayons:
  • They can’t be melted with the paper on so I found it helpful to soak them for a few hours and most of the paper seemed to come off quite easily.
• Break up the crayons:
  • Depending on the size of your mold, you’ll likely have to break up the larger crayon pieces that will fit into your mold and allow colour mixing if you’re planning to marble colours
• Decide how you’ll use the colours you have:
  • I decided to create piles of similar coloured crayons and then mixed colours in each of my molds for a marbled effect. You could also keep the colours quite similar in each new crayon, but any way you do it just have fun with colour!

Steps to build your solar oven:

1. Prepare the box:
   • If you’re using a pizza box, open it up and clean out any residue. If you’re using a larger cardboard box, make sure it’s clean and sturdy.
   • Use the ruler to measure and draw a square or rectangular flap on the top of the box. Leave about an inch of space between the flap and the edges of the box.
2. Cut the flap:
   • Carefully cut along three sides of the drawn flap, leaving one side attached to form a hinge. This flap will serve as your solar oven’s reflector.
3. Line the flap with aluminum foil:
   • Cover the inner side of the flap with aluminum foil, making sure the shiny side is facing out. Use tape to secure the foil in place. This will reflect sunlight into the oven.
4. Line the inside of the box:
   • Line the bottom and the inner walls of the box with aluminum foil, shiny side up. This will help to maximize the heat inside the oven by reflecting sunlight.
   • Cover the bottom of the box with black construction paper. Black absorbs heat, which will help heat your items more efficiently.
5. Create the oven window:
   • Cut a piece of plastic wrap or a large plastic bag to fit over the opening of the box. This will create a transparent window that lets sunlight in while trapping heat inside.
   • Tape the plastic wrap securely over the opening of the box. Make sure there are no gaps where heat could escape.
6. Adjust the reflector:
   • Use a wooden skewer or stick to prop open the flap at an angle that directs sunlight into the oven. Adjust the angle as needed throughout the day to capture the most sunlight.

Using Your Solar Oven:

1. Preheat the oven:
   • Place your solar oven outside in direct sunlight. Allow it to preheat for about 30 minutes before using.
2. Put your items in the oven:
   • Place the food inside the oven and close the plastic-wrapped lid. Adjust the reflector to direct as much sunlight as possible into the oven.
   • Melting time will vary depending on the weather. Check periodically to see if wax is entirely melted and adjust reflector as needed.

Tips for Success:

• Optimal Sunlight: Solar ovens work best on sunny, cloudless days. Position your oven to face the sun directly for the best results.
• Insulation: To improve your oven’s efficiency, you can add extra layers of insulation, such as rolled-up newspapers or an additional box, around the cooking chamber.
• Safety First: Always supervise children when using the solar oven, as the interior can become very hot. Use oven mitts or gloves to handle hot items.

Building your own solar oven is a rewarding project that combines creativity, science, and sustainability – and in my case a budget-saver! Not only will you end up with food or a fun craft, but you’ll also gain a greater appreciation for renewable energy. So gather your materials, head outside, and start baking with the power of the sun!

Looking for other fun and budget-friendly activities to do with kids? Check out our past posts here!

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