How to Build a Solar Oven

From Survival and Beyond

Solar cookers or solar ovens have been in use for years in parts of the world where fuel and firewood are scarce.  For those of us in the first world, a solar oven can be invaluable in a grid collapse or TEOTWAWKI situation when our energy infrastructure or fuel delivery systems no longer function.  They also come in handy on camping trips to save on firewood or in the summer time when you just don’t want to heat up the house by cooking indoors.

Many people are shocked to discover that it’s actually possible to cook food, boil water and even bake bread using the power of the sun (yes, even in the winter!).  This solar oven design can reach temperatures from 212 degrees F (hot enough to boil water) to 350 degrees or higher (hot enough to bake bread).  So not only is it possible to cook and dry all kinds of foods, but it’s highly efficient and quite easy.  Granted, it takes a while longer, so if you’re one of the types who can’t wait for their Hot Pocket to heat up in the microwave, you may have to acquire a little patience (besidea, any food that requires heating in a microwave, is not really food, anyway, so…)

In this article, you will learn how to make a solar oven out of materials that you most likely already have in you house.  Here’s what you will need:

• Corrugated Cardboard (large flat sheets)
• Duct Tape
• Magic Marker
• White Glue
• Aluminum foil (25 ft. roll)
• Utility Knife
• Yard Stick or Tape Measure
• Paintbrush (2 -3”)
• 1 Large Aluminum Cake Tin (6”x12”x3”)
• 1 Large (Turkey-Size) Oven Bag
• Cardboard Box w/ Flaps (10”x14”x6” )
• Black Tempra Paint (powdered)
• Plastic container (Approx. 16 oz.)
• Shredded Paper (for insulation)
• Oven Thermometer
• Plastic Spoon
• Sunglasses
• Oven Mitts

Step 1 – Making the reflector panels

1. Using a yard stick and felt pen, measure draw the outlines of the reflector segments on your cardboard. Use the measurements on the template to the right.

2. Carefully cut out the 4 cardboard segments with your utility knife. Use a ruler or straight-edge to help guide your cuts.

3. Pour approximately 4oz. of glue into the plastic container. Add 4 tablespoons of water to the glue and stir thoroughly (the water will thin out the glue and make it easier to spread evenly).

4. Carefully unroll enough aluminum foil to completely cover one section. Try to keep the foil as smooth and flat as possible, as wrinkles and creases will reduce the reflective effectiveness of the reflector. Use two pieces of foil if the the cardboard is wider than the foil is and plan to join them near the middle.

5. Using the paint brush, apply a thin layer of white glue over the entire surface of the cardboard. Be sure to spread the glue right to the edge of the cardboard. Use the flat edge of a piece of scrap cardboard as a squeegee to spread the glue out evenly.

6. Before the glue dries,  carefully place the foil on the cardboard (shiny side up!), and smooth it down over the entire surface. Try to press out any wrinkles, bubbles, or creases in the foil.

7. Trim the foil around the edges with your utility knife so that it is flush with the edge of the cardboard all around.

8. Repeat steps 3 through 5 for the remaining panels.

9. Rinse the paint brush thoroughly to remove all glue.

Step 2 – Join the Panels

1. Arrange the segments as shown in the photo to the right, foil side down, wide sections alternating with narrow ones. The narrow end of each should point toward you.

2.  Cut 8 pieces of duct tape, approximately 2 feet long, and set them aside (stick them to the edge of the table for easy retrieval).

3. Carefully position the first two panels, keeping about 1/8” space between them. Position one of your 2 foot strips of duct tape over the joint between the panels. Press it onto the joint, being sure it sticks securely to both panels over its full length.

4. Join the third and fourth panels as in step 3 above.

5. Carefully flip the joined panels over on the table. This may require two people. Reinforce the joint between each panel using another strip of duct tape.

6. Stand your reflector up (foil side in), bringing the edges of the outer two panels together. Have your partner hold the reflector in position while you add he last piece of duct tape.

7. Finish the last joint inside the reflector by applying the remaining piece of duct tape.

Step 3 – Add the insulator box

1. Shred some newspaper by tearing it lengthwise into thin strips. Place some of the shredded paper in the bottom of a medium-sized box (large enough to hold the bottom of the reflector assembly securely). Using duct tape, fasten the cardboard box securely to the bottom of the reflector by its flaps.  Be sure the box is centered. Add a few strips of duct tape to the corners to make the assembly more rigid.

2.  Stuff shredded paper into the gaps between the box and the reflector. Leave a little of the paper on the bottom of the box, as shown in the illustration.

Step 4 – Prepare the Baking Chamber

1. In the plastic container, use the plastic spoon to mix 2 teaspoons of black tempera paint with one teaspoon of white glue, and two teaspoons of water (you can substitute glue and water from Part A above if you had any left over).

2. Using the brush, apply the black paint evenly over the inside of an aluminum foil loaf tin. Set this aside to dry. It may be necessary to apply two coats of the paint to ensure full coverage of the aluminum.

Step 5 – Test and prep the solar oven for use

The solar oven is now ready to be tested. If the glue and paint are all dry and it is a sunny day, you can warm up your oven in preparation for its first cooking job.

1. Place the oven thermometer inside the painted baking tin.

2. Slip the baking tin into the transparent plastic oven bag by placing the tin inside the oven plastic oven bag. Arrange the bag so that the plastic forms a smooth, unwrinkled window over the baking chamber.

3. Press the baking chamber tightly into the bottom of the reflector.

4. Outside, and with your sunglasses on, arrange your cooker so that the cooking chamber is fully illuminated by the sun. The diagram below shows you how to orient the reflector to get the most heat from the sun. You will need to prop the reflector up on some stones, bricks or other objects to keep it at the right angle.

Position the oven so that the baking chamber faces the sun squarely and the shadow of the reflector is minimized. If the day is sunny, clear, and warm, the temperature inside the cooker should begin to reach 212º F or more within 20 minutes or so. Allow the cooker to reach its maximum temperature (about 390º F or higher) and maintain that for an hour or more. This will burn off any unwanted substances inside the baking chamber.

If your cooker reaches 212º F, you can use it for heating foods. If it gets to temperatures of 350º or higher, you can actually use it for baking.

The plastic oven bag is extremely fragile and easily torn. Handle it carefully, especially when the cooking chamber is hot.

For cooking and baking, you will need to find small baking tins that fit easily into your baking chamber. To improve the baking efficiency, paint the OUTSIDE of any small baking tins you want to use with the same paint and glue mixture you used to blacken the inside of the baking chamber. Be sure to heat your painted tins in the oven without food to burn off any impurities before cooking with them.

You can use your solar oven to bake bread, cook and dehydrate meats, heat up soups, stews, and other foods. You can also roast vegetables such as carrots, potatoes, and onions. And it’s great for freshly caught trout!

You may need to support the pot or tin using small stones or metal jar lids to keep them level inside the baking chamber. Make sure that whatever you use in the cooking chamber is oven safe.

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