Make and Use a Solar Oven

Around the world, solar ovens or "solar cookers" are increasingly used to reduce reliance on firewood and other fuels. Even if you have electricity, a solar oven can be an effective, energy-saving addition to your cooking tools. To make either a lightweight or a heavy-duty solar oven, follow these instructions.

Steps

Lightweight Solar Oven

  1. Place a cardboard box inside a larger cardboard box. Make sure there is at least an inch of clearance between the sides, and fill the gap with shredded newspaper, which will act as an insulator.
  2. Line the inside of the smaller box with black construction paper, to absorb heat. Next, cut the flaps from flat cardboard sheets in the shape of slightly flared squares. Since you will be attaching these to the walls of your box, the width of each narrow end of each square should equal the width of the side you’ll be attaching it to; the width of each flared end should be several inches wider than the width of the narrow end.
  3. Cover each piece of cardboard with reflective material such as foil. Make sure it sits tightly around the reflector, and smooth out any wrinkles or folds. Secure the material with rubber cement or tape on one side of each cardboard piece.
  4. Attach each reflector to the top of one side of the box. You can glue, staple, or thread them as necessary, allowing them to flop over for now.
  5. Prop each reflector up at around a 45 degree angle. The easiest, most secure way to do this is to connect the reflectors together at the flared top corners (ex. by piercing adjacent corners and tying them together with thread, then untying them for disassembly). You can also stick rods in the ground underneath the reflectors, stack something underneath each reflector, or use any other method that will hold them securely in place. If it’s a windy day, make sure your reflectors won’t blow over.
    • If using rods, glue the reflectors to the rods to add more stability.
  6. Position the oven in full sun, place food in the smaller box, and wait for it to cook. It is best to cook the food in jars or on a small, dark baking pan. Experiment with cooking times and how and where you place the box. You may need to reposition your box several times during cooking to catch the sun.

Heavy Duty Solar Oven

  1. Cut a large metal drum in half vertically with a jigsaw. An oil drum will work well for this purpose. Be sure to use a metal-cutting blade; when you’re done, the half-drum should look like a cradle. You only need half of the drum to make the oven.
  2. Clean the inside of the half-drum thoroughly with a de-greasing soap. Be sure to use a scrub brush and pay extra attention to the corners and crevices.
  3. Size and cut three pieces of sheet metal to contour to the insides of the half-drum. You will need one large rectangle for the curved interior and two half-circles for the end pieces.
    • To make the large rectangular piece, one side should equal the length of what was formerly the interior height of the drum; the other should equal the curved length of the interior, which you can measure using a flexible measuring tape (ex. sewing tape).
    • To make the two half-circles: measure the radius (i.e. half the diameter) of the half-circular ends; tie a marker to the end of a piece of string and then cut that string to the length of the radius; holding the end of the string in the middle, use the marker to draw a perfect circle on the sheet metal; cut the circle out and cut it in half to make each half-circle.
  4. Attach the sheet metal to the inside of the drum. To attach the pieces with pop rivets, drill holes through both the sheet metal and the drum with a 1/8-inch (3-mm) drill bit, then apply 1/8-inch (3-mm) pop rivets. You can also drill holes through the sheet metal and drum and then attach them together with sheet metal screws; though this will leave screw tips sticking out of the back of your oven, they will later be covered by insulation.
  5. Paint the inside of the oven with a reflective paint rated for barbecues. This will maximize the amount of heat inside the oven.
  6. Create a continuous metal lip around three of the four top edges of the oven. This will hold the glass top (which you will slide in and out through the fourth, open side) in place. The easiest way to do this is to with six pieces of metal flashing:
    • Measure the short top edge of the oven and cut two pieces of flashing to this length. Then, measure the long side edges of the oven, subtract the width of the flashing from this measurement, and cut the remaining four pieces of flashing to this length; this will allow you to apply flashing to the sides while making room for the piece at the end.
    • Place a piece of flashing over the end edge so that the bent metal “folds” from the vertical outer side up over the horizontal top edge. Place a second piece of flashing over the first so that the vertical sides are flush but the horizontal sides leave a gap wide enough to accommodate the thickness of a piece of glass. Place a strip of something (ex. thick cardboard) between the two pieces of flashing to keep this space open, drill through both the double-stacked flashing and the drum, and attach them using pop rivets. Remove the cardboard and repeat on the other two edges.
      • Making a flashing “sandwich” (as opposed to simply applying one layer of lip all around the top) will keep the glass from grinding across the uneven edges of the barrel that you cut by hand.
  7. Flip the half-drum over and apply spray-on insulation to the outside walls.
  8. Attach a base to the bottom of the oven. Simply drill and screw the drum to the base that is most convenient for your location (ex. a piece of wood, a square aluminum frame with wheels, etc.), making sure that the base is wide enough to keep the oven from tipping over. Depending on your location, you may want to angle the oven to make the most of the available sunlight (ex. in the northern hemisphere, you may want to angle it southward whereas at the equator, you should face it directly upwards).
  9. Drill drainage holes in the bottom of the oven. Simply drill a small hole every few inches in a straight line across the bottom, making sure to pierce the insulation; this will allow liquefied steam that drips down the sides to escape the oven.
  10. Slide a custom-sized sheet of tempered glass into the metal lip. Tempered glass not only is tougher than regular glass, but also comes with the sharp edges ground off, meaning you can use it as is. Since you will be sliding the glass in and out regularly, choose a thicker piece (ex. 3/16 inches / 5 mm) for additional sturdiness. You will have to custom order this at a hardware store based on the dimensions of your solar oven.
  11. Insert a magnetic thermometer. Wood stove thermometers, for example, have magnetic backing and can withstand high, constant heat.
  12. Place a thin aluminum grill along the bottom (optional). Simply set a rectangular grill or two in place to allow for easy food placement.
  13. Test your oven’s heat capacity on a sunny day. Though you can reasonably expect a max heat of between 250 and 350 degrees F (90 and 175 degrees C), the size, materials, insulation of your particular oven will determine how hot your particular model gets. Use this temperature to slow-cook meat over several hours as you would in a crock pot. A roast beef or chicken might need 5 hours, for example, whereas ribs might need 3 (plus 5 to 10 minutes of barbecuing at the end). Gauge your meat’s internal temperature with a food thermometer as you would while using an indoor oven.

Solar Veggie Steamer

  1. Obtain 2 cardboard boxes with {{safesubst:#invoke:convert|convert}} different dimensions, 5 cardboard panels, one vastly larger than the rest, Styrofoam, transparent wrap, aluminum foil, black craft foam, black Tupperware (with lid), water, your favorite veggie, glue, and 5 sturdy sticks.
  2. Place the large box onto the large cardboard panel, glue in place. Place the smaller box inside the larger box, glue in place. Trim off any difference in height.
  3. Line the empty space in between the 2 boxes with Styrofoam. Do not glue. Line the inside of the small box with 2 or 3 layers of the black craft foam, glue together. Completely line 4 cardboard panels with the foil and glue the foil to the cardboard. Try to avoid creasing the foil.
  4. Glue the panels at a 45 degree angle to the box. Trim the sticks to fit perfectly under the panels at an angle. Glue the sticks in place(to the panel and the foiled panels to hold up the panel and foiled panel ).
  5. Cut a rectangular hole just large enough to slip the Tupperware through on one side of the cooker. Glue the remaining stick to the Tupperware. Slip the Tupperware inside the hole.
  6. Take the transparent wrap and stretch it over the entire mouth of the solar cooker. Glue in place.
  7. Wait for a sunny day. Fill the Tupperware with one inch of water. Put your veggies inside. In full sunlight, let the solar cooker sit for an hour. Then come back and see if it is done. Repeat step 7, if necessary.

Tips

  • You can always make light weight ovens for school projects on waste.
  • To make your lightweight oven more efficient and to get it to cook at higher temperatures, you need to trap in the heat. (Without a cover, hot air will rise, bringing in a constant flow of cooler air.) Oven cooking bags are cheap and easy to use; simply seal the cooking pot in the bag. A pane of glass, preferably double-pane glass is an alternate solution. The glass should be slightly larger than the smaller box but not so big that it won’t fit inside the larger box.
  • In a pinch, you can heat precooked foods such as canned goods with the double ziplock bag trick: put the food in a small zip lock bag and put the small zip lock bag in a big zip lock bag to trap heat. If available, set these on a reflector such as an inside-out chip bag or car windshield reflector.
  • Positioning the rods supporting the reflectors will be much easier if you have someone to hold the reflector at the correct angle while you position and glue the support rod.
  • You must use the oven in a sunny area. The heat energy comes from the sun.

Warnings

  • Lightweight solar ovens are effective almost anywhere you can get direct sunlight, but you can't set the temperature and determine cooking times as surely as you can in a conventional oven. Make sure food is cooked to the recommended temperature by using a meat thermometer.
  • Never wash the glass of the heavy-duty oven with cold water while it’s still hot; the difference in temperatures can crack the glass.
  • Be careful when handling food or utensils inside the oven or when removing the pane of glass (if present). Since this is an oven, these can get very hot. Use potholders, tongs, etc. as you would when working with a conventional oven or heat source.
  • Do not put hand in hot oven without protection, you may burn yourself.
  • The lightweight oven doesn’t offer much protection against hungry animals. Be sure to place it in a safe area.

Things You'll Need

Lightweight Oven

  • 2 boxes, one capable of fitting inside the other with at least an inch of clearance on all sides
  • Newspaper or shredded paper
  • Black construction paper
  • 4 pieces of cardboard
  • Razor/Exacto knife (utility knife)
  • Mylar food packaging, metallic auto sunshade, aluminum coated or Mylar bubble wrap, Mylar balloons, space blankets, mirrors, or polished metal
    • Aluminum foil can temporarily be used but will tarnish quickly and need to be replaced often
  • Tape or rubber cement
  • 8 rods (optional)
  • Hot glue/strong glue (optional)

Heavy-Duty Oven

  • Metal drum (ex. oil drum)
  • Jigsaw with metal-cutting blade
  • Sheet metal
  • Sheet metal shears
  • Measuring tape
  • String
  • Marker
  • Drill and 1/8-inch (3-mm) drill bit
  • 1/8-inch (3-mm) pop rivets (alternatively, sheet metal screws)
  • Barbecue-rated reflective paint
  • Metal flashing
  • Spray-on, expanding insulation
  • Base of your choice (ex. rectangular piece of wood) and applicable screws
  • 3/8-in (5-mm) sheet of custom-sized tempered glass

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Sources and Citations

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