Successful Cardboard Solar Oven

by David
(Port Isabel, TX)

Not a real good picture of it, but you get the idea.

Not a real good picture of it, but you get the idea.

I am a retired person living full time in a RV so I needed a very lightweight oven that I could make fairly cheapfully. I knew better than to ask the Mrs. if I could buy the oven I really wanted. I did a good deal of research on the net I decided on a 60/30 oven without a door because of it being cardboard I did not want to weaken the one side.

OK I got lucky on this part. On the way home one day I drove past the back end of Walmart and there sat an empty cardboard box display that they used in the grocery department for cantaloupe just setting there. In fact there were two of them. After asking about them, they were in the back of the truck. The cardboard is double thickness or right at 1/2 inch thick.

A good place to look for cardboard is to go to the grocery store and ask the produce manager or head butcher or the person in charge of restocking the shelves. Check in department stores also. You don't need new cardboard just clean stuff. You can use the small boxes for insulation cut to fit inside the two bigger boxes.

I already had a blue and white speckle ware roasting pan and knew how big to make the box to fit it. Now read kind of carefully now on how I constructed it. It is 3 ply thick or 1 1/2 inch thick total.

I made the first, inner, layer so the corrugated walls go up and down. The back and front cover the ends of the side pieces and the bottom sits INSIDE the 4 walls. I used plenty of Elmer's glue full strength and "Masking" tape on the outside to hold it all together while the glue dried. The corrugation on the bottom went from side to side.

The middle layer I put the corrugation running sideways not up and down. The side pieces cover the corrugation of the front and back. The bottom fits full sized all the way around with the corrugation running front to back. I made the sides and front and back 1/2 inch taller then the inner box to form a shelf for the glass to sit on. I glued the layer to the outside of the inner box and bottom.

The outer layer I made the same way I made the inner box with the corrugation running up and down. The bottom inside the sides and the front and back. The sides covering the front and back ends. I glued this layer to the middle layer.

I figured that with the corrugation running at 90 degrees opposite of each other it would reduce the heat loss of the cardboard. Next I cut single thickness cardboard into 4 inch wide strips and creased the cardboard folding it to 90 degrees. These I glued to all 4 edges of the front and back and sides and the 4 edges of the bottom. This helped dress up the finished box and sealed the corrugations.

I glued tin foil to the inside of the box rather than painting it black. It would have been easier to glue on the tin foil before gluing it together. I gave the outside of the box two heavy coats of outdoor latex paint I had, it is black but, Oh Well.

Next I made a collar out of 1/2 inch plywood I had laying around. The collar is about 2 1/2 inches wide. I made it so that the inside of the collar just comes to the inside edge of the middle layer. That way I can get the glass in and out of the box as it sits on the shelf or top of the inner box. This collar sits flat on top of the middle and outer layers. I glued and screwed another strip of wood to the bottom of the collar that just fits the outside of the outer layer. This keeps the collar from sliding off the oven. I glued a 1/2 inch wide strip of paste board to the shelf and put a coat of silicone on top of it to form a seal for the glass.

I bought 8 of the 4 inch 90 degree corner brackets. Two for each side of the collar. The brackets are used to hold the reflectors to the collar. I closed the 90 degrees down to 60 degrees. In other words I brought the two sides closer together by 30 degrees so it looks like a check mark instead of an "L". I attached these to the collar with bolts and Tee-nuts flushing the bottom of the bolts even with the bottom of the collar. I set the bend of the brackets back from the inside edge 3/4 inch so the reflectors set back 1/2 from the inside edge.

There happens to be a sign supply warehouse that sells to the public in my town. I bought 6 of the corrugated plastic blank signs to make the reflectors with. They are 18 inches by 24 inches. They also had some very shiny silver sign making material rolls on hand so I bought a roll of it also. It is 18 inches wide. I cut the plastic signs to fit the sides and back and front 18 inches tall. I cut 4 triangle pieces also to fit. I covered them with the shiny self adhesive silver material. I found that the material will scuff easily so I coated it with very clear packing tape.

I punched 2 holes in each of the reflectors to attach them to the brackets with nut and bolts and washers. I attached the triangle pieces to the sides and front and back with self adhesive industrial strength "Velcro" strips. This way I can completely take the thing apart and collapse the reflectors and put it in my under compartments of the RV. All except the box itself of course it fits the compartment but will not collapse.

The glass is just a piece of double strength plate glass. It is not tempered but so far there has been no problems with it. I used silicone to attach two wooden knobs to the glass to take it in and out with. The only trouble I had with it is that the glass must have got too hot and one of the knobs came off but I made another work around for it until I can get back home to drill holes in the glass to attach the knobs with.

The last thing I did was to put in small cup holder hooks in the edges of the front and back of the collar to put on bungee cords to hold the collar to the box in the wind we get here in Texas. They go from front down under the oven and around to the back. They are green so you can see them.

The hottest the oven got so far was 347 or 348 degrees so I am well pleased with it.




_________________________________________________

Wow David,

That is a really great and detailed narrative of how you were able to build a solar oven from scratch.
That is a lot to write about.

Thank you for taking the time and effort and for sharing with all of our visitors, I am sure it will be very inspiration for many and very instructive when they do decide to build their own.

Thank you for the photo also.

If you do have any other photos that you would like to send later on, we can do the editing (fitting) for you and share them on our photos page.

Again,

Thank you very much for sharing this and good luck with your solar cooking endeavors.

Happy Solar Cooking!

Nathan
Admin.

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