Monday, March 18, 2013

Cheap Solar Oven You Can Make

You can make your own solar oven very inexpensively. I think it is a good idea to make my cardboard one before you invest in making a sturdier, and more expensive one.

I decided to make this cardboard solar oven when I read that the town that I lived in got more sunny days a year than Arizona did. That sounded like a good opportunity to use all of that sunlight to save money and the Earth at the same time.

This cheap oven is not super efficient, so it is probably not a good idea to think of it as something permanent for cooking. It takes quite a while to get the temperature up high enough to cook in it and it is also slow.

I was patient and poor, so I cooked two meals a day all summer in it for several years. It does not work well enough that I even wanted to try it in the winter.

It is kind of fun to make this stove and it feels good not to feed the electric company and save the Earth by using it.

The materials I used to make my stove were:

Two cardboard boxes that will nest, the smaller inside the larger with several inches of space between them all around, except on top. The tops need to be even. I cut my boxes and used duct tape to get the sizes I wanted.

Styrofoam to fit in the space between the cardboard boxes, including underneath the smaller one on the inside. Packing peanuts are okay, or waste cardboard in whole slices or cut or broken into bits.

A piece of glass for a top to fit across both boxes. A little larger is okay, but not too much because it will interfere with reflectors.

Aluminum foil to make reflectors to get more light/heat into the interior. The more light you can get into your box, the hotter it will get.

Black paint to paint the inside of the inner box to absorb more heat. It is best to make sure the paint is not toxic since it will be in there with your food. I just used some water based acrylic I already had. I had to touch it up once in a while though because of spills and cleanup.

Hinges for the glass top. I just used duct tape to begin with. The duct tape loses its stickiness even at the low temperatures of this oven after a short time, however. If you want to use this oven longer, you need better hinges. I settled on leather for later. I did not have a drill to make holes in the glass, so I had to constantly re-glue it.

Sticky stuff like glue or tape to hold things together. Regular duct tape does not do well longer term from the heat. You can get higher temperature tape. There are glues that handle higher temps also. Be careful what you put inside the box because of the food in there. Check for toxicity and fumes. I look on the internet at the site of the manufacturer if necessary. The USA mandates that manufacturers have information like this available.

String, twine, yarn, etc. to adjust and hold the angle of the reflectors. 

A sunny spot to position your solar oven in for several hours, a lot of hours if you intend to cook two meals in it. I used a cinder block wall behind my home. The cinder blocks absorbed more heat and got the oven hotter too.

A timer to keep track of when to adjust the reflectors as the sun moves.

If you try this and like it, you can use the same basic idea to make a more permanent version out of wood instead of cardboard and you can use a mirror for part of the reflectors. There are other better designs, however. I think a Fresnel lens is a good thing to use to raise the heat a lot more. 

You will have to watch the oven a lot closer if you use a Fresnel lens. It is possible to melt metal with a big Fresnel lens. Some people have devised a sun tracking system with a motor that automatically adjust the reflectors as the sun moves across the sky.

I will end this post with a picture of how to put it together.

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