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How to Build an Improved Solar Oven

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Simple family project which can substitute for your slow cooker, but no home power needed.

A friend of mine lives off the grid. He does quite well for himself, and he does not skip any of the modern conveniences. I do not personally believe that such a lifestyle is feasible for everyone, particularly when you live in an urban area. My thoughts of converting an existing home into a green one and being prepared for a major storm has led me to think of how a home’s systems can continue to function after a power outage.

This post is meant to show you one simple device that I want you to be familiar with, before I detail an idea in the next post which is more to the point of this blog. Recently, I was discussing the idea of a solar oven with people interested in green home design, and I found that they had never heard of them. In a recent story about an inventor in Africa, he discussed inventing a solar oven with his daughters to win a prize for inventing it. His goal was to help people fully cook meals where other forms of power/fuel did not exists. The only problem was that the solar oven had already been invented over thirty years earlier. Maybe some readers here have never heard of it, so this could be a service to you.

How to build a basic solar oven: you will need two cardboard boxes; aluminum (tin) foil; black paint; and a piece of glass or plexiglass to cover the box. The larger box will have its interior covered with the foil. You may not know, but foil has two different sides. There is a bright shiny, reflective side, and then there is a duller non-reflective side. Make sure that the shiny side is facing up. The exterior of this box could be painted black if you want, but it is the second box which goes into the first box that has to be all black. High school science class will have taught you that black absorbs the lights energy, and white repels it. The food to be cooked is placed inside the black box, which is set inside the box with the foil. The plexiglass cover fits over the opening of this box. Place the oven in a location that receives sun throughout the day. Follow your slow cooker recipes, because the internal temperatures in the oven will mimic them.

How can you improve on this design? They do sell solar ovens, but it is such a simple device that you should not have to buy one. First, cardboard boxes are not the sturdiest material. A plastic box or pail could do, but I built a simple box out of scrap wood. I could hinge my plexiglass to the box to prevent it from coming off. Next, I lined the box with radiant barrier insulation. I took an old one for my car window, but this is the same material used to create a barrier in your attic. To create a little more insulation between the box and the barrier, I crumbled up paper. I attached the radiant barrier with staples, so it will stay in place. Instead of another box inside this unit, I use a cast iron Dutch oven used in camping fires. Cast iron is black; it retains heat; and I can cook the stew in it. I created a plastic cylinder from a planter that a tree came in from the nursery. In this tube, I can foil wrap items to cook inside the tube. The plexiglass is held in place with some wood blocks over the ends. By creating a insulation barrier with the paper and radiant barrier more heat is kept in the cooking chamber, instead of escaping through the walls of the box. I had the Dutch oven on hand, and this gives me a great space to cook in. This upgrade would be the most expensive item to buy ($30 to $50). The rest of the materials you may have on hand like I did. (I even keep a spare sheet of plexiglass on hand to make repairs to window panes, but this product will be around $5 for a basic smaller box. Solar oven are never too big, about 2’x2′ is typical with most being smaller.

On a really gray day, these will not work, but they can work decently on days with clouds, as long as you are getting some bright light. This is a good back-up if you do not have propane or coals for your bar-b-cue after a power failure. Braised dishes or stews work best. Any energy saving appliance is great for the home, but this one will not use any power that you have to pay for, so maybe you would use it more often. Now you have to read the next post to see where I am going with this, and how could a solar oven be of use to your home.


Adding garden edging as siding

box for solar oven

box for solar oven

Crumpled newspaper as insulation

Crumpled newspaper as insulation

Sun Shade used as a radiant barrier

Sun Shade used as a radiant barrier

Dutch Oven under acrylic sheet in oven

Dutch Oven under acrylic sheet in oven

It was mentioned that I di not include photos with this post, so I built a new unit to show the steps. For this one, I took a box and used some old garden edging as a siding. My daughter Katya screwed dry wall screws into the box to hold it in place. (I tried staples, but they did not work well). My wife has a collection of those sun shades, so I cut one up to fit in the box over the crumpled paper. I used the reflective HVAC duct tape to seal all the edges, and to fasten the shade to the box. I had to go buy a piece of clear acrylic sheet ($12), since I did not have more plexiglass. The plexiglass did not show up weel in the photos, but it is over the dutch oven in the last shot. Katya is two, so it slowed me done some, but it took us a half hour to complete the project with most of the material on hand. If you do not have the reflective tape, you could use duct tape.

Update: I came home one day to find that my wife and son had taken apart a teak/metal bench. I took the teak and turned my box into a table. The plexiglass has been replaced with a piece of glass that I had (3/8″ thick). I also added a mirror and a rack for the dutch oven. Stews have been good, and preparing grains, like bulghur, has worked well. What I have not tried, but I need too, is heating up a cast iron skillet to fry an egg. I have seen this done. The thicker glass has helped.

« « Looking at the Smart Grid as it Enters Your Home| Green Building Initiatives in Houston, May 2009 » »

© Frank Schulte-Ladbeck Professional Home Inspector Houston, Texas
Frank Theodor Schulte-Ladbeck
home inspector, TREC# 9073
Houston , Texas , 77063 United States

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