Learn how to make reflector cookers and other homemade solar ovens with scrap materials found around your home.
By using only the sun and some scrap materials, it is possible to make a solar oven that is perfect for cooking biscuits, bread and sometimes vegetables.
Photo by Fotolia/Andriy Solovyov
Let the sunlight do some of your cooking with a homemade solar cooker. By using scrap materials, such as aluminum, glass and cardboard, you can have a solar oven at a low cost. In Extreme Simplicity: A Guide to Urban Homesteading (Dover Publications, 2013), Christopher and Dolores Lynn Nyerges share some methods they use to utilize the sun to cook their meals. The “Breadbox” Cooker and Reflector Cooker are basic, simple and good for beginners looking to use their first solar oven. This excerpt is taken from Chapter 7, “Homestead Energy.”
You can purchase this book from the MOTHER EARTH NEWS store: Extreme Simplicity.
We have also invested considerable time and some money experimenting with the many ways to cook food with the sun. Just imagine! You can actually take scrap materials—old cardboard boxes, newspaper, a few short cans, plastic, or glass—and create a device that cooks with free sunlight. Using the sun as much as possible is always less expensive and less harmful to the environment than using gas or electricity for cooking. Plus, although there's no way to prove this, we believe that food cooked with the sun not only tastes better, but is better.
We have a solar oven built from plans found in the early 1970s in the MOTHER EARTH NEWS. This oven, which has served us well for more than twenty-five years, is a fiberglass-insulated box with a sloped pane of glass on top, set at a 45-degree angle. We have seen these made of wood, but we made ours of sheet metal because that's what MOTHER EARTH NEWS recommended, and it was therefore easy to rivet the pieces together. Food is put in and taken out through a little door in the back. We once had rigid aluminum reflectors on this oven, but found them more trouble than they were worth, difficult to keep in a set position, and so we removed them. Even without the reflectors, on sunny days we typically get temperatures of 250 degrees Fahrenheit and above, and this is fine for our style of cooking. Usually we use the solar oven for making breads and biscuits, and sometimes for cooking vegetables.
We also purchased a commercial solar oven, the Burns brand Sun Oven. This has basically the same design as the oven in the magazine article, but the commercial one is constructed better than our garage-made model and not only achieves temperatures of 350 degrees Fahrenheit but also maintains that concentration of heat better. (Note that we do not recommend cooking foods at temperatures above 250 degrees Fahrenheit because the higher temperatures decrease the digestibility of the food.) We have found that we can put anything in this oven that we'd put into a conventional oven. Of course, there is less space in the solar oven, but with a bit of planning, we can cook a full meal in there. We've cooked squash and pumpkins, potato dishes, pizzas, stews, and soups—you name it—in the solar oven, all with free sunlight for heat.
Most folks still think of solar cookers as some sort of novelty, perhaps a good weekend project for Scouts but not especially useful otherwise. This viewpoint is unfortunate. In part, the skepticism follows from the high cost of prefab solar cookers; some of them cost several hundred dollars! Moreover, many people believe that their yard doesn't get enough sun to make solar cookers practical.
In fact, solar cookers are practical in every region of North America except Alaska for at least six to eight months every year. As for the cost—well, you really can make your own. Here's how.
Solar "Breadbox" Cooker
If you have a more limited budget or want a "get acquainted" project, you can try making this simple "breadbox" solar cooker, which for the most part requires only scrap or recycled materials.
First, find two cardboard boxes, sized so that one is able to fit into the other, ideally with an inch or two of space all around. If you can't find boxes in the right sizes, you can cut your own boxes from larger pieces of cardboard. Next, cover the inside of the smaller (interior) box with aluminum foil (it is not necessary to cover the inside of the larger, exterior box with foil).
When the little box is placed into the bigger box, the tops of each box should be at the same level. You can support the inner box—so that it is resting off the floor of the bigger box—by placing four small pieces of flat wood or cardboard (we used tuna cans) inside the big box to serve as "legs" supporting the inner box. Once you've placed and glued the legs, pack all the space between the two boxes with crumpled newspapers. Though most people have no problem obtaining old newspapers for the required insulation, you can use many other substances for insulation: cotton rags, straw, dried grass, coconut fibers, whatever is readily available. Though you might be tempted to use those white blown-foam packing "peanuts" for insulation, don't! At high temperatures, they may melt or give off undesirable fumes.
Now that you have one box inside another, with their tops level and with the insulation packed between the boxes, you are ready to seal the insulation. This is done simply by taping or gluing pieces of cardboard on top of the opening or "seam" between the two boxes.
The next step is to make a lid for your cooker. If you were lucky enough that the larger cardboard box you found had a tight-fitting lid already, you can use that. Otherwise, you can cut a lid from cardboard. Measure the size of the big box, cut the cardboard at least one inch larger on all sides, and then cut diagonal slots in the four corners and fold down the edges to form flaps so the lid sits snugly on the box. Tape the folded-down corners securely.
Once you have made a tightly fitting lid, you are ready to cut an opening in the lid that is exactly as big as the opening of the inner box. Just cut this opening on three sides of a square, so that you can fold the loosened Piece of cardboard upward and create a reflector from the attached flap.
The opening in the lid should be covered with a single pane of glass or Plexiglas or a piece of heavy-duty, transparent plastic sheeting. Plastic sheeting is cheaper and easier to install, but glass will retain heat better. We use only glass because it is inert and will not give off fumes. The glass or plastic must be secured to the inside of the lid by glue or silicone caulking. Make certain that the glass is securely mounted before proceeding.
See how the flap that you cut on the lid for the opening can fold up and down like a cover? Line the inside of this flap with aluminum foil, and you have an "automatic" reflector. When the solar cooker is in use, you can prop up the lid with a stick.
Presto! Your solar oven is complete!
Here are a few more pointers on building and using an oven like this.
By planning carefully before you begin the actual construction, you will produce a quality cooker with minimal effort. Rather than obediently following the dimensions in someone else's plan, first see what supplies you have at hand. For example, you may have a good pane of glass, in which case you can adjust the cooker's dimensions according to the size and shape of that pane of glass. Or you may find two ideal cardboard boxes, then adjust all the other sizes accordingly.
To cook in the breadbox oven, you can place a black metal cookie tray or a pie pan in the baking compartment of the cooker. To absorb a maximum amount of heat, all cooking pots should be black and should be covered, but if you allow extra time foil will work pretty well. When using regular recipes in a solar cooker, at times you must allow at least twice as much cooking time as needed for a conventional oven.
Solar Reflector Cooker
We have also built one of Dan Halacy's solar cookers, first described in his 1959 book, Fun with the Sun, and in his more recent book, Cooking with the Sun (cowritten with Beth Halacy). Solar cookers work either by absorbing heat within a closed, insulated box or by reflecting the sun's heat to a focused point on a cooking container. Some cookers use both methods. Dan Halacy's cooker uses only reflection.
This reflector cooker utilizes a cardboard disk covered with shiny aluminum foil and propped up facing the sun. A grill mounted on stand is then placed next to cooker, with a black-bottomed pan or pot (to absorb heat better) resting on the grill. The sun's rays reflect off the shiny surface of the disk, which is curved (concave) to focus the fleeted light. The disk can be tilted and turned to focus its beam of concentrated light directly on the cooking container. Because there is no stored heat, the temperature the oven reaches depends on air temperature, clearness of the sky, and focal point, but we've heard of people achieving 300 degrees Fahrenheit or higher with this cooker. With that amount of heat you can bake bread, brew coffee, cook vegetables, fry eggs, boil water, cook soup, sauté escargot or mushrooms, and so on. The main drawbacks of the Halacy design are that this cooker is difficult to transport, because of its size and number of pieces, and you should never leave it outside in the rain, because the cardboard will get soft and fall apart.
Want to learn more skills for self-reliance? Learn How to Make Your Own Water Filters and Purifiers.
This excerpt has been reprinted with permission from Extreme Simplicity: A Guide to Urban Homesteading, by Christopher and Dolores Lynn Nyerges, published by Dover Publishing, 2013. Buy this book from our store: Extreme Simplicity.
With more than 150 workshops, there is no shortage of informative demonstrations and lectures to educate and entertain you over the weekend.LEARN MORE