Did you know you can fry an egg on a southern Arizona sidewalk? At least, it’s possible on the hood of a car, if you put a bell jar over the raw egg to help heat up the hood. In fact, the Sonoran Desert is one of the best climate zones in the country for such a feat, with our low humidity and powerful sun. (Strange but true: The town of Oatman, Arizona, is famous for its annual Solar Egg-Frying Contest, held every July 4.)
So yes, you can turn a car hood into a solar frying pan. But what if you want a solar oven? Solar baking is different from solar frying, but it relies on a related principle—to demonstrate, we’ll move this discussion’s focus from a car’s hood to its interior.
That’s right—you may already own a solar oven of sorts: a car.
A closed vehicle in the Arizona summer—a figurative oven, everybody knows—actually does get as hot as a gas oven, capable of reaching temps greater than 200 degrees. If you leave some raw cookies on a reflective tin pan beneath the car’s windshield, eventually those cookies will bake through. (It generally takes a 350-degree oven to bake chocolate-chip cookies in 10–15 minutes … you do the math.)
Of course if you want a hotter solar oven—and one that you don’t also happen to drive—it’s easy and cheap to make one, following the steps below. Note: Solar ovens have limitless designs; these directions describe the construction of a simple “box oven.”
Find or make a box with an open top that’s the size you want the inside of your oven to be—with space for a pan or pot, plus your oven-mitted hands. The box can be made of wood, most kinds of metals or even cardboard. (Stay away from plastic and galvanized metal since plastic melts, and both these materials can emit yucky chemicals when heated.)
Find a bigger open-topped box into which your first box will fit easily, leaving gaps at least a couple inches wide between the boxes’ walls and bottoms. The boxes may be made of different materials and be slightly different shapes.
Fill the gaps between the boxes’ walls and bottoms with some kind of nontoxic insulation—rags, cotton, straw: whatever won’t change structure much with heat—as you place one box inside the other. Fill the bottom of the bigger box first, preferably with just enough insulation so that when you set the smaller box in place, the boxes’ tops are level. Then fill in the gaps between the boxes’ walls. If your insulation is flammable, cover the still-exposed stuff with anything that’ll protect it from direct sun (like metal tape or cardboard strips).
Step Four: Coat all inside surfaces with nontoxic black paint, which absorbs the heat.
Top your structure with a piece of glass that covers both boxes. This is your oven’s lid.
And you’re done!
Unless you have time to do …
The oven you’ve so far made will certainly suffice in the Sonoran Desert’s super-hot summer, but most box ovens also have one or more flaps to focus the sun’s heat inside the box, which is good for winter (even here). These flaps will be flat, reflective-surfaced panels (like shiny tin sheets or foil-topped cardboard) sticking out of the top of the oven and angled diagonally upward to direct more sunlight inside. For maximum heat you can also add wedges to tip the entire oven toward the sun, wherever it is in the sky, changing your oven’s aim periodically to follow the sun’s arc. (Make sure you do something to keep the food container inside from spilling its contents if you tip your oven.)
Other ways you can improve your oven are endless: Add wheels, lid hinges, an internal thermometer …
or bedazzle it!
So there you go. Once you’ve completed your first oven, you can make others, improving your method and design. You can build a solar oven with almost anything: Local solar-oven enthusiast Kay Sather made one using an old top-loading washing machine, stuffing insulation between the machine’s outer walls and inside spinner and switching out its metal lid with glass. Rob Crosland, vice-chair of the Tucson group Citizens for Solar, built one with multiple metal strips, acting as flaps, welded around the rim of a crockpot and bent outward in a pretty flower-petal formation: both oven and art. Crosland says he’s also made crude ovens simply using old cooking pots and attaching sunlight reflectors from the windshields of cars (which are a different kind of “oven,” remember!).
Just be practical, have fun, and make the most of our desert’s oven-like heat. ✜
Anna Mirocha is a Tucson-born writer and artist who loves cooking, conservation and every aspect of the Sonoran desert (even its heat—really).
Editor’s note: An earlier version of this article misidentified the vice-chair of Citizens for Solar as Barbara Rose. The vice-chair is Rob Crosland.