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Cookin Under tne S

Rose Woofenden

©2005 Rose Woofenden

Next time you're in the mood for slow food—a savory casserole, or even home-baked bread— consider cooking with the sun. Almost anything that can be prepared on a conventional stove or in an oven can be cooked in a solar cooker, with delicious results. And while you're enjoying your tasty, sun-warmed meal, you can also take comfort in the fact that you've saved energy—and prevented some pollution— in the process.

Delicious and nutritious meals can be prepared in a solar oven. Here, the author uses a Sun Oven, a commercially manufactured box cooker.

Delicious and nutritious meals can be prepared in a solar oven. Here, the author uses a Sun Oven, a commercially manufactured box cooker.

Inside or Outside the Box?

Although three distinct types of solar cookers exist, they all have one thing in common—they harness the sun's energy to cook food. Parabolic solar cookers use curved or multifaceted reflectors to focus and concentrate the sun's energy onto a cook pot or food item. With a parabolic cooker, frying food is even possible. Panel cookers, the most basic type of solar cooker, use reflective panels around a black glass jar, or a cooking pot wrapped in a plastic bag or covered with a clear glass bowl. Although these cookers are simple to build, their open design compromises cooking performance and heat retention.

Solar ovens and box cookers are the most common type of cooker used. Simple box cookers and ovens use glazing materials, such as glass or clear plastic, to admit the sun's short-wavelength energy. (Glass performs better—it lets in more energy, and insulates better than plastic.) They are a little more complicated to build than panel cookers, but perform better. Reflectors, which create a larger surface area to concentrate more of the sun's energy into the box, can be paired with a box cooker or oven to boost cooking power. They can be made from a variety of materials, from foil-covered cardboard to sheet metal.

With box cookers, once the heat has been captured, it must be retained and absorbed by the food, instead of being reflected or leaked out of the box. A good seal between the box and glazing material is crucial to prevent convective heat losses. Insulation minimizes heat loss through the sides and bottom of the box.

To aid in heat absorption, the box bottom is painted black or fabricated from a dark material, and black cookware, such as cast iron or dark glassware, is also used. (Note that cast iron cookware, which has more mass than glass cookware, can add to cook time.) For cooking that requires a constant heat, thermal mass such as bricks or stones can be placed inside the cooker to help maintain a more consistent temperature in the cooking box.

Commercially available cookers range from the rudimentary and compact (small, foldable reflectors) to the complex (parabolic cookers that require detailed manufacturing processes). Off-the-shelf cookers can range in price from US$18 for a foldable, aluminum foil-covered foam reflector to US$250 for an insulated Sun Oven, complete with a gasket-fit, tempered-glass door. With a few on-hand materials, and minimal skill and effort, you can even make your own simple solar cooker.

Energy Efficient Cooking

According to energy research scholar Richard Heede, cooking accounts for about 6.5 percent of the energy used in the average U.S. home. A standard electric range uses 750 kilowatt-hours a year. If your electricity comes from a fossil fuel-fired power plant, that means you're adding more than 500 pounds (227 kg) of carbon dioxide to the atmosphere annually, just from cooking.

Tapping into a natural, renewable resource, such as the sun, wind, or falling water, to make electricity is more environmentally friendly than using nonrenewable resources. Because solar cookers use the sun's energy directly, solar cooking is even more efficient (and less expensive) than cooking with solar electricity. Regardless of how your electricity is produced, when you use a solar cooker, less energy is used and fewer resources are consumed. With their minimal parts, solar cookers require far fewer raw materials to make or manufacture than a conventional stove—a significant savings in embodied energy.

Parabolic cookers like this Zomeworks Sunflash can actually get hot enough to fry food. Beside it, a foldable, cardboard Sunspot backpacker's cooker.

Basic Anatomy of a Solar Box Cooker

Sunlight: Enters oven box and heats the air, pot, food, and other thermal mass

Reflectors: Redirect more sunlight into oven box for higher temperatures

Glazing: Allows sunlight in; helps keep heat in

Pot: Dark color heats up more quickly

Oven Box: Insulated to retain heat

Pot Rack or Gimble:

Keeps pot level as oven is tilted toward the sun

Foot or Prop: Allows oven to be tilted to face the sun

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