Cooking Without Fuel?

Solar cooking is so low-tech that it’s hard to believe it really works. There’s no flame. No glow. No hum.

The simple materials most solar ovens are made from--cardboard, aluminum foil and glass--make it seem even more unreal.

Solar ovens are simply heat traps. They heat up much the same way that the interior of a car does on a hot day, says Rick Palkovic, electrical engineer, technical writer and co-author of a solar cookbook.

In a closed car, sunlight enters through the windows, is absorbed by dark interior material and turns into heat, which radiates back from the material as infrared energy. The longer wavelength of infrared keeps it from escaping back through the windows, and the car gets hotter and hotter.

In a solar oven, visible light (both direct and reflected) enters the glass top. When it is absorbed by a dark plate at the bottom of the oven and dark cooking pots, it turns into heat energy, radiates from the interior materials and can’t pass back out through the glass.

Insulation on the bottom and sides of the box-within-a-box-style cooker helps keep the heat from escaping, and the food in the pots cooks by conduction.

Most solar ovens cook at 250 to 300 degrees; manufactured solar ovens get up to 400 degrees. To speed the cooking process, more reflectors can be added and the oven can be frequently rotated to follow the sun.

Worried that the cardboard box might get so hot it catches fire? Don’t be. Just remember Ray Bradbury: Paper burns at 451 degrees Fahrenheit. Box ovens just never get that hot.