Appalachia--Science in the Public Interest

SOLAR FOOD COOKER

A solar box cooker or "solar oven" is an insulated box-within- a-box which uses solar energy for cooking food. A solar oven can be built in any size so that it will be able to cook the foods placed within it.

The solar cooker is based on three simple physics concepts: dark objects absorb sunlight and convert the energy to heat;
shiny surfaces reflect rather than absorb heat; and light passes through transparent materials, while heat (to a large degree)
does not.

The solar box is designed so that an adjustable reflector directs sunlight through a tight-fitting glass lid. The sunlight
enters the insulated box and is reflected off the sides, which are lined with aluminum foil or other reflective material (Mylar
for example). Inside the box, the cooking pots, which are dark colored (black works best) absorb the sun's energy and convert it to heat, which cooks the food.

1. Advantages of the Solar Oven

Free Fuel -- it uses no electricity and THE SUN IS FREE.
Inexpensive to build -- the materials cost relatively
little and readily available in most areas.
Can be built by almost anyone -- The design is
simple and requires no special expertise or tools.
Fuel at hand -- no collecting of firewood or dung is
necessary.
No constant watching of the cooking food is required.
Several foods can be cooked at the same time.
No smoke, so there is less chance of lung disease.
The cooker can be used to purify water, so there is less
danger of intestinal disease from drinking unsafe water.
Reduces deforestation and desertification, fossil fuel
use, soil depletion, and air pollution.

2 . Solar Locations

The solar oven needs to be placed in a spot that will be in
sunlight for several hours. In the sunny tropics it works year-
round, and in temperate zones it can be used for 6-8 months of
the year. Mid-day and midsummer are the peak cooking times.
When the sun is at least 1/3 of the way from horizon to overhead
(30 degree sun angle), easy-to-cook foods will cook. The closer
the sun is to a 90 degree angle (directly overhead), the greater
the cooking power. The most intense cooking takes place from
10:00 a.m.- 2:00 p.m. In the winter, when the sun is farthest
away, it doesn't get as high in the sky; therefore cooking power
is decreased. Wind, humidity and outdoor temperature affect the
cooking very little. The oven also works well at high altitudes.
However, dust and smog will slow down the cooking time.
In some places the Solar Box Cooker cannot completely replace
current cooking methods, but it can offer convenient seasonal
relief from the high cost of fuel. In cloudy or winter weather,
or when a higher temperature is desired the cooker can be moved
with the sun for maximum effect.

3. Cooking with the Solar Box Cooker

The amount of food the solar cooker will cook at one time
depends upon the size of the box. The box described in this
paper will cook 5-7 kilograms (10-15 pounds) of food per meal on
a sunny day. Food will not spoil during slow cooking. The
bacteria that cause food spoilage as well as disease-causing
organisms (germs and parasites) stop growing at 49 C (120 F) and
are killed at 65 C (150 F), well below the cooking temperature of
the solar box cooker.

4. Other Uses

Water Pasteurization and Heating. To kill water-borne
disease organisms, water needs to be heated to a temperature of
at least 65 C (150 F). A four-liter jar of water heated for 3
hours in a solar box on a sunny day will be free of biological
contamination.

Food Preservation. Acidic foods (fruits and vegetables) can
be preserved or "canned" for long term storage in heated sealed
containers with a solar box. DO NOT CAN MEATS or non-acidic
vegetables unless pickled (with vinegar).

As a Traditional "Wonderbox." (Also called "hayboxes" or
"hotboxes") Food is brought to boil over a fire, then the pot is
wrapped in a blanket and placed in the insulated box to continue
cooking by itself. This will also be of use on sunless days or
at night.

REFERENCES

Alward, Ron. Solar Cooker Manual. Ste, Anne de Bellevue,
Quebec: Brace Research Institute, MacDonald College of McGill
University (HOA 1CO, CANADA).

Bowen, Thomas. Understanding Solar Cookers and Ovens Arlington,
VA: VITA Publications ( P.O. Box 12082, Arlington, VA 22209).

Brown, Norman, "Renewable Energy Resources for Developing
Countries." Annual Reviews Energy 5 (1980): 389 - 413.

Chiochetti, David A. and Robert H. Metcalf. "Pasteurizing
Naturally Contaminated Water with Solar Energy" Applied and
Environmental Microbiology (February, 1984): 223-228.

How to Build and Use a Solar Box Cooker. Sacramento: Solar Box
Cookers International (1724 llth St. Sacramento, CA 95814
(916) 223-228).
Schimmoeller, Mark and Andy McDonald. A Solar Cooker. Obtained
from ASPI Publications. (Mt. Vernon, Kentucky 40456).