Scientists Design Solar Oven to Dampen Use of Firewood
Published: December 11, 1990
SOLAR ovens are a promising alternative for millions of people in the developing world who rely on firewood to cook their meals, a recent project in Central America has shown.
The rural poor in developing countries often live on the edges of swamps, deserts and rain forests fragile ecosystems that cannot withstand further stripping of trees and the consequent erosion. Wood-burning also increases carbon dioxide in the atmosphere and may contribute to global warming.
For the past three years two American physicists and a handful of volunteers have been working in Guatemala, El Salvador, Honduras, Nicaragua and Costa Rica to introduce a simple box-type solar oven that people can build in a few hours and use for most of their cooking.
The scientists, Daniel M. Kammen of California Institute of Technology and William F. Lankford, of George Mason University, report on their project in the Nov. 30 issue of the British journal Nature. Wood Shortages Loom
More than a third of the world depends primarily on wood for cooking, burning nearly half of the annual world wood harvest of three billion tons. According to the United Nations Food and Agriculture Organization, 84 percent of Africans will face wood shortages by the end of the decade.
In many countries women spend hours a day scavenging for firewood.
"Every year the forest moves further and further from my house," an Indian woman in Guatemala told a visiting American scientist.
Cooking over wood fires is also a health threat. Cooking fires in confined indoor spaces are a primary source of respiratory, skin and eye infections among women and children in developing countries.
Conservation and an increased reliance on alternative, renewable energy sources can reduce the demand for firewood. In sunny countries solar ovens are a feasible component to a solution, Dr. Kammen said.
The cooker that the scientists introduced in Central America is an insulated wooden box with a glass window. Pots rest on a conducting metal plate inside the box, and a flip-top lid covered in aluminum foil doubles as an extra solar-collecting panel. Boil, Bake, Braise and Saute
In strong sunlight the ovens can reach temperatures of about 350 degrees Farenheit. Unlike some other designs, box cookers can work even in partial sunlight, and they do need to be constantly moved to directly face the sun.
They can be used to boil, bake, simmer, braise, and saute foods, and to kill germs in naturally contaminated water.
"They work like a Crock-Pot," Dr. Kammen said. "In some ways they are better than regular ovens, because they don't lose moisture, and the food retains more vitamins and minerals."
Solar cookers do have drawbacks. They cannot be used at night or in the rain or on very cloudy days. Cooking times are about twice as long in solar boxes as over fire.
Solar Box Cookers International, a nonprofit organization in Sacramento, Calif., publishes a pamphlet on building solar cookers, which can be used in the tropics all year and in most other climates in spring and summer. Beverly Blum, the group's executive director, said the cost of building a cooker depends on local circumstances. A simple one, like a cooker in her back yard, can be made from cardboard, a pane of glass, a roll of aluminum foil, wads of newspaper and glue -- adding up to about $10. Those made with wood and metal, which last longer and are better for humid areas, can cost up to $100. Technology Aimed at Women
Some previous efforts to introduce solar cookers to the developing world failed to gain acceptance, in part because they used more complicated cookers and were seen as an imposition of foreign technology.
In Central America the scientists supervised the building of about 200 ovens. Dr. Lankford revisited seven of the communities last summer and found that in La Trinidad, Nicaragua, the first village to receive the ovens, the people rarely use them. But in several villages in Guatemala, the ovens are used almost every day, he said.
The scientists attribute the success to a change in approach, from a well-intentioned donation of technology to a collaboration with residents. THE SUN IN A BOX A solar cooker that can reach temperatures of 350 degrees Fahrenheit can be built from cheap materials. It is basically an insulated box with a glass window to let in sunlight and hold in heat and a reflector to capture extra rays. Source: Solar Box Cookers International