BOSTON — IT took us four hours to cook one cup of rice on a partly sunny summer day in Boston, but there will be no gas or electricity bill to pay, and we didn't use a nonrenewable energy resource. Plus, cooking in a solar stove was fun: following the moving shadow of the sun; re-aiming the panels to get maximum sunlight on the food; frowning when clouds moved in, covered the sun, and quadrupled the usual cooking time for rice.
But in some climates, where clear days are more abundant than firewood, cooking with the sun is a sound alternative.
Fifty years ago, inventor Merton (Bud) Clevett set out to make such a solar cooker, spurred by an article in this newspaper that described an African woman's daily, 10-mile trek to secure firewood. Mr. Clevett wanted to design a cooker that could be shipped and copied easily.
Since then Clevett has designed more than 100 solar stoves; he and his wife manufacture six models at their Clevlab headquarters in Littleton, Colo. The stoves range in size - from one-person meals to enough for 10 - and in price - from $20 to $475. He once custom-made a unit that used photovoltaic cells to operate a rotisserie.
His most popular model, the one we tried last week, is the Sunspot, a 10-inch-square cardboard box surrounded by foil-laminated panels that direct sunlight downward, through a clear plastic window over the food. Temperatures can reach 375 degrees F. on a sunny day, and the oven can cook a range of foods: meat, potatoes, bread. Sunspot weighs only 20 ounces and folds to 4-by-10-by-10 inches - convenient for backpackers to carry on camping trips.
Solar stoves aren't big sellers - since 1962 Clevett has sold 29,000, just over 1,000 per year. Science teachers and students interested in learning about solar applications are his biggest market. He has sold several special, durable stoves to the United Nations, which has ``sent them all over the world,'' says Clevett.
Raymond J. Krisst, a nuclear physicist at the University of Hartford (Conn.), says that in order to generate one kilowatt of energy - the equivalent of a hot plate - you need at least nine square feet of sun-capturing surface. He designed a four-foot, parabola-shaped solar grill, which he says works perfectly in the backyard - weather permitting. The greatest drawback to solar cooking is the need for cloudless, windless days.
Joe Deahl, owner of Solar Technology, a marketing company in Bascom, Ohio, no longer sells solar stoves because few people are buying them. ``Interest in solar devices peaked in 1981,'' he says, and has fallen dramatically since 1984 because of lower fuel costs and the ending of the solar tax credit.
Mr. Deahl is not optimistic about the future of solar cookers. ``I hate to say it, but there's no reason to use a solar cooker, other than to conserve resources, which most American people don't pay attention to,'' he says, adding that the best market for solar stoves is overseas.
But, notes Dr. Krisst, resources to make the stoves in developing countries may be in short supply. ``You have to have the raw materials, even the food to cook in them,'' he says. Sunspot solar stoves are available for $20 from: Clevlab, P.O. Box 2647, Littleton, CO 80161.