Concentrating and storing solar energy to cook food, pasteurize water or dry fish and grain.
Half the world still cooks its meals over wood fires, and in East Africa about 85% of families do. Lack of fuelwood and deforestation are major and increasing problems worldwide. This firewood shortage is not likely to improve spontaneously. The consequences include a growing burden on family budgets, more time spent for the collection of wood and partly irreversible damage to the local environment. These effects will continue to hit the rural and semi-urban poor, particularly women, the hardest. A logical solution is the use of the sun where it shines brightest and where it is needed most. Solar cookers can do just that, and solar cooking has the potential to become one of the most important contributions to a solution of the firewood problem.
Solar drying is done at 3 major levels: the 1st one is the family or small social group that consumes much of its own produce and sells to the local market; the 2nd is the small enterprise or co-operative that sells to the local market as well; and the 3rd is the medium and large enterprise that sells to far away markets and exports. Solar drying is an economic activity that is normally involved in a market mechanism. There are several types of market, for example: local market which mainly requires low drying cost and better quality than sun drying; larger market and international markets which mainly require high quality standards; market of dried products where products dried in different ways are competitors of solar dried products; and market of solar driers where other different methods of drying are competitors.
One model of solar cooker with a parabolic reflector delivers 750 Btu/hr (compared to box-type solar cookers which deliver below 240 Btu/hr). This can boil water adequate for sterilizing medical utensils. A production company is also building a complete tool and jig kit for village scale production. However, parabolic cookers are more difficult to build, require specialized material and skills (for refocusing, for example), and may not be accepted in certain social and cultural contexts.
A solar box cooker is designed to receive and trap direct solar radiation, reduce heat loss from conduction, radiation and convection and store heat gained for long periods of time. Sunlight, both direct and reflected, enters the solar box through the glass or plastic top. It turns to heat energy when is is absorbed by the dark absorber plate and cooking pots. This heat input causes the temperature inside of the solar box cooker to rise until the heat loss of the cooker is equal to the solar heat gain. Temperatures sufficient for cooking food and pasteurizing water are easily achieved. The material used can be quite cheap and portable, including cardboard or a shallow pit in the ground, straw, rice husks or other dried vegetation, aluminium foil or scrap tin, and scrap glass and perspex. A non-portable cooker is built of earth and brick and may be double-glazed.
It is reported in 1996 that solar ovens are becoming an accepted form of cooking in Afghan culture, and knowledge of solar cooking is widespread in certain areas of Afghanistan resettled by refugees who learned to use solar ovens while in refugee camps in the Northwest Frontier Province, Pakistan or Kabul during the previous decade.
In the Dadaab Refugee area, almost directly on the equator in northeast Kenya near the Somali border, the 100,000 refugees find gathering fuelwood increasingly difficult and dangerous. A development agency (GTZ) funded by the German government has introduced fuel efficient cook stoves, fireless "haybox" cookers and tree planting. In the past, the 35,000 refugees in the Kakuma Refugee Camp in northwest Kenya had to barter away part of their meagre food rations for enough fuel to cook the remainder. In 1996 it was reported that over 1,200 families are able to solar cook and solar pasteurize milk and water. Of the refugee women who became solar cooks, 24 volunteered for extra training so they could teach their neighbours.