Nepal was once known for its dense forest, however in present only 29% of the cover remains. About 87% of the domestic energy in Nepal is produced by firewood. This percentage is close to unity in remote regions. Wood is used for cooking as well as space heating.
The shortage of fuel wood in many parts of Nepal is prominent and collection has become more and more time consuming. Usually it is women and children who collect and carry wood to their home to use for food preparation. On an average, 4-6 hours a day is spent on collection of fire wood. In this context, cooking with the help of solar energy can be one of the solutions for this alarming situation.
Solar cooking is a matured technology which many of the developing countries like India, China etc. has successfully promoted. There are several hundred thousand solar cookers in India and China.
Though there is various type of solar cooker. The basic principle is to convert the sunlight into heat. Some of the basic principles are –
• Concentrating sunlight: A reflective mirror of polished glass, metal or metalized film is used to concentrate light and heat from the sun into a small cooking area, making the energy more concentrated and increasing its heating power.
• Converting light to heat: A black or low reflectivity surface on a food container or the inside of a solar cooker will improve the effectiveness of turning light into heat. Light absorption converts the sun's visible light into heat, substantially improving the effectiveness of the cooker.
• Trapping heat: It is important to reduce convection by isolating the air inside the cooker from the air outside the cooker. A plastic bag or tightly sealed glass cover will trap the hot air inside. This makes it possible to reach similar temperatures on cold and windy days as on hot days.
In general there are two type of solar cooker. The box-type and concentration type –