A solar cooker is a device which uses the energy of direct sunlight to heat, cook or pasteurize drink and other food materials. Many solar cookers currently in use are relatively inexpensive, low-tech devices, although some are as powerful or as expensive as traditional stoves, and advanced, large scale solar cookers can cook for hundreds of people. Because they use no fuel and cost nothing to operate, many nonprofit organizations are promoting their use worldwide in order to help reduce fuel costs and air pollution, and to help slow down deforestation and desertification. History In ancient times, the use of solar energy was believed to have existed in civilizations amidst the Greeks, Romans and the Chinese, though not for cooking. The first academic description of the principles of a solar cooker is by the Swiss geologist, meteorologist, physicist, and Alpine explorer Horace-Bénédict de Saussure, in 1767. The principle of cooking meals by sunlight was largely developed in the French Foreign Legion, in the 1870s. Working principles Concentrating sunlight: A mirrored surface with high specular reflection is used to concentrate light from the Sun into a small cooking area. Depending on the geometry of the surface, sunlight could be concentrated by several orders of magnitude producing temperatures high enough to melt salt and metal. Such high temperatures are not really required for most household solar cooking applications. Solar cooking products are typically designed to achieve temperatures of (baking temperatures) to (grilling/searing temperatures) on a sunny day. Converting light energy to heat energy: Solar cookers concentrate sunlight onto a receiver such as a cooking pan. The interaction between the light energy and the receiver material converts light to heat and this is called conduction. The conversion is maximized by using materials that conduct and retain heat. Pots and pans used on solar cookers should be matte black in color to maximize absorption. Trapping heat energy: It is important to reduce convection by isolating the air inside the cooker from the air outside the cooker. Simply using a glass lid on your pot enhances light absorption from the top of the pan and provides a greenhouse effect that improves heat retention and minimizes convection loss. This "glazing" transmits incoming visible sunlight but is opaque to escaping infrared thermal radiation. In resource constrained settings, a high-temperature plastic bag can serve a similar function, trapping air inside and making it possible to reach temperatures on