A solar cooker is a device which uses the energy of direct sunlight to heat, cook or pasteurize food or drink.
Solar cooking is done by means of the suns UV rays.
A solar cooker lets the UV light rays in and then converts them to longer infrared light rays that cannot escape. Infrared radiation has the right energy to make the water, fat and protein molecules in food vibrate vigorously and heat up.
It is not the sun’s heat that cooks the food, nor is it the outside ambient temperature, though this can somewhat affect the rate or time required to cook, but rather it is the suns rays that are converted to heat energy that cook the food; and this heat energy is then retained by the pot and the food by the means of a covering or lid.
This occurs in much the same way that a greenhouse retains heat or a car with its windows rolled up. An effective solar cooker will use the energy of the sun to heat a cooking vessel and efficiently retain the energy (heat) for maximum cooking effectiveness.
There are three main components to most solar cookers, or you could say three main principles to effective solar cooking; these being:
Concentration (reflection, or reflectance) Absorption (ability to attract or hold heat. Retention (means or capacity to retain heat)
Concentration – Concentration of the sun’s rays is performed most often by reflecting panels, petals and such surfaces that can “focus” or concentrate the rays of light (UV) to a point or concentration.These reflecting panels are usually made of materials that are shiny and reflective due to the substance used in their manufacture, such as silver, chromium and aluminum.Without a means to concentrate the sun’s rays it can take longer to heat objects or surfaces, thus most solar cookers are constructed with reflector panels to speed up the process of heat accumulation.
Absorption –Absorption of the sun’s energy (heat)in solar cooking is best achieved when a surface is dark in color, thus the most common solar oven interiors are usually black in color as well as the color of the cookware used for cooking the food.
Dark colors absorb the heat, whereas light colors do not absorb heat well. And some colors can reflect the sun’s energy away, such as silver for example. Generally, the best cookware for solar cooking is the dark, thin variety because it absorbs the heat (energy) well; and because it is thin, it can then transfer the heat more quickly and evenly to the food.
Retention –Retention is the final principle in solar cooking.If a solar cooker is not well insulated and if it does not have a cover, or lid, then all of theconcentrated heat (energy) and all of the absorbed heat would quickly dissipate into the air and be lost to the surrounding environment.A solar cooker must have the means to “trap” or hold the concentrated heat allowing it to accumulate and to “build up” to sufficiently high enough levels to be able to effectively cook.