what role is played by shiny reflective materials and by dark absorbing materials
by Cesar Quental
My question is: 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 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 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 the concentrated 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. * * A fourth principle, though not vital in all forms of solar cooking (parabolic cooking is one)is: transparency of your retentive materials, or in other words, your lid on a solar oven or your enclosure around your pot/pan on a solar panel cooker needs to be able to allow the sun's rays to penetrate inside to where the food/cooking vessels are located. This ability of the sun to penetrate is usually achieved by using clear glass, or plastic coverings on a solar cooker lid/door/enclosure which then in turn acts as an inhibitor, trapping the heat as well. tips and ideas on how to get the most out of your solar cooker Nathan Admin. |
