Solar Thermal cooking
Solar cooking systems have been developed in many diverse forms ranging from hot box ovens to focusing dish cookers. Hotbox oven systems have been widely accepted in India and other countries where there is a shortage of energy and pressure on LPG, Coal, Natural Gas, and biomass resources.
Solar cookers in which the cooking pot is placed at the focus of a concentrating mirror have not been widely adopted due to the need to continually adjust the orientation of the concentrator. Hot box ovens and concentrating solar cookers are cheap and effective; however they are limited to cooking during clear sky periods and require the cook to work outdoors.
For a solar cooking system to be adopted in kitchen the following objectives need to be satisfied.
The primary elements of the solar cooking system are:
Asolar cookerisadevice,whichcooks food with the help of solar energy and can save the conventional fuels to a significant amount. It, however, supplements the cooking fuel and cannot replace it in total. Solar energyis abundantly available in India. On clear sunny days, it is possible to cook noon meal for 4 to 5 people in a normal Box solar cooker and if one desires either full or part evening meal could also be cooked in it.
There are three main components to most solar cookers:-
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 theconcentratedheat (energy) and all of theabsorbedheat 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.
Types of Solar Cookers
Basically, there are 3 types of solar cookers:
Box Cookers Solar box cookers (sometimes called solar ovens) are the most common and inexpensive type of solar cookers. These box cookers have a very simple construction and they are made of low cost materials. The outer box is often made of wood. The inner box is made of insulating material, which is covered with clear glass or with plastic, and often has a reflector of aluminum. According to Solar Cooker International, solar box cookers cook at moderate temperatures and often can accommodate multiple pots. It can reach a temperature of 140˚ C. The solar box cooker, like other solar cookers, needs direct sunshine to operate and produces zero emission. However, the temperature is low and it cannot store and save solar heat for later use. Many nonprofit organizations promote these cookers worldwide in order to help reduce fuel costs and to slow down deforestation caused by firewood collection and charcoal production.
Panel Cookers have a flat panel which reflects and focuses sunlight for cooking and heating. Panel cookers incorporate elements of box and curved concentrator cookers. The panel cooker is quite similar in operation to the solar box cooker. The same principles are employed but instead of an insulated box, panel cookers typically rely on a large reflective panel. Panel cookers are unable to collect and store sunlight for later use and they are unstable in high winds. Also it cannot retain much heat when the sun is hidden behind the clouds.
Parabolic Solar Cookers in comparison to solar box and panel cookers, parabolic cookers (sometimes called curved concentrator cookers) can reach much higher temperatures and can cook more quickly, but require frequent adjustment and supervision for safe operation, according to Solar Cooker International. It needs more precision to focus the sunlight on the food in the pan. If the sunlight is not correctly focused on the food in the pan, the food will not be cooked well.