Solar Cooker:- " The solar Cooker is a device which is used to cook food by utilising the energy radiated by the sun". A solar Cooker consists of an insulated metal box or wooden box which is painted all black from inside. There is a thick glass sheet cover over the box and a plane mirror reflection is also attached to the box as shown in picture. The food to be cooked is put in metal containers which are painted black from outside. These metal containers are then placed inside the solar Cooker box and covered with the glass sheet.
We will now describe how the solar is kept in sunshine, outside the house. The reflection of solar Cooker is adjusted in such a way that it faces the sun. When the sun's rays fall on the reflector, the reflection sends them to the top of solar Cooker box on the form of a strong beam of sunlight. The sun's heat rays pass through the glass sheet cover and get absorbed by the black inside surface of the cooker box. Once the sun's heat rays enter the cooker box, then the glass sheet cover does not allow them to go back. In this way, more and heat rays of the sun get trapped in the box due to which the temperature in the solar cooker box rises to about 100°C to 140° in two to three hours.
This heat cooks the food material kept in the black container. For example, the food materials like rice, pulses (dal) and vegetables can be cooked in a box- type solar cooker.
The box- type solar cooker can be used to cook only those food material which require slow heating. The box- type solar cooker cannot be used to cook those foods where strong heating is required. For example, the box- type solar cooker cannot used for baking (chapattis, etc) and for frying because they require stronger heating.
In order to achieve higher temperatures required for baking and frying , spherical reflector- type solar cooker (having concave reflector) is used. When a concave mirror reflector is attached to a solar cooker, it converges large amount of sun's amount of sun's heat rays at its rays at focus due to which a high temperature is produced in the focus area (which is suitable for baking and frying). Thus, a concave mirror reflector is best suited for use in a solar cooker. We will now give the advantages and limitations of a solar cooker.
The important advantages of a solar cooker food are the following:
* The use of solar cooker for cooking food saves precious fuels likes coal, kerosene and LPG.
* The use of solar cooker does not produce smoke due to which it does not pollute air.
* When food is cooked in solar cooker, its nutrients to not get destroyed. This is because in a solar cooker, food is cooked at a comparatively lower temperature.
* In a solar cooker, up to four items can be cooked at the same time.
Some of the important limitations (or disadvantage) of a solar cooker are given below:
* The solar cooker cannot be used to cook food during night time (because sunshine is not available at that time).
* If direction of reflection of solar cooker has to be charged from time to time to keep it facing the sun.
* The direction of reflection of solar cooker has to be charged from time to keep it facing the sun.
* The box- type solar cooker cannot be used for baking (making, chapattis, etc.) or for frying.
If a coil of copper tupe painted black from outside is placed in a box similar to that of solar cooker, if will work as a solar water heater. This is because when water is passed through the copper coil, it will absorb sun's heat rays and became hot.
Solar water heater are used to supply hot water in big buildings like hotels and hospitals. A solar water heater cannot be used to get hot water during the night or on a cloudy day.
