We normally use a stove or an oven to cook vegetables, meat and rice. Using a solar cooker we cook the same things, but by using sunlight instead of gas or electricity. In the article let us discuss the working and construction of a solar cooker.
Using Light to Cook
Sunlight isn’t hot in and of itself. It is radiation generated by fluctuating electric and magnetic fields. The sunlight to heat conversion occurs when the photons of light waves interact with molecules of the substance. The electromagnetic radiation emitted by the Sun possesses energy in them. When they strike, the energy causes the molecules of the matter to vibrate. The molecules get excited and jump to higher levels. This activity generates heat.
A mirror surface with high specular reflection is used to concentrate light from the Sun into a small cooking area. The sunlight can be concentrated by several orders of magnitude producing magnitudes high enough to melt salt and metal. For household solar cooking applications, such high temperatures are not required. Solar cookers available in the market are designed to achieve temperatures of 650C to 4000C.
Converting Light Energy to Heat Energy:
The concentrated sunlight is focused onto a receiver such as a cooking pan. The interaction between the light energy and the receiver material converts light to heat by a process called conduction. The conversion is maximized by making use of materials that conduct and retain heat. Pots and pans used in solar cookers should be matte black in colour to maximize the absorption.
Trapping Heat Energy:
The occurrence of convection is reduced by isolating the air inside the cooker from the air outside. Using a glass lid on the pot enhances light absorption from the top of the pan and improves heat retention and minimizes convection loss. The glazing taps the incoming sunlight but is opaque to escaping infrared thermal rays.
Box-type Solar Cooker
The most commonly used form of solar cooker is the box-type solar cooker. In this section, we will be discussing the construction and working principle of a box-type solar cooker.
A box-type solar cooker consists of the following components:
- Black Box – The box is an insulated metal or wooden box which is painted black from the inside to absorb more heat.
- Glass Cover – A cover made two sheets of toughened glass held together in an aluminium frame is used as a cove for box B.
- Plane Mirror reflector – The plane mirror reflector is fixed to the box B with the help of hinges. The mirror reflector can be positioned at any desired angle to the box. The mirror is positioned so as to allow the reflected sunlight to fall on the glass cover of the box.
- Cooking Containers – A set of aluminium containers blackened from the outside are kept in box B.
The solar cooker placed in sunlight and a plane mirror reflector is adjusted in a way such that the strong beam of sunlight enters the box through the glass sheet. The blackened metal surfaces in the wooden box absorb infra-red radiations from the beam of sunlight and heat produced raises the temperature of a blackened metal surface to about 100°C.
The food absorbs heat from the black surface and gets cooked. The thick glass sheet does not allow the heat to escape and thus, helps in raising the temperature in the box to a sufficiently high degree to cook the food.
Advantages & Disadvantages of Solar Cooker
- Solar cookers use no fuel. This saves cost as well as the environment by not contributing to pollution.
- Reduces carbon footprint by cooking without carbon dioxide-based fuels.
- Solar cookers are less useful in cloudy weather.
- Some solar cookers take longer to cook food than a conventional stove or an oven.
- Some solar cookers are affected by strong winds which can slow the cooking process.
- It might get difficult to cook some thick foods such as large roasts and loaves of bread.
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