Solar cooker works on solar energy. Solar cooker can directly utilize solar energy or can use deflected solar energy from a large concentration rays surface.
Solar cooker consists of a well-insulated box, the inside of which is painted dull black and is covered by one or more transparent covers.
The purpose of these transparent covers is to trap heat inside the solar cooker. These covers allow the radiation from the sun to come inside but do not allow the heat from the hot black absorbing plate to come out of the box.
Because of this, the temperature of the blackened plate inside the box increases and can heat up the space inside the temperature upto 140°C which is adequate for cooking.
The second type of solar cooker uses a lens or a reflector suitably designed to concentrate the solar radiation over a small area. This cooker is able to provide higher temperatures on its absorbing surface when suitably designed but is usually more expensive than the box cooker.
i. The outer box:
The outer box of a solar cooker may be made of wood, iron sheet or fibre reinforced plastic having suitable dimensions.
ii. The inner box:
The inner box can be made from galvanized iron or mild steel or aluminium sheet. All the four sides and the bottom of the inner box which are exposed to the sun are coated with black paint.
Mirror is used in a solar cooker to increase the radiation input on the absorbing surface. Sunlight which falls on the mirror gets reflected from it and enters the box after passing through the glass covers.
This radiation is in addition to the radiation entering the box directly and helps to quicken the cooking process by raising the inside temperature of the cooker.
The use of a mirror can enhance the solar radiation input to the cooker by about 50 per cent.
iv. Cooking containers:
The cooking containers with covers are generally made of aluminium or stainless steel.
The containers are painted dull black on the outer surface so that they also absorb radiation directly.
v. Thermal insulation:
The space between the outer box and the inner box is fitted with insulating material such as glass, wool or thermocole. This prevents heat losses from the cooker.
vi. The double glass covers:
These covers have length and breadth slightly greater than the inner box and can be fixed in a wooden frame maintaining a small spacing between the two glasses.
This space contains air which acts as an insulator and prevents heat to escape from inside. The wooden frame is attached to the outer box by means of hinges.
A rubber strip is affixed all around on the edges of this frame to prevent any heat leakage.
(i) It does not require any cooking gas or kerosene or any conventional fuel.
(ii) Simultaneously more than one recipe can be prepared.
(iii) Keeps the environment clean.
(iv) Less expensive compared to conventional source of energy.
(v) Conserves the conventional source of energy.
(vi) Constant attention is not required.
(vii) Cost of the cooker and maintenance cost is low.
(viii) No smoke and no soot hence cleaning the vessels is easy.
(i) Depends on sun and on cloudy and rainy days it may not be possible to use.
(ii) Takes longer time and planning is required.
(iii) Special vessels need to be used.
(iv) Loss of vitamin C is more compared to cooking on gas.