Q3Power Generation Sources
Question
Q.3. Describe principle of operation of solar cookers.
Answer
A solar cooker operates on the principle of the greenhouse effect: sunlight passes through a transparent glass cover and is absorbed by a blackened cooking vessel, converting to heat that is trapped by the glass and insulated box, raising the temperature enough to cook food.
A solar cooker uses direct solar radiation, trapped via the greenhouse effect, to cook food without any external fuel. The basic box-type solar cooker consists of an insulated box painted black inside, with a double-glazed glass cover on top and a plane reflector mirror hinged to the box to concentrate additional sunlight onto the glass cover.
Solar radiation (mostly short-wavelength visible light) passes easily through the transparent glass cover and strikes the blackened interior surfaces and cooking vessels, where it is absorbed and converted into heat. The heated surfaces re-radiate energy as long-wavelength infrared radiation, which is largely opaque to glass and cannot escape easily — this selective transmission/absorption is the greenhouse effect, causing heat to accumulate inside the box. The insulated walls minimize conductive and convective heat losses, allowing the internal temperature to rise to 100-140°C, sufficient for slow cooking, boiling and baking.
The reflector booster mirror increases the effective aperture area, concentrating more solar flux onto the glass top and improving cooking speed. Because it depends entirely on solar insolation, a solar cooker works best during clear, sunny hours (typically 10 am to 3 pm) and cooking is slower than conventional stoves, but it requires no fuel, has zero running cost and no emissions, making it valuable for rural and remote household cooking in sunny regions.