Solar cooking experiments

Solar cooking uses energy from sunlight to heat, cook or pasteurise food without any fuel or electricity. As a hands-on subject it illustrates several principles of physics at once: the radiant energy carried by sunlight, the way dark surfaces absorb light and convert it to heat, how reflective surfaces can concentrate that light, and how trapping heat raises temperature. Building and testing a solar cooker is therefore a common physics experiment as well as a practical technology.

There are three broad designs. A box cooker is an insulated container with a transparent lid; sunlight enters through the glazing, is absorbed by a dark interior, and the heat is trapped much as it is in a greenhouse, slowly raising the inside temperature. A panel cooker uses flat reflective panels to direct extra sunlight onto a dark pot, often enclosed in a clear bag or sleeve to retain heat. A parabolic or concentrating cooker uses a curved reflective dish to focus sunlight onto a small area, producing high temperatures quickly enough to fry or boil but requiring the cooker to be aimed accurately at the sun.

The performance of any solar cooker depends on the strength of the sunlight, the cleanliness and angle of its reflectors, how well it is insulated, and how often it is realigned as the sun moves across the sky. Simple experiments can compare how fast different designs raise the temperature of a measured amount of water, or test the effect of pot colour and insulation. Because the apparatus is cheap and the results are easy to measure with a thermometer, solar cooking is a useful way to demonstrate energy transfer, heat retention and the optics of reflection.

Frequently asked questions

How does a solar cooker heat food?

It converts sunlight into heat: dark surfaces absorb the light, reflectors concentrate more of it onto the cooking vessel, and insulation or glazing traps the heat so the temperature rises.

What are the main types of solar cooker?

The common types are box cookers, panel cookers and parabolic (concentrating) cookers, which differ in how they capture and concentrate sunlight and in the temperatures they reach.

Why must some cookers be aimed at the sun?

Concentrating cookers focus light to a small point, so they only work well when pointed directly at the sun and must be realigned as it moves across the sky.