The Sun continuously provides Earth with tremendous amounts of solar energy, most of which comes in the form of visible light. Sunlight, when transformed into usable heat, can be a practical source of energy for everyday jobs such as cooking food, heating water, or warming houses. A solar cooker is an insulated box that traps the heat of the Sun for cooking food.

The most efficient way to transform sunlight into heat is to shine lots of sunlight onto a dark surface. When light energy (also called radiant energy) is absorbed by an object, it is changed to heat energy. Darker objects absorb more and reflect fewer of the visible light waves that hit them than lighter objects do. That is because darker objects have a much lower albedo. It follows that while dull black objects readily absorb more light, shiny silver ones reflect more. Mirrors or other reflective materials including aluminum foil, then, can catch more light and redirect it to the cooking surface, where the energy in the light can be used.

The direct and redirected sunlight is converted to heat. Some of the energy heats the air. By using a plastic or glass cover that allows light in but prevents heat from escaping, the energy that arrives as radiation can be used to cook food -- such as the "s'more" featured in the ZOOM segment -- much like a convection oven cooks things by circulating hot air through the cooking chamber.

Both of the solar oven designs in this demonstration use similar materials, though the cone-shaped light reflector exposes additional surface area to the light, amplifying the amount of light it can capture, and redirecting that light more specifically. The result: Its cooking surface is raised to a higher temperature, melting the marshmallow and chocolate more thoroughly than the pizza box design does.


Source: Teachers' Domain, Cooking Cookies with Solar Power, published February 20, 2004, retrieved on November 4, 2010, http://www.teachersdomain.org/resource/phy03.sci.phys.mfe.zsolar/