Cooking with the sun
February 18, 2010
The power of the sun's rays striking the earth can produce energy levels of up to a kilowatt on each square meter of the planet's surface. This is the equivalent of just half the energy output of a modern electric hot plate. That is why sunlight first needs to be collected and concentrated on a small area if it is to be used for cooking.
Reflectors or mirrors are the best way to do it. Solar cookers can be outfitted with reflectors ranging from high-quality ones such as anodized aluminum plates, which reflect 95 percent of the sun's radiation, to inexpensive tin foils, which reflect just 50 percent. The latter, however, requires longer cooking times.
A solar cooker that uses a parabolic reflector with a diameter of one and a half meters can absorb energy levels of up to two thousand watts during periods of intense sunshine. It then concentrates it onto a cooking surface.
Depending on the quality of the reflector, between 750 to 1500 watts of energy is produced on the cooking surface, allowing for three liters of water to boil in 10 to 20 minutes.
Solar oven produces enough heat to melt metal
By contrast, a reflector with a diameter of half a square meter can produce just 200 watts in a simple cooking pot with a tin lid. That means it would take at least an hour to get those three liters of water up to a boil.
Another option is to use a solar oven, like the one developed at the Cologne-based German Aerospace Center, which boasts a high level of energy efficiency. A massive reflector with an area of 57 square meters absorbs sunlight and focuses it on a small surface measuring just a few square centimeters.
The concentrated energy of 22 kilowatts is so powerful it could melt a hole through a thick metal plate. Scientists are using the solar oven to experiment with new technologies to further develop, among other things, solar thermal plants.
These plants play an important role in the ambitious DESERTEC project. The project aims to meet around 15 percent of Europe's electricity needs from eco-friendly energy harnessed from Africa's deserts.
Author: Antonia Rötger/Helmholtz Association (sp)
Editor: Mark Mattox