How to Use a Parabolic Solar Concentrator without the Sun How to Use a Parabolic Solar Concentrator without the Sun
A parabolic solar concentrator is a concave array of mirrors that reflect all incident sunlight onto a single focal point. A high quality parabolic concentrator used near the equator at solar noon generates an intense amount of heat and light. Large scale versions of the technology are employed in concentrated solar thermal power generating stations. However, the technology is still extremely useful even at a small scale! Parabolic solar cookers are widely used by campers and in developing countries. These resemble nothing more than mylar umbrellas. During daylight hours, they can concentrate enough heat to boil a liter of water in twenty minutes or less. What you may not know is that parabolic reflectors can also help you out at night. If you find yourself hungry and low on fuel, a parabolic concentrator can increase the efficiency of your fire or grill. Whether they are used during the day or at night, parabolic solar concentrators require constant tracking and realignment to remain on point.
Step 1 - Fabricate Solar Concentrator
The first step is to pull out your parabolic reflector if you have one, or make one if you don't. An umbrella makes a great basis for a reflector. There are many different materials which can function as mirrors. These include rolled plated polished stainless steel, rolled plated aluminum with a polymer finish, silver coated acrylate foil, or aluminum-coated acrylate foil. Unfortunately, you probably don't have any of these. In that case try aluminum foil wrapped over corrugated cardboard. Bend the reflector into a fan or semicircle shape. You must work quickly if you have unrefrigerated raw food.
Step 2 - Ignite Heat Source
They are many ways to cook using a parabolic reflector. During the day, a good reflector can easily cook many foods. At night, it can be used over a campfire or barbecue. Allow time for kindling and lighter fluid to burn off. If you are really desperate you can try using a lamp. Kerosene lamps will obviously work for this, but electric lights can also generate some results. However, the lamp must emit a broad continuous spectrum of light, including infrared light. Fluorescent bulbs emit light in discrete wavelengths, wasting little as heat. This efficiency makes them great for lighting but poor for emergency cooking. Use an incandescent or halogen bulb, which generates a lot of waste heat. With such a weak heat source you must hold the food and reflector very closely, and maintain realistic expectations.
Step 3- Cook Food
Curve the concentrator around the food, slightly above and downwind of the fire. The food must be located at the focal point of the reflector. Adjust the parabolic concentrator as the flame shifts. If the concentrator is exceptionally powerful, take care not to sear streaks into the food. Handle the concentrator with tongs or mitts if it gets uncomfortably hot. Place the food on a skewer and rotate it slowly inside the focal length of the parabolic concentrator.