Many canned foods are precooked, so it’s okay to eat them right out of the can. However, eating hot food is a great way to add some normalcy to your life during an emergency situation. So having a simple solar stove can become a treasure during an emergency. Of course if the sky is overcast a solar stove will not work, but if you can see your shadow, you have enough sunshine to use a parabolic solar stove. And, they are simple to make if you have access to a few basic materials.
You can purchase a ready-to-use solar stove, but you can also make one from materials you might have on hand during an emergency.
CAUTION: This is not a project for children as a solar stove can produce blinding light and extremely high temperatures. These simple-to-build stoves can quickly burn skin, and can ignite fires in less than two seconds. A solar stove can produce a substantial amount of heat.
Probably the easiest method for building a solar stove is to utilize a television satellite dish. Even a small one, such as the gray 18-inch dish in the photo (above right), is large enough to boil a small quantity of water or cook a small pot of food. As you would expect, the bigger the dish and the more reflective the mirror-like surface, the larger the cook pot that can be accommodated. For the sake of simplicity, the directions and photo illustrations used in this article are for a TV dish, but any parabolic dish will work. Other readily obtainable parabolic dishes can be found in certain types of space heaters, light fixtures, wok cooking pans, etc.
If you would like to purchase a pre-polished parabolic metal dish to keep with your emergency supplies, or purchase an already built stove (or oven), there are several online vendors listed at the end of this article.
What is a parabolic dish? In the non-technical practical sense, it is like half of a ball. These are commonly used to gather and concentrate televisions signals from satellites, for concentrating and projecting heat in certain types of portable room heaters, and also in some light fixtures to reflect light in a certain direction.
To make a solar stove, it’s a simple task if you have access to a parabolic dish that is 12-inches (30 cm), but twice this size is much better for cooking a meal. The larger the dish, the more heat it can generate and therefore the larger the pot of food that can be heated. But creating a mirror-like surface on the dish is extremely important, too. Even if the dish is not perfectly curved, it may still work if you apply a mirror-like coating to the dish (described below).
The conversion of a satellite dish into a stove is a simple do-it-yourself project. You just need to mount your dish on some type of bracket or fixture, so that you can aim it at the sun. It needs to remain solidly in place while your food cooks, and yet it needs to be sufficiently adjustable so that you can keep it aimed at the sun.
If the surface of your dish isn’t already mirror-like, you will need to polish it, or cover it with a highly-reflective foil. Then, to make it function as a stove, you will need to add a bracket or design a hanging method, to hold your cook pot in place while the stove heats the food or water.
Materials Needed: Parabolic dish (such as a satellite TV-dish); space blanket or highly-reflective foil; spray adhesive; metal tubing, wood scraps or other materials to fabricate a stand and pot bracket; and, a suitable cook pot, ideally with a lid.
1. First, mount your dish so that it is adjustable, as you will need to point your solar stove directly at the sun to make it work. This can be an elaborate mount, or this can be accomplished by using sandbags, a stack of tires, or anything else which can prop the parabolic dish in place while it’s operating as a stove. The focal point of the sunlight is the place on the stove which gets hot, so the rest of the stove does not necessarily need to be fireproof.
2. Clean, and then coat the surface of the satellite dish with spray adhesive. Be sure that your hands are clean and glue-free before proceeding, as glue on your hands can tear the foil. Glue left on the surface of the foil will also attract dirt. This dirt, and even dust left on the shiny surface between uses, will reduce the reflectivity of the shiny surface. This will diminish heat production.
3. Cover the surface of the dish with highly reflective material. An inexpensive silver-surfaced Space Blanket works great for this purpose. The shinny-side of tin foil will also work, but it is far inferior to the more mirror-like surface of an inexpensive emergency (solar) blanket.
Cut your shinny material oversize, to make it easier to handle, but still large enough so that you can form it, and mold it, to completely cover the entire surface of the dish.
If you want to be more precise, cut the foil material into triangular strips, spray glue onto the back of the foil, and apply it with a pointed corner to the center of the dish. Repeat with other triangular pieces of foil until the surface of the parabolic dish is completely covered. To avoid coverage gaps, the triangles of material should overlap, as precise placement is difficult. Use a soft rag or t-shirt to make the finish smooth, making sure that the foil follows the curvature of the dish. Patch if necessary with small pieces of foil. Be sure to keep the cloth from becoming contaminated with glue. If you cloth gets glue on it, immediately switch to a new piece of cloth.
Apply the reflective foil to the dish carefully to avoid tearing and crinkling. If the dish is large, start in the middle. If it is smaller than 2-feet (approx. 60 cm) you may want to start on an edge. Either way, keep in mind that your objective is to make the surface of the dish mirror-like and smooth. Ideally, you don’t want any bubble-like gaps between the foil and the surface of the dish. Use care to keep from crinkling the foil, too. Some crinkling of the foil is inevitable, but it is important for a majority of the surface to be as smooth and mirror-like as possible.
4. Your next step is to determine the focal point of the dish. (The focal point is the precise point where the reflected sunlight becomes highly concentrated. If you are using a piece of wood to find the focal point, it should start to burn after a few seconds of exposure to concentrated sunlight at the focal point).
You can go online and find the mathematical formula for determining the focal point of your dish. Or, you can simply aim the dish directly at the sun and experiment. This trial-and-error method can usually be accomplished in a minute or two, by using a scrap piece of wood.
All you need to do is carefully position your dish to directly face the sun, then move a piece of wood from the edge of the dish outward until you see a bright focal point of light develop. Move it in and out until you have found the location where the spot of light is the smallest (most concentrated). This is the focal point. (If you have used a magnifying glass to capture sunlight and start a fire, this is a similar process. However, the concentrated light beam on a homemade solar stove will be much larger than the focused spot of light produced by a magnifying glass.)
6. Once you have determined the focal point for your dish, take rough measurements to help you design and position a bracket or holder for your cook pot. Then, make your bracket. Remember, with your cook pot attached to the bracket, the pot must be held precisely in the right place–and kept stationary.
The concentrated beam of light, when at its smallest size, must be centered on the bottom of the cook pot. The beam of sunlight needs to be concentrated to the smallest possible circle of light to achieve maximum heat. If the beam is not focused precisely on the bottom of your cook pot, your solar stove will not work.
7. Select a cook pot that is heavy-duty and capable of distributing the heat. Cast iron cookware, such as those made by Lodge Manufacturing Company, are the best commercial option.
Caution: On a sunny day, a well made solar stove will create a tremendous amount of heat. It is possible to generate more than a thousand degrees of heat, so if you are using a tin can or standard metal pot, it can melt.
Unlike the stove in your kitchen which distributes the heat across the bottom of a pot, a solar stove concentrates the heat on a very small spot. As a result, it is far more dangerous than your kitchen stove as it is capable of melting metal and quickly catching things on fire. Therefore, you need to either select a pot which will help distribute the heat, or you will need to design another method to distribute the heat.
Pot Selection: Most people find that they prefer to use a cook pot with a lid, rather than a pan. The lid will help keep heat in the pot, and it will also reduce the chance of spilling your food when you are attaching, and removing, the pot from the stove. As a result of this heat retention, your food will cook faster and more uniformly. But be sure to stir your food often, regardless. Once the pot is heated, food can quickly burn, especially at the bottom of the pot near the spot where the heat-beam is striking.
If your food takes more than a minute or two to cook, you may need to slightly reposition the dish of your solar stove. Keep your eye on the heat-beam while cooking, to make sure that it hasn’t moved off of the bottom of your pot. Small adjustments are better than waiting until the beam moves off of the bottom of your cook pot.
The earth’s rotation makes it necessary to keep adjusting the solar stove to keep the beam of sunlight concentrated at the bottom of your pot. You will be able to maximize the reflected heat of the sun by repositioning the stove, as necessary, to keep the beam in the same spot. As a result of this diligence, your food will cook much faster.
If you don’t have matches, another advantage of the solar stove is that it can be used to ignite a scrap of wood, thereby making fire-starting quick and easy, too. However, this same benefit can also create a safety hazard if the solar stove is left outside and unattended. When not in use, the solar stove must be either brought indoors, the dish upended to face the ground, or the stove’s dish covered with something to prevent the sun from striking its mirrored surface and accidentally starting a fire.
Cooking with a solar stove does take some practice, but once your stove is built, it can provide you with a free, easy and almost microwave-quick heating solution for both food and water.
Links to Vendors and Other Resources:
Other Designs for Solar Cooking: http://solarcooking.org/plans/
Solar Cookers and Supplies: http://www.solarcooker-at-cantinawest.com/buy-a-solar-cooker.html
Solar Cookers: http://www.solarovens.net/
Retailers of Solar Cookers by Country: http://solarcooking.wikia.com/wiki/Category:Manufacturers_and_vendors
Sources for Parabolic Dishes:
Edmund Scientifics: http://www.scientificsonline.com/large-parabolic-reflectors.html