Last edited: 20 March 2015
- During optimal conditions, when cooking foods that take less than 3-4 hours, it is not necessary to turn the box to follow the sun. However, by turning the box more often you can increase the efficiency of your oven. For foods such as beans, it is essential to turn the box at least once.
- To achieve frying temperatures in a single reflector cooker elevate a shallow, dark pan (without a lid) so that it touches the glass inside. Then attach a small three-panel reflector that concentrates extra light onto this pan. Other food can be baked at the same time in the rest of the oven.
- If black pots or paint are not available, cook in clear jars. When using jars other than canning jars, the lids should be loosely closed to prevent explosions.
- If you are a single person cooking for yourself, or if you just want to experiment with solar energy, you can make your oven rather small. If you plan to cook for a family, then you will want to make yours close to the standard size (18" x 24" glazed opening) (45 cm x 60 cm), and you will want to make it more substantial to stand up to everyday use. One way to decide on the depth of your cooker is to measure the pans you will use. Make the cooker about 1" (2.5 cm) deeper than your pots are high (including lid).
- To allow easy removal of unwanted condensation between the double panes of glass in a wooden cooker, drill one or more holes into the airspace from the side. Stop these holes up with corks during normal cooking. To clear condensation between the panes, remove the corks and allow the cooker to heat.
- Build a cooker with the sides and glazing permanently attached. To open the cooker, lift this assembly off the base upon which the pots are resting.
- In areas where theft might be a problem, attach the lid with hinges and a padlock.
- In general, it's best to make your reflector as large as the entire lid -- not just the size of the glazed opening. This is true especially in areas far from the equator or when cooking during the winter. See "Minimum" Solar Box Cooker.
- Foods should be cooked in dark pans or canning jars that have been painted black (use masking tape to make a viewing strip). Pots that are otherwise suitable but too light in color can be painted on the outside with the non-toxic when dry spray paint. If you also want to use the pots on a conventional stove, use the black paint that is made for barbecue grills. In some places people use blackboard paint to darken pots.
- Pots or cooking jars need to be enclosed in an oven cooking bag or clear glass or plastic enclosure to help concentrate the heat. It is possible in some cases to just enclose the pot while leaving the lid exposed. Theoretically, the heat that is lost is made up for because you don't have to worry about condensation on the cooking cover blocking the sunlight.
- For longer unattended cooking, when you start cooking, aim your cooker to the point where the sun will be in 1-2 hours.
- If you are making something like a soup or stew that mixes hard vegetable (carrots or potatoes, for example) with tender ones (spinach or baby peas, for example), add the hard vegetables first. Wait until your soup is boiling and the harder vegetables have begun to tenderize before you add the tender vegetables (but don't wait until the sun is too low to get it all hot again).
- Until you become confident with judging the sun and your cooker, vegetarian foods are safest.
- Panel cookers make wonderful soup stocks! Just stuff a cooking jar with vegetable scraps (tough asparagus stems and leek tops are especially good) and/or remnants of roast chicken or other meat scraps and bones, add some salt, a little wine or vinegar (this pulls calcium out of the bones and into your soup stock), some garlic and/or onion, and any herbs and spices you think would be good. Let it cook for a day, then strain, skim fat if needed, and use for the next day's soup.
- If it seems as though your food is not heating evenly, give the pot a half-turn now and then.
- Each time you finish cooking in an oven bag (with a panel cooker), turn the bag inside out to allow it to dry. Then use it inside-out the next time you cook.
- Be careful to not cover the cooking food with aluminum foil , as it will redirect the heat away from the pot.
- The single biggest reason for failure in solar cooking is not putting in the food early enough in the day. For this reason, it's best to follow the advice and "Get it on early, and don't worry about overcooking!"
- Foods take longer to cook when there is smog or haze. Since the clarity of the air can make as big a difference as the sun angle, learn to check out the color of the sky and adjust time accordingly. At times the sun may be shining, but the sky is white, indicating that smog or haze are present. A blue sky indicates clear air.
- While some cooking can be done in any non-reflective pot, ones made from thin, black metal work best. Cast iron works but its weight can delay cooking or inhibit it completely during marginal conditions. Shallow pans cook better than deep ones.
- If materials are scarce, build ovens made from papier maché held together with wheat paste . This can then be painted to make it waterproof. If sufficient paper is not available, try using corn husks or some other crop residue.
- A cardboard cooker can be made water-proof using glue and wax (beeswax or candle wax):
- Cover the outside of the cooker with pieces of cloth that have been dipped in white glue or wheatpaste. Make sure the cloth adheres everywhere, applying extra glue to the loose spots. Allow to dry completely.
- For an alternative method that is much less messy and results in a smoother, better appearance, coat the relevant cooker surface with a thick but not dripping layer of white glue (a sponge brush works very well for this). Lay the fabric on the glue and smooth with a pad of paper towel. When fabric is lined up and smoothed out satisfactorily, use the sponge brush to completely cover the fabric with a generous amount of glue, making sure that the fabric is completely saturated with glue. Another layer of glue can be added once the first layer is dry, if it seems to need it.
- Rub a generous amount of wax over the entire cloth surface paying special attention to the seams.
- Heat the cooker near a fire or inside a larger solar cooker or other oven until the wax melts into the cloth. If the weather is warm and sunny, a parked car can also be used to melt the wax into the cloth.
- Repeat steps two and three until you are sure that beeswax has saturated the cloth completely. This process also strengthens a cardboard cooker to a significant degree. Testing is needed to see how these materials hold up over time.
- When arranging transport of solar ovens from a large city to rural users, Dick Wareham recommends finding free space on trucks heading back out into the rural areas after delivering their load of produce or other products in the city.
- Solar cookers as gardening equipment: 1) Gallon cans of dried manure or soil can be pasteurized to 150 degrees to kill wild seeds and insect eggs. 2) Plant material infected with insects, nematodes, or viruses can be cooked and dried in a solar oven and made safe to return to the garden or compost heap. This is particularly useful for greenhouses or urban gardeners. 3) Metal instruments can be sterilized as well as ceramic pots and wooden flats. 4) Water can be warmed in the field to soften plastic dripline fittings. 5) Pruning instruments can be sanitized either with dry heat or oiled and steamed.
- Some alternative cooking pots:
- Smoked-glass casserole dishes. Pyrex makes a low-cost model available for $5 - $10 in stores in the US.
- Rough up glass jars with sandpaper and paint these black. Use masking tape to leave one clear strip for viewing.
- Cook in gourds with a small sheet of glass for a lid.
- Put shiny pots in a brown paper sack.
- Paint a shallow cake pan black and fashion a lid from a sheet of black-painted aluminum flashing with its edges folded down.
- Buy dark baking pans in matched pairs and use one upside-down as a lid for the other. Metal binder clips of the right size—medium to large range, depending on the pan rims—work well for holding them securely together.
- Where large cardboard boxes are hard to find, you can glue together small boxes to form a larger cardboard sheet that can be folded into the shape of a larger box.
- When cooking uncovered cake or bread, sprinkle cinnamon on top to darken the surface and catch more sun. Doughs and batters containing eggs and milk will brown more readily.
- Heat dry grain in an SBC before storage to kill off any insect larva or eggs.
- We have learned with Rocket Stove experiments that floating a small amount of cooking oil on the surface of the food increases the efficiency of the stove significantly by preventing evaporation (which accounts for significant heat loss). In dishes such as rice or beans where some oil will be placed in the recipe anyway, try putting the oil on top and stirring it in later.
There is very little different about cooking in a solar box apart from doubling cooking time and leaving water out when cooking fresh vegetables or meats. All foods are cooked in dark covered pots except for roasting nuts and some baking. Use your own recipes and spices. By making small adjustments in time or the amount of water, your favorite foods taste as good or better than ever. The following approximate times are for 4-5 servings. Increase cooking times for larger amounts.
COOKED DRIED CEREALS AND GRAINS - (barley, corn, millet, oats, quinoa, rice, wheat) : 2 hours. Start with usual amount of water. Next time adjust to your taste. If your sky conditions are less than ideal, you may have better luck if you preheat the water and grain separately, as suggested for pasta. This is especially helpful if the grain is either very slow to tenderize (brown rice, hulled but not pearled barley) or gets mushy easily (quinoa, millet). To learn about using barely-sprouted grains and beans, which take to sun cooking very well, see Sprouting seeds and grains.
VEGETABLES - Add no water. Artichokes: 2 1/2 hours; Asparagus: 1 1/2 - 2 hours; Other fresh green vegetables: 1-1 1/2 hours. If cooked longer they will taste fine but lose their nice green color. Beans - dried: 3-5 hours. Usual amount of water, can be soaked ahead of time; Beets, Carrots, Potatoes and other root vegetables: 3 hours. Cabbage, eggplant: 1 1/2 hours if cut up. Eggplant turns brownish, like a cut apple, but the flavor is good; Corn on the cob: 1 - 1 1/2 hours. The corn kernels will fade slightly if left longer in direct sunlight. The husk will hold the moisture in and protect the kernels naturally. A clean black sock can be put over an ear of corn to help absorb heat for faster cooking time. Squash, zucchini: 1 hour. Will turn mushy if left longer.
EGGS - Add no water. Two hours for hard yolks. If cooked longer the whites turn brownish, but the flavor is the same.
MEATS - Add no water. If cooked longer they just get more tender. Fish: 1-2 hours; Chicken: 2 hours cut up, 3 hours whole; Beef, Lamb, etc.: 2 hours cut up, 3 - 5 hours for large pieces; Turkey, large, whole: all day
PASTA - Heat water in one pot and put dry pasta with a small amount of cooking oil in another pot, and heat until water is near boiling. Add hot pasta to hot water, stir, and cook about 10 minutes more.
BAKING - is best done in the middle of the day (9 or 10 am - 2 or 3 pm) Breads: Whole loaves - 3 hours; Cakes: 1 1/2 hours; Cookies: 1 - 1 1/2 hours. Do NOT need to be covered. Avoid bottom crusts - they get soggy. Black socks can also be used to cover foil-wrapped garlic/herb breads. Takes awhile for the heat to work through, but with the sock to dull the foil it eventually will, and the sun makes wonderful fresh garlic bread.
SAUCES & GRAVIES MADE WITH FLOUR OR STARCH - Heat juices and flour separately, with or without a little cooking oil in the flour. Then combine and stir. It will be ready quickly.
ROASTING NUTS - Bake uncovered. Almonds: 1 hour, Peanuts: 2 hours.
TYPICAL COOKING TIMES FROM Solar Cookers: How to make, use, and enjoy, Solar Cookers International, 2004
SUGAR CARAMELIZATION - Sugar may be caramelized in a pot/pan, or in a box cooker. The usual temperatures in standard cookbooks can be a bit too high for solar cooking; the slow heating of solar cookers means more time is spent at a given temperature, so various stages of caramelization actually happen at lower temperatures than on a conventional stovetop. Roughly, browning (in a box cooker) begins at 140 °C (284 °F). Once the temperature starts to get above 149 °C (300 °F), the sugar will start to burn.
See main article: Guidelines and cooking tips
Many factors affect the length of time it takes to cook things in a solar cooker. In a super efficient solar oven that can reach temperatures similar to a household oven, times should be similar (though some of the special flavors will be lost). In most homemade panel or funnel cookers or box ovens, cooking is a slower, gentler process that generally takes two to five times as long, but the food tastes better, is more nutritious, and needs very little fussing (sometimes none) while cooking.
Factors That Can Affect Cooking Time
- Sunshine — Cooking is fastest when you can see your shadow most of the time and your shadow is shorter than you are. Cooking is possible with some clouds or haze, but times will be slower.
- Solar Cooker — Some solar cookers cook faster than others. The ratio of food + pot to the surface area of the reflectors can affect cooking time as well, and in an enclosed box oven you need room for the hot air to circulate and the UVs to bounce around. Your panel or funnel cooker needs to be decidedly bigger than your pot, and there should to be some space between or around items in a box oven. An overloaded cooker will cook slowly if at all.
- Cooking Vessels — Darker pots heat up faster. Pots with thin walls that conduct heat well heat up faster. Shallow pots get hot faster than deep pots. Splitting a big batch of something into two pots (either in your box oven or using two panel or funnel cookers) will get it done more quickly, too. Blackened canning jars (use masking tape to leave a viewing strip) often cook the fastest because of the slight pressurization.
- Food — Small amounts of food cook faster than large amounts. Foods cut into small pieces cook faster than large pieces. Equal pots of stew (veggies and meat cut large) and soup (veggies and meat cut smaller) might get hot at about the same rate, but the stew will take a longer time of simmering for the vegetable and meat to tenderize. A whole roast or chicken will take more time to get done than chicken or meat cut into pieces.
What This Means In Practical Terms
The general rule in solar cooking is to get the food out early and don't worry too much about overcooking. Most foods need little tending or stirring, so except for turning the cooker a little every hour or two (for some things you can just point the cooker south and not even worry about turning it), you can just go on with your day doing other things while the sun takes care of your food. While there are a few things that can be overcooked in a solar cooker (vegetables such as tender greens, broccoli, and asparagus, or soft fruits, for example), most foods will only get more tender and flavorful. If time is an issue, choose foods accordingly. If the forecast is less than ideal or you want to eat your main meal earlier in the day, choose foods that will cook more quickly.
Save foods like whole chickens or roasts for bright, sunny days when you can get the food out early and leave it until the rays start to lengthen and temperatures begin to drop, and use a meat thermometer if at all possible, to make sure the interior has reached a safe temperature. If the food doesn't quite get done, you can switch to Heat-retention cooking if the food is still at boiling temperatures (if not, heat briefly on the stove to get it back to the boiling point and then move to a heat retention cooker), or you can finish the food in a low oven or slow cooker or on a stove burner turned down low. If food is done but it's not time to eat yet, you can keep the food warm by heat retention means or you can cool it and reheat it briefly (which is still way less fuel or power use than actually cooking the food) on your stove.
As for when to check on the food, if skies are clear and you haven't overloaded your cooker, check it at twice the time recommended for conventional cooking and judge accordingly. For less-than-ideal skies or slower cooking foods, give it longer. If you can get one of the digital thermometers that have a metal probe attached to a long silicone-covered wire that leads to the base where you read the temperatures (under $20. at Wal-Mart) and that can track minimum and maximum temperatures, you can just put it in many foods (center and relatively near the top, since most things tend to cook from the sides in and the bottom up in a solar cooker, so kind of slant it in) and track how your food is doing without having to open the cooker and lose heat to check.
- Chart of safe cooking temperatures for various foods.
- Tips on Construction and Cooking (English), (Italian), (Spanish) - Louise Seeley