Why and How to Cook with Solar
Nearly 3 billion people cook over wood, animal waste, charcoal fires, or other non-sustainable fuel sources. They breathe in smoke and soot for hours every day. Indoor air pollution from combustible fuels causes millions of deaths with women and girls accounting for 6 out of every 10 of these. Worldwide, three out of seven people lack sustainable fuel to cook their meals and make water safe to drink And, even more rely on expensive, unsustainable fossil fuels.
By using solar energy to cook and make water safe to drink, we can improve health, empower women and children, and break the cycle of poverty. People who harness free solar energy for cooking and water purification, breathe cleaner air, drink safe water, and preserve the environment. Solar cooking helps reduce the high social, economic, and environmental costs of soot and fossil fuel emissions that impact all humans and environments today.
There are many types of solar cookers with the most common being box, panel, evacuated tube, and parabolic cookers.
The most popular are solar box cookers and solar panel cookers because they work well for slow cooking, are generally less expensive to buy than other styles, and are fairly easy for people to build themselves. Starting in the 1950s, these designs have typically been used to introduce solar cooking in deforested developing countries. High-quality manufactured models are available for purchase from vendors in a number of countries.
Evacuated tube solar cookers are compact and can cook quite efficiently due to the insulating properties of the evacuated tube cooking chamber. Several models are offered commercially, and insulated glass tubes are available for building your own cooker.
Parabolic solar cookers also have a long history of use, primarily in Europe and Asia. They cook at higher temperatures and usually require more complicated fabrication. A variety of designs are available from manufacturers. They can also be used in series to create steam for institutional kitchens, feeding thousands of people per day.
Solar Cooker Design Basics
Solar Box Cooker
Can be constructed with simple materials, with several high quality commercial designs also available
Tipping the cooker towards the sun can eliminate partial shading of the cook pot
Cooking temperature range is 135 – 200 °C (275 – 392 °F)
Some are large enough to cook with multiple pots, great for baking and slow cooking
Solar Panel Cookers
Inexpensive to build or buy, and typically can be collapsed for storage or transport
Slow cooking retains flavors and nutrients, and requires little, if any, reorientation to the sun
Usually achieves temperatures of 110 – 140 °C (230 – 284 °F)
Weatherproof materials should be considered for construction
Evacuated tube solar cookers
- Usually compact, and can cook quite efficiently with relatively small reflectors
Contemporary designs have aesthetic appeal
The cooking chamber requires careful handling
Glass technology somewhat limits the size of opening of the cooking chamber
- Cooking times are similar to a traditional stovetop
- High temperatures will allow for food to be fried and grilled, typically 120 – 230 °C (248 – 446 °F)
- Requires periodic reorientation, often every fifteen minutes, which may be done with a mechanical solar tracking apparatus
- Generally more expensive than panel and box cookers, and requires more storage space
Parabolic solar cookers
Cooking times are similar to a traditional stovetop
High temperatures will allow for food to be fried and grilled, typically 120 – 230 °C (248 – 446 °F)
Requires periodic reorientation, often every fifteen minutes, which may be done with a mechanical solar tracking apparatus
Generally more expensive than panel and box cookers, and requires more storage space
General solar cooking guidelines
After a bit of experience, you’ll see how readily you can adapt your present cooking and baking to solar cooking. Using the solar cooker can actually reduce the total amount of effort in meal preparation. Also cooking outside in the summer allows you to eliminate extra heat in the house. With solar cooking, you start your meals early in the day and then relax. At lunch or later in the afternoon or evening, when you’re tired after a day of work, the sun will have cooked your food.
- Most food, except, cakes, cookies and open-faced cheese sandwiches, are cooked in containers with the lids on.
- Unless you are cooking with a parabolic solar cooker that focuses light on the bottom of the pot, it’s important to use dark-colored pots that absorb light nd transform it into heat. Cooking vessels should be black or very dark in color with tight fitting lids. With rare exceptions, the lid is kept on the pot while cooking. Clear pots will also work, and pot lids can be either dark or clear. It is important to always cook with the lid in place so that the moisture from the food doesn’t escape and fog the plastic bag or other glazing. (See Solar Cooking Pots below)
- Be sure to use potholders when removing the pots from the oven; the pot will be very hot
- You do not need to stir food while cooking. However, it’s OK to check the food if you quickly replace the lid. One exception to this rule is if you are cooking an exceptionally large mass of something very thick, in which case it can be a good idea to stir at least once after clear signs of steam appear, with the goal of moving the cooler middle of the food towards the side of the pan and the hotter food against the sides into the middle.
- If you are cooking a large amount of food, it will cook more quickly if distributed between two or three smaller pots instead of one large pot.
- Several small, uncovered bowls may be placed inside a large covered pot to cook.
- Most recipes take slightly less liquid when cooked in a solar oven.
- Time for cooking depends on the temperature of the food as it is placed in the oven, as well as the brightness of the day.
- Foil is not generally recommended to wrap food for solar cooking because shiny foil insulates by reflecting sunlight and heat away from the food.
- Focus the oven to obtain the most sun and check food about once an hour when you’re just getting started. Later, you’ll relax and tend the cooking only once every two or three hours. Many meals may be cooked without repositioning the oven to refocus with the sun. You will learn by experience. Just face the cooker so that halfway through the cooking time the sun will be right in front of the cooker with the prop stick casting a shadow on the proper stick holder. With lots of food, or on less than fully sunny days, you may need to refocus the oven once or twice.
- Most recipes calling for a higher cooking temperature will do fine if you give them more time instead.
- Time for cooking depends on the temperature of the food as it is placed in the oven, as well as the brightness of the day.
- Allow plenty of time. With the exception of breads, cakes, and cookies, most foods hold well in the solar oven without scorching or drying out.
- Leftovers are easily reheated in the solar cooker.
- If you are unable to cook in the early morning or evening, then cook during the midday to save firewood/cooking fuel. Then use a small portion of the saved fuel to reheat the food right before eating breakfast or dinner.
- To keep the food hot after the sun goes down, add several bricks or heavy stones when you begin cooking. To maximize heat retention, lower the reflective lid onto the glass, and cover the cooker with a blanket.
Solar Cooking Pots
Keep in mind that pots made from thin material heat faster than thicker ones. Metal pots will heat faster than ceramic or earthenware, and cast iron is slow to heat initially, but will hold heat better than thinner metals.
Dark speckled graniteware is a good choice for home solar cookware.
Cast iron should be preheated in the cooker and be used during good solar cooking conditions, as it requires strong sunlight to achieve the best results.
Glass jars make good pots either clear or painted on the outside since they may cook slightly better when darkened. Also, darkening the outside of food containers will protect some of the B Vitamins. If you paint the jars, rough up the glass with sandpaper for better adherence and, preferably, use food-grade paint. A strip of masking tape placed from top to bottom before painting can be removed when the paint is dry to leave a tidy strip of clear glass for visual inspection of the inside. When using jars for cooking, make a hole in the lid of any non-canning jar, such as mayonnaise jars, peanut butter jars, etc., to prevent steam buildup. Dome and ring canning jar lids that are designed for food preservation automatically release excess steam pressure yet are safe only when used on canning strength, food preservation jars. The thickness and strength of non-canning glass jars is not intended to take the strain of steam under pressure and could break explosively unless vented.
Dark colored, hard-fired, Earthenware Pots with glazing work very well; however, some low-fired earthenware pots do not initially cook well. Perhaps the poor performance of some earthenware is due to liquid soaking through and evaporating on the outside, or perhaps it is due to the thickness and porous nature of low-fired clay pot sides. Experimentally, in the efforts to use low-fired, unglazed earthenware, the goal has been to approximate the hard-fired pots by filling the pores and to providing a form of glazing. On a homecraft basis, this has been done by saturating the pot with food-type oil, fat or natural resin which both closes the pores and changes the surface. Oil also will conduct heat rather well and this may be part of what improves cooking in low-fired, earthenware pots following oil treatment. Light colored earthenware needs to be darkened on the outside only, perhaps by rubbing a dark food, nontoxic dark powder or soot from clean wood into the oil coating. Even so, there may be forms of low fired earthenware that are difficult to use.
Specific Food Cooking Guidelines
Put these foods in the oven early and don’t worry about overcooking: roasts, stews, casseroles, poultry, potatoes, carrots, pot roasts and rice are almost impossible to overcook; therefore, the timing on the food is not critical. Chicken will still be juicy and will fall of the bone when solar cooked four hours instead of the needed two hours. The major advantage of solar cooking is the flexibility in cooking times. You can remove the food any time after it is done.
For best results, do not overcook the following foods: green vegetables, cookies, cakes, and bread.
BAKING – is best done in the middle of the day (10 am – 2 pm). Breads: Whole loaves – 3 hours; Cakes: 1 1/2 hours; Cookies: 1 – 1 1/2 hours and do not need to be covered. Avoid uncooked bottom pie crusts as they get soggy (precook before adding filling). To bake cakes or bread in a solar box cooker, preheat the cooker for at least ½ hour before adding the food. If the oven heat can be maintained at the recipe temperature, follow the recipe cooking time (and adjust if necessary).
COOKED DRIED CEREALS AND GRAINS – (barley, corn, millet, oats, quinoa, rice, wheat): 2 hours. Start with the 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). Baaely-sprouted grains and beans take to sun cooking very well.
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).
Recommendations about adding water to the pot: The difference is in the heat transfer medium – boiling water, condensing steam, and hot air respectively. The three methods produce different results, and have different efficiencies. Boiling takes longer because there is more water to heat to boiling point, and leaching can take place. Steaming is more efficient, because we can get away with using less water. Baking is the least efficient, and tends to dry out the veg, though if this is done inside a tube cooker, some steaming is inevitable, too. Boiling offers an opportunity for even deployment of salt, and baking allows browning and caramelising to occur.
EGGS – Add no water. Two hours for hard yolks; if cooked longer the whites turn brownish and may get rubbery. Try less time initially if you are willing to eat the yolk partially cooked.
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, pork, etc.: 2 hours cut up, 3 – 5 hours for large pieces; Turkey, large, whole: all day. Cooking chicken too long will result in a mushy consistency. When cooking fresh fish, you can judge when the fish is cooked thoroughly when juice begins to drop. If you cook fish on a rack, it is easy to see this change. Then check to see that the fish is cooked to the bone in the thickest part.
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.
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.
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.
High altitude adjustment
The temperature of boiling water is reduced as the altitude increases. For instance, the boiling temperature of water is only 95 °C (203 °F) at 2000 mt (6561.7 ft). and this slows the cooking. Dried beans may be difficult to cook at high altitudes because of this effect. You may try cooking your food in darkened canning jars with regular canning lids and rings tightened. The rubber seal allows excess pressure to be released but a low increase in pressure is retained and speeds cooking. We only recommend standard canning jars and lids as they are designed for pressure.
Additional Resources
How to Build a Simple Box-Style Solar Cooker by Earth Water Alliance.
How to Make a Copenhagen-Style Solar Cooker by Earth Water Alliance.
Advantages and Disadvantages of Solar Cooking by Somdrij Solarcooker on YouTube
How to Make a Solar Cooker by Hillsborough County, University of Florida, IFAS Extension.
Sources: Solarcookers.org; solarcooking.fandom.com/wiki/; UN.org
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