Cooking with the Sun
Making and Using a Solar Cooker
Reading Time: 6 minutes
By Kristi Cook – Do you enjoy cooking outdoors? Then stretch those outdoor living skills by cooking with the sun. Requiring little more than a pot, a couple of boxes, aluminum foil and glazing, a solar oven is the way to go when fuel is scarce, temps are high, or you just want a change of pace. Even better, you can make your own set-up for minimal cost and have dinner cooking in no time.
Solar Ovens 101
Solar ovens, or solar cookers, are simple outdoor ovens that trap the sun’s energy and work on the same principle that heats your car to excruciating temps on a hot summer day. Sunlight enters the cooker through glazing — similar to a vehicle’s windows — and gets trapped. This trapped sunlight converts to heat energy which in turn cooks the food. On a bright, sunny day, temps in the most basic cooker can reach 250 degrees F. Temperatures are maintained by occasionally refocusing (or reorienting) the cooker to the sun.
To achieve safe cooking temperatures, solar ovens depend on the sun being high in the sky. So, just as your vehicle stays cool and comfortable on a cold winter’s day, solar ovens can’t work if there’s not enough sun or the sun is too low. While this dependence on solar energy makes many areas of the U.S. incapable of year-round solar cooking, most regions have sufficient conditions for four to six months out of the year. To determine the sun’s cooking capability at any given time, check the length of your shadow. If it is shorter than you are tall, then the sun is high enough for solar cooking.
The slow heat of the sun allows for long, slow cooking similar to a crockpot. There are, however, a few guidelines. When selecting cookware, use the thinnest material and the shortest pot possible. The outside walls and lid of cookware need to be black, or a very dark color, to help the vessel absorb and retain heat. You also need tight-fitting lids to prevent heat escape and to reduce evaporation. For foods such as cookies or pizza, choose thin, dark-colored cookie sheets.
Divide food into smaller pots rather than one large one since smaller sizes heat faster and cook more evenly. Place larger meats and longer cooking foods toward the back of the oven which tends to run hotter than the front in many ovens. When mixing different foods, such as stews or roasts with vegetables, load the pot with meats and root vegetables first and add faster cooking veggies such as asparagus or corn once the pot is boiling. To keep heat in, don’t open the lid unless necessary.
To cook, put foods in the cooker as early in the day as possible. If you are making lunch, for instance, you’ll likely need to begin close to 8:00 a.m. in most regions. For an early evening meal, you’ll likely need to start around noon. The goal is to allow enough time for food to properly cook before the sun begins to go down and temperatures begin to fall.
Several factors affect cooking times such as food density, size, amount, intensity of sun, wind, and type of cookware and cooker. Always cook food to the recommended internal temperature. In ideal conditions, here are time guidelines for various types of food:
1-2 hours: Chicken (boneless), eggs, cookies, fish, fruits, grits, oats, rice, pasta, vegetables (fast cooking) such as asparagus, broccoli, corn, English peas, greens.
3-4 hours: Homemade bread recipes, lentils, black eyed peas, whole
chicken, pork chops (most average cuts of meats), pizza, root vegetables such as potatoes, carrots, turnips.
5-8 hours: Dried beans (soak overnight before cooking to shorten cooking times), large roasts or hams, soups, stews.
As a general rule of thumb, when cooking for three hours or less in optimal conditions, many cookers won’t require refocusing. Just position the cooker so that the sun will be directly in front of the oven halfway through the anticipated cooking time while angling reflector(s) to direct as much sunlight as possible directly onto the cooking vessel. With longer times or in less than ideal conditions, refocus periodically to keep the sun in front of the oven to maintain temperatures. Monitor inside temps with an oven thermometer to get a feel for how your particular set up functions in varying conditions.
As with all things, experience is the best teacher. Over time, you’ll learn which sky conditions and cooking times work best for each type of meal. And before you know it, you’ll be an old pro at solar cooking.
DIY Solar Cooker
- Enough plywood to build two topless, floored boxes, one smaller than the other. To determine how much plywood is needed, follow these guidelines:
- The smaller box must accommodate the largest cookware to be used. Allow for 5” or more of airflow around the sides of the cookware, 1/4” or more underneath the cooking rack, and 2” or more between the lid of the pot and the glazing. (If the box is too small to allow for airflow, cooking will be slower or nonexistent.) The larger box must be approximately 1”-2” taller, wider, and longer than the smaller box to allow for insulation. The back wall of the box should be a few inches taller than the front to allow for better light penetration.
- Insulation. Foam sheets, wadded newspaper, old sheets, hay, or dried grass
- Black, non-toxic spray paint
- Aluminum foil
- Glazing such as Lexan, Plexiglass, or clear plastic, sized to larger box’s outside dimensions — like a lid
- Cardboard or wood to build a frame for the glazing (optional)
- Hinges (optional)
- Nails/screws (optional)
- Duct tape
- Cardboard to make a reflector the same size as the opening of the larger box
- Sticks to prop reflector
1. Build the two boxes according to needed dimensions.
2. Apply black, non-toxic paint across the bottom of the smaller box.
3. Line all four inside walls of smaller box with aluminum foil, avoiding
wrinkles and tears. Secure with tape.
4. Line bottom of larger box with 1”-2” of insulation.
5. Place small box on top of the larger box’s insulated floor.
6. Stuff insulation between the walls.
Optional: Build a frame according to the larger box’s outside
dimensions and secure glazing with silicone adhesive, duct
7. Place glazing on outer box like a lid. Add hinges to one side or
allow glazing to rest on the outer edges.
8. Cut cardboard to outer box’s dimensions for the reflector.
9. Line one side of reflector with aluminum foil, avoiding wrinkles or
tears. Secure with tape or glue.
10. Attach reflector to outer box with the aluminum foil side facing the
glazing. Secure with duct tape.
11. To adjust the reflector’s angle, use sticks of varying heights to prop
the reflector at the desired angle.
Do you enjoy cooking with the sun? Do you use a solar cooker similar to the above mentioned or do you have other ideas and designs? We’d love to hear from you in the comments below. Don’t forget to add your delicious recipes!
Originally published in Countryside May/June 2020 and regularly vetted for accuracy.