Frequently Asked Questions - 23-Apr-2008

Do you have to turn the cooker to follow the sun?

Box cookers with one back reflector don't need to be turned unless you are cooking beans which take up to 5 hours. Panel cookers need to be turned more often than box cookers, since they have side reflectors that can shade the pot. Of course turning these cookers more often to follow the sun would result in faster cooking. Parabolic cookers are the most difficult to keep in focus. These need to be turned every 10 to 30 minutes, depending on the focal length.

How do I cook in a season when the sun is very low in the sky?

Make sure you are using a light-weight, dark-colored pot not much bigger than the food to be cooked. It also must have a dark lid. Box cookers shouldn’t be much deeper inside than the pot is high. You’ll need to prop the back of the cooker up to lean it toward the sun and adjust the reflector very carefully so that you can see that light illuminating the inside of the cooker. If there is wind, put the cooker in a sheltered location.

Should I take the time to build a box cooker out of "real" materials like plywood and glass or is cardboard good enough?

Unless you need a cooker that can stay outside even in the rain, you'll do just fine with a cardboard cooker. Cardboard is much easier to work with and holds heat just as well. Some people we know have used the same cardboard box cooker for over 10 years. You can also make the cardboard cooker more durable by painting it on the outside.

Would a mirror make a better reflector?

While mirrors are more reflective than simpler materials such as aluminum foil, the added gain is probably not worth the increased cost and fragility involved with using a mirror. Also remember that the light bouncing off of a mirror has to go though the mirror's glass sheet twice, each time losing strength.

Does it help to paint the walls black?

Some people prefer to paint the walls black thinking that the oven will get hotter. It seems, however, that the walls will get hotter, but the food won't necessarily get hotter. It is generally recommended to cover the inner walls with aluminum foil to keep the light bouncing until it hits either the dark pot or the dark bottom tray. Since the bottom tray is in contact with the pot, the heat the tray collects will move into the pot easily.

What type of paint should I use?

In developed countries you can buy flat-black spray paint that says "non-toxic when dry" on the label. Otherwise, black tempera paint works, but you have to be careful not to wash it off when you wash the pot. Solar cookers in Uganda report that they use aluminum pots that have been blackened on the outside by fire.