Solar cookers — when used properly — safely and conveniently cook all types of food, including meats, grains, legumes, vegetables and fruits. As with any cooking method, however, care should be taken when solar cooking to maintain food safety, particularly with meats, legumes and grains.
Harmful food microbes, including bacteria and viruses, are killed when heated to 65°C (150°F). This is called pasteurization. Food cooks at 82°C (180°F) to 91°C (195°F), and is therefore free from disease-causing organisms when fully cooked. Simple solar cookers cook gently at temperatures just above these, so foods maintain moisture and nutrients, and rarely burn or overcook. Some solar cookers can cook at temperatures much higher than this.
With all cooking methods, certain bacteria produce heat-resistant spores that germinate after food has been cooked. Therefore, cooked food should be kept at temperatures above 52°C (125°F). If cooked food is allowed to drop to temperatures between 52°C (125°F) and 10°C (50°F) for a period of time, these bacteria can spoil the food and lead to food poisoning. Food that stays in this temperature range for more than four hours should be heated again to cooking temperatures before consumption. (Even after reheating there is still a risk of illness. If you are unsure you should discard the food.)
Solar cookers require direct sunlight to function properly. Shadows, clouds and inclement weather limit their effectiveness. Solar cookers should be used on sunny days, in locations where shadows are not a concern.
In most regions of the world there are a few months when simple solar cookers have limited usefulness, due to low solar radiation intensity. In general, you can solar cook when the length of your shadow on the ground is shorter than your height. This is an indicator that the sun is high enough in the sky to cook. Some solar cookers, however, are efficient enough to be used year-round.
You can typically solar cook two meals per day — a noontime meal and an evening meal. You cannot cook early in the morning or after sunset. The sun is most intense between 10:00 a.m. and 2:00 p.m., which is when breads and pastries should be baked if possible.
And, of course, always wash your hands before and after handling food, and use clean utensils and pots.