SOLAR COOKERS How to make, use and enjoy - Chapter -2

CONCEPTS
SOLAR COOKERS How to make, use and enjoy
There are many types of solar cookers — heat-trap boxes, curved concentrators and combinations of both.
Box cookers
Box cookers are the most widely used in households. There are several hundred thousand in India alone.
TYPES OF SOLAR COOKERS
Curved concentrator cookers
Curved concentrators (often called parabolic cookers) cook fast at very high temperatures like fire, but require more frequent adjustment and supervision for safe operation. They are not covered in this booklet, but several hundred thousand households in western China use them. They are especially useful for large-scale institutional cooking.
Combination cookers
Combination cookers (often called panel cookers) incorporate elements of box and curved concentrator cookers. SCI’s simple “CooKit” is the most widely used combination cooker.
Compared to curved concentrator cookers:
• it doesn’t need to be moved to track the sun during several hours of unattended cooking
• temperatures are more even
• the flat shiny surfaces are safer for your eyes
Compared to a box cooker:
• it requires no window or insulation
• it cooks just one pot at a time, but several units cost less than one box cooker
Compared to both:
• it is easier and cheaper to produce
• it folds compactly to carry and store
• it requires 10-20 clear, heat-resistant plastic cooking bags per year
SOLAR COOKERS INTERNATIONAL
Fuel: sunlight
Sunlight is the fuel. A solar cooker needs an outdoor spot that is sunny for several hours and protected from strong wind, and where food will be safe. Solar cookers don’t work at night or on cloudy days.
Convert sunlight to heat energy
Dark surfaces get very hot in sunlight, whereas light surfaces don’t. Food cooks best in dark, shallow, thin metal pots with dark, tight-fitting lids to hold in heat and moisture.
Retain heat
A transparent heat trap around the dark pot lets in sunlight, but keeps in the heat. This is a clear, heat-resistant plastic bag or large inverted glass bowl (panel cookers) or an insulated box with a glass or plastic window (box cookers).
Capture extra sunlight
One or more shiny surfaces reflect extra sunlight onto the pot, increasing its heat potential.
HOW SOLAR COOKERS WORK
SOLAR COOKERS How to make, use and enjoy
FREQUENTLY ASKED QUESTIONS
What can I cook?
Use your solar cooker to cook vegetables, fruits, meats, grains, legumes and most other foods. You can even bake breads and desserts! Simple solar cookers cannot stir-fry or cook flat breads that require high temperatures.
Do I need to add water to foods that will be solar cooked?
Vegetables, fruits and meats cook great without water, which tends to slow cooking and wash away nutrients. For grains and legumes, use the amount of water you use with other cooking methods. If the food comes out too moist or dry, adjust the amount of water next time.
What time of year can I cook?
In general, you can use your cooker 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. In many countries there are a few months each year when simple solar cookers cannot be used. People living in the darker areas on the following map tend to have longer cooking seasons.
What time of day can I cook?
You can typically 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, cakes and pastries should be baked if possible.
Faster cooking Slower cooking No cooking
SOLAR COOKERS INTERNATIONAL
How long do foods take to cook?
There are many factors that affect the speed with which your food cooks in a solar cooker, including time of year, amount of sun, type of pot and amount of food. The following table summarizes some important factors.
Faster cooking
Slower cooking
Time of year and day:
Amount of sun:
Amount of wind:
Thickness of pot:
Amount and size of food:
Amount of water:
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SOLAR COOKERS How to make, use and enjoy
Simple solar cookers, under normal conditions, will cook at temperatures from 82-121°C (180-250°F) or more. Since food cooks at 82-91ºC (180-195ºF) these temperatures are hot enough to fully cook food, but not so hot as to burn or dry out food or damage healthful nutrients. Also, many foods can cook for several hours without overcooking, which allows food to be placed in the cooker early in the day and left until mealtime without needing to be stirred or monitored. (“Absentee cooking.”)
As with any cooking method, cooked food that is allowed to cool to temperatures between 52-10ºC (125-50ºF) for a period of time may contain bacteria that can spoil food and lead to food poisoning. Food that stays in this temperature range for more than four hours should be discarded.
Here are some typical cooking times for 4 pounds (2 kilograms) of food on a sunny day: