We are all familiar with how hot a car can get on a sunny day. As the sunlight hits the interior, it warms up the enclosed air. The trapped air can't escape and continues to get hotter and hotter and can reach temperatures up to 75 degrees Celsius. Simple solar ovens work in the same way. If we concentrate the sunlight, even hotter temperatures and faster cooking times can be achieved.
This is the simplest solar oven to construct. Take a small, black box with a removable lid and insulate the interior with a layer of newspaper or bubble wrap to trap the heat inside. Using a food container, place the food in the middle, close the lid and place in the sun. Just like a parked car with the windows rolled up, the interior will trap the heat and the air will get hotter and hotter. Limit the number of times you peek into the box to keep as much heat inside. Cooking time will depend on how large the box is relative to the size of the food item.
Take a large, open-top box and line the interior with a layer of newspaper or bubble wrap and cover this insulating layer with tin foil (the shiny side out). To allow more sunlight to enter, cut the front of the box to half of the original height and slope the sides to the full height of the backside. Sunlight will enter the front and top of the box, reflect off of the shiny sides and concentrate heat in the middle. Use a piece of transparent or translucent plastic as a cover to trap the heat inside. This type of solar oven collects more heat and can even bake bread in just a few hours. Make sure you keep the box pointed directly at the sun.
This type of oven uses a parabolic-shaped support to reflect the sunlight to a central point. Costly mirrors can be used, but aluminum foil works well. Depending on the size of the reflector, enough sunlight can be reflected to boil water and barbecue foods (it may take a few hours to raise the oven's temperature). These are the most efficient solar ovens but require a proper mechanical support that will raise the cooking surface to the central reflection point. These types of ovens usually produce too much direct heat and are not good for baking.
Solar cookers or ovens have become more popular in recent years, especially with a shift in consumer interest towards 'greener' or more environmentally-friendly alternatives to gas or coal-fired barbecues. Many types are now commercially available; for example, the GoSun High-Efficiency Solar Cookers have had great reviews thus far.solar cookbook or two, like Cooking with Sunshine.
People tend to think of cooking with solar power as a novelty. Although it may not be practical for everyday use, it can provide a hearty meal when travelling outdoors or in an emergency situation.