This article is a guide to building your own box solar cooker. To learn more about solar cookers and what they do, read this article: SOLAR COOKERS: AN INTRODUCTION.
Box solar cookers tend to be the most effective solar cookers (or at least, the most effective of the cheaper, easier to build kinds). They utilize all the methods (concentrating sunlight, converting light to heat, trapping heat and the greenhouse effect) of solar cooking very efficiently, leading to higher cooking temperatures than their panel-style brothers. And the good news is, box solar cookers are about as cheap and easy to make.
So let’s begin.
WHAT YOU’LL NEED
The items you’ll need are:
1) A cardboard box with each side greater than 16 inches in length.
2) A second, larger cardboard box, that can fit the first smaller box (1) inside of it with at least half an inch of space between any side (so an 18×18 inch box if your first one is 16×16. At least 2 inches greater in length and width).
3) A third piece of cardboard, a few inches larger all the way around than the top of the smaller box (1) (this is going to be your lid).
4) A fourth piece of cardboard, slightly smaller than the top of your smaller cardboard box (1).
4) Aluminum foil
6) Black paint
7) A foam paintbrush
8 ) A wire coat hanger
9) Oven cooking bags
10) A black cooking pot with a black or clear lid
PUTTING IT TOGETHER
1) Building Your Oven
Close the larger box, and turn it over, bottom up. Place the smaller box on top of it, and trace the outline of the smaller box on the bottom of the bigger box with your pencil or pen.
Remove the smaller box, and cut along the lines you traced on the bigger box with scissors or a knife. You will now have a hole in your bigger box where your smaller box will fit snugly.
Place the smaller box inside of the hole you just cut in the bigger box, leaving an inch of space between the two boxes on the bottom.
2) Selecting the Size Of Your Oven
You’ll want your oven to be 1 inch deeper than any pots you might use. Figure out how deep this is.
Use scissors or a knife to slit from the top of the small box up to this point. Fold the sides down to create flaps for the top of your oven.
3) Adding the Foil
Combine your glue with water to create a 50/50 mix.
Separate the two boxes, and use this mixture to glue the tin foil to the inside of both boxes, and to the inside of the flaps on the smaller box. Apply it the way you would wall paper- tight and smooth.
4) Putting it together
Put the small box back into the hole of the bigger box. Glue the flaps of the inner box to the frame of the outer box, to keep them in place. Trim them if they’re too long, so the length matches the length of the bottom box.
Stuff crumpled newspaper between the boxes. It will help keep everything in place, and serve as insulation.
5) Building Your Cooking Pan
Cut a piece of cardboard to a size slightly smaller than the opening of your inner box.
Apply foil to one side of the cardboard in the same way you did to the boxes.
Paint the foil side black, and let it dry overnight.
When dry, place it in your oven, black side up. This is your cooking area.
6) Building Your Lid
Take the piece of cardboard that is larger than the smaller box. Place it on the opening of your oven. Trace around the opening.
Trace a second box, an inch or two larger all around than the first.
Cut along the second line, creating a lid a few inches wider than your oven’s opening.
Cut two slits from the outside of the corners into the first box you traced. This will allow you to fold your sides in, creating top that will close snugly on your oven.
7) Turning Your Lid Into a Reflector
Go back to the first box you traced on the lid (the one the same size as your oven opening). Cut along 3 of the lines, keeping the one at the back of your oven intact.
Fold this part upwards. This will be your reflector flap.
Paste tin foil on the inside of your reflector flap.
Fashion the wire coat hanger into a shape that will hold your flap open, at angle of less than 90 degrees.
8 ) Utilizing the Greenhouse Effect
To take advantage of this effect and increase your cooking temperatures, tightly glue an oven bag on the inside of the lid, so it creates a plastic layer that blocks your opening. Make sure though to NOT glue the plastic bag to your reflector.
COOKING WITH YOUR BOX SOLAR COOKER
To cook with your new solar cooker:
1) Place it on a flat, dry surface away from any shadows (or future shadows- your cooker will have to stay shadow-free for many hours).
2) To cook a meal for noon, have your cooker facing south east, and begin cooking between 9-10am.
To cook a meal for the evening, have your cooker face south west and begin cooking between 1-2pm.
For all day cooking, have your cooker face directly south.
3) Remove the lid and place the food you would like to cook into a black pot. Place the pot in an oven bag, then put this inside another bag (double bagging will help increase the cooking temperature by around 20 degrees C).
4) Place your pot in your solar cooker, put the lid back on and open the reflector flap, holding it in place with your wire.
5) Allow your food a few hours to cook. Don’t worry, with the lower temperatures the food won’t dry out or burn, so you won’t need to check every few minutes like you do with traditional stoves.
A solar cooker is best used in conjunction with other cooking methods, as weather conditions are not always ideal for solar cooking. With a few hours of cooking, this solar cooker can feed up to 5 people.
On windy days, stones or bricks can be used to keep the panels in place.
When not in use, fold the panels up and store in a safe, dry place away from animals. If taken care of, this solar cooker can last for 2 years or longer.
For more information on building various other solar cookers, check out solarcooking.org, a phenomenal resource on the subject.
Good luck and stay prepared!