- Renewable & Alternative Energy
How to Make and Use a Solar Oven | Box Cooker Plans and Recipes
What Exactly Is a Solar Oven?
A solar oven, sometimes referred to as a solar cooker, is a device that allows you to cook food using the sun's energy as fuel. The most common kinds of solar cookers are curved concentrators (also known as parabolic cookers,) panel cookers, and box cookers. Curved concentrators resemble a mirrored satellite dish. They cook at high temperatures, but require frequent adjustment. Panel cookers combine elements of a curved concentrator and a box cooker.
Homemade solar oven designs range from simple, inexpensive cookers that can be made in an hour, to complex systems that can cook at higher temperatures. One uncomplicated panel cooker design uses an automobile sunshade reflector to concentrate sunlight onto a black surface to cook food. Solar box cookers reflect and collect heat into a box, in which multiple cooking pots can be placed. This article will show you how to make a simple box cooker using common household supplies.
Is it really possible to cook with the sun? Yes! With a few simple adjustments, almost any recipe can be cooked in a solar oven. This article will show you how to make, use and enjoy a solar oven. Included is a solar oven construction plan that is easy to follow and can be constructed from simple materials on one day. I will provide tips along the way to make the process even easier and your oven more efficient. Solar cooking recipes links are included so that you can begin to enjoy the benefits of using a solar oven right away.
Photo credit: Self-Sufficient-Blog.com
How Do Solar Cookers Work?
First, heat must be collected. Sunlight is the fuel. In order to use sunlight, it must be collected and converted to heat energy. Dark surfaces get very hot in sunlight, so it is recommended to cook in a black, shallow pot with a tight lid to hold in the heat and moisture.
Next, heat must be retained. A transparent heat trap around the dark pot lets in sunlight and keeps in the heat. Types of wraps include clear, heat-resistant oven bags, inverted glass bowls, clear plastic or window glass.
Finally, increase and concentrate the heat. Shiny surfaces can reflect more sunlight onto the pot, increasing the potential for heat.
Photo credit: PracticallyOffTheGrid.com
What are the Benefits of Solar Cooking?
There is a rise in interest in solar cooking, with good reason! Solar cooking has many benefits.
- Solar cooking saves fuel and is environmentally benign. It uses the power of the sun, which is a free, renewable resource.
- Solar cooking saves money spent on utility bills for fuel. And your kitchen stays cool on hot days!
- Slow cooking in a solar oven retains moisture, flavor and vital nutrients. Scientific evidence shows that foods cooked at a moderate temperature may be healthier.
- Solar cooking is easy. Solar ovens do not burn foods, so no periodic or constant stirring is necessary. Foods cook virtually unattended.
- Pots used to cook in a solar oven are easy to clean, with no burned on spots or sticky cooking oil film caused by high temperature cooking.
- There is no risk of smoke, fire, or carcinogenic burning of food. There is very little danger to children.
- Solar cooking is versatile, portable and wonderful for camping.
- Solar ovens do not depend upon electrical or gas power. Solar cooking is a skill everyone should know for emergency food cooking, as well as water and milk pasteurization.
What Can I Cook in a Solar Oven?
Almost anything! Fruits, vegetables, meats, grains, even bread and desserts! A solar oven functions like a slow cooker, so it is able to cook roasts, casseroles, soups and other items that would normally be prepared in a crock pot. It can dehydrate foods, such as dried fruits, herbs and meats. It can also function like a conventional oven, giving you the ability to bake breads, cakes and cookies. Rice, beans and even pasta can be made in a solar oven, though they take a longer to cook than they would on the stove top.
Solar cookers do not get hot enough to boil liquids, stir-fry, sear meats or to bake pancakes and other flat breads. However, water can be pre-heated in a solar oven so that it boils quickly on the stove-top, and foods such as pasta and rice that are generally cooked by boiling can be prepared in a solar oven at a lower temperature. Meats can be seared or browned on the stove, and finished cooking in a solar oven with a tender, juicy result.
Photo credit: KnowledgePublications.com
Is Solar Cooking for You? - Solar cooking may be a great way to cook if you can answer "yes" to the following questions.
Do you have mostly sunny days several months of the year?
Do you have a sunny space outside that is protected from wind and tampering?
Are you willing to experiment and learn a different way of cooking?
What do you think?
When is the Best Time to Use a Solar Oven?
Any time that the length of your shadow on the ground is shorter than your height, the sun is high enough to cook. The sun is most intense between the hours of 10:00 am and 2:00 pm, which are prime solar cooking hours. However, a solar oven can be placed in the sun early in the morning, in order to begin heating up, and a well-insulated, hot oven will cook for an hour or two later than 2:00 in the afternoon.
The sun's angle as it moves across the sky can effect solar cooker temperatures. The angle of the sun is highest during summer months, but in many places, solar cooking can be done during most of the year.
How Much Longer Do Foods Take to Cook in a Solar Oven?
In general, you will need to add one hour to your conventional cooking time. Approximate cooking lengths for different types of food can be found in the following PDF file (you will need Adobe Acrobat to open the link:) How to Make, Use and Enjoy Solar Cookers.
The cooking times provided in the publication are approximate because solar cooking is not as uniform as conventional cooking. Many factors can affect the speed of solar cooking, including the following:
- Time of year: cook times are longer in the winter than they are in the spring and fall, and cook times are shortest during the summer.
- Amount of sun: Cloudy days require longer cook times than sunny days.
- Amount of wind: Wind dissipates heat, which causes the oven to cool and require a longer cook time.
- Type of pot: a large pot will take longer to heat than a small pot. An insulated pot also takes longer to heat up than a pot made of thinner material. Black pots heat up faster and hotter than light-colored or shiny, reflective pots.
- Amount of food: Larger amounts of food take longer to heat up and cook than smaller amounts of food.
- Amount of water: Water takes a long time to heat in a solar oven. A lot of water means a longer cooking time. In general, solar cooking requires less water than stove-top cooking.
- Orientation of the Cooker: A cooker that is moved periodically throughout the day to follow the sun will cook faster than a cooker that is not facing directly directly towards the sun.
Under normal conditions, a solar oven will cook at a temperature of 180Âº-250Âº Fahrenheit. Foods cook well at temperatures between 180-195ÂºF. The temperatures inside a simple solar cooker are hot enough to fully cook meals, but not so hot as to burn or dry out food, or to damage healthful nutrients.
Warning: food allowed to cool to temperatures between 50 and 125ÂºF for four hours or longer should be discarded as it may be harmful if ingested, causing bacterial food poisoning. If in doubt, throw it out.
Photo credit: SolarCooking.Wikia.com
Helpful Places on the Web - Solar oven info, plans and recipes
These are some place that we like on the web. If you have a related web page that you would like posted here, send us a message including the link. Kindly add a link to this lens on your web page.
- Solar Cookers International
Solar Cookers International (SCI): Harnessing the sun to benefit people and the environment.
- How to Make, Use and Enjoy a Solar Cooker
What exactly is a solar cooker? It is a device that allows you to cook food using the sun's energy as fuel. Is it really possible to cook with the sun? Yes, and this booklet will show you how. It will walk you through the process of building a simple
- Recipes for Solar Ovens and Solar Cookers | Solar Oven Society
The following recipes have been sent in by avid solar cookers who want to share the good things they have discovered when solar cooking. The recipes have not been test
- Daily Solar Cooking Recipe
Delicious recipes posted daily by the Sun Oven company.
- Solar Oven Recipes
Learn to cook eggs and potatoes in a solar oven. More recipes, as well.
- SOLAR COOKING RECIPES
Solar oven cooking is easy. Exact timing is not important. The gentle, solar heat is what gives food the enhanced flavor that is always present in this method of cooking. You will become an expert in no time at all. Just experiment a little!
- Solar Oven Recipes | Preparedness Advice Blog
You can make great meals with your solar oven.
Solar Oven Cookbooks
There is not an abundance of solar oven recipe sites online. But there are some good books available on the subject. Amazon offers free Super Saver shipping on qualified orders of $25 or more.
How to Make a Solar Box Cooker - Basic Design
The basic design for our cooker includes 2 boxes of different sizes, a lid piece, a black oven liner, reflective material (foil,) insulation and a glass lens (or a clear oven bag.)
Gather the following materials in advance:
1 roll of foil to cover the interior of the oven
1 box cutter or breakaway knife
Non-toxic glue, such as Elmer's school glue
1 large clear oven bag
Aluminum foil tape (available at hardware stores)
Pen or pencil
2 boxes (one large, one smaller)
Third box or large piece of cardboard for a lid
String or yarn
Sponge or paintbrush
Crumpled newspaper or shredded paper for insulation
Hole punch or stapler to attach string
Solar Oven Supplies
Amazon has better prices on solar oven supplies than I have found at local retail stores. Shipping is free on qualified orders of $25 or more, so I generally stock up on the items that I need.
Select foil tape and avoid silver duct tape. Foil tape will stick at high temperatures, while duct tape tends to peel when it gets hot.
Select turkey-size bags for your project.
You will need two boxes to form the body of your oven. One box should be several inches smaller than the other, so that it fits inside the larger box with room to spare for insulation. Boxes are available on Amazon in 6-packs. Get together with a few friends to make the supply cost more economical. You can use one of the larger boxes for a lid, as well.
Aluminum foil is a little bit more expensive if you by the pre-cut sheets, but they make the project much easier.
This box is just the right size to serve as your inner box for the project.
This box is just the right size to serve as your outer box.
Pre-cut sheets make the job easier.
Step 1: Select and Prepare Your Boxes
Select two boxes that will become the body of your solar oven. These boxes do not need to be brand new. Recycled moving or shipping boxes make great ovens. The boxes can be square or rectangular, as long as they are similar in shape.
You will need a small box, approximately 14"-16" in length and depth, which will be the inner box of your oven. It should be large enough to hold the pots in which you would like to cook, but not so large that it will take a long time to heat up. Tape the bottom of the small box closed.
You will also need a larger box, approximately 18"-20" in length and depth, which will become the exterior of your oven. Fold the top flaps down and tape them securely closed. Do not close the bottom flaps at this point.
Additionally, large piece of cardboard (or a third box) is necessary to form a lid. It should be several inches larger than the open end of your large box, so that the lid can fit over the top of the large box.
At this point, you can spray paint the large box and the cardboard with black paint. Or, you can wait until the project is complete to paint the exterior. Choose a flat, non-toxic paint for this project. Most water-based paints are non-toxic once they dry.
Step 2: Cut a Window Opening in the Large Box
Center the small box on top of the taped end of the large box,and draw a line around it.
Cut along this line to form a hole in the top of the large box that is the same size as the small box. Be sure to cut through both the outer and inner flaps.
Photo credit: All black and white drawings are the property of SolarCooking.org
There will be a small rim remaining. Tape the remnants of the inner flap to the outer flap . Use your hands to press on the tape and stick it firmly to the box.
Save the pieces that you cut out for a drip pan and extra foil panels. Instructions for making these items will be explained later in Step 4.
Step 3: Create a Lid
If you are using a box instead of a sheet of cardboard to make the lid, open the box at the seams and lay it flat. If this piece of cardboard is much larger than your lid needs to be, place the large box on top of the cardboard and use a straight edge to draw a line around the box, about 3 inches from each of the edges of the box. You now have a square or rectangle drawn on the cardboard that is 6 inches longer and 6 inches wider than the large box. This will allow your lid to have a lip that extends over the edge of the box.
Cut along the lines that you drew. This is your new lid piece.
Center the large box on the lid piece and trace around it with a dashed line. These will be fold lines. Extend the lines out to the edges of the lid piece. You will fold the box edges after you make the window flap.Hint: When drawing this line, make sure that your pencil stays outside of the perimeter of the box and is not drawing under the edge of the box, or your lid will be too small.
To make a window flap, center the small box between the fold lines that you just drew. Draw around the box, using solid lines on three of the edges, and a dashed line on one of the longer edges.
Cut along the three solid lines using a knife. Fold the resulting flap upwards on the dashed line. You now have a reflector flap and a window frame.
With the lid upside down, make one small cut at each of the corners, just to the first fold lines. Make your cuts parallel to each other. Score all fold lines with the tip of your knife, cutting only through the top layer of the cardboard. Fold the edges upwards along the scored lines.
Overlap and glue the corners, and hold with tape or clothespins until the glue is dry.
Step 4: Line the Interior of the Box with Aluminum Foil
Prepare your adhesive by placing 1 part water to 3 parts glue in a bowl and mixing well. This is not an exact recipe, so adjust the amounts as you please. White glue spreads much more easily onto the foil when it is thinned with water, and the water also allows you more time to adjust the foil before the glue dries. Reserve some full-strength glue for later applications.
Cut sheets of foil or pull several pre-cut sheets out of the box. Using a brush or a sponge, spread glue on the back (dull) side of one piece of aluminum foil, and apply it to the interior of one of the boxes with the shiny side facing outwards. Repeat this process until the interior of both boxes is completely covered with overlapping sheets of foil. Be certain to cover the box seams with foil as well, to seal up any areas where air and heat can escape the box.
To conserve glue and time, you do not need to completely cover the back of the foil with glue. Instead, paint the glue around the edges, like a picture frame, and also a large 'X' in the middle of the foil. The edges are the most important area of the foil to cover with glue so that the foil does not peel up or get torn with use. Keep in mind that the interior of the large box will not show nor be subject to wear and tear, so it will not need as much attention to detail as the smaller box will require.
Make certain that all of the edges of the foil in the smaller box are flat and glued securely so that the foil does not get torn with use. To reinforce the interior of the box, you can secure the aluminum foil edges with clear packing tape or foil tape.
Use the aluminum foil to cover the reserved pieces of cardboard that you cut out of the large box when making the window. The largest piece will serve as a drip pan in the bottom of your solar oven. If necessary, cut the piece so that it will fit inside the bottom of the small box. If you do not have a large enough piece to cover the bottom of the small box, cut one out of the excess cardboard from the lid piece, or join a couple of the smaller pieces together with tape to form one larger piece.
The smaller pieces will be used as insulation for the oven in Step 6.
The last item to cover with foil is the lid flap. Line the bottom side of the flap with foil (the side that faces downwards into the oven.) This flap will serve as a reflector to direct more sunlight into your oven.
This photo views the lid piece from the bottom side, with the reflector flap closed.
Step 5: Trim the Flaps of the Small Box
Trim off the lid flaps of the small box to 1 inch. These flaps will be used to connect the small box to the large box, so do not cut them off any smaller than an inch.
Step 6: Join the Boxes
Turn the large (outer) box so the window opening is facing downwards. Spread full-strength glue inside the window rim.
Turn the small (inner) box upside down, lowering it into the larger box, onto the glue. Make certain that it is centered so that the window of the large outer box is directly over the opening of the small inner box. Press the small box flaps firmly against the edges of the rim around the window opening to join the two boxes. Press down on the small box or place a weight on it to hold it down firmly until the glue dries.
Place the small pieces of foil-covered cardboard into the empty spaces between the boxes, and then fill the spaces with shredded or crumpled paper. Do not pack the paper tightly in the sides of the box, as the air in the spaces will serve as a thermal barrier.
Place several pieces of tightly crumpled paper on the bottom of the small box. Here you should pack the insulation tightly to support the weight of the food that will be placed into the box. Close the box and tape it securely shut.
Step 7: Secure the Boxes with Foil Tape
Turn the oven right-side-up. Use aluminum foil tape to secure the connection between the smaller and larger boxes. Pay special attention to any gaps, especially in the corners, sealing them up completely with the tape.
Note: do not substitute duct tape for the foil tape. Duct tape will peel away from the boxes in high temperatures. Foil tape is made to withstand temperature extremes, and it will hold securely when the oven heats up.
Step 8: Attach the Oven Bag to the Window
Turn the lid upside-down and use foil tape to secure the oven bag in place, covering the window opening. Use a large or turkey size bag. Cut the bag open and spread it flat. If you prefer to use the bag without opening it up, you will have a double layer of plastic in your window for extra insulation. As the oven heats up in the sun, the air between the two layers will expand, forming a thermal layer that helps to prevent heat from escaping from the box through the window.
When using the double-layer method, it is important to first tape the open end of the bag closed, and then tape all the way around the edges of the bag to secure it to the lid. Press the tape down firmly, smoothing out any wrinkles. This stops water vapor from entering the bag and condensing, forming a film on the bag that will hinder sunlight from entering the oven.
Alternately, you can cut the bag open to form a single, flat sheet to cover the oven window. Whether you use a double-layer or single-layer window, pull the bag tight to remove as many wrinkles as possible. Over time, the bag will deteriorate, and will need to be replaced occasionally.
Clear plastic sheeting or window glass can be substituted for the oven bags. However, do not use any material that has been treated with UV protection, or it will prevent the sunlight from entering the box. For this reason, archival quality glass or plastic are NOT recommended for this project.
Step 9: Attach Hooks to Hold the Reflector Flap Open
Cut two pieces of scrap cardboard, approximate 3 inches each in length to form two hooks. Fold each piece in half, and place a thick dot of glue on the fold. Attach the pieces of cardboard to the back of the oven, one on each side, parallel to the edges of the reflector flap.
Cut two 18" lengths of string and place a knot in each end. Staple one end of each string to the edges of the reflector flap, using two or three staples each for a secure attachment.
When the cardboard hooks have dried thoroughly, lift the reflector flap and wrap the ends of the strings around the hooks to hold the flap open.
When using your oven, adjust the angle of the reflector flap so that it reflects sunlight down into the oven. This angle will change as the angle of the sun changes. The string allows you to move the flap and secure it at the correct angle.
Step 9: Paint the Oven Exterior and Drip Pan
If you have not already done so, paint the exterior of your oven, using a non-toxic, flat black spray paint. Be careful when painting the lid so that no paint gets on the oven bag. Paint the cardboard drip pan black, as well. Place the drip pan inside the oven, lying flat on the bottom of the small box.
Place your oven outside, facing toward the sun with the reflector flap propped open. Leave the oven in the sun for several hours to thoroughly dry the glue and dissipate any paint fumes.
Your oven is complete!
For a copy of these instructions that you can print, follow the link below:
Let's Get Cooking!
Place food in a dark colored cooking pot with a dark, tight-fitting lid. If you do not have a dark pot or lid, you can paint the exterior of a pot and lid with the non-toxic black paint with which you painted your oven.
Set the cooker in full sun on a level surface. If you have a Lazy Susan turntable, place the oven on the turntable for easy turning throughout the day. Turn the cooker so that it is facing slightly west of the sun's current position.
Place pot(s) in the oven with quicker cooking items towards the front of the cooker (opposite the reflector) and slower cooking items towards the back, where they will receive the most direct sunlight. To increase the oven's efficiency, place a rack or bricks in the bottom of the oven to elevate cooking pots. This will reduce heat loss via conduction from the cooking pot to the bottom of the oven.
Replace the lid and adjust the reflector flap so that sunlight is directed downwards into the oven.
Turn the oven every few hours so that it is oriented slightly west of the sun's current position. Foods cook fastest when the shadow cast by the oven is directly behind it.
Leave the cooker in the sun according to the number of hours recommended by your recipe. Keep in mind that cook times are approximate, so you will need to check your food when it nears the end of the cooking time. Try not to remove the lid too often, however, as it allows heat to escape. There is no need to stir food while it cooks in a solar oven.
Leave pots in the cooker with the lid closed if you won't be eating right away.. The oven will keep the food warm for several hours.
Improve and Maintain Oven Efficiency
Here are a few tips and reminders to help make your solar oven more efficient:
When the sun is low in the sky, tip the oven forward and place a board under the back edge to face the lens directly towards the angle of the sun.
Move the reflector flap periodically to ensure that it is reflecting sunlight directly down into the box.
Add more reflector flaps to the lid, one opposite the existing flap, or for greatest efficiency, one on each side of the window.
Carefully seal all cracks and gaps to trap as much heat as possible inside the cooker.
Pack the bottom of the cooker with thick insulation so that the inner box does not sink down with the weight of your cooking pot.
Use only non-toxic materials to build and insulate your cooker.
Cook in a black pot with a heavy lid. If you don't have a black pot, paint one with non-toxic paint.
Periodically wipe the reflector and the lens so that dust and dirt do not hinder sunlight from entering the oven.
Essentials for Solar Cooking - A few items that you will need:
1. Black cookware with lids
2. Thermometers to measure the oven temperature and the temperature of your food
3. A rack to lift cookware off of the bottom of the oven, for more even and efficient cooking
This is the pot that I use most often.
Use a thermometer like this one to measure the temperature of your food.
Use a thermometer like this one to monitor the temperature inside your oven.
A rack on the bottom of your oven will help to prevent heat loss by conduction and help your food to cook faster.
Commercial Solar Cookers
If you don't want to make your own solar oven or you want one that is more sturdy, there are several options available online. These ovens are portable, cook at higher temperatures than homemade ovens, and have good reviews by users.
I would love to hear from you. Leave your comments, questions, kudos or suggestions here.