How to build a solar oven
I wrote an article previously about solar reflective ovens in which I included information on commercially made solar ovens. It was clear that to buy a good one would cost a lot of money. While I was writing the previous article it occurred to me how I could build a solar oven more cheaply and possibly better than commercial ones.
What is a solar reflector oven?
Solar Reflector Ovens use solar energy, that is energy sourced directly from the sun, They use this energy to cook food. They could also be used to pasteurize water or for the sterilization of metal instruments.
Solar ovens work on a very simple principle. They are built to absorb more heat than they release. The surplus energy is used to heat the food.
Why Would You Need a Solar Reflector Oven?
There are several reasons why you might want a solar oven. These reasons range from as simple as reducing your electricity bills, to some form of disruption in power supplies. This disruption might be just a day or two or in the case of a serious disruption to society, it could last weeks or even months in the case of a serious natural disaster.
Buying a Ready-Made Solar Reflector Oven
Buying a ready-made one from the store is easy enough but I think that for a simple oven it is not necessary and that you can make a perfectly good alternative yourself. If you want a more sophisticated model I think there is even more reason to make one designed specifically for your needs by adding features from several commercial models into your own design.
Two Types of Construction Projects
In this article, I am going to give you step by step instructions on how to make your own solar reflector ovens. Not just one model but two. The first model will be a very simple one that you can make in a couple of hours from things you may well have in your house. The second project will be a more serious project that will need you to purchase materials.
Simple Solar Oven Project
Introduction – Simple Solar Oven Project
In this project, I am going to show you how to build a solar oven from materials you may have laying around the house and garage. This oven is ideal to make quickly if you have not prepared in advance and there is a power outage. It’s an emergency oven that could prove invaluable.
You never know when there will be a power outage and you will otherwise be stuck eating cold food. This simple project can mean that you can at least feed yourself. It will not work as well as the model in the second project but can be built fast and economically
- Large Pizza Box
- A Ruler
- A Black Marker
- A Box Cutter or Utility Knife
- Heavy-Duty Aluminum Foil
- All-Purpose Glue
- Clear plastic wrap
- Black Construction Paper
- A Stick
- Using your ruler and the black marker you should draw a square on the lid of the pizza box, leaving a one-inch border on all sides. Make sure it is perfectly square.
- Using the box cutter, you will cut three sides of your square, leaving the side where the lid hinges uncut (the back).
- Fold this flap you have just created so that it stands up when the pizza box lid is shut.
- Cover the inside of the flap with the Aluminum foil, gluing it flat, with no crinkles. This is going to be the reflector.
- Using the scissors cut a piece of the clear plastic wrap into the same shape that you cut into the pizza box, but make it one inch bigger on every side.
- Open the flap and affix the plastic over the hole so that it overlaps one-inch around. Use the tape to fix this plastic to the box firmly. The plastic should not have wrinkles.
- Using the scissors cut a piece of the clear plastic wrap into the same size and shape as the first one.
- Close the pizza box and fix this second sheet over the window and tape it into place. The box must be air tight.
- Glue a piece of Aluminum foil to the bottom and sides of the interior of the box., this helps to insulate the box.
- Cover and glue the foil you just inserted with the Black Construction Paper, which will absorb heat and generate more heat inside the oven.
- Close the lid and you are ready to cook your first meal.
On a bright day, you then place the new solar oven outside in the direct sunshine. Do not place it where it will later be in shadow, choose your spot carefully.
Adjust the foil-covered flap to the optimum angle to reflect the sun’s rays into the box window. You can use the stick to prop up the lid at the correct angle.
Once set up, preheat the oven by leaving it in the direct sunshine for half an hour. After 30 minutes hopefully, the box oven temperature should have reached around 200 degrees.
This type of oven will not be able to cook great chunks of meat but it can warm up pre-cooked food, melt cheese, and pizza. If you are organized you can leave a shallow dish in the oven all-day and cook vegetable soup,
For more substantial cooking you need to build our second design.
You may want to test the angles of reflection of the lid. If you have a laser pointer held up in the position of the sun and shone at the lid will show you where the lid is reflecting the sun.
If you want to increase the heat, you may consider covering more sheets of cardboard with foil and arranging them so that they reflect more sunshine into your oven’s window.
This project has allowed you to construct in around one hour an emergency cooking device. Having a dish of hot soup at the end of a day, when otherwise you would only have cold food is going to be quite a boon if you find yourself without power. If you have a family, build a solar oven or three so you can use one for the all-day cooking and the other ones for warming food.
Advanced Solar Oven
Advanced Solar Oven Introduction
Having established that it is possible to build a simple solar reflector oven in around one hour we will now move onto building a more substantial version for permanent placement in your property. This model will require the purchase of materials for the construction. It is designed to be a permanent installation and is going to be built of more long-lasting materials.
The Northeast USA blackout of 2003 some outlying areas were without power for 14 days. Can you imagine not having electricity for two weeks? This was merely a technical problem where circuits became overloaded across a wide area and affected some 55,000,000 people for varying lengths of time.
Studies of the likely implications of the expected earthquake in California (The Big One) suggest that power would be out for several weeks or more. In this kind of scenario having an alternative mode of cooking could be very valuable.
As someone who understands the importance of being prepared for these events, you will appreciate the importance of preparing an alternative cooking method independent of the grid. You will also want an oven that maximizes what sun there is. Not every day is 100% bright sunshine. Using the enhancement techniques in this design it should work when it is partly cloudy.
Outline of the Design
The solar reflector oven that we are going to create in this project is an insulated box design with a free-standing reflector array. It has Fresnel Lenses to focus the sunlight through a glass lid into the oven and onto a rock base which retains the heat much longer than alternative bases.
If ever you have walked barefoot on a paved footpath on a hot day you will know how hot the stone becomes. By combining various ways of increasing the heat and a selection of insulating techniques, the heat in this unit should be much higher than in other designs. Because we have added a built-in oven thermometer it is also safer as you know you are cooking at the correct temperatures.
- 2 Pack – 8.3″ x 11.75″ Large Premium Grade Fresnel Lens $15
- Buy from local glass merchants
- Two Stick-on Cabinet Handles Buy from local hardware store $8
- SunWorks Construction Paper, 18 x 24, Black, 50 Sheets/Pack (6317) $15
- Cardboard box 22x22x22 inches(standard size) Free if you search around
- Cardboard Box 24x24x24 inches(standard size) Free if you search around
- Gorilla Heavy Duty Spray Adhesive $16
- 3M Duct Tape, 1.88 inches x 30 yards, 2230-HD, 1 roll $ 6
- Old newspapers for insulation $0.00
- Broom Handle $1
- ManYee 50 Pcs Wire Card Holder Metal Wire Alligator Clamp Clips $10
- Small bag of concrete $5
- Heavy-duty Aluminum foil $10
- Flour, $2
- Rubbermaid Products Stainless Steel Instant Read Oven Monitoring Thermometer $7
The total price is $125 if you purchase ALL these items new from Amazon. In reality, you can probably source alternatives at a lower price locally or use items you already have, thus reducing the cost. The price should be the maximum total price.
Part 1 – The Oven
- We will start work on the outer shell (the larger cardboard box). I cut off the tops of both boxes, so they are completely open on the top. The dimensions of the box are 24x24x24 inches and we line this box with heavy-duty Aluminum foil, Using the glue to stick the foil in place. For decoration, I chose also to paint the outside with some old white household paint I had in the garage, but this is not necessary. You can use any color of paint, it is only for decoration. Whatever scraps you have laying around.
- Next, I lined the second box, which is 22x22x22 inches, with black construction paper. I glued this to the inner side of the box. I then dropped a couple of drops of glue on the base of the second box and positioned it inside the outer box. Leaving an equal-sized gap between the two boxes.
- Using the flour and old newspapers I made paper mache and filled the gap between the two boxes with this mix. This mix once set both provides insulation and also strengthens the boxes.
- When this is dry the boxes are very firm and stable, solid feeling. Again for decoration, I ensured the top of the paper mache was smooth and I painted that with the old white paint. We have now completed the oven container.
- The open top of the inner box is 22×22 inches. Using the cardboard from the tops of the boxes I cut four pieces of 24×3 inches, and I glue them so that I double the thickness and have just two pieces of double-ply cardboard 22×16 inches.
- I glue the two pieces at the opposite end of the top of the box so that the remaining gap is 16×22 inches. That is where the sheet of glass will go. In order to strengthen this cardboard, I paint both pieces completely with white paint. It is important that all of this cutting is done accurately and squarely.
- Finally, to ensure the strength of the oven I ran duct tape along each of the corners of the box, and across the edge of the strips of cardboard on the top (to fix them more firmly in place and reduce any air gaps.
- On the base of the box put a slab of old stone or paving as stone retains heat when heated for a long time. You can use a layer of small pebbles instead if you cannot find the right stone.
- At either end of the glass use the stick on knobs to provide a way of picking up the glass to give access to the oven.
- Place the oven thermometer in such a position that you can read the temperature, without removing the glass, and know when you are operating at the correct temperature.
- That is the oven completed, now we will move onto the reflector array.
Part 2 – The Reflector Array
- First, we glue the Fresnel lenses onto the glass (on the outside). These lenses will concentrate the power of the light that is reflected onto them and shine it onto the stone base of the oven, which will warm up.
- Using the (now empty large paint tin) fill it with concrete and position the broom handle in the tin so that it is vertical. You will need to support it in this position while the concrete dries.
- Duct Tape the bases of the Wire Card Holders to the pole at various intervals, on both sides of the pole and you can bend them into position to hold the reflectors. You can attach as many as you like from low down almost touching the oven to higher up the pole. Normally, because of the weight of concrete in the stand, there are no stability problems with this array, but if you find that it is not stable, simply fix the can to a hardboard platform.
- The reflectors are made with any light scrap cardboard covered completely in foil. These reflectors are attached to the clips at the end of the Wire Card Holders and the wires are bent in the required angles and directions to reflect the sun onto the glass lid of the oven. You can fit as many reflectors onto the pole as you wish
- You have now built a free-standing reflector array that should be stood adjacent to the oven when in use.
Summary of the Advanced Solar Oven
When you build this solar oven, despite it being homemade, this oven has features that many commercial ovens do not possess.
- The design features a larger array of reflectors than most other models because it has been built separately to the oven.
- The glass top features magnifying lenses to enhance the power of the light passing through.
- The oven walls are much thicker and better insulated than other models.
- The addition of the stone floor provides a lasting heat that other models do not possess
Because of this hybrid design, this model should serve better than many commercial models and although by adding features like the oven thermometer, Fresnel lenses and free-standing lighting array, it has made the model more expensive than basic commercial models, if it is compared to the most efficient commercial models it is substantially cheaper.
When not in use, just unclip the reflectors and they can be stored compactly. The box is quite solid due to its construction and will last many years.