Flat Pack Solar Oven (200°+)




Introduction: Flat Pack Solar Oven (200°+)

About: I am a 18 year old high school student who loves making! I hope to eventually turn my passion into my career by innovating new technologies to fuel the maker movement in America, and bringing large scale manuf…

Addendum: The kind folks at Pop Science were kind enough to feature this project in their print version, as well as online, so please check out their link as well and support them for supporting many makers in this community! It is truly and honor and a blessing for them to reach out! (http://www.popsci.com/build-diy-solar-oven)

In this instructable I will show you how to create a DIY solar oven which can get up to around 200°F. I was able to use all materials I had laying around, so for me there was no additional cost, but you may need to buy a small piece of glass or acrylic. The entire base of this project was basically saved from the garbage, and I used all materials I had around, and even used many extra pieces from other projects. It's lightweight, compact, and ergonomic design makes it great for bringing camping or hiking, and it's sure to capture the attention of others.

- Flat pack design
- Heavily insulated
- Sturdy frame
- Adjustable angle reflective panels
- Fold out expandable reflective panels
- Compact
- Lightweight
- Ergonomic
- Gets up to around 200°F
- Endless possibilities for add-ons and customizing

For this instructable you will need:
- Box
- Insulation
- 5mm Black Craft Foam
- Duct Tape
- Skewers
- Construction Paper
- Aluminum Foil
- Paint
- Glass, Acrylic, or any clear plastic sheet

Step 1: Adding Insulation

The first step is finding a sufficient box, and insulation that will go with it. I used a box I saved from fresh chocolate covered strawberries my family received, and the insulation that went with it. Any box will do, and for insulation you can use styrofoam, Eva foam, sheets of craft foam, fiberglass insulation, old shirts and sweatshirts, foam insulation sheets (come in large sheets from places like Lowe's and Home Depot), or anything else. Worse case you could even use newspaper or thick sheets of cardboard.

The insulation I used that came with the box was a simple closed cell foam which was about 1.5 to 2 inches thick. It came in 2 pieces (see pictures) which were cut so that they overlapped and made a sort of miter joint. I had to cut off the top flap to allow for a space to let the sun through, but depending on your insulation you probably won't have to do that. Lastly, use any adhesive (preferably not hot glue for obvious reasons) and secure the insulation to the inside of the box.

Step 2: Structural Additions

Extended flaps
I figured that for a solar cooker you want as much surface area for reflecting the sun towards your oven, and I didn't think the flaps on my box were sufficient, so I measured them and duplicated 4 more flaps the same exact size. I used a strong duct tape to connect the flaps so that they could still fold out when the cooker is deployed. (See pictures)

Supporting arms
To support the reflective panels I used bamboo skewers and poked a hole through the side and flap of the box to hold it up. This works phenomenally well and is very useful for this particular application because you can poke holes in multiple spots vertically on the box so that you have multiple different places to put the skewer. This allows you to adjust the angle of the reflective side panels, which is a great feature for a solar cooker. For a more durable approach you may also experiment with adding a separate piece of foam board, but for me the cardboard has worked fine and there have been no issues yet.

Just found this article on calibrating your reflective panels while writing this and figured it could really help:

Step 3: Black Insulation “Absorption” Liner

After the general structure and all the mechanics were finished, I started adding the details. The first important detail was adding black 5 mil Eva craft foam on top of the main foam. I cut sheets to fit in the bottom and on all the sides, then I cut skinny strips the cover up like trim around the top. Again, you can use whatever adhesive you might like, but try to avoid hot glue because the intense heat will weaken it, and there is a possibility the craft foam will come apart from the other insulation. It is important that this is black because it has to absorb the light, turning the energy of the light from the sun into heat for cooking. This style of cooker is formally known as a “solar box cooker”, but I use “solar oven” because it is more unique and it works similar to an oven in the way it cooks and heats the food. A solar box cooker lets UV light rays in through the transparent lid, then converts them to longer infrared light rays when it comes in contact with the black foam walls. The longer infrared light rays cannot escape the box because they do not have the energy to penetrate the glass, a surprisingly great insulator. (See the graph in Step 5)

Step 4: Adding the Foil

In this step you will see how I added foil to the sides and how I added foldout corners to capitalize on the addition surface area. The reflective foil is crucial to the design of this oven style cooker because it directs a lot more sunlight, and therefore, heat, into the oven. Remembering back to the last step, the side panels can move and change angles due to the design of the supporting mechanism, and that feature plus the corners helps tremendously at increasing the efficiency of your oven because you can direct maximum sunlight into the oven regardless of where the sun is located (basically mandatory features for evening cooking and early morning cooking when the sun isn't directly overhead).

Adding the reflective foil to the side flaps is quite simple, and again you can just use any adhesive you would like. In this case, it is fine to use hot glue because the area will not be experiencing intense heat, but it might just be easier to use the same adhesive throughout the project. As silly as it sounds, just make sure to use reflective side of the foil to optimise the efficiency.

I wanted to maximize my flat pack design, so I went through the extra effort of adding fold out corners. These corners went through multiple concept and design changes, which included everything from a flexible reflective sheet to an accordion design (see images). I ended up with a fold out design, which was the most logical for the flat pack design because it only added the thickness of 2 sheets of paper, and doesn't impede the folding at all. The process used to create these sheets is easy enough to replicate, and the majority of the time it takes to add corner panels comes during the sizing. I took 4, 12×12 inch sheets of scrapbooking paper, and rolled out a 50+ inch long strip of the 12 inch wide foil I was using to accommodate the 48 inches of paper. I used a glue stick and covered the sheets completely with glue, then pressed them down onto the foil and added weights to the top to hold it down. When the glue dried, I roughly cut between the sheets, then took them to a slicing machine and squared up the edges. I then set up the side panels and traced the rough shape between each side, and cut the panels to fit. I only attached the panels to one side to allow for flexibility when changing the angles of the sides. Once installed, fold the sheets along the edge of the side panels, and then once in between the original panel and the extention so that it can easily fold back up into the box, and close securely (see images- number 9 and 10 show it perfectly).

Although it took multiple concepts and a bit of engineering because I wanted it to accomadate the flat pack design, adding corners ended up being worth it because it added and extra 72+ sq. in. (15+%) to the already 403 sq. in. surface area.

Quantity Equation Combined Area
(4x) 12×12×0.5= 72 sq.in.
(2x) 13×13= 169 sq.in.
(2x) 13×18= 234 sq.in.

(Sub)Total Surface Area= 475* sq.in.
*Plus the 234 sq.in. of area inside the box

Total Surface Area= 709 sq.in.

Although it seems nominal, this 15% change by adding corners could be a change of almost 15°, which could be the difference between reaching boiling temperatures and not. Depending on your box size, I would seriously consider going through the extra effort of adding corners.

Step 5: Adding the Transparent Lid

This step is actually one of the simplest, and depends mostly on the size of your personal oven and the type of glass/acrylic/plastic sheet you are using. I built a simple frame from foam board, because it was the perfect thickness for my glass. I used a foam cutter to melt out a groove in the foam, and I slipped my glass inside of that. After I knew the glass fit inside, I slid it back inside and glued all of the corner together so that it was impossible for the glass to come out unless the device broke (which it hasn't yet and has proved to be super strong). Also note that the foam core I used was black so that it matched the rest of the interior of the oven. Again, this step relies heavily on what materials you are using, but if you roughly use my outline you should easily be able to make your own.

I chose glass because it has very high insulation properties, even better than the acrylic in the pictures. If you look above, I included a graph which I found while doing research on the best material to use.
Picture citation: http://www.wintergardenz.co.nz/glass-vs-poly-vs-film.html

Step 6: Painting

For painting you can obviously use any design you would like but I will be briefly walking you through on the particular style I used.
I personally came up with this painting style when I was working on a cardboard post-apocalyptic storage unit. I think it looks so cool and it is really quite simple to achieve. First you have to paint the entire exterior f your oven all black, then mix up some light gray paint, and dry brush it onto the face of the box with a large (1+ inch) brush. The natural ridges on the corrugated cardboard make this painting style look awesome, and I would highly recommend you try it!

Step 7: Creating a Custom Logo With a Cricut

For this build I also added a custom logo I created using the Cricut and a modeling software that goes with it. I know very few people own machines like the Cricut, so alternatives would include: cutting letters out by hand, using precut letters or stickers, printing and cutting out a custom logo, drawing or painting a logo, or anything else you might want to try. The process of creating custom letters and designs is actually quite long and difficult to explain, so I won't add it in this instructable, but look out for one on this topic in the future! (Plus I'm sure if you own a Cricut you most likely know how to use it) I will still include the pictures I took to show you, and if anyone would like, I will post screenshots in the description of me actually creating the logo. Again, just remember there are loads of alternatives, and I guarantee a few minutes in photoshop could also yield some great quality custom logos.

Step 8: Conclusion

I know there are probably thousands and thousands of different ideas for solar cookers and ovens, but I wanted to share my high quality design made from all previously owned materials and a salvaged insulating box for shipping food. I obviously knew what solar cookers were, but I had never really looked into them in great detail. I saw the box and insulation those strawberries came shipped in, and I figured that would be absolutely perfect to use as a base for a solar cooker. I hadn't done any research on the topic previously to me building this, and only did reasearch when writing this instructable (and the two websites I looked at I included links in the instructables). However, I am confident in my design and it has worked exceptionally well for me whenever I have used it.

The lightweight, ergonomic, flat pack design makes it easy to carry and great to bring on trips. All the engineering I put into it with the fold out, collapsible corners, and the adjustable side panels to allow you to track the sun really increase the potential surface area, making this solar oven incredibly efficient for its size in my opinion. You can store all of your cooking pots, pans, and utensils, and any other cooking tools neatly inside the box, and close up the lid for easy storage and transportation. I absolutely love the design I came up with, and is overall incredibly versatile.

I would also like to encourage you to expand on this “concept”. I know i will personally try to make one out of wood with hinges, handles, and other hardware in the future, but make sure to keep it light.

I would love to see people's different spins and takes on this concept to see how I may be able to improve mine. Mine is different from the rest because it uses insulation from shipped chocolate covered strawberries, and it seemed quite unique to me. Please reach out to me if you made this or if you have any ideas for improvements on my model.

Thank you!
- Brandon (16)

Renewable Energy Contest

Runner Up in the
Renewable Energy Contest

Outdoor Cooking Challenge 2016

Runner Up in the
Outdoor Cooking Challenge 2016

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Participated in the
Trash to Treasure Challenge

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    9 Discussions

    Dr. Joe
    Dr. Joe

    3 years ago

    I am impressed with your skills at design and writing such a good Instructable. I have built a few simple solar ovens. To increase the temperature I have used a black pan with a glass lid. I also angled the bottom of the solar cooker to match the latitude. The more area you have on your reflectors the better and the more they track the sun. I tied a series of ropes to the reflectors that make the angle easy to adjust for tracking the sun. Another useful tool is a dowel on a board mounted on the oven at the same angle as the glass. When the shadow of the dowel is smallest the oven is angled directly at the sun. The more tracking of the shadow the better it heats. I look forward to seeing more of your brilliance.

    P.S. I was sixteen forty nine years ago.

    Modern Rustic Workshop
    Modern Rustic Workshop

    Reply 3 years ago

    WOW! Thank you so much for the tips!!! I really appreciate it! I will have to try them on the next one I plan to make. They really are just brilliant ideas! And I have to ask just out of curiousity, did you happen to come from the Pop Science article or did you find me through my comment on your most recent post?


    4 years ago

    93 ºC for the non-american.


    4 years ago

    Very good design, brilliant explaination!


    4 years ago

    Awesome DIY Solar Oven! I tried making one, with a pizza box and tin foil, but it didn't work. Part of it was that it didn't achieve high enough temperatures and also my lack of patience! What makes this one reach 200 degrees Fahrenheit?

    Modern Rustic Workshop
    Modern Rustic Workshop

    Reply 4 years ago

    Thank you! What allows this to reach temperatures of 200+ degrees Fahrenheit is that it has a huge surface area for the sun to reflect of off, the black foam lining on the interior, and its phenomenal insulation properties. The base of this project is a fresh food shipping box and its insulation, which are designed to keep fresh/frozen food chilled or frozen for days and days while they are shipped to their location. The insulation ratings of these boxes are incredibly high, which allows it to retain a lot of its heat. The black insulating foam sheets which line the interior of the box are also crucial to this, because the sheets are what turn the light from the sun into heat (I explain this in a lot of detail in step 3). Other small little factors such as the adjustable side panels also help, but the main three factors are the ones mentioned above. This still could have loads of improvements such as improving the glass insulation (see the comments above), so any other recommendations would be greatly appreciated!


    4 years ago

    It looks good !
    And simple and light enough !
    I want to make something similar as well. But I think it would be nice to have it made like a popup, you unply it and it already has the oven shape, then you just have to put the insulation and a glass or plexiglass for green house effect. This way would be more effective and quicker to settle. It is just an idea of course.
    200°F is not bad for a packable solar oven, but I am pretty sure a glass with the edges fitting well the box (almost airproof) would do a lot better. Or even better, two glasses separated by a thin layer of air for better insulation.
    With this kind of oven you really need patience, and need to anticipate mealtime. But the food is said to be more healthy and nutritive this way.

    Modern Rustic Workshop
    Modern Rustic Workshop

    Reply 4 years ago

    I think this definitely could be improved by adding a double insulated glass layer, which would make it exponentially more insulated because not only do you get an extra piece of glass to insulate, but the air pocket in between helps a lot too. I believe the extra glass helps with the green house effect, and the air pocket inside helps insulate the heated interior from the outside. For my MKII, I will definitely improve the top insulation (I'm only 16, so I wasn't able to run out and get an extra piece of glass super easily). Thank you so much for your input... people like you are the best on this website, and allow the younger audiences to learn and improve their creations!