The Perfect DIY Solar Oven

Welcome to another kick-ass Instructable from Disc Dog!

I love cooking with a solar oven! It's like using the perfect slow cooker, but no heat in the kitchen and best yet, the energy to run it IS FREE! I have a Sun Flair solar cooker on our sailboat and use it every time we're on the hook. I used it as a basis for this design.

I wanted to design a very functional solar oven for the DIY'er, but not something that is big, bulky nor permanent. Something for the backyard...something you can use on the picnic table in place of your grill! I also wanted to make it as low cost as possible, and something that can be built on the kitchen table with nothing more than some office supplies, fence wire, left-over blanket case and a windshield sun protector/dash cover.

I also wanted it portable and foldable, that's why I didn't build a permanent frame. Built correctly this little oven should last you years and years.

I went through two designs (rectangular and round/oval) and each had their advantages, however I found that the oval one was a better performer; it got hotter quicker.

I also wanted to design a solar oven that doesn't get over 200F (95C). That's important, because at [or below] those temperatures you don't have to worry about over-cooking your dinner or drying it out. Think of it as a slow-cooker, but solar powered!

I did a lot of engineering in the design, and I provided some simple drawings for both designs, but once you read through the Instructable, and build one you may find some better (or more permanent) improvements to this design. Please let me know!.

I noticed that the Sun Flair portable solar oven I bought for the boat was made from reflective, Mylar coated insulation/bubble wrap. There's a picture of one above. So when it came to my design, right away I went to the cheap, folding windshield suncover; it's the same stuff. So that's where I started and that's where you need to start. Everything else you buy/fabricate will be based on the size of suncover you start with.

They come in all sizes, but I bought the largest I could find (to maximize insolation). As you can see from the photo, mine was about 30" tall so I based all of my dimensions of this height. You will also find that the windshield suncover can [usually] be cut in half to make two ovens. Not knowing which design would work out best I made two designs from the same suncover; one similar to the Sun Flair design (flat-sided) and one based on a parabolic reflector.

Whatever size you buy, the drawings provided [in following steps] are based on the height of the suncover, so you should be able to fabricate one from any size you buy. Note, I can tell you that the amount of BTU's that your oven will generate is based on the opening size, so the bigger the suncover the hotter the oven.

So, first you will need a windshield suncover. I bought my 30" tall cover from a street vendor; cost $5 [new].

The second thing you'll need is a clear cover for the front of the oven. This is probably the most important component of your solar oven. For this I recommend a good, used clear blanket/duvet case. (These are the cases that new blankets/duvet covers are sold it at places like Walmart, Target, etc.) I like using them because [most] of them have a wire along the periphery so I didn't have to make a frame for it. You can also make it out of a clear piece of acetate, or from a good, used garment storage bag. If you look at the oval wireframe in the pictures above you'll see I used it as a pattern for a clear cover made from a garment bag. (Keep in mind that none of the materials used in the construction of this oven have to be able to withstand any high temperatures; the only thing that get's really hot is the cookware inside the oven).

I stole one of my wife's duvet cover case so it was free.

You will need to get some stiff fencing wire from the local hardware store. You will make the frame opening from this. As you will see later on I made two shapes from this wire. You'll need about 5 ft for each shape. I don't know the cost of 10 ft, but I bought a 25' long roll [many moons ago] for about $7.

I used a combination of Binder clips and adhesive-backed velcro to hold my clear covers on to the flanges of the solar oven. You'll see why later on.

You'll need about a dozen Binder clips; you can get a 100 various sizes from Amazon for $9, or you can do like I did and steal them from your wife's desk. Cost: $0. Or, you can use a 10' roll adhesive-backed velcro to hold things together; cost: $6. If you have access to a sewing machine, that would be a good thing. Later on you'll see the advantage of each.

You will need some cookware. I found a used set at Goodwill for $3. The only ones I could find where actually too nice; they were stainless steel. However, you'll want aluminum ones if you can find them. Aluminum can be scuffed up and painted with a good, long lasting coat. SS does not lend itself to a good painting surface. If you can find a good, used set of camping cookware (especially painted blank!) then jump on it! Oh yes, make sure your cookware has lids.

Aluminum Cookware: $3-$5 at the local thrift store.

(If you can't find aluminum cookware that is already painted in a dark, matt color then you'll have to chase up some flat black enamel spray paint. Preferably some of the 'High Heat' spray paint. Keep in mind that you're cookware will not get as hot a boiling water, so 'high heat' paint is not a necessity, but it doesn't hurt.)

Flat black enamel spray paint: $4/can.

One last thing; you'll need to stitch or staple the shape(s) together. I don't have access to a sewing machine so I stapled one of mine together and [like the Sun Flair] I used adhesive-backed velcro on the other. I did not add in the cost of the staples. (But if you have access to a sewing machine that would be good.)

In summary:

$5; Car/truck windshield suncover.

$0-$3; Clear cover for the opening

$2-$4; Fencing wire

$1-$2; Binder clips and/or adhesive-backed velcro; $6 (access to a sewing machine would be nice too!)

$3-$5; Aluminum cookware

$4; flat black spray paint

Total (max): $15-$20 (may be more if you're starting from scratch and an empty workshop)

There are 2 types shown, one rectangular and one oval. This page covers the rectangular version and the next page covers the oval version. Read both pages before deciding which to build, or (if your suncover is wide enough) build both.

I built the rectangular one first; you'll see pictures of it above. It worked well, and folds up nicely. I made a scale paper model of it just to get the geometry correct. You'll see pictures of that above as well. If you would like to build a rectangular oven use the PDF drawing to get your dimensions correct. You can refer to the photo for the general layout of this design, but the PDF drawing will be more accurate. As with the oval design, the dimensions on the PDF are based on the width of your oven (height of your suncover). Take the overall width of your oven (W) and multiply the factor in the drawing to get the dimensions for your windshield.

Start with measuring your suncover and fold it along the cutout for the mirror. Refer to the picture(s) above. This should serve as the fold at the base. Measure up the distance to the right distance and cut the opening.

(You'll note that on one of the ovens I used the center fold at the base. On the other I just stapled the base of the two remaining halves together. That way the mirror cut-away doesn't interfere with the opening.)

If you have a sewing machine, stitch the edges/base as shown on the PDF. That would work best, and not require any trimming or cutting. Even the weakest sewing machine can sew this material so don't worry about using large needles or heavy-duty thread. Since I didn't have a sewing machine I just stapled along the dotted line. Or, if you have some spare adhesive backed velcro use that at the joints (like the Sun Flair oven).

I built the prototype with a set of rigid boards bonded to the top and bottom [pictured above], but later found they made little difference in holding the proper shape and added weight so I didn't include them in the final build. (I wanted to use old campaign poster boards but couldn't find the material.) You can add them to yours if you would like. I've indicated the general dimensions of this rigid back.

After I removed the rigid backs I folded the excess material [on the sides of the oven] up to the sides of the oven and used adhesive backed velcro to secure them to the sides of the oven. This worked well to hold the shape.

The rectangular wire frame (shown) is simple to make. Due to the size of my windshield suncover my turned out to be 12" x 20". After I bent the proper shape I used simple wire to bind it together. You can solder the ends together or weld them together to hold shape. I experimented with the circumference so that it fit snug inside the oven's opening and used binder clips to secure it. Properly fit it will force the oven into a rigid shape. Refer to the picture for reference.

Once the shape of the oven took hold I initially used adhesive backed velcro to secure/open the clear cover but found it unnecessary and cumbersome. To which I used a large binder clip to secure the oven to the table as well as the base of the cover to the oven's opening. That way it the oven doesn't blow away, and it makes it easy to open and close the cover to put the cookware in. Once again, refer to the pictures for proper use of the binder clips.

Once you secure the base of the clear cover to the oven and you put your cookware in place, use binder clips to secure the periphery of the clear cover to the periphery flanges of the oven (see picture above).

I recommend building the oval solar oven; it's just as simple and I had better results, but it does sit higher. You can refer to the photo for the general layout of this design, but the PDF drawing will be more accurate. As with the rectangular design, the dimensions on the PDF are based on the width of your oven (height of your suncover). Take the overall width of your oven and multiply the factor on the drawing to get your dimensions for your oven. (You'll note that if you compare the two designs the base of the oval design is more narrow than the rectangular design.)

Start with measuring your suncover and fold it along the cutout for the mirror. Refer to the picture(s) above. This should serve as the fold at the base. Measure up the distance to the right distance and cut the opening. You will note that I used a yardstick to help define the radius (curved) cut. Mark your cut lines and stich lines with a Sharpie/permanent marker.

(You'll note that on one of the ovens I used the center fold at the base. On the other I just stapled the base of the two remaining halves together. That way the mirror cut-away doesn't interfere with the opening.)

If you have a sewing machine stitch the edges/base as shown on the PDF. That would work best, and not require any trimming or cutting. Even the weakest sewing machine can sew this material so don't worry about using large needles or heavy-duty thread. Since I didn't have a sewing machine I just stapled along the dotted line. Or, if you have some spare adhesive backed velcro use that at the joints (like the Sun Flair oven).

The Oval wire frame (shown) is simple to make. Due to the size of my windshield suncover my turned out to be about 18" x 19". It will be slightly smaller in diameter than the radius of your suncover. After I bent the proper shape I used simple wire and a pare of pliers to bind it together. I left the wire a bit loose so I could adjust the diameter for a good fit in the opening. Once you have the right diameter you can solder the ends together or weld them together to hold shape.

After I experimented with the circumference (so that it fit snug inside the oven's opening) I used binder clips to secure it in place for good. You'll see I cut some small, fold over flaps to clip the wire frame in place. Unless you need to fold the oven up to put it away, you can leave the wire hoop in place. Properly fit, the wire frame will force the oven into a rigid shape. Refer to the picture for reference.

I cut a clear opening cover from a piece of stiff acetate, as well as a piece of clear clothes storage bag, using the wire hoop as a pattern. When you cut your clear cover material leave about an inch or so past the frame to use as a lip to cover the wire frame, or [as I did with the acetate] use it as a lip to secure in place to the flanges of the oven. Once I figure out a way to stretch, and secure, the clear garment storage bag to the wire frame I may permanently affix it in place. If I do I'll update this Instructable.

I also found that if I secured the acetate to the bottom of the opening with some adhesive-backed velcro strips [instead of binder clips] it worked well to temporarily open the top of the oven to place or remove the cookware. I'm still experimenting with both, but I do like the rigid acetate because it holds it's shape.

I also put some velcro tabs on the side of the oven to secure the excess flaps to the side [while it is open] to help the oven holds it shape. Depending on your suncover you may or may not need this feature.

As I wrote earlier, if you can find some cheap, aluminum cookware buy that, it works best; for heat transfer as well as painting. I found these three pieces for a few bucks at a thrift store, took them home and rattle-canned them flat black. You'll need to thoroughly wash the exterior of the cookware, and if it's aluminum scuff it up with some scotchbrite or some steel wool. Then, wash it again with a good degreasing soap. Let it dry very thoroughly and then spray THE EXTERIOR with 2 or 3 good, even coats of flat black enamel spray paint. If your paint of choice needs a primer, be sure to use that first. Do not paint the interior of your cookware. Paint is not good for you nor your food.

In order to maximize your cookware, and heat it up the quickest, put it on a small piece of wood to center it in the oven space. That way it gets hit from sunlight on all sides and it is at the focal point of the insolation. (That's why the oval design works better; the parabolic shape of the interior concentrates the sunlight into a smaller spot...right where you have your cookware at.)

After the cookware had dried I convinced my wife to throw in some stew meat (sausage), potatoes, peppers, onions and spices in the largest pot and give the oven a whirl.

I removed the knob from the top of the pot [before I put it in the oven] so I could stick an oven thermometer through the lid and into the pot and monitor the temperature rise over time (3 hours). See photos above for results.

I mounted the oven on my portable work bench, set it up at a small angle upwards (since the sun was quite high in the sky) and aimed it about 10 degrees into the path of the sun. It was about 12:30. Every hour I went out and checked. I had to rotate the table once to keep tracking the sun (at 14:30) while cooking.

The goal should be a maximum of 180F-190F. I like this temperature range for several reasons: you don't want to dry out whatever you are cooking, it will thoroughly cook poultry (use a thermometer just to make sure), and you don't have to monitor the oven (it won't over-cook your dish if you forget about it); you can't overcook at 185F no matter how long you leave it in.

Since mine was headed north of 195F when I took it out, the next time I used it I didn't tilt the oven upwards. This time I tossed a couple of chicken thighs [covered in BBQ sauce] in the same pot, stuck a thermometer in it and cooked it from 2pm until 5 pm. The temperature got to 185 in 3 hours so I pulled the pot out. Results?...fall-off-the-bone done! Then I put some more BBQ sauce on the chicken and stuck it under the grill for 10 minutes to crisp the skin. ;-)

Conclusion: now we're cookin' with fire!

Like I alluded to in previous steps, I think the logical evolution of this design is to cover the wire frame with a clear cover. So, I took the garment bag I mentioned earlier, cut it down to about 1 inch over the diameter of the round wire frame, and [using scotch tape] I affixed it to the wire frame as shown. (If I had a sewing machine I would have followed up the tape job with a stich line along the inside periphery). Doing this eliminated the need for the rigid acetate cover I used in the previous steps.

Then I took it on a test run...

I think it might have worked too well. Despite covering the dish with Cling-wrap I think it got too hot, melted the Cling-wrap and steamed up the window. I do like the design (it simplifies the setup of the oven) however I think I need to put some vents in the design to bleed off some heat if it's a really hot day. I'll verify this with a thermometer on the next test run, but I think it will be necessary.

I didn't know if I should put these in the associated steps or just add them as an epilogue ...so I decided to put them where a returning viewer may notice. I was at IKEA and spotted this set of matt-black painted aluminum pots for less than $13 (10 Euros) and this package of dark-grey rigid silicon lids for $8 (6 Euros). I would have bought the smallest lid [if it was sold separately] I would have bought just it because it's perfect for for all 3 pots. But my wife wanted the larger ones so it was a no-brainer to by the set. But, if you want a lid for each pot you can easily cut them down to size with a pair of scissors

Total cost: 12 Euros ($14)

These are PERFECT for almost any size solar oven AND the handles are screwed on, so it you want to remove them for storage (or for a better fit into a smaller oven) you can do that. Or, if you want leave the handles on, but they are too big for your oven, they are made of plastic so you can cut them off to any length required. I plan on leaving mine on for now but my take them off at a latter date.

I included the product label for faster look up on the IKEA catalog if you want to check for local availability.

Editors note: these are much cheaper than a set of good aluminum camping cookware, so if you're looking for a good set, look no further!