A solar oven is a fun way to cook your meals off the grid or without heating up the kitchen on those hot summer days. A solar oven works by using the passive heat from the sun collected in an insulated box that works a lot like a greenhouse. Follow my instructable for detailed step by step instructions on building your own solar oven.
Step 1: Gathering Our Tools and Supplies
This project requires one 4'x8' sheet of plywood. I chose a .451" sheet at my large home improvement store. I had them cut it in store. They do 2 cuts free usually and its something like 50 cents for additional cuts at most of the big guys. Cutting it enabled me to carry the wood home without breaking my back and so it fit in the car. The first cuts are usually the most awkward ones and having the employees do it with the big machines its easier and saves time. The first cut was to slice it down the middle into 8' lengths 24" wide. Now the blades will eat some wood so ask them to make one side be 24" and the other side to be whats left over. Then have them cut both halves at 24" deep. you will be left with an 72' x24", 24x24, a 24"x(a little less than 24"), and 72"x(a little less than 24". One big sheet and one 24x24 inch will make the outer box and the smaller big sheet and 24x24 will make the inside box; this why its okay if one half has smaller parts. If you want you can have the employee cut 2 more pieces 24" wide (so about 24x24) on each large sheet to save you the trouble of doing it yourself at home.
Step 2: Cutting the Outter Box Parts
Using your saw (table saw and/or jigsaw), cut the bottom 24"x24" piece (you should have this one from the store already cut although it may need trimming), also cut your back piece 24"x20", and two square pieces which will be trimmed even more to make the sides. Also cut a piece to be 24"x5 1/4" (Top piece) and a 24" x 6" (for the front piece).
After all are cut pick up the 2 that will become the sides. on the 20" side measure 5 1/2" and make a mark,
on the 24" side (diagonally from the previous corner, look at picture for clarity) measure 5 1/4" and make a mark.
Make a straight line connecting your 2 marks. This should create a triangle in one corner.
Cut this triangle out.
Step 3: Start to Build the Outter Box. Bottom Piece.
Start by adding a perimeter around the bottom (24"x24") piece with (3/4" x 3/4") piece. Start with the front adding a (3/4" x3/4") 24" long piece, this front piece must be placed slightly in from the edge. How much off the edge? The thickness of your plywood. If you got the .451" plywood like me then it would be that much. you can place a scrap piece of plywood on edge for the propper fit and then clamp down the 3/4" rod. Like in the first figure in this step. Then drill pilot holes with the 3/32"bit, then screw in the 1" screws in the pilot holes. drill from plywood to rod not from rod to plywood.
Then add 3/4"x3/4" rod around the sides and back. This time place it against the edge. Drill pilot holes then screws.
Step 4: Adding the Back Panel
Add the back piece a 20" x 24" piece. Adding clamps at both corners using the 3/4"rod as support will get things flush. Once in position you can drill your pilot holes and screw it in place. Remove clamps. then add 3/4"x3/4" rod around its perimeter always against the edge like we did with the bottom.
Step 5: Adding the Sides
We will start this step by rotating out previous progress on its side so we can add the side from the top. The side that's 24" goes with the 24" side of your in progress box. And 20" goes with 20". when its flush, level and at 90 degrees clamp the side piece to the box using the supports (hidden in picture, look at another in this step to see the 3/4" supports) at both corners. (IF you have long 24"+ clamps you can clamp it down in other parts too.) Then drill your pilot holes and screw in the 1" screws. Your box should now look like the second image. Notice the supports. This is where you are drilling into and using to clamp to.
Repeat the process for the other side and you should end up with the third image. *Notice that in the image the box has the bottom down.
Now add support along the edges of the sides. DO NOT however add both small pieces that would be for the top and front, the 5-6" piece supports or you will have to remove them later to slide the inner box layers in. Wait on that.
Step 6: Adding the Inner Box Bottom Piece
Now we will start to add the bottom inner piece. Measure the back side panel to the front side of the bottom support (not the edge of the bottom piece). This should be about 22 1/4", this will be your depth.
Now measure your side inner panel to other side inner panel. This should be about 23", this will be your width.
(the reason it might be off is that you used a different size thickness of plywood or you cut your pieces at different precision than me, maybe better).
Out of one of your roughly 24" x 24" pieces from the store, cut it down to your width x depth (about 22 1/4" x 23")
Now cut notches that are 3/4" x 3/4" on each corner like the picture shows. you can simply hold a scrap piece of 3/4" x 3/4" rod and trace around it to figure out where to cut.
Test that it fits snugly in place inside the4-sided box you built. If you need to trim the notches or the entire panel do it until it fits tightly into place. A tiny crack between edges is okay since it will be filled in with silicone later on.
Once it fits perfectly into place remove it and crumple old newspaper and fill the bottom area between supports as picture shows for insulation.
Paper burns at 451 deg F (remember Ray Bradbury's novel by the same name?) so it should be fine in the oven. The crumple newspaper will add air pockets that work as the insulation. Paper is not a good conductor and neither is air making it a decent insulation.
Then carefully place inner bottom panel into place and drill pilot holes and screw into place.
Step 7: Insulate and Add Back Piece.
Start by trimming one of your 24" x 20" pieces down to your width x height. you can measure these as indicated on the first image in this step.
your width minus 1 1/2" will be the length of the support that goes along the bottom against the back panel between the vertical supports on each side. cut a piece of 3/4" x 3/4" to this size (you can measure it) and screw into place.
with your trimmed back piece, cut two (2) notches on one of the wide sides at both ends. The notches are 3/4" x 3/4" . See picture.
Insulate the area between the supports with crumpled old newspaper. Try to keep it clear of the supports for good contact.
slide into place, clamp it down where possible to insure its straight and plumb. Drill pilot holes and screw the panel into place.
Step 8: Inner Side Panels.
First complete the perimeter of the sides with 3/4" x3/4" rod and screw it in place.
you will be using 2 pieces of 24" x 20" plywood for this step.
grab one plywood piece and from the inside place it into the position it will be in. With pencil/sharpie trace around. cut piece along your trace for a perfect fit. Repeat the process for the other side.
OPTIONAL STEP: with your pentagon sides measure up 6" and across 6" and drill a hole to pass a 1/2" thick x 3" long bolt with a washer on each side and a nut holing it in place as shown. This bolt and the other one on the other side panel can hold a tilting tray so you can rotate the whole oven up and down to catch more sun. I won't be doing this now but I want to keep the option for the future so I'm leaving it ready for it.
Insulate a side with newspaper, clamp down a side panel with long bolt side facing away from the newspaper. clamp down wherever possible and drill pilot holes and screw it into place.
Step 9: Installing Front and Top Panel.
screw in the 24" x 6" piece to the front as in the picture.
Measure the top where from the back panel to where it starts angling down, this will be your depth.
Trim a 24" x 5 1/4" to the proper depth if needed.
clamp down with 24" clamps if you have them and screw into place.
Around all the edges pass a bead of silicone to make a good seal.
Paint inside and out with black HIGH TEMPERATURE grill paint (spray paint), you can skip the underneath of the grill where it lays on the ground.
Step 10: Building the Framed Glass Door.
Now that the main body of the oven is done we will turn our attention to making the glass door which will let in the solar heat.
Measure the opening of the oven including the frame around the opening. You will make the framed glass door to meet this specification.
The hard part about making a frame is 2 fold. first the top and bottom have to be equal lengths and the sides have to be equal lengths. Second the cuts have to be 45 degrees exactly or it wont make a square.
grab two 2" x1" rods and clamp them together. Make sure they are even throughout. If you have a miter saw cut it at 45 degrees on both ends as shown in the first image, otherwise measure and cut with a jigsaw or table saw. get it as close to 45 degrees as possible. Repeat again for the sides. Note that the length of the side must match the length of the long end of the 2x1 for the frame to match the opening in the oven.
once cut into size we will create a groove down the middle of the rod as shown in the second picture. This can be done with a table saw as shown in pics 3 and 4 or with a router table. If neither of these are options you can use 3 pieces of wood sandwiched together with the middle one being smaller to create the groove we are looking for.
Picture 4 shows how the groove is done. Please note that the saw was OFF when taking the picture. This procedure is VERY DANGEROUS!!! Use scrap wood as a guide as shown in picture 5 so your hands are NEVER close to the blade.
Push the piece you want grooved through the saw with a third piece of scrap wood NEVER BY HAND!!!!!! note 3rd piece of scrap wood not shown.
The blade is what causes the groove. Move the blade up or down until 1/2" is exposed to create a 1/2" groove.
The wood should look like the 2nd picture when done.
Get a piece of glass cut to size and your home improvement store. I had the good folks at OSH do it for me and they cut the glass perfectly to my size. The size of the glass will be (the width of the frame opening + 1" ) x (the height of the width opening + 1").
Its an extra inch in both directions because the glass will go into the grooves half an inch on both sides.
Test to make sure the frame fits nicely and square around the glass. ensure that the grooves match up with ech other. You may need to flip a frame piece to do so.
Once you are happy how it fits take one frame piece of at a time and add a small bead of silicone in the grooves (picture 6) and push back into place. finish 3 sides and you have a frame like image 7. add the last frame piece then secure with metal L supports (picture8).
Paint the frame and not the glass with HIGH TEMPERATURE grill paint available at your home improvement store. Picture 9.
Okay you are almost done. time to add the glass frame to the oven box. If you need to because of the hinges you purchased (like I did) then add a small piece of scrap plywood to the top corners so the frame will open and close fine. Like in the first image.
add an optional but helpful handle to the bottom of the frame. Picture 2
Okay you are almost done. Check the openings around where the door meets the box and shave any areas as needed with a leveler so its a good fit. Then add door jam weathering around the perimeter of the box opening. Note that the top part may fit better on the top of the door from underneath. When choosing your weathering go for the sponge version as opposed to the rubber version since it wont melt at high temperature.
Add a oven thermometer inside.
Add a hook and eye lock to the oven so it closes secure are you are done! (Picture 4)
Now I plan to use my oven in the Nevada desert during burning man so I will do without adding reflective sides but you can easily add them using a shiny reflective surface like aluminum foil on a thin piece of wood to maintain its rigidity. If you prefer not to use aluminum you can use a Mylar sheet available at hydroponics stores. Alternatively you can use a car shade reflector (the kind you put on your windshield on hot days) found at auto stores or 99cent stores.
The oven reached 240 degrees in my backyard with an ambient temperature of about 75 degrees, in the desert I expect this to climb close to 300 degrees, enough for my lasagna and cookies!
I hope you enjoyed this instructable and it encourages you to go out and make one of your own. This is the first instructable I write so I would appreciate any positive criticism on how to make future instructables better. Also thank you Teresa for helping out!
Finalist in the
Off the Grid Contest