Our friend Carl Peters helped me build a solar oven recently.  I've seen it get to 350ºF in the afternoon.  It's a

double-walled box made out of plywood.  It's really heavy and bulky, which makes it stable in the wind and very sturdy, but

not very portable.  Carl found a few nice pieces of tempered glass about 16x19 for $5 each.  He sold me the glass, cut most of

the wood, and held my hand through most of the process to make sure I could finish the project.  Also, my father-in-law

happens to be a carpenter, so he helped me frame the glass and build the sheethes I made to hold the reflectors.  Between the

plywood walls is about 1.5-inch pieces of wood Carl made by ripping 2x4s in half.  The 2x4 wood makes the box very sturdy,

provides wood to screw into, and creates insulating space between the walls, which I filled with carboard wrapped in aluminum

foil.  I think the glass sits at about a 30º angle from horizontal.  Where we are is latitude of about 36.5º, so I figure the

sun gets to about 60º from vertical in the winter and about 13º from vertical in the summer (23.5º shift at solstice).

The sheethes secure the base of the reflectors and the reflectors are strapped together at the edges near the top.  Each

sheeth is a 2x4 cut along its length at the reflector angle, with a thin piece of wood screwed on top with spacers in between

to make room for the reflector to slide in.  The reflectors are 4x8 political signs I harvested immediately after the

election.  It's a good idea to ask the candidates permission for these, even though they're usually very dirty and have

graffiti all over them.  I made a spreadsheet to calculate the widest angle at which I could position the reflectors so that

light reflected from the top would make it through the glass.  It came out to about 71º to 73º from horizontal.  Carl gave me

some radiant barrier material (used for insulation in home construction) for the reflectors, which seem like they may reflect

about 80% of incident radiation.  I put some of that on the outside surface of the reflector sheeths, too.

Against the advice of our friend Carl, I glued and screwed the glass down to the oven box.  Carl likes to be able to remove

it, to both facilitate cleaning and to allow for better use of the box in the off-season.  When the sun is at a lower angle

during late fall, winter, and early spring, Carl gets more use out of his oven by tipping the box up on its back.  This puts

the glass at a much steeper angle, allowing more sunlight in and he's able to continue reaching high temperatures when other

folks have already put their ovens away for next year.  Being able to remove the front glass allows him access to the food

when his door is facing down.  I opted to put a door on the back to make it more like a conventional oven.  I figure, the

easier this thing is to use, the more use it will get.  A kind gentleman at a local appliance repair shop gave me a strip of

silicone oven seal for free when I told him what I was doing.  Its arrow-shaped attachment rail (not sure what to call that)

plugged right into the table-saw cuts we made in a rectangle around the back opening, maybe a quarter of an inch wide.  With

two front-door hinges on the side, even though my oven door is huge and heavy, it swings open really nice and closes tight

against the seal with a hook and eye-screw latch.

Inside the solar oven, I put a piece of drywall we had lying around to further insulate the bottom and then a fairly thin

piece of steel we cut out of an old filing cabinet.  I recommend using clean steel from a scrap metal place instead of trying

to clean off old (lead?) paint like we did.  This is an oven for food!  I sprayed the steel with a flat black high temperature

paint (for barbecues).  Still, no food goes on the steel!  It's just a heat absorption plate, which is a key component of the

oven.  I applied a stain to the outside of the oven to weatherproof it.  The outside doesn't really get hot, except for the

screws.

If I were to build this again, I'd put in fewer screws, or maybe use shorter screws.  They seem to conduct a lot of heat out. 

This oven really seems like overkill in terms of the amount of wood and the amount of work it was to make.  It's heavy and

doesn't fit in the truck of my Honda Civic, but it should last a long time and get a lot of good use as a permanent fixture in

the back yard.  I've been looking into sun-tracking circuits and have some motors I could use to automate this thing's

operation a little, but it's really not necessary.  Turning it every half-hour to an hour seems to keep a fairly stable

temperature.

Materials
Lots of screws (nails no good because of deformation due to heat!)
High temperature wood glue (I think it's high temperature...)
Plywood (4x8 sheet)
Corrugated plastic political signs (2 - 4x8 sheets)
Radiant barrier (shiny - like 16x4)
2x4s (maybe 12 feet?)
Scraps of thin wood and cardboard
Tempered glass (won't break when hot)
Door hinges
Hook and eye latch
Silicone oven seal (rubbery strip)
Silicone high temperature caulk
Steel plate
Flat black high temperature (barbeque) paint