Since becoming a home owner (2010) I've gotten much more cost conscious and much more indignant about energy costs. So I started thinking how I can use the sun instead of electricity or gas. Taking baby steps, instead of using an electric dryer, I've regressed/progressed to hanging many items outside on a line. It's a bit more labor and time consuming, but after watching the electric meter spin madly when the dryer was running...
Next little step, solar cooking. Clothing drying on the line, while practical, is exceedingly boring. Solar cooking is more fun! Thankfully many fine folks have already gone down this path and have graciously shared their plans. I've found these sites, so far, to be of great help towards my learning and building my own solar ovens.
This first version wasn't what I'd really call an oven. I thought to copy, in concept, the parabolic model.
It's a large ceramic bowl that's lined with aluminum foil. Inside is a black ceramic tile, thermometer and a piece of white polymer clay*. (see note)
The bowl is topped with an old window.
Max temp reached: about 120 deg F.
Not quite what I had in mind for an oven. I wanted something that would reach 300-400 deg F.
After the first oven, I realized I needed to do a lot more reading and studying. Next version was a little more involved in that it required constructing something. I found plans for a double cardboard box model. They're fairly simple, requiring readily available parts and supplies. One box sits inside another. The gap between the two is for insulation. This version had one large reflector. All inside surfaces are lined with aluminum foil. I already had everything I needed and it took about 5 hours to cut, glue and assemble it.
I already had a bunch of boxes from moving into the house, so I started with these two cubed ones.
I cut an opening in the medium box so the smaller book box could snugly slide inside.
After lots of foil and glue, I lined the insides of the cubed boxes and constructed a foil-lined lid.
Sliding the smaller book box inside the medium box.
All cardboard parts assembled and in place. A small wire is used to prop up the reflector. Inside is a black baking pan that holds a black ceramic tile.
Fully assembled second oven with an oversized tempered glass lid.
Max temp reached: about 230 deg F.
The second oven was at least an oven; low temp perhaps, but on the right path. I needed to squeeze in more heat, however. The polymer clay I like to use prefers high 200s - low 300s F, so I needed more focused energy - more sunlight reflected into the oven chamber, and a chamber that can absorb and retain more heat.
Enhancement plans for the 3rd oven:
fiber glass insulation in the space between the two boxes
spray paint the inside of the smaller box with black matte Rust-oleum High Heat paint
place a sheet of aluminum in the bottom of the oven (also sprayed black)
replace the single panel reflector lid with a large multiple panel reflector cone model
I trimmed down the height of another medium box, lined the rectangle panels with foil. Then I cut out 4 triangles, lined those with foil, glued those to fill in the gaps between the rectangular panels. The whole thing looks like a gigantic shiny funnel.
I custom cut and placed a plain piece of float glass inside at the base of the reflector lid.
Since the temp exceeded my other thermometer, I had to get an oven thermometer. The enhancements worked!
Max temp reached: about 345 deg F; 310 deg F on breezier days. Works for me. The thought of being able to have an oven baking nearly all day, every day and not have to pay one red cent to a greedy power company just warms me to me toes. :)
If I could figure out an equivalent option for being less victimized by the cable and phone companies, I'd sell those plans and be rich beyond my wildest dreams!
While there are a few more things to squeeze out a bit better performance, it's likely I'll stop at this point. For a more durable model, I could try:
make the base(oven) out of wood
use aluminum flashing and mirrors for reflectors
replace the fiber glass insulation with expanding foam (e.g. "Great Stuff")
construct the reflector lid so it tilts about 15-20 degrees.
And if I want to really make things more complicated, I'll try to figure out how to make the reflector part collapsible for storage efficiency.
* My original motivation to explore solar baking was because I wanted to bake polymer clay without sucking off the grid. When baking polymer clay projects, I don't really optimize by loading in lots of projects at a time. So it's always seemed wasteful when I've frequently powered up an oven for a few small projects.
Since the weather has been quite warm lately and I didn't want to heat up the kitchen anymore than necessary, it seemed like a good time to explore solar baking.
I was told the more stable the heating environment was, the better the outcome for polymer clay. Standard electric and gas ovens cycle up and down within a temperature range. Unless there are clouds drifting by, a solar oven doesn't cycle up and down. So it could be a far more stable environment and thus perhaps a better environment for curing polymer clay.
Who knows? It may also be a better baking environment for food. Save money, better tasting food and better cured polymer clay pieces? How can one go wrong? Now that I've started and it's been quite an exciting DIY project, I just wonder why I didn't start this sooner.