solar oven project - still no joy

[Marianne]

I just used a little stand up oven thermometer when I was experimenting with solar ovens.

 

[Toulle]

Progress (or lack thereof) on the solar oven

Picked up a grill thermometer that goes up to 700F (as if.....) at the local home box for $7. Bent an aluminum bracket and riveted that inside so it can be read thru the glass cover.
Rain or heavy clouds for just about 2 weeks.
So today, it finally cleared up. As of 2 this afternoon there were only scattered wispy clouds - otherwise hot and muggy as usual.

I installed two handles made of scrap leather and carried the stove outside. There is a black anodized pot we found in one of our cabinets that works perfectly in it, which I put 2 cups of water in just to see if it would boil.
As soon as i set the oven down, the thermo was reading just over 100F. Promising.
15 minutes later: 150F. Very promising.
1/2 hour after that: 200F. Now I'm stoked.
Still another 1/2 hour: 200F. Hmmmmm.
Again another 1/2 hour: 200F. Not so stoked anymore.
Now here it is coming on 4:30: 200F.

Reflector is set at 30degrees, very good for me being at latitude 31. Keeping it turned to face the sun.
Interior is aluminum sheet painted with black grill paint. It's got 1" of corrugated cardboard between the inner box and the 1/2" plywood exterior.

Wonder about the glass. It was the sliding front window of a truck bed camper-cover, maybe some sort of reflectiveness (language fails me here.....)

 

[Marianne]

I'd suspect the glass, too. If you can scrounge up an old storm window, try that.
My first attempt (many years ago) got up to 250F in a plain wooden box with no insulation. Yours should have performed better than mine.

 

[Toulle]

Went and got a new pane of glass today at the big "home improvement" box store. Of my entire shopping list, that was the only thing I could find. I am certain that American retail giants do things to deliberately P me off. Me in particular - but that's another story.

Anyway, with the new pane of glass alongside it, the old pane does appear to have a very very slight tint to it. I got the new pane of glass installed and put the oven out in the yard, carefully oreinted towards the sun. Several hours later - 210F.

Running out of ideas

Glass is sitting at a 30 degree angle, which is almost perpendicular to the angle of the sun most of the day.
Reflectors are shiny aluminum, sitting at just a bit steeper than a 45, or 135 if you look at it that way, degree angle to the pane of glass.
Interior is painted flat black
May lose a little heat around the door, but I can't feel any going out

 

[k0xxx]

Odd. I would think that such a well designed and built box would be working for you. What type of insulation between the inner lining and the exterior? Was there any wind? These are the only other variables that I can think of at the moment, that may have affected the temperature.

 

[Toulle]

Odd. I would think that such a well designed and built box would be working for you. What type of insulation between the inner lining and the exterior? Was there any wind? These are the only other variables that I can think of at the moment, that may have affected the temperature.

I'm glad you chimed in - I think I remember seeing that you have a successful solar oven.

Insulation is corrugated cardboard
There was a breeze

I'm starting to wonder if the aluminum flashing I used isn't shiny enough. I understand that people make solar ovens with aluminum cooking foil, so I figured the flashing is better (no wrinkles, sturdier)

 

[Marianne]

Sure could be, if it's anything like the flashing I have here - mine's not really that shiny when comparing it to foil. JMO

 

[moolie]

I'd guess that it's the flashing, perhaps combined with a lower than styrofoam R value in the cardboard insulation?

Is the interior totally sealed when the lid is closed?

 

[xpc]

Try lining the inside with aluminum foil - shiny side, dull side, crinkled or not makes no difference, the only flat black inside should be the cooking pot. What are you using as a sundog?

The reflector shroud you have is serving no purpose as it's focal point is above the glass, remove it and put a nail in the top that is perpendicular to the glass surface and then tilt and angle the oven so as not to leave no shadow from the nail. Cheap single pane glass is still the best to use as leaded and dual pane chases off the UV rays more so then it insulates.