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Through the wall solar oven

 
pollinator
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I've built a through-the-wall-solar oven for my tiny house (please note that the tiny house's south wall is aligned perfectly with solar south-a VERY important fact).

I'll need to change the 1/4" plexiglass which has a melting point of 320F before I add reflector wings on the sides.  

I want to insulate the inside of the oven so it doesn't heat my tiny house during the summer and so the oven will get hotter during cold periods in the winter.  

I'm thinking thin firebrick right now but I want to hear what the community has a suggestions:  anyone care to share some suggestions on what material I should use to place inside the oven???

You can see the build here:
Twobirdstone's through-the-wall-solar oven build
ttwsoMain_20180903.jpg
[Thumbnail for ttwsoMain_20180903.jpg]
 
pollinator
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Once it gets hot, will the silicone emit toxic fumes into your food or did you use one of these fancy expensive ones?
My friend has build a similar thing on the side of his straw bay house out of a discarded window,boxed it in and painted the inside black and it rises heat into his home. But the hole is on the top and he blocks it in summer. I made a herb dryer using the same solar idea ,insulated it and stuff, it doesn't dry peaches though, they mold before they're dry.
 
Orin Raichart
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Hi Hugo,

Hugo Morvan wrote:Once it gets hot, will the silicone emit toxic fumes into your food or did you use one of these fancy expensive ones?


Do you know exactly what fumes are released and what makes those fumes toxic?
I seal my containers that I put in the oven; none of my juicy solar cook dishes had a "taste" to them.



Hugo Morvan wrote:My friend has build a similar thing on the side of his straw bay house out of a discarded window,boxed it in and painted the inside black and it rises heat into his home. But the hole is on the top and he blocks it in summer.


Glad to hear your friend got some free heat from the sun!!! and no moving parts to maintain!!!   That's what it is all about.

Could you ask your friend what his maximum temperature was coming out of the hole in the top?
 If you'll notice, I have two 2" pipes: one down low on the west and one up high on the east protruding from the solar oven. I close these pipes with end caps during the winter and open them during the summer when I'm not cooking however, the rear back wall transmits a great deal of heat into the structure.

Hugo Morvan wrote:I made a herb dryer using the same solar idea ,insulated it and stuff, it doesn't dry peaches though, they mold before they're dry


I'm sorry you experienced failure on your fruit dryer.

Maybe I could help, can you post some pictures of your dryer?
What was your maximum temperature inside your fruit dryer?  
What is the size of the air intake and air output?
How thin did you slice the peaches?

My solar oven even without the reflective wings, tops out at 227F which is plenty to dry fruit with during the summer, plenty enough to cook and, with the end caps off, enough air flow to dry food with.

So my solar oven, during the summer atleast, is really a through the wall solar oven AND fruit dryer" but I didn't want to brag too much my first time out :)

 
Hugo Morvan
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Hi Orin, i don't know what putty you used , if you've sealed the food you'll be alright i guess. It will be bad in the long run if you eat it everyday without container over a long period, i'd think..
The solar food dryer, i made it when my daughter was around in summer, she was struggling at physics, it had some elements to raise her curiosity for the subject. She pretended to be really interested, but her grades were still low the next time, she dropped the subject shortly after. Haha. I'm stuck in my shed with this huge odd looking object.
The first time around the peaches molded, because the weather changed and the slices where too thick, the second time it worked, but i found out i didn't like them too much like that anyway. I make jams now. For herbs, i found that a slow dry in the attic retains the taste much better. Waiting for my apple tree to get big, i like dried sliced apples! In general these feats are more suitable for the tropics than central Europe, where are you Orin?
I'll ask my friend what temperature he reaches.
Maybe you can cover your house in a nice looking climbing plant, that seems to work as a coolant as well !
 
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A wood oven? I think I’d throw out that design. I’d go for steel or aluminum. I can’t believe you could insulate it enough to keep it from heating your house. I check with someone better informed than me before you put too much effort into it.
 
Orin Raichart
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Dennis Mitchell wrote:A wood oven? I think I’d throw out that design. I’d go for steel or aluminum.


Most solar ovens operate around 320 to 375F.... wood burns around 451F -I feel safe with wood given the geolocation of the through the wall solar oven.  
...but I will keep an eye on the wall temps after I add the reflective wings just for safety any way.


Dennis Mitchell wrote:I can’t believe you could insulate it enough to keep it from heating your house.


You are right, since the energy of heat tranfer is defined by convection, radiation, and conduction, the solar oven will always transfer heat to the house. So my solution must cut down the amount of heat transferred....hmmmm.....I could use foil for the radiant portion of the heat transfer...guess I could've airgapped the oven and the outside wall (which was my first design but it seemed too complicated), for the convection and conduction portion of the heat transfer

Dennis Mitchell wrote: I check with someone better informed than me before you put too much effort into it.


personally, I've never heard of a through the wall solar oven so I suspect I'll have to experiment more than I'll wait for answers.

 
Orin Raichart
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Hugo Morvan wrote:... In general these feats are more suitable for the tropics than central Europe, where are you Orin?
I'll ask my friend what temperature he reaches.
Maybe you can cover your house in a nice looking climbing plant, that seems to work as a coolant as well !


I'm in a zone where the minimum solar radiance per day is around 500W/m^2 per day during the winter...but I'm kinda like Waldo, where is he?

The reflective wings will fold over the glass face of the oven when I'm not using it. I'll use stiff wire rods through the wall to control the wings.
I'll probably use an awning to cover the solar align south wall that I can raise easily to cook with....but during cooking I need an insert material for the maw of the oven that will cut down on the heat transfer....do you know of any?
 
Dennis Mitchell
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“Most solar ovens operate around 320 to 375F.... wood burns around 451F -I feel safe with wood given the geolocation of the through the wall solar oven.”
One site I checked had thermal degradation of plywood at 230 to 308 degrees F. Also check carefully, charcoaling will look very much like the black paint. Maybe those thin bricks on the inside would be a good idea.

 
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Orin Raichart: I have been watching this thread with interest, I'm chewing on how to modify it to work for myself. Won't look anything like yours, but the idea, having the oven accessible from inside the house, is an idea well worth considering. Thank you!! :D
Welcome to Permies, a fantastic first post concept!
 
Orin Raichart
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Pearl Sutton wrote:Orin Raichart: I have been watching this thread with interest, I'm chewing on how to modify it to work for myself. Won't look anything like yours, but the idea, having the oven accessible from inside the house, is an idea well worth considering. Thank you!! :D
Welcome to Permies, a fantastic first post concept!


Thank you Pearl!

Below is my first design which I decided was too complicated (and required to many materials beyond my time/money). The solar oven box was to swivel on two axis so it could manually track the sun east to west and tilt according to the seasonal angle of the sun. It was meant to pull back in thru the wall and push out without actually leaving the rubber boot which is not shown in the cartoon drawing. The solar oven box would have a rear hatch which would match the portal in the wall.

As you can see, that is very complicated compared to just attaching two reflective wings and two stiff wires to the wings to control the angle of the reflective wings.

I came up with this design in 2009 but I later found that there is another version that uses parabolic mirrors to reflect the sunlight into a hole or window in the wall I first found here:Tamera's Solar Kitchen

Tamera's oven will get hotter than mine but it seems expensive in materials and time.

By reducing my complexity, i found my solar oven cooks when the ambient temperature is above 50F at 227F right now (this means I have a crockpot which I load in the morning and eat at night). But when i add the wings, I hope to see temperatures above 300F on sunny days.

I hope you share your version!
solarOvenDesign01_2019-03-26-165659.png
[Thumbnail for solarOvenDesign01_2019-03-26-165659.png]
 
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You could line the inside with aluminum flashing and do something similar for a door with fiberglass or Rockwool insulation. The reflectors folding over the oven will solve your summer heat gain. I've used cardboard with ceramic BBQ paint for 13+ years in a box cooker and it's not caught fire yet.
 
Orin Raichart
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James Sullivan wrote:... I've used cardboard with ceramic BBQ paint for 13+ years in a box cooker and it's not caught fire yet.



Thanks James for your input. BTW, what is your box cooker's temperature range in the winter?   In the summer?  

I ask because I've only had one solar cooker before and I used it in NM  during the fall and summer. That solar oven reached 350F max and 300F regularly. With the through-the-wall solar-oven I can see its temperature from the inside every time I glance at it since I put a oven thermometer thru the wall too.

 
James Sullivan
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Orin Raichart wrote:
what is your box cooker's temperature range in the winter?   In the summer?  



I've never used it in the winter, yet.
Summer I've maxed out at 220F, once I'm not using cardboard I'm sure it will be better.


Orin Raichart wrote:
That solar oven reached 350F max and 300F regularly.



That's great.
 
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Orin, for insulation consider the possibilities of these common griddle bricks. They have quite a few nice features that I feel apply to your situation.

They are:

-lightweight
-easily carved into any shape
-food safe
-dark color
-cheaper than firebricks
-very high melting point
-easy to find/order online
-insulating

These are just a few I could think of off hand. I have never actually used these other than their intended purpose but the more I look into them the more I'd like to give them a try in a wide range of uses. Just a thought, good luck!




 
pollinator
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I don't know about a through the wall solar oven but some apartments I've stayed in north west China have a fridge that is just a cupboard door to a platform that is on the outside of the building for use in winter.  It's covered to stop the snow falling onto it.
 
Orin Raichart
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Graham Chiu wrote:I don't know about a through the wall solar oven but some apartments I've stayed in north west China have a fridge that is just a cupboard door to a platform that is on the outside of the building for use in winter.  It's covered to stop the snow falling onto it.



Nice, now your talking about what I call a cool box which I also built inside the tiny house...you can see it here https://twobirdstone.blogspot.com ....I got the idea from an Urban Homesteader book. This belongs in a different thread though I think. Mine is more than just an door to the outside: it's insulated, mostly below floor and has a 6" cool or cold air intake....it also has an above floor 4" output which has a screw cap which is closed most of the time unless I want to try to pull cool air into the tiny house...sorta belongs in passive cooling threads but it's not ready for mainstream yet.

It keeps about 10 degrees cooler than the ambient temperature...unless it's really cold outside.
 
Orin Raichart
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Aaron Tusmith wrote:Orin, for insulation consider the possibilities of these common griddle bricks. They have quite a few nice features that I feel apply to your situation.

They are:

-food safe

These are just a few I could think of off hand. I have never actually used these other than their intended purpose but the more I look into them the more I'd like to give them a try in a wide range of uses. Just a thought, good luck!



Great idea Aaron, I need to check on what the griddle bricks off gas when heated. when I cleaned a cooking grill as teenager, I was told the residue was toxic and had to be cleaned off with one last flush....I suspect the bricks have changed a great deal but I will definitely check the current ones and post any findings here.

Thanks!

****UPDATE****
Some, not all griddle bricks are made from foamed recycled glass (quoted source here). Others are pumice. Who knows what the ones from china are made from. So for pumice and foamed glass griddle bricks, I'm all for their use in a solar ovens which operate below 900F. Pumice would probably go higher since lava flows created them.

**************
Thank you Aaron for a great usable solution!
 
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