Which interior is better for the inside of theSolar Oven?

by Jordan
(Florida,USA)

I built a solar oven 24 by 15 by 8 in. outside measurement and 22 by 13 by 8 in. inside measurement. I have 1/2 in. thick tempered glass that rests on top. I also added a mirror to the back side, left side, and right side. I lined the inside of the wood box with aluminum foil. Is it better for heating the oven to leave it reflective or paint the aluminum black? If I need to paint it, where can I get non-toxic and zero VOC (volatile organic compounds)paint? I'd prefer if it was spray paint.


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Thank you for your question Jordan.

It sounds like you are well on your way to a nice homemade solar cooker.

One thing you did not mention in your description is whether you have your box insulated or not, because this can make a big difference in how much heat your solar oven will retain as it cooks...

Now, as for whether a dark oven interior or a shiny interior is better, the answer is that both can work well.
There is debate amongst solar cooks as to which interior is best and that can mostly depend on how you build your solar cooker.

In brief, you can use an all shiny, reflective oven interior which will concentrate the suns rays onto your cooking vessel which will then absorb the heat energy of the suns rays into the cooking vessel. And of course this vessel will need to be dark in color for better absorption of the heat.
I would even recommend in such a case to also place the cooking vessel inside of an to help retain more heat closer to the pot/vessel. This would be very similar to how a solar panel style cooker functions, but with the added benefit of an oven cavern surrounding your cooking vessel as well.

The purpose for a dark solar oven interior would be for higher absorption of more of the heat, that can then be transferred to the cooking vessel from the oven interior itself.
A dark interior helps to create more heat around the cooking vessel, whereas a shiny interior only sends or reflects the rays to the dark pot which then absorbs the heat energy. Ideally you would want the floor of your oven to act as a heat sink that can absorb the heat energy without losing it out to the atmosphere through conduction. This heat in the sink can then be conducted and even radiated to the vessel/food.

You could make your solar oven with a combination of the two, using shiny sides of the interior walls and a dark floor or base of cooking stone, metal etc. Or just do it all black, which would then require possibly painting the box interior unless you had materials that were already black.

If you do paint you can use the high temp bbq paint available at most home improvement stores, but then you would have to "cure" or harden the paint to release the toxins by "cooking" the paint in the sun for some time until the smell is gone. Most manufacturers indicate it is non toxic when dry.

Other do-it-yourself solar cooks suggest using tempera paint which is all natural and toxin free, but can require re-application of the paint with time and use.

I could probably go on and on, but I think this should help you a bit with your project.

(I invite any others that would like to share their ideas and suggestions to comment as well.)

Nathan
Admin.

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Feb 14, 2018
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answer part 2 NEW
by: Jordan

Black paper vs. black paint may not make much difference, if any. It also depends, because I don't know if you plan on using the paper as another layer of insulation and/or using it to prevent air loss through any cracks/imperfections/holes

Feb 14, 2018
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answer to question NEW
by: Jordan

It depends. If the black colors are equal in tone and assuming neither are reflective at all, the object that gets hotter and stays hotter longer and can heat up quickest, is best. what are you painting? wood? what type of wood? how thick is it? what type of paper? how thick is it?

going back to before, you may want to choose something that is the least reflective on the inside.

Feb 14, 2018
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question NEW
by: Anonymous

what would work better for a solar oven interior, black paint or black paper?

Jul 24, 2016
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30 Degrees NEW
by: KurtisT

Thank you Anonymous! Knowing you added 30° by painting the inside black will save me more research or testing.

Jul 18, 2016
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painting the interior black NEW
by: Anonymous

My homemade solar oven had polished stainless steel interior panels. I was not thrilled with the cooking temperatures, so I painted the interior black. Temperatures increased by 30 degrees.

Jul 11, 2013
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Inside of an what?
by: Anonymous

"I would even recommend in such a case to also place the cooking vessel inside of an oven bag to help retain more heat closer to the pot/vessel. "

Inside of an what?

Sep 07, 2012
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Update
by: Jordan

Thank you for your help. I was thinking about painting just the bottom, because otherwise I'm thinking that the light would reflect up and out of the box. Also, I am using 1/8 in. cork sheets that I wrapped with the aluminum foil first, before I placed it in the box. The last time I tested it, it got up to 155 F degrees. After this next test it should be at least 180 F degrees.

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