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Can you convert a non-working conventional oven into solar oven? Answered

I have two wall ovens that don't work and I'd like to recycle them into solar-ovens... if possible.

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rickharris

3 years ago

Probably - what type of solar oven do you anticipate?

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RickC47rickharris

Answer 3 years ago

Nothing special I don't think. Just trying to save energy and still have hot meals. As I said, it's two wall ovens, upper and lower, that no longer work... Any gotcha's that you can think of, would be greatly appreciated. Or, if you know of a website/video about someone who has already done this...

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rickharrisRickC47

Answer 3 years ago

Ok considering the options you have your going to try to heat a box with sunlight.

1. A BIG Fresnel lens focusing the sunlight through the glass door onto a black fireproof surface say a fire brick will bring the brick and so the oven up to pretty high temps, Controlling it will be the hard part. You need to keep facing the sun you need to control the temp in the oven.

2. A set of curved mirrors can shine the suns energy onto the oven, which will of course be at the focal point of the mirrors again control will be an issue.

3. You can set up a parabolic mirror as a long trough and pass a pipe down the center at the focal point. A heat transfer medium, fluid or gas, will be heated by the sun then you can use the oven as a heat exchanger to extract the heat from the medium.

https://www.youtube.com/results?search_query=solar...

https://www.google.co.uk/search?q=Solar+oven&biw=1...

https://www.google.co.uk/search?q=solar+furnace&bi...

You might be better off looking to make a wood fired garden pizza oven out of them

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Jack A Lopez

3 years ago

Speaking generally, an oven is an insulated box, with the inside hotter than the outside.

Because the inside is hotter than the outside, heat flows through the insulated walls of the oven.

In order to maintain the high temperature inside the oven, energy must be supplied into the oven at the same rate, time-averaged, energy is being lost as heat flow through the walls. This energy input to the oven can come from burning fuel, an electric heating element, a glass window with bright sunlight streaming in, or even just a big mass of made of some rare isotopes. These can all be used as a source of heat, for to supply the heat that is inevitably lost through the walls of the oven.

So that's sort of an overview of how an oven works: Build an insulated box. Pour energy into it. Then the inside of the box gets hot.

But it would be perhaps be helpful to have some more detailed knowledge, about how this works.

First, consider the units for measuring heat flow: joules/second, or equivalently watts.

Second, I claim the amount of heat flow needed to keep an oven with some temperature difference across the walls of the oven is proportional to that temperature difference (call it deltaT), and also proportional to the sum area of the oven's walls.

For a solar oven, it turns out the amount of power (energy flow) you collect is also proportional to an area, i.e. the area of sunlight reaching the light concentrator.

Just as sort of a round number estimate, bright sunlight delivers about 1 kilowatt (1000 watts) per square meter.

Coincidentally, the amount of area of solar collector for a typical solar oven, one of these portable flower-shaped ones, is about 1 square meter.

The oven compartment for the typical portable solar oven, is roughly cube shaped, with the length of one side being about 1/3 meter, or 33 cm.

So in summary, that's about 1 kW of heat, into a box with 6 sides, each 1/9 m^2 in area, or 6/9= 2/3 m^2 of surface area for the walls.

However, a regular sized oven is much bigger, so I would guess the heat loss through the walls will be much bigger. If it were just proportional to wall area, I would expect a cube with 66 cm sides (twice the lenght of the little solar oven), would have four times the wall area, and require four times as much power (4kW compared to 1kW) to keep it hot.

So what I am saying is, because your old wall ovens are large, that itself may be a problem, because this oven will have large wall area through which the heat flows out. So this would require you to build a proportionally larger solar concentrator, for to provide enough power to match that being lost through the walls.

If you happen to know how many kW of heat were required to keep these ovens hot (this will be some fraction of the oven's full rated power), in these oven's previous incarnation as electric, or gas fueled, ovens, then that number might be helpful. I mean just multiply the power consumption in kW, by 1 square meter, and that should be roughly the size of the solar concentrator you would need to supply the same amount of heat power.

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Kiteman

3 years ago

You'll need to focus a lot of sunlight in through the door (assuming it has a window).

Maybe loads of old CDs on a frame, with them all angled to reflect sun in through the door?

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RickC47Kiteman

Answer 3 years ago

Actually I was thinking I'd replace the existing doors with just glass, due to the oven doors themselves having such a small window...

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KitemanRickC47

Answer 3 years ago

If you can target the sunlight carefully, the small window / proper oven door will be better. Ordinary glass might shatter at oven temperatures.