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Need Help Building a Good Solar Cooker

by Irene

Dear Mr Parry,

Thank you for your informative website. Our family has been working on three different models in the past three days, and none of them worked (well)! We live in India and it is 44 degrees C, so sunshine should be no problem.

The first was was a tin trunk with a sheet of plastic and some shiny steel on the sides as reflectors. That heated water up to 80 degrees.

With one that looks like the 'heaven's flame' we had some success, The water heated till 95 degrees C, but that took 5 hours, and then the sun moved behind the house.

Then we tried 'the minimum', and put it on the roof, so no problem with the sun disappearing. But the water never got hotter than 75 degrees!

Of course we didn't have an oven bag so we put some ordinary plastic in the lid instead. It was not very clear plastic, would that be a problem? Shall we try glass?

Our aluminum foil is rather wrinkled, would that be a problem?

We couldn't find any information on the angle of the lid. That might be a reason why it failed as well.

We painted a pot black, but the lid on it was silver colored. Could that be a problem?

We would rather use a system with glass than using plastic bags, as we are trying to avoid waste.

I hope you have some ideas for us, though I realize that it is hard to advice from a distance!




Thank you for sharing your experiences and your request for guidance.

I think that our site visitors might be able to help you with some information and I will do the same shortly.


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Jun 18, 2012
some help.
by: Ravindra Pardeshi

Irene, As you have stated you have to use some kind of green house cover. If you do not want to use plastic, you can use two large glass bowls. Since I am from India I know that they are easily available. Even polycarbonate bowls are also available. Another option is to use round clear plastic storage containers.

You can try Jim's all season cooker design which is very good.

Another is our Parvati solar cooker, Fun panel cooker and Sharon's Copenhagen solar cooker.

If you are using box cooker proper thermal sealing is must.

Jun 14, 2012
Some tips
by: Jim La Joie

Good questions and responses. Here is what I can share:
The foil reflector should be smooth. A few minor wrinkles are ok but it should be smooth to the surface it sticks to.
You should use some sort of glazing. Clear glass, or glass bowls, containing your dark cooking pot.
The reflector angle should be at 60 degrees to the plane of your oven door, if you use one, or the plane of the oven door if there were one.
The reflectors should be the same size at the oven face. Larger gains nothing if you use the 60 degree angle. Smaller is also a waste. The GSO is a great example.
If you set your reflectors at 60 degrees and they are the same size as your oven face, all of their reflected light will enter the oven. Lastly - be sure to point your oven at the sun and to refocus about once an hour.
Good luck with your project

Jun 14, 2012
What are you using for insulation?
by: Joyce Lee

I have seen several home made box style cookers,and built one like your Heavens Flame model and have come to the conclusion that what you use for insulation makes all the difference. What are you insulating with? I think several layers of cardboard with a thin material I found that is used to line hot pads and oven gloves is much more effective than a blanket.
Also in my experience, wrinkled foil won't reflect as well as smooth foil.
Don't give up! Once you get all the right materials and angles figured out you will be surprised how much your oven will heat!

Jun 14, 2012
Improving solar cooker
by: N K Srinivasan

I have made several simple solar cookers and used them to cook potatoes ,bake them and rice also routinely in Bangalore India...
If you are using a box cooker, a good back reflector with the tilt required is essential to reach high temperatures.
The box cooker must have good insulation below the tray and air leaks must be prevented from the sides.
I have used simple polythene sheets--so glass glazing is not required.
Aluminum foil will work as such.
Increase the size of box cooker or cardboard box if you are using one. You must turn the cooker to face the sun every 30 minutes or so.
You may measure the air temperature inside the cooker .But the temperature of cooking pot is different.
Use a black metal sheet below the cooking pots.That would absorb lot of heat and keep the temperature steady.
Keep trying!

Jun 14, 2012
more on 'need help'
by: Irene

Hello Bruce,
yesterday we managed to cook rice (for 3 people) in our attempt at the 'Heaven's Flame.' Today we failed to cook potatoes. we put them in 9:30 in the morning, in a black pot with a black lid, and stuffed the remaining space of the box with a blanket. But when we looked at 13:00 the potatoes were discolored and not at all cooked. The temperature inside the box was about 125 degrees C.
I would think that since it is 45 degrees outside, we should be able to reach higher temperatures than this.

with the 'minimum' we are having no success at all. we have a jar of water sitting in it, about a liter size jar, half filled with water, a hole in the lid, and a food thermometer sticking out of it. The water never gets hotter than 75 C. We have trouble knowing what the angle of the lid should be in relation to the sun. (and trouble keeping it there).


Jun 14, 2012
More Information
by: Bruce

It is hard to know how well your solar cookers performed without more information. For example, about how much water were you trying to heat?

Also, what type of cooking do you plan to do? And, for how many people?

Best of luck,

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