how or where should I place additional reflective panels for pizza oven?

by Holly Wetz
(Tampa FL)

My daughter is doing a science project and she is going to make 2 solar ovens. I suggested doing the simple pizza box style oven and then perhaps same thing but add additional flaps and compare how her smores cook. on the 2nd oven where should I add the additional flaps and how to angle them. Thanks! Holly

__________________________________________

Greetings Holly,

Thank you for your inquiry about the pizza box solar ovens.
Due to a time constraint that I am under I am going to publish this and see if any of our site visitors would like to offer some of their expertise on solar cooker building that would be helpful to your, then I will follow up to see if I might add anything more.
I hope we are quick enough to answer your question.

Nathan
Admin.

Comments for how or where should I place additional reflective panels for pizza oven?

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Jan 16, 2012
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My Results
by: Brad

Last year, we took two turkey roaster granite ware pots and placed them within turkey-sized oven bags. The pot contained 13 lbs of water and the top of the pot was drilled to accommodate a small meat thermometer. We altered the construction of the panel cooker with various angles, removing various panels, and removing the bag. Comparisons were made, and when a final design was agreed upon, we conducted a capacity test on the final panel cooker design.

The area of the panel cooker’s footprint was 30 inches long by 23 inches wide = 690 square inches or 0.45 sq meters. A square meter on the surface of the Earth, on a clear day collects 1000W of solar energy, or 3412 BTU. Therefore 3412 * 0.45 = 1535 BTU/hr is theoretically perfect, with all of the sun's energy being absorbed directly into the water, and the water retaining all of that heat.

Note: Heat lost from bag, absorbed by pot, or solar energy not perfectly reflected into the pot, are factors that decrease efficiency.

Over the course of 3 hours, the 13 lbs of water increased 100F, or 1300 BTU. This gave us a 28% efficiency, because it could have theoretically absorbed 1545 BTU x 3 hrs = 4635 BTU.

1300 / 4635 = 28%.

Jan 15, 2012
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Mylar
by: Brad

Mylar is a brand name for aluminized polyester film, and something I haven't worked with yet, but I am now on the look out for discarded projection TV's, thanks to the previous comment. I considered working with Mylar over aluminum foil tape, until I read a piece in the November 2007 Solar Cooker Review:

SCI newsletter

Where a study was performed by Ohio State University students, to determine the best materials to use for CooKit panel cooker designs, and they found, "...standard aluminum foil was determined to be the best all-around choice."

Jan 13, 2012
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where to place mirrors
by: Anonymous

Adding a mirror to your oven will increase its heating and add versatility to your cooking. All you need to do is put the mirror at an angle (depending on the time of day and year) that increases the amount of light going into your oven. Id recommend taking the Mylar optical grade mirror out of an old big screen tv ...it wont break and its free. I get them every time i take garbage to our local garbage facility. Id also grab a Fresnel lens out of one too...they are great toys for solar heat collection.

Jan 13, 2012
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Solar Math
by: Brad

I found a post I made a while ago on this site, throwing out some of the solar oven math I use regularly:

Solar Oven Mathematics

Like this:

A BTU is the energy required to raise a pound of water, one degree Fahrenheit. A square meter above the Earth's atmosphere receives 1350W of solar energy, which is 4606 BTU (since 1,000 W = 3412 BTU). A square meter on the surface of the Earth, on a clear day collects 1000W of solar energy, or 3412 BTU. A square foot on the surface of the Earth will collect 3412 x 0.093 (rounded conversion factor for sq.feet to sq.meters) = 317 BTU.

This should get you guys into the top three, at least...

Jan 13, 2012
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Thank you for the info
by: Anonymous

Dear Brad: Thank you very much for your help with our Science project!
Holly

Jan 13, 2012
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Angles
by: Brad

For a science project, I would emphasis the amount of energy captured by the two designs, not the fact that a pizza is being cooked. Since pizzas vary in mass and dimension, for a science experiment, you do not want to introduce more than one tested variable. Using a pot of water is ideal because the weight and temperature can be matched in the two cookers, which guarantees that there is no other variable, and that differences in water temperature are related directly to the design of the two solar cookers. Since water captures heat well, and stores it with an easy to read temperature (using household objects on hand, like a meat thermometer), water is the way to go.

Using this website:

Sun Design

You can enter your latitude and the day of the test, to find out what the altitude angles will be throughout that day.

The altitude angle (sometimes referred to as the "solar elevation angle") describes how high the sun appears in the sky. The angle is measured between an imaginary line between the observer and the sun and the horizontal plane the observer is standing on. The altitude angle is negative when the sun drops below the horizon.

In my own testing, I have found that 30-35 degrees greater than the angle of the sun, is the prime angle for the top panel.

The side panels are different, in that the sun is not changing it's orientation to the side panels, like it does the top panel, so a standard angle of 65-80 degrees should be fine. You should be able to move the side panels and see the reflection into your cooking area, and feel confident that you can "fix" that angle.

The lower panel angle will change with sun position. I have found that following the thumb-rule used by users of the CooKit panel cooker, is preferred. You will find it here:

Cookit

"Keep your shadow visible but just in front of your cooker’s front section." Page 15 of PDF link above. This link also contains instructions on how to make the very popular CooKit.

The solar catch area formed by your two panel cooker may also be measured and compared. With a little searching, you will find the amount of sun energy in BTU's or Watts that a known area can absorb at 100% efficiency. You may have one panel cooker with 5% less catch area, but with equal performance measured by water temperature increase, showing you that the panel angle efficiency of the smaller footprint is actually superior, since less sun energy is reflected out of the cooking area, vice focused inward.

That should give you a solid start. Good luck.

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