I have a confession to make. I wish I were better at math, so I could become a solar energy technician. It's true. Unfortunately I don't see any offers for brain transplants, so I shall have to make do with simpler things, like radiant heat and passive solar toys.
I found this fun science project for the purposes of experimentation, and I thought that I would share it with you. It's a pizza-box solar oven.
Basically the goal is in this experiment is to build a passive solar oven using a pizza box, black construction paper, plastic sheeting or wrap, and tin foil.
What I like about this experiment: It's cheap and nothing catches on fire. Follow me through the orange portal for further instructions.
A fellow home school mom turned me onto this experiment, and so I got online to see what I could find out about building cheap, simple, solar ovens. There are all sorts of makes and models to choose from online.
Because I have smallish kids, I chose this pizza box version, due to the ease of construction, and the cheap materials, though we are going to build other kinds of solar ovens as a follow up to this experiment, to see if we can improve on designs for more solar gain.
You can also watch this youtube video for instructions:
Major differences between the video and Stanford instructions:
We did not line the bottom of our box with foil. We did glue black construction paper to the inside of the bottom of the pizza box and let it dry over night. We used a heavier plastic sheet, 4 mil plastic to cover the window and sealed the sides with clear packing tape.
Our window was a bit smaller too.
We also placed two 1 1/2 inch thick rolls of news paper around the inside of the boxes outer edges, taped into place, as insulation.
The first time we tested the box, we used a meat thermometer. On a sunny, windless day, the peak temperature was about 220 degrees inside the box. However what we discovered is that the temperature fluctuated after peaking.
I believe that the hot air rising as it's heated inside the box, escapes periodically through the cardboard, especially through the areas with small holes, perforated for bending.
So then we brought the oven back inside and sealed those holes with clear packing tape and added flaps using extra sheets of that plastic, to lay over the areas that had gaps for large amounts of air to escape.
This only helped our temperature issues slightly.
In the end, we were only able to melt chocolate on some S'mores. Most store bought chocolates begin to melt somewhere around 77 degrees, so that's not saying much. We tried to increase the gain by putting the solar oven on a dark brown towel and wrapping the towel over the edges of the box, leaving the window exposed, and not much happened.
We were trying to melt the marshmallows as well. We were unable to get the inside of the box hot enough to accomplish that.
Since this experiment happened over a series of days, and the last two were cooler and windy, I suspect that atmospheric conditions helped stymy our attempts at higher temperatures inside the pizza box.
However, that being said, the kids had a blast with it. Our next couple of ovens will be wildly different. We have purchased emergency space blankets to glue inside of a thrift store umbrella, to see if we can get it hot enough in this structure to boil water. I have found similar concepts on youtube, however these are larger, some are prefabricated to be solar ovens, so there is some doubt that our version will be as efficient.
The stand this person is putting together is impressive, and I am unsure how to mimic that in our umbrellas. I do not believe that their handles will unscrew like that, further reading indicates this is a kit for sale on E-bay. My thoughts are with Oklahoma winds, I would definitely recommend some kind of anchor. Some people make a similar oven but with old satellite dishes.
This next video is by a guy who used a big umbrella in attempt to make a solar oven, he said it didn't work at all. My first observation was that the umbrella opened too wide. Other comments on his video echoed that sentiment.
Our umbrellas are smaller and they have a deeper bell shape [see example here]. However I am sure that is no guarantee that the experiment will work. The kids will enjoy though, playing with the glue and scissors regardless.
Our goal is to build an oven that will heat well enough to bake cookies. If we can do that, then we might be able to build an oven that will cook other foods like meats and vegetables.
The point of these exercises isn't necessarily to get it all right the first time. The purpose is to inspire the kids to think about how to improve or alter these designs to accomplish the goal of creating a working solar oven. This is about teaching them the creative process behind problem solving, using the Scientific Method.
There are a variety of designs to choose from, in addition to the pizza box and umbrella designs
The cool thing is that, as we progress through different models of these ovens, we will find a design that works well, we could cook conventional meals outside in the summer. Cooking in your oven in the summer in Oklahoma, even when we aren't in the midst of a hellishly hot drought, will heat your house up something awful.
So this will save you double. It can lower your energy usage because you are not turning on a gas or electric oven, and in the summer you will not be heating up your house with said oven inside, which means having to run the AC more, to compensate for that added heat indoors.
I am hoping we build some gear that works well enough to use with regular food, such as chicken or pot roast. My big concern with some of these, is that I prefer to use glass instead of plastic for cooking food, due to the chemicals outgassed by heated plastic, such as BPA.
Have you built a solar oven? How well did yours work?