# Let's Go Green! Build a Solar Powered Parabolic Cooker!

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## Introduction: Let's Go Green! Build a Solar Powered Parabolic Cooker!

Let's face it, energy is expensive. Gas, electricity, whatever. So why pay to cook your food? The challenge I gave myself, was to cook a hot dog, without spending any money at all. No electricity, no new materials, nothing. And, there are no negative side effects on the environment, resulting from my hot dog.

What I came up with was...the parabola. So by using the properties of parabolas, we're going to cook a hot dog. Essentially, we're using math to cook hot dogs :D

I believe I've just proven that I'm a nerd? Oh well, I'm in good company here.

## Step 1: How It Works

"A parabola can also be defined as locus of points in a plane which are equidistant from a given point (the focus) and a given line (the directrix)."

The way it applies to us, is that the light that hits the parabola, will reflect back to one intersection point. That intersection point is called the point of focus. By placing the hot dog in the point of focus, all of the sun's rays that hit anywhere in the cooker, will reflect onto the hot dog...thus cooking it.

By the way...the shape of the entire cooker is a parabolic trough.

## Step 2: What You'll Need

After rummaging around my house, this is what I used to build a cooker:

• Poster board
• Foam board
• Tin foil
• Plastic wrap (optional)
• two blocks (can be anything..shoes, wood..rolls of tape)
• Skewer
• Various cutting supplies
• Packing tape, and scotch tape.
• The attached stencil
• A nice sunny day.

## Step 3: Cut Some Shapes!

First, assemble the stencil. There are instructions in the zip file on doing this, but it's pretty self explanatory. Then, trace it on to the foam board twice. Cut those out.

Now you need to cut a rectangle from the poster board. The short side of a standard piece of poster board is just the right length to wrap around the parabola. It should be about a foot wide.

Next, wrap one side of each cut out piece with the shiny side of tin foil. Make sure not to wrinkle the tin foil. Some other suggestions for what to wrap with (provided by other members) are:

Plastic mirror
The material that chip bags are made of (use the inside, reflective side)

Draw a dot onto the foam board through the stencil where the point of focus is...then poke a hole through that dot.

## Step 4: A Bit of Assembly

Assemble the parts so it resembles a trough..with the foil on the inside. Tape along edges to keep everything together.

## Step 5: Alignment

The two blocks are for keeping the cooker at the right angle. You put one on either side of the curve, and adjust everything to be just right. What is just right? That's what we're about to find out.

Tape two squares of scrap foam board onto the cooker. Using something sharp, poke a hole through the first one, and about halfway into the other. (while they're stacked on top of each other) Tape the one with a hole all the way through it to the top, middle of the cooker, and the other to the bottom middle...they should be right above one another. Now, when you put the cooker out in the sun, there will be a shadow, with a dot on the ground. You just need to align the dot with the hole on the other square, and you will know that it's all good to cook!

Note: It's helpful to tape a small piece of board over the whole on this side. You need the hole for the skewer to rest on, but you don't want it to stick out and obstruct your alignment dot. Not necessary, but helpful.

## Step 6: Cooking

Woo, it's time to cook your hot dog! Stick the dog on the skewer, and put it through the holes in the cooker. I like to cover the top of it with plastic wrap, so no bugs bother it. Now, use the blocks to align the cooker, and leave it to cook. Every few minutes, go out and re align it (the sun does move). Once the hot dog is finished, take it out, and enjoy!

Yes, it does work, and no, it doesn't take an hour to cook. Sure, it takes a bit longer than a grill, but I would suggest that when you try it, after a few minutes, touch the hot dog. You'll see just how hot it gets...

WARNING: Wear sun glasses when you go to realign it, or you won't be able to see well for a minute or so once you go back inside. This thing gets bright

Side note - If you wanted to, you could make a parabolic trough frame out of knex, and then line the inside with something reflective.

Let me know if there are any problems.

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• ### Cold Challenge

This may sound silly, bit I have to ask. If the sides dont provide any reflection, what is the main purpose to covering them in reflective material ?

@Blofish - Sides might not reflect much light BUT they will reflect heat. And keep a barrier from outside temps.

Awesome project. Thanks for sharing. :)

u should ry or my guess 30 min

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I made this, and cooked a wiener, i also took a old meat thermometer and put it at the focus point of the oven, which i accidentally made sideways, so its like a big, curvy rectangle, and i got to 175 degrees Fahrenheit, when i cooked the wiener, it only got to 135 about unfortunately

yeah, but they use solar panels to power a battery charger to charge a battery and the end user (the machine or electronic gadget) gets the power from the batteries, not the solar panels.

I wonder what would happen if a battery powered a solar panel in the dark (with no diodes or anything to keep the flow in one direction). That would be the dumbest thing ever.

Great Instructable - very innovative use of simple materials.

What would I need to do to make it on a larger scale?

this idea is stupid but if you had dismantled a calculator and took the solar panel out of it and used that to make a circuit of the solar panel and something that provides heat, and then attatched that to the cooker, will it cook faster? (i think that the solar panel won't give out enough electricity to power the heat source).

the solar panels in a calculator dont put out anywhere near enought voltage to cook with or let alone put out any noticable heat. besides, the panel would have to be connected to a battery, then to the heat source. solar panels slowlycharge batteries, they dont usually directly power things

If you attached it to a clock's motor somehow :D

Thanks for pointing that out guys. I'll either amend this instructable to say so, or make it a real parabola. (or both). Of using other materials: As I said in the intro, a main goal of this was to only use stuff I had laying around. But I will add your ideas as suggestions for what you could use instead. Thanks again!

Have you already made a parabolic one? if not, two simple options: 1) use a yardstick to draw a graph on the sides and graph a parabola, or 2) shine a flashlight sideways and trace the beam. I love the power of the sun. We once had (possibly still do) two reflectors from searchlights. It you aimed it at the sun, a piece of paper instantly burst into flame at the focus. I also singed clean through an oven mitt with it.

What size were your reflectors and were they parabola's or concave? I had an 8 ft. carbon arc search light I built with an 8 ft. satelite dish I covered with mylar. It was 9 sections bolted together, which made it easy to disassemble it and cover it with spray on glue and add the mylar reflector to it, then reassemble it. It was pretty intense light. I first used a 5 kW generator to power it up. Later I found a bigger generator at 50 kW. Sold it to some advertisement agency later on.