# Let's go green! Build a Solar Powered Parabolic Cooker!

6 Steps
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.
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## 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.
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Blofish says: Sep 13, 2010. 4:56 AM
(removed by author or community request)
jblover in reply to BlofishApr 25, 2012. 8:02 PM
y r u jeulos srry me dont know how ton spell
musicismylifeXD in reply to jbloverOct 4, 2012. 9:42 AM
No, you do not.
Blofish says: Sep 13, 2010. 4:53 AM
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 ?
Elac. in reply to BlofishSep 28, 2012. 4:15 AM
@Blofish - Sides might not reflect much light BUT they will reflect heat. And keep a barrier from outside temps.

Awesome project. Thanks for sharing. :)
justin1h6 says: Jan 16, 2009. 6:08 AM
I am making it my project for the science fair
jblover in reply to justin1h6Apr 25, 2012. 7:58 PM
me 2 but got a da** F
mclovin808 says: Dec 1, 2009. 9:24 AM
how long did it take you to cook the hotdog
jblover in reply to mclovin808Apr 23, 2012. 5:52 PM
u should ry or my guess 30 min
Brennn10 says: Jul 30, 2007. 4:37 PM
MMMMMMMMMMM
jblover in reply to Brennn10Apr 20, 2012. 12:38 PM
that does not look good

(>>>)
_Scratch_ says: Jan 8, 2011. 7:56 PM
subscribed.
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
Earths_hope says: Dec 2, 2010. 3:19 AM
Exellent. Subscription time.
knektek says: Jun 14, 2009. 1:14 PM
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).
dasgemuse in reply to knektekOct 26, 2009. 6:19 PM
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
merseyless in reply to dasgemuseSep 30, 2010. 11:49 PM
a solar panel acts as a power source. not as a battery charger
beehard44 in reply to merseylessNov 1, 2010. 12:50 AM
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.
nutsandbolts_64 in reply to beehard44Nov 2, 2010. 3:12 AM
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.
zoltzerino says: Sep 14, 2010. 9:18 AM
Can you provide an equation for the parabola. out of curiosity, would it come in the form Y = Xsqrd + a?
Blofish says: Sep 13, 2010. 4:47 AM
Thanks for your work and insight!
WerdnaN says: Nov 6, 2009. 8:50 AM
What would I need to do to make it on a larger scale?
quantumkittty in reply to WerdnaNSep 2, 2010. 7:23 PM
MASS PRODUCTION >:( jk XD you would only need more of it, and proper calculation.
quantumkittty says: Sep 2, 2010. 7:22 PM
HELL YEAH FOR QUADRATICS AND CONICS!!
matt392 says: Mar 8, 2010. 9:00 PM
Great Instructable - very innovative use of simple materials.
QwertyuioLP says: Jul 27, 2009. 4:25 AM
Could you modify this to follow the sun? It is possilble...
cowscankill in reply to QwertyuioLPSep 30, 2009. 2:40 PM
If you attached it to a clock's motor somehow :D
Weissensteinburg (author) says: Jul 18, 2007. 1:21 PM
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!
CameronSS in reply to WeissensteinburgJul 18, 2007. 8:34 PM
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.
extrordinary1 in reply to CameronSSJun 3, 2009. 11:05 AM
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.
Weissensteinburg (author) in reply to extrordinary1Jun 3, 2009. 11:06 AM
Parabolas are concave.
extrordinary1 in reply to WeissensteinburgJun 3, 2009. 1:22 PM
There are two types of parabola's I am aware of, concave, and compound which is deeper, and tracks the sun up to 3-4 hours without movement. Compound's are typically used in flashlights. Some modern searchlights now use compound parabola's where the older ones used concave dishes with long focal lengths. That is why I was asking about the parablola or concave shape.
Parabola's are usually deeper than plain concave reflectors, like satelite dishes are just concave parabola's, with longer focal lengths. There is a difference. I call satelite dishes, old search lights, concave shapes, and parabola's have two different shapes, deeper than concave dish reflectors with very long focal lengths, where the parablola has a short focal length.

I'm not disputing it is concave or not, I hope you can see the point I am trying to convey in my question. My satelite dish search light and older search lights that used dish reflectors, were concaves with very long focal lengths compared to true parabola's that have very short focal lengths like flashlights, headlights, modern search lights... I'm writing you right now using a parabola dish with a short focal length concentrating my wifi signal to my antenna just an inch from the center of the reflector, I made from a link on here at Instructables. Thus keeping my focal point very short. See what I am trying to say? Pretty soon I will add a satelite dish reflecting my signal to the parabola to gain even more signal strength to continue running the wifi at full potential at 48 Mbps speeds. Right now I am only getting enough signal to hit 18 Mbps speeds. I don't dispute parabola's are concave, simply asking what kind of parabola are you using in your search light?
Weissensteinburg (author) in reply to extrordinary1Jun 3, 2009. 2:38 PM
I see, I thought you were implying that if it's concave, it's not a parabola.
extrordinary1 in reply to extrordinary1Jun 3, 2009. 1:37 PM
BTW, I am 2 blocks from my wifi free source. Before I got the larger antenna and made the parabolic dish, I was only getting about an average of 43% signal strength, when weather conditions allowed it. Now I am getting 79% signal strength, and it is always on now, not tempermental to weather. A storm came through last night and I never lost signal. My cable modem has been taken out by lightning before, so I disconnect it and run wifi, especially when I want to use higher download and upload speeds compared to my cable at only 1.5 Mbps speed. At minimum, my speed tests have doubled compared to my cable. They have gone much faster too.
Weissensteinburg (author) in reply to CameronSSJul 19, 2007. 2:06 PM
I have made one..to make it easy, I'm attaching a parabola stencil to the ible, so you can just print it out, and cut.
CameronSS in reply to WeissensteinburgJul 19, 2007. 3:44 PM
Fancy!
Weissensteinburg (author) in reply to CameronSSJul 19, 2007. 5:27 PM
Ok, the instructable has been fixed. Let me know what you think.
CameronSS in reply to WeissensteinburgJul 19, 2007. 6:28 PM
Nice stencils! Does it cook better with a parabola?

Also, in Step 1, you link to this image. I attached a modified version that better illustrates the reflection. If you want to use it, feel free.
nagutron in reply to CameronSSDec 13, 2007. 11:36 AM
Nice. I just added a similar image to the Wikipedia entry on Parabolas. It actually looks like we worked off the same base SVG!

Here's my caption on that image: "Parabolic curve showing arbitrary line (L), focus (F), and vertex (V). L is an arbitrary line perpendicular to the axis of symmetry and opposite the focus of the parabola from the vertex (i.e. farther from V than from F.) The length of any line F - Pn - Qn is the same. This is similar to saying that a parabola is an ellipse, but with one focal point at infinity."
RiddleOfSphinx in reply to nagutronApr 2, 2008. 4:27 PM
I can just see "roughrider" 's head exploding now...lmao.
gaiatechnician in reply to CameronSSAug 26, 2007. 6:36 PM
You do not need any math to construct a parabola! If you have a vertical post going through point f and a horisontal swing arm attached on top of the post reaching out to point P3 and a slidable vertical arm coming down from Q3, all you do is attach a piece of string from f to p3! (through a hole3 in the bottom of vertical slider q3) . Keep the string taut and your slider pottom will touch every point on the parabola as you pull it in from Q3 towards the pole at the centre! Thats how I made my parabolic solar cooker. (Currently on utube). The problem with math is it is scary stuff. You can make a parabolic cooker (a big one) with no math at all! Do not be afraid!
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