Introduction: Pie Tin Solar Reflector

Picture of Pie Tin Solar Reflector

A pie tin, a sheet of aluminum foil, and a little glue to make a spherical reflector. I call it a Reflexor.

I first made one of these around 1980 and I am unable to recall the circumstance of my inspiration. It's quite easy to make and the results can be quite good depending on the care you put into it and the materials used.

This demo uses household aluminum foil which has the drawback of being unpolished resulting in some difusion of the sunlight.

I once made one with the blank side of an aluminized mylar balloon and it proved to be a very good reflctor. I remember that I was able to reflect a near perfect inverted image from the window onto the wall beside the window.

Caution is advised! Focused sunlight is VERY intense, and this is so lighweight, you can flash yourself while handling.

Step 1: Puncture the Pie Tin.

Picture of Puncture the Pie Tin.

I had originally made this many years ago with a home baking cake tin, but what I had on hand, and sufficient for this demonstration, was a Marie Callender's pie tin. Adding a small hole with a straight pin was not difficult. I hammered it in with a spoon.

Step 2: Lay the Foil Out.

Picture of Lay the Foil Out.

If you want to be perfectionist, you can stretch the foil out a bit with tape to make it slightly taut.
For this demonstration, I just wanted to get it done quick for photos.
I did take care to tear the foil carefully to avoid wrinkles.

Step 3: The Adhesive.

Picture of The Adhesive.

I used E6000 for this, but later found that it didn't cure well between the tin and the foil.
It worked well enough, but I recommend epoxy, or some other adhesive that doesn't require evaporative curing.
Put it all the way around. If you use a 5 minute epoxy, you want to get it all on in a couple of minutes.
Alternatively, you could put invert the tin on the foil first, then epoxy the seam.

Step 4: Invert the Tin.

Picture of Invert the Tin.

Just place the tin on the foil. If you use the alternative suggestion from the last step, add epoxy now.

Step 5: Press and Cure.

Picture of Press and Cure.

Weight the tin against the foil while the adhesive cures for a good, smooth seal.

Step 6: Trim the Foil.

Picture of Trim the Foil.

It looks much better this way, and the excess foil won't get in the way.

Step 7: Prepare the Valve/seal.

Picture of Prepare the Valve/seal.

The first time I did this, i used black plastic electricians tape and use my mouth to suck air out and close the seal.
Place a piece of tape over the pin hole so the hole is not sealed shut, because next...

Step 8: Vacuum Pump

Picture of Vacuum Pump

This is a wine bottle sealer which uses a silicon rubber cork replacement and a hand vacuum pump to pull air out of the wine bottle that you didn't finish drinking.

Step 9: Evacuate and Seal.

Picture of Evacuate and Seal.

The cork is placed in the pump then placed over the tape, being careful not to seal the tape, and pull a few strokes on the pump to remove some air from the tin. The MC pie tine I used actually began to collapse a bit. When done pumping, slide the cork to the side to seal the tape around the hole.

Step 10: Take a Look.

Picture of Take a Look.

You should see a distinct curvature in the foil. Notice the grain on the foil.
If you can get polished foil, you'll get much better results.
I once used the plain side of an aluminized mylar balloon, it worked beautifully and could actually cast images from the outside onto a wall by a window. Mylar leaks air more than aluminum.

Step 11: Check the Focus.

Picture of Check the Focus.

Be Careful. The focal area is intensely bright and hot.
I did this several years back and obtained such a tight focus that a piece of wood I held in the focal point burst into flame in about 15 seconds.

That's it.

I have a snow disc hanging out in the garage.
When I get the time.

Comments

morsed2 (author)2016-04-27

I want to say its a great instructable. But everyone else has already said it. How about it's better that great?

One quick question, do you know if the concave form is a parabola?

I have added it to my fav's and collections and may try to make it in a couple of days.

Thanks for taking the time to document this instructable.

Steve

Sam Grove (author)morsed22016-04-27

It's a spherical section as the pressure difference is equal over the surface.

piaferre (author)2010-12-10

this is GREAT!

renuka (author)2010-05-05

this info needs to be more helpfull its lame lame lame

godofal (author)2010-03-13

how about using this with a regular 12 volt solar panel?
would that couse any damage to the panel?

Sam Grove (author)godofal2010-03-13

If you mount it so the focal point does not fall on the solar panel, why not?
You'd want the concentrated sunlight to cover the entire solar panel.

Kiteman (author)2007-05-19

Nice. I wonder if it would work with tougher plastic film, sprayed silver? That would last longer before you accidentally crush it.

Sam Grove (author)Kiteman2007-05-19

Aluminized mylar works very well. I discussed this in one of the steps. I have some very wide aluminized mylar out in my garage which I want to install on a snow disc. I wanted to get this published before I attended the Maker Fair in San Mateo county today

macrumpton (author)Sam Grove2009-08-10

http://www.Mirrorsheeting.com has mirrored vinyl and mylar up to 52" wide for a reasonable price.

regularbasscase (author)2007-07-26

I'm thinking emergency blanket and a childs wading pool.

You're thinking of the aluminized mylar sheet that can be used as survival gear. Yes, as long as it is free of pinholes or cracks. The child's wading pool is another matter. You will be able to evacuate some air, but it may be susceptable to buckling if you try to take too much out. Snow discs are much sturdier.

macrumpton (author)Sam Grove2009-08-10

Snow disks! Perfect! Now I wonder who carries them in Miami?

I think unless it is a very sturdy wading pool it would collapse or at least distort unless you reinforced it before removing the air. Perhaps you could stack two or three of the pools together to make them stiffer.

macrumpton (author)2009-06-06

Very cool! A couple of thoughts: if you were to heat the pan/reflector after you punched the hole, and then clogged the hole before the pan cooled the air cooling/contacting inside should create enough vacuum to create the parabola. No pump necessary! if you made a larger hole so you could pour some plaster inside before you suck the air out, then when the plaster cured it would keep the shape of the parabola without the vacuum. To make a larger one you could stack a couple of bike wheel rims with the spokes removed. You would have to plug the spoke holes. A shopvac might do the air removal/

ehudwill (author)2008-01-02

I tried making a reflector out of an old satellite dish. I lined it with aluminum tape, but it doesn't reflect the light to a single point but in a line. Do you think the pie tin would work with aluminum tape?

toogood (author)2007-06-26

would the bottom of a coke can work if it polised?

Sam Grove (author)toogood2007-06-26

Maybe, the solar flux area is rather limited though. The key point with the pie tin is you get a decent area and really light weight making it easy to handle or mount.

toogood (author)Sam Grove2007-07-02

cool i'll try it

meddler (author)2007-05-19

Hey Sam, i have made a few solar ovens (the panel reflector type) and i bought an emergency survival blanket and cut up the material then glued it to cardboard. It worked great, i wonder if it would work here? It does rip fairly easy though.

Sam Grove (author)meddler2007-05-19

Aluminum foil is very vulnerable. I used the regular thin stuff for this demo. Good thing, I bet getting a decent curvature on the heavy duty foil would have collapsed this cheap pie tin. I think mylar film might be more durable, as it is more flexible.

lemonie (author)2007-05-19

This looks good, but I don't see the wood busting into flames. Do you know why your previous build worked better? L

Sam Grove (author)lemonie2007-05-19

It was an early sun, I was holding the reflexor (my name for it) in one hand and camera in the other. I wasn't using a 2 x 4 then either, I did detect a whiff of smoke, though. Tthe pie tin is pretty flimsy and probably distorted a bit and the texture of the foil disperses the focal point. Also, I was tilting the tin a fair amount so the board wouldn't block too much sun. I just wanted to get the picture.

lemonie (author)Sam Grove2007-05-19

Under the circumstances you described, a whiff of smoke is pretty good going. I've had fun with a Fresnel lens, but I like the look of this much more. L

HOMEPIE64 (author)2007-05-19

dude i love this

Sam Grove (author)HOMEPIE642007-05-19

Thanks. This demo was so easy to make, I did a rebuild this morning which took about 20 minutes.

About This Instructable

16,448views

39favorites

License:

More by Sam Grove:Articulating irrigation sprayers.Pie Tin Solar Reflector
Add instructable to: