Mirrored Parabola part 2

back to part 1

I needed a way to connect the mirrors to a frame, so I used hot glue to attach wooden brackets to the backs. 

I could have calculated the angle needed to direct the sunlight to one spot, but I figured it would be easier to aim them by hand.


I used a pine 2x4 for a base and attached thin 1x2 posts every 14 inches or so. At the top, I put one screw into the mirror bracket. This single screw allowed me to pivot the mirror's angle. I aimed it, and used the other screw to set the angle firmly.

The sun is so far away that the rays of light come in parallel to one another. At noon on July 4th, the rays were striking Sacramento at an 18 angle.
The summer sunlight would be concentrated onto a can of water hung from the top of a post.

I painted it black, to absorb as much heat as possible.

The first strip held seven mirrors. Each bounced the sunlight to the can, which was heating up very nicely. In the hour it took to build this mirror stand, the water had heated up considerably. I didn't have a thermometer, but it was so hot that little bubbles were forming on the inside of the can.

I started building a second strip of mirrors, but these were a lot harder to aim.

As I worked, the sun moved slowly across the sky, causing my static mirrors to become less and less well aimed.

In addition to the movement of the sun, the second strip of mirrors wasn't hitting the target.

It was very tough to slope them towards the first mirrors. My mirror-on-a-stick construction technique wasn't suitable for more a single strip.

This curvy bowtie shape is what I should have been building.

The sun was already moving down the sky, so I hauled the twin strips of mirrors out into the front, where the block party was scheduled to be.

I tried to place the target can where the most sunlight was hitting. Out in the open, it became very difficult to see where the concentrated light was aimed.

A large projector screen would have been nice to have for this part of the project.

Elm tree shadows crept across the street and spelled doom for my project. The water remained hot, but never came to a proper boil.

I made one more strip of mirrors with a slightly different technique. I built a wooden frame, then suspended the mirrors using long wires along the edges. The hanging wire provided a smooth curve for the mirrors, and was easier to build than the multi-post arrangement.

Chris and Melanie gave it a critical look.

With my solar heating experiment finished for the day, I arranged my three mirror strips around the can-holding post.

Instead of a water-filled coffee can, I taped a road flare to the top (the white X). This configuration would reflect the bright red emergency road flare into the sky.

Night fell and block party started.

People started setting up lawn chairs, barbequing and lighting fireworks. Music filled the street, and crowds of people began to form.

Many nice folks came by and asked about the crazy mirror structure. Mike joked that I had build a huge device to focus the attention on myself.

The giant parabolic mirror didn't really come together the way I expected. It would have been great to see a pot of water boiling away in the middle of the street.

I'll settle for the lesson in solar engineering...and the excellent tan.

part 1

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October 16th, 2003.  

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