Make: Technology on Your Time Volume 21

The Solar Catenary Reflector

Build 21st-century renewable technology using 17th-century mathematics.

By Tho X. Bui

You can divide most solar power research into two camps: increasing efficiency or reducing cost. A few years ago, when I decided to do some amateur solar research of my own, I chose the “cheap” route.

I had the idea to use mirrors with a catenary curve to concentrate sunlight. The catenary, described by y = cosh x, is the curve that ropes or other flexible materials naturally fall into between two supports. This curve was mistaken for the parabola (y = x²) until the difference was cleared up by 17th-century mathematicians.

Parabolas are often used for concentrators since they focus parallel rays into one point. I reasoned that if ...