Spiral Fresnel Reflector (a simple solar concentrator)

I happened across this clever trick for making a solar concentrator in an 1981 Popular Science magazine.

Masonite and aluminum foil – that’s all Rick Steenblik, a research engineer at the Georgia Institute of Technology, needs to bring the sun into focus. Conventional point-focusing solar concentrators are paraboloid dish types. Made of metal, these complex-shape reflectors must be prcisely molded and machines – therefore they’re expensive.

Steenblik’s simple design begins with a computer program that prints a spiral pattern. This pattern is transferred onto a flat material already covered with a reflective medium, then cut out on a band saw. By lining up mounting points (also printed by the program) along a straight frame member, the proper twist is given to each segment of the spiral to concentrate sunlight at the selected focal point. The computer program can vary the focal length of the spiral or even alter the design to focus light behind the reflector.

Nine Georgia Tech Spiral Concentrators have been built thus far. For such simple applications as solar cookers Steenblik has used as materials aluminum foil and hardboard. Other models have been made with sheet aluminum. Steenblik believes his reflector can replace parabolic concentrators in some present applications at much lower cost.

For $7 Steenblik will send instructions and a pattern of his concentrator suitable for a solar cooker. Write to: Richard Steenblik, Suntwist, Box 342, Stone Mountain, Ga 30086 – Paul Bolon.

Here’s an example by Larry Breed, used at Burning Man (link here):

The Steenblik’s patent #4350412 is here.

There’s a very short comment about it on hackaday here.

Tobin Fricke has posted a PostScript program for computing the spiral.

There’s also a 7 page (would be 4 page but every post is doubled up) forum discussion on www.HomeBuyersTalk.com here.

I might give this one a try sometime.