STRICTLY PARABOLIC

Enlarge Image Image Gallery

Article Tools

Image Gallery

Print

E-mail

Comments

RSS

(THE HOTTEST CURVE KNOWN)

Solar energy is in! All the way in ... as a quick glance at almost any magazine, newspaper, or evening television news. cast will demonstrate. Everyone, it seems, is now interested in substituting some of the boundless energy from the sun for our increasingly expensive fossil fuels.

And that's relatively easy to do for a few fortunate folks . . . the ones with enough bucks in their bank account to just go out and buy the "latest and greatest" solar energy hardware on the market.

Most of us, however, have more ambition than money. In short, if we expect to harness the sun for our own personal use any time soon, we're probably going to have to go down into the basement or out into the workshop and build our own hardware. Which is where the rub all too frequently comes in: Far too many would-be constructors of do-it-yourself solar equipment are ready, willing, and able to fabricate the gear they want ... but they simply don't know where or how to begin .. . especially when it comes to one of the most efficient solar collection devices of all, the parabolic curve.

Ah, but that's exactly where I can be of help. I've been calculating, constructing, and working with parabolic curves for years and I've come to the conclusion that it's no wonder parabolics baffle so many would-be solar energy experimenters: The amount of downright false and misleading information about them currently in circulation is appalling.

Suppose, for instance, that you desire to create a parabolic mirror, or half-mirror, or extended half-curve of rectangular shape (see Fig. 1). You know you need to calculate and draw the supports and surface for the mirror you want . . . but that's about all you know. So you begin to look around and-hot dog!-you discover an article or an advertisement or some other piece of literature which glibly leads you to believe that almost any old curve will do the job.

Do not be fooled by such misinformation! A parabolic curve is the only curve that will collect the sun's rays over a broad surface and then-under conditions of ideal efficiency-direct all those rays to a single given spot or surface. No other curve or shape will do this. For maximum efficiency and maximum focus, your curve must be parabolic.

As an example of the misstatements I refer to, 1 direct your attention to George Salmon's works on conics, higher plane curves, analytic geometry, and higher algebra . . . which are considered to be standard authorities in the field by many knowledgeable experts. Yet, on page 199 of Salmon's Treatise on Conic Sections (6th Edition, Dover), Article 209 states that " . . . If we suppose one vertex and focus of an ellipse given, while its axis major increases without limit, the curve will ultimately become a parabola." THIS IS NOT TRUE! 1 also refer you to Article 214 on page 202 of the same book: " . . . and we shall show, in the present section, that a parabola may in every respect be considered as an ellipse, having one of its foci at this distance and the other at infinity." Again, NOT TRUE!

RSS | Comments | E-mail | Print