The Hot-Line Solar Collector

Iowa entrepreneur invents a fixed-position, concentrating solar collector. Learn how it works and how to build your own. Including photos, diagrams and detailed instructions.

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    Hot-Line modules furnish most of the heat used by this Iowa firm.
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    Fig.1 Diagram of solar reflector construction.
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    Fig. 2 Diagram of the change in reflection direction as related to the sun elevation in degrees.
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    Close-up of modules mounted vertically on south wall of a house.

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  • 039-108-01-fig1
  • 039-108-01-fig2
  • 039-108-01-close-up

Like many backyard inventors, Dan Lightfoot of Sigourney, Iowa has been interested in alternate energy concepts for some time — about 22 years, as a matter of fact. Unlike most of his peers, however, Dan has managed to make a major breakthrough in his field — one which even has the "experts" shaking their heads in disbelief.

That breakthrough is the Hot-Line solar collector you see pictured in the Image Gallery. At first glance, the Hot-Line module looks just about like a conventional flat-plate collector. What makes Lightfoot's panel highly unconventional is that it [1] contains a specially curved reflector which acts to concentrate incoming sunlight on a wedge-shaped absorption tube, [2] operates with an efficiency far surpassing that of any "normal" flat-plate solar panel, and [3] actually "tracks" the sun through a 50 degree vertical arc — and through 150 degrees in the east/west plane — without moving!

Impossible? That's what a University of Iowa physics professor said when Dan Lightfoot first explained the design to him. Rest assured, though, the device does work, and rather well, at that.

So well, in fact, that Lightfoot (after selling exclusive manufacturing rights on his invention to the Iowa City-based NRG Corporation) has recently been able to quit his job with a mining firm and devote full time to energy research. Lightfoot now heads up an outfit called Aerco, which is short for Alternate Energy Resources Company.

Dan Lightfoot came upon the idea for the Hot-Line collector quite by accident a decade ago. It seems Dan had been observing a sheet of aluminum that was resting up against his garage wall and noticed how the sun's reflection from that curved sheet formed a bright spot on an adjoining wall. Moreover, he noticed that the bright spot stayed in roughly the same place throughout the day, despite the sun's constant movement.

This got Dan to thinking, and to experimenting. With the aid of a small sheet of aluminum, a few scraps of wood and a handful of bolts and clamps, Lightfoot found (by trial and error) that he could curve the metal in such a way that it would focus light in a line — a line that, furthermore, moved only a small distance in or out from the metal as the jury-rigged reflector was tilted through various angles to the sun.

Mark Michaels
12/24/2008 3:39:43 PM

Great idea! Where can I get these materials? I have a great idea of how to apply this. thanks.

Peter Cross
12/3/2008 9:24:03 PM

I have worked on a simpler very inexpensive design for a parabolic trough, and its production approach could be used for the reflector in this one. (I see even molding the Styrofoam as a production expense one should work around if possible--that much foam is not needed--and I am looking for a durable reflecting medium more along the line of metalized polyester--although it might want to be in strips installed with a narrow central adhesive bead lengthwise, to prevent thermal distortions--or stretched between small springs lengthwise.) Thus far I've developed models of simple molds for the basic structure of a parabolic trough, basically out of cardboard, Styrofoam and light drywall compound, and then bent / glued two skins of some kind of paper--manila folder stock, etc.--over this mold with a layer of the CORRUGATED style of paper honeycomb in between. This type of honeycomb will mold around a curve, whereas the diamond-shape or "Hex-cell" honeycomb will not. Once you have a good mold, the honeycomb material is cheap, one can use any quality of skin one wants, from very durable fiberglass (already in thin sheet or laid up within the process) on down, and anyone in a neighborhood / community can ante up for the honeycomb, and pick whatever quality skin they can afford and figure out a way to protect for as long as they want to protect it for, while jointly working on alternative reflective surfaces, pointing mechanisms, and so on. Some long, narrow format of photocells has to be found if you are into direct electricity, and you would want to heat water via a tubular heatsink running behind them. This approach to a collector trough can be done at any level of precision (pretty crude is good for photo electrics, otherwise you risk burning them up!), and can be scaled up quite simply to, potentially, some huge, lightweight- cement- skinned units that are rotated on a floating lid which sits on top of a large storage tank. In a dry area that&

11/19/2007 10:48:59 PM

Hmmm, someone comes up with a way to make solar energy more efficient, and they disappear... Its the government Mulder. Trust no one.



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