Northrup’s break-through technology was a collector that used a  long curved acrylic fresnel lens to concentrate or focus sunlight at a theoretical ratio of approximately 12 to 1 onto a linear flat copper tube, coated with a variant of Dr. Tabor's “black chrome” absorptive surface.
The array, approximately 10’ long, tracked the movement of the sun during the day (east to west),  automatically, with the elevation generally fixed (at approximately the same angle from horizontal as the latitude of the installation).
The tracking device was ingenious – it consisted of two photoelectric cells at the base of a tube with a baffle between them.
 Current from the cells went to a control board that controlled the tracking motor.
When the cell output was equalized, the baffle and the tube would be pointing at the sun.
This was sufficient to enable the array to track the sun’s azimuth and generate considerable heat, as reported in tests published in the ASHRAE Journal, which noted that ". . .
the array of collectors . .
.follow the sun from just after sunrise to just before sunset and often results in the collection of twice as many usable BTUs of energy at a higher temperature than provided by high quality flat plate collectors.".

These arrays proved popular – and were used to drive absorption refrigeration equipment on large commercial installations at Trinity University in San Antonio, Texas, at Frenchman’s Reef Hotel in St Thomas, USVI, residences,  and were sold to prominent individuals, including movie actor and entrepreneur Steve McQueen, actor Stuart Whitman and environmentalist Robert Redford.

The early success of these concentrating collectors was due in part to grants from the Department of Energy and its predecessor the Energy Research and Development Administration.
They created a good deal of publicity for Northrup, Inc., including the cover of Popular Science Magazine and an article in Fortune Magazine that noted, "By squeezing (sic) sunshine optically, Lynn Northrup's unique new rooftop solar collector produces higher temperatures than are obtainable from most solar heating systems now on the market".
 Technically, these concentrating collectors were among the first commercially successful “east-west” tracking solar collectors.
 The fundamentals of their systems are still in use in daily azimuth and elevation tracking parabolic collectors.
Most linear concentrating collectors are, as of this writing in 2010, of the less costly and less complicated seasonal tracking variety in the form of parabolic troughs.
Northrup’s break-through technology was a collector that used a  long curved acrylic fresnel lens to concentrate or focus sunlight at a theoretical ratio of approximately 12 to 1 onto a linear flat copper tube, coated with a variant of Dr. Tabor's “black chrome” absorptive surface. The array, approximately 10’ long, tracked the movement of the sun during the day (east to west),  automatically, with the elevation generally fixed (at approximately the same angle from horizontal as the latitude of the installation). The tracking device was ingenious – it consisted of two photoelectric cells at the base of a tube with a baffle between them.  Current from the cells went to a control board that controlled the tracking motor. When the cell output was equalized, the baffle and the tube would be pointing at the sun. This was sufficient to enable the array to track the sun’s azimuth and generate considerable heat, as reported in tests published in the ASHRAE Journal, which noted that ". . . the array of collectors . . .follow the sun from just after sunrise to just before sunset and often results in the collection of twice as many usable BTUs of energy at a higher temperature than provided by high quality flat plate collectors.".
These arrays proved popular – and were used to drive absorption refrigeration equipment on large commercial installations at Trinity University in San Antonio, Texas, at Frenchman’s Reef Hotel in St Thomas, USVI, residences,  and were sold to prominent individuals, including movie actor and entrepreneur Steve McQueen, actor Stuart Whitman and environmentalist Robert Redford.
The early success of these concentrating collectors was due in part to grants from the Department of Energy and its predecessor the Energy Research and Development Administration. They created a good deal of publicity for Northrup, Inc., including the cover of Popular Science Magazine and an article in Fortune Magazine that noted, "By squeezing (sic) sunshine optically, Lynn Northrup's unique new rooftop solar collector produces higher temperatures than are obtainable from most solar heating systems now on the market".  Technically, these concentrating collectors were among the first commercially successful “east-west” tracking solar collectors.  The fundamentals of their systems are still in use in daily azimuth and elevation tracking parabolic collectors. Most linear concentrating collectors are, as of this writing in 2010, of the less costly and less complicated seasonal tracking variety in the form of parabolic troughs.
Leonard L. Northrup Jr.