Leonard L. Northrup Jr.

Leonard "Lynn" L. Northrup Jr. (March 18, 1918 – March 24, 2016) was an American engineer who was a pioneer of the commercialization of solar thermal energy.

Influenced by the work of John Yellott,

Maria Telkes, and Harry Tabor, Northrup's company designed, patented, developed and manufactured some of the first commercial solar water heaters, solar concentrators, solar-powered air conditioning systems, solar power towers and photovoltaic thermal hybrid systems in the United States.

The company he founded became part of ARCO Solar, which in turn became BP Solar, which became the largest solar energy company in the world.

Northrup was a prolific inventor with 14 US patents.

Lynn Northrup Jr., a fourth generation Texan, was the son of L. L. Northrup Sr., an inventor in his own right, and Dolly McKaskle Northrup, a retail entrepreneur, both members of pioneer Texas families.

He was educated at Woodrow Wilson High School in Dallas, Texas, and received a BA from Southern Methodist University, a MS from the University of Denver, and a Master of Business Administration from Harvard Business School.

Northrup served as a captain the United States Army Corps of Engineers during and shortly after World War II.

After the War, Northrup went to work for Storm Vulcan, a Dallas company, where he invented a machine to clean aircraft engines.

He also embarked on a venture to fit cars with air conditioning equipment, putting the machinery in the trunk and piping the cooled air through tubes in the headliner.

This caught the interest of engineers from General Motors, who copied the system in Cadillacs in the late 1940s.

In the late 1960s, Northrup bought a controlling interest in Donmark Corporation, a manufacturer of residential air conditioning and heating equipment from Curtis Mathes, his lifelong friend.

Northrup promoted the use of “all electric” central heating and cooling equipment, building a manufacturing facility in Dallas and later in Hutchins, Texas and selling primarily to apartment developers.

In designing these systems, Northrup focused on the total installed cost of the unit, including the framing and plumbing costs.

During the mid-1970s, Northrup became interested in boosting the efficiency of air conditioning systems, and began looking at novel approaches, including water-source geothermal heat pumps, and the innovative use of scroll compressors in split system central air conditioning systems to achieve a higher efficiency rating, which have since become the standard compressor for high-efficiency residential air conditioning equipment.

In the early 1970s, before the Arab Oil Embargo and the spike in oil prices, Northrup became interested in the commercialization of solar thermal systems, particularly for heating potable water and swimming pools.

Such systems had already been commercialized in other countries where climatic conditions were favorable, energy costs were high, and there was a tradition of scientific innovation notably solar power in Israel.

Work in the United States had been limited to academia and a few companies in Arizona, Texas, and California.

Northrup began experimenting with solar collectors to heat air, using finned heat exchangers, and engaged solar pioneer Professor John Yellott as a consultant on the absorptivity and emissivity or various surfaces and configurations, and on the transparency of various glasses and glazing material that exhibit the "greenhouse effect" - transparent to incoming solar radiation, but opaque to the re-radiation of infrared from the heated surface - hence a thermal trap or collector that exhibits the "greenhouse effect".

Additionally, he hired Maria Telkes, an expert on phase change materials, particularly molten salts, as a way to store thermal energy, and consulted with Israeli solar thermal pioneer Harry Tabor on surface coatings, including “black chrome” for solar panels.

This work lead to the commercialization of flat panel solar water heaters, and solar pool heaters, marketed as Northrup Energy products directly and via dealers, with particular success in Hawaii, where solar thermosiphon systems could be used with antifreeze.

With low temperature products in production and distribution, Northrup turned his attention to achieving higher temperatures – which would entail various methods of concentrating incoming insolation and tracking the sun - with varying degrees of success.

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.

"After market" automotive AC units were manufactured in Texas until the 1980s.

He also sold some of the first air conditioning units, built by the Curtis Mathes Corporation, an early leader in manufacturing window units.

Northrup married Jane Keliher and started a family in Dallas, where he designed and built one of the first single-family houses in the United States with central air conditioning.

He founded a company to install air conditioning in residential and commercial buildings.

With a Marketing Plan from G F Sweetman (CEO of American Awards Co), he became one of largest suppliers of Curtis Mathes fans and compressors in the nation.

He also developed a company to manage, install, update, and clean air filtration systems.

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.