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No. 2871:
Solar Power in 1884

Today, an idea, long before its time. The University of Houston's College of Engineering presents this series about the machines that make our civilization run and about the people whose ingenuity created them. 

My 1884 volume of Century Magazine has a story taken from Mark Twain's not-yet-published novel Huckleberry Finn. And its frontispiece shows Ulysses S. Grant who was publishing his memoirs in the magazine. Stirred in with all that is an article about the latest solar power technology. It's by Samuel Pierpont Langley. 

Nineteen years later, Langley would build an early aeroplane that fell like a stone into the Potomac River, nine days before the Wright Brothers flew. But here, Langley is not talking about flight. He's talking about getting energy from the Sun.

He begins with a rambling discussion of light. It gives a very accurate picture of the growing confusion over the nature of light. That confusion would later come to a head in Planck's new quantum theory. But all this is prelude to Langley's real concern: How to utilize that vast flow of energy. 

He goes through elaborate hoops to explain the immense influx of solar energy. He devotes a thousand or so words just to explain how the solar power reaching Earth is enough to raise 37 billion tons of room-temperature water per minute to its boiling point. 

Now, says Langley, all this power is what feeds our engines indirectly -- through fossil fuel, and living organic material. But why shouldn't we use it directly? A few visionary inventors actually already had. He shows an engraving of a huge 18th-century burning glass being used to boil a pot of water. 

Berniere's Burning Glass

And, four years before this article, inventor Augustin Mouchot displayed one of a series of solar powered steam engines at the 1878 Paris Exhibition. He used a large parabolic mirror to collect and focus the sun's rays on a boiler that drove a steam engine. 

Mouchet's Solar Engine

Close on Mouchot's heels came the great John Ericsson who'd invented many things -- including the Union Monitor in the Civil War. One of those inventions was a form of external combustion engine. It was kin to an earlier engine suggested by a Scot named Stirling. The Stirling/Ericsson engine alternately heats and cools air that flows through it. One of its two cylinders compresses the air; the other lets heated compressed air deliver power. 

Ericsson's solar engine

Stirling/Ericsson engines give higher efficiency than the kinds we use in trucks and cars today. But they're naturally heavier and slower. Ericsson tried to power a ship with one and it was far too big and heavy. Later on he saw that his engine would be ideal for use with parabolic solar heaters. He substantially improved Mouchot's idea. 

Langley suggests that these units would ideally serve in desert areas. Well, if we GoogleStirling Engine today, we find commercial units, much like Ericsson's, doing just that. Langley finishes by imagining Ericsson/Stirling engines making the deserts bloom -- populating the Sahara. Well, he failed with his flying machine. But he heralded one very real future of solar power.

I'm John Lienhard at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)

S. P. Langley, "The New Astronomy", Century Magazine, Dec. 1884, pp. 224-241.

See the Wikipedia pages on Samuel Pierpont LangleyAugustin MouchotJohn EricssonStirling Engine, and Ericsson Cycle. This Land Art Generator Initiative page gives a nice brief account of these old solar generators. This BYU page displays the thermodynamic cycles for the Stirling and Ericsson engines. See also Episode 795 on Ericsson's attempt to power a ship with his engine.

Strictly speaking the Stirling cycle has adiabatic expansions and compressions linked by constant volume heating and cooling, while the heating and cooling is done at constant pressure in the Ericsson cycle. Today, the term Stirling engine is fairly loosely applied to any engine using the Stirling cycle, the Ericsson cycle, or (more commonly) some cycle that has attributes of either or both. Hence my use of the term Stirling/Ericsson cycle.

This episode was first aired on March 25, 2013