19th Century Solar Energy Engines
Augustin Mouchot’s Solar Concentrator, 1869.
19th Century Solar Energy It was not until the late 19th century that a concerted effort was made to harness the sun’s power. The man behind the Tours library boiler, Augustin Mouchot, was a mathematics professor at the Lycée de Tours. When he began experimenting with solar energy in 1860, it was not with a parabolic mirror but with a little box. “Hot boxes” – imagine a miniature heat-trapping greenhouse ceiling built over walls and floors made of insulating black cork – had been pioneered by Horace de Saussure a century earlier. Astronomer John Hershel was inspired in the 1830s to hold little family cookouts with just such a box. “A very respectable stew of meat was prepared,” he reported, “and eaten with no small relish by entertained bystanders.”
Mouchot was drawn to the idea of finding new alternative energy sources, believing that the coal which fueled the Industrial Revolution would eventually run out. In 1860 he began exploring solar cooking, drawing on the work of Horace-Bénédict de Saussure and Claude Pouillet. Further experiments involved a water-filled cauldron enclosed in glass, which would be exposed to the heat of the sun until the water boiled; the steam thus produced would provide motive power for a small steam engine. By August 1866, Mouchot had developed the first parabolic trough solar collector, which was presented to the emperor Napoleon III in Paris. Mouchot continued development and increased the scale of his solar experiments. The publication of his book on solar energy, La Chaleur solaire et ses Applications industrielles (“Solar Heat and its Industrial Applications”) (1869), coincided with the unveiling of the largest solar steam engine he had yet built. This engine was displayed in Paris until the city fell under siege during the Franco-Prussian War in 1871, and was not found after the siege ended.
In September 1871, Mouchot received financial assistance from the General Council of Indre-et-Loire to install an experimental solar generator at the Tours library. He presented a paper on the generator to the Academy of Sciences on 4 October 1875, and in December of the same year he presented to the Academy a device he claimed would, in optimal sunshine, provide a steam flow of 140 liters per minute. Later the following year he sought permission from the ministry to take leave from his teaching position in order to develop an engine for the Universal Exhibition of 1878, and in January 1877 obtained a mission and a grant for the purchase of materials and execution of his solar engines in French Algeria, where sunlight was in abundance. The director of science missions recommended Mouchot to the Governor of Algeria, stressing the importance of his mission to France, “for science and for the glory of the University”.
Augustin Mouchot taught secondary school mathematics from 1852-1871, during which time he embarked on a series of experiments in the conversion of solar energy into useful work. His proof-of-concept designs were so successful that he obtained support from the French government to pursue the research full-time. His work was inspired and informed by that of Horace-Bénédict de Saussure (who had constructed the first successful solar oven in 1767) and Claude Pouillet (who invented the Pyrheliometer in 1838).
Mouchot worked on his most ambitious device in the sunny conditions of French Algeria and brought it back for demonstration at the Universal Exhibition in Paris of 1878. There he won the Gold Medal, impressing the judges with the production of ice from the power of the sun.
Unfortunately, the falling price of coal, driven by efficiencies of transport and free trade agreements with Britain, meant that Mouchot’s work would soon be deemed unnecessary and his funding was cut soon after his triumph at the Universal Exhibition.
His assistant, Abel Pifre, would continue his work, however, and demonstrated a solar powered printing press in the Jardin des Tuileries in 1882. Despite cloudy conditions that day, the machine printed 500 copies per hour of Le Journal du Soleil, a newspaper written specially for the demonstration.
Meanwhile, the great inventor and engineer John Ericsson had decided to devote the last years of his life to similar pursuits. His work on solar engines spanned the 1870s and 1880s. Instead of relying on steam, he utilized his version of the heat engine, a device that would prove very commercially successful when powered with more conventional fuel sources such as gas.
From Paul Collins’ 2002 essay The Beautiful Possibility:
“You will probably be surprised when I say that the sun-motor is nearer perfection than the steam-engine,” [Ericsson] wrote one friend, “but until coal mines are exhausted its value will not be fully acknowledged.” He calculated that solar power cost about ten times as much as coal, so that until coal began to run out, solar power would not be economically feasible. But this, to him, was not a sign of failure—there was no question that fossil fuels would indeed run out someday.
The great engineer maintained an unshakeable belief in the future of solar power to his last breath; he had set up a large engine in his backyard and was still perfecting it when he collapsed in early 1889. Though his doctor made him rest, Ericsson could not sleep at night: he complained that he could not stop thinking about his work yet to be done.
Both Mouchot and Ericsson were driven by the prescient understanding that access to coal, the predominant fossil fuel of the time, would eventually run out. And while, new discoveries of petroleum and natural gas have extended our inexpensive access to energy, we are finally now, 140 years later, reaching a time when their predictions are coming true. For the wisdom behind the premise is still as valid today as it was then—nothing that is finite can last forever. These inventors were so far ahead of their time, it is almost scary.