From ancient civilizations to the industrial age

A point of departure for understanding humanity’s longstanding regard for solar energy is the deep religious and symbolic meaning it held for people in the earliest civilizations. Religiously based solar myths included the twelve Hindu Adityas, the Greek god Helios, the Egyptian god Ra, and the Aztec god Tonatiuh, among others.

Solar orientation of architecture, then, was more than a utilitarian concept. In many cases it was a token of respect and, as noted by Greek playwright Aeschylus, the hallmark of an advanced civilization’s ascent from barbarism. The search for practical ways to use of the sun’s power was also evident in solar experiments by Archimedes and other classical engineers.

Solar Physics and the Scientific Revolution

While reverence for the sun anchored early cultures, the scientific revolution of early modern Europe was animated by the Copernican revolution. Renaissance astronomers like Nicholas Copernicus, Tycho Brahe and Galileo Galilei realized that Aristotle’s geocentric model could not explain observations. The  fact that the earth was not at the center of the universe shattered the notion of received wisdom from scripture and classical philosophers.  Instead, the discovery itself became the model for a scientific revolution based on observation, experimentation and verification.

In subsequent centuries, the study of solar physics involved observations of sunspots, flares and other phenomena, but most puzzling was the apparent size and power of the sun. Isaac Newton was the first to calculate the mass of the sun, establishing a basis for the gravitational forces that held the solar system in place. Early speculation about the nature of the sun revolved around the issue of how such a large fire could burn for so many millions of years.  Scientists such as William Thompson (Lord Kelvin) theorized that gravitational forces compressed matter, creating solar energy through  mechanisms that, as he acknowledged in the 1850s, were as yet unknown.

Other scientists were also fascinated by the nature and possible usefulness of solar energy, including Horace de Saussure, a Swiss physicist who built the first “black box” solar oven in 1767. De Saussure tested solar gain by comparing temperatures at 4,800 feet on Mt. Cramont in the Swiss Alps and the plains below.  His observations that the temperatures were more or less equal led him to conclude that sunlight had equal force at both higher and lower altitudes.

Measuring  the sun’s force also intrigued French scientists Alexandre-Edmond Becquerel, who discovered the photovoltaic effect in 1839, and Claude Pouillet, whose 1837 estimates of the solar constant (1228 watts per meter) were within 11 percent of the current accepted value.  Others who experimented included British scientist John Herschel, whose “black box” solar experiments in South Africa in 1838 attempted to quantify the solar constant.  Subsequent research by Langley and Abbot at the Smithsonian on the solar constant were further off the mark.

Even more puzzling, the “black box” experiments did not seem to account for all of the energy in solar radiation.  Although these experiments continued in the form of solar cookers and widespread use of hot water systems, solar physics remained a highly speculative field until the 20th century, when the nature of the sun’s internal structure was explained by the development of atomic theory.

A Dangerous Rival to King Coal:  Solar energy in the 19th century

When Augustine Mouchot, a professor at the university in Lyons, France, began his solar experiments in 1861, he felt he was already traveling down a well-worn path. In his history of solar energy published a few years later, Mouchot described experiments from the solar prototypes developed by Archimedes at the Library of Alexandria to Claude Pouillet’s search for the solar constant.  His experiments with solar cookers and industrial scale solar machines were taken up by his protégé, Abel Pifre.   In 1882, Pifre built a conical solar collector and used it to power a printing press, which he demonstrated in the Tuileries garden in Paris.

The public demonstrations in France were widely hailed as a response to the pending coal shortage, predicted by British economist William Stanley Jevons in 1864.  British scientist William Adams, who experimented with solar cookers in India, wrote that solar energy would be “a substitute for fuel in tropical countries.”

Worried about how his ironclad steam ships would fare in a future without coal, the famed Swedish-American naval engineer,  John Ericsson, built a set of industrial solar collectors on his rooftop in Manhattan, during the 1870s and 80s.  He found that a concentrating solar collector could obtain the equivalent of one horsepower for every hundred square feet of mirrors reflecting onto a steam generator.  This was a considerable improvement over Lord Kelvin’s 1852 estimate of about one horsepower for 1800 square feet of solar collector surface.  While not commercially successful, Ericsson devoted the last two decades of his life to the idea of sustainability through engineering.

Three other American engineers were notable for taking this same path around the turn of the 20th century.  An eccentric engineer from Pasadena, California —  Aubrey Eneas —  built a massive solar collector that could pump 1,400 gallons of water per minute. The collector was featured as part of an ostrich farm, which was a popular tourist attraction at the time.  A contemporary journalist described the invention as a “dangerous rival to king coal.”

Another American engineer, Frank Shuman of Philadelphia, built the largest solar power plant to date near Cairo, Egypt in 1913.  Endless power for the human race was his vision. “One thing I feel sure of,” Shuman said in 1914, “is that the human race must utilize direct Sun power or revert to barbarism.”  Yet the experiment had to be shut down when World War I started only a few months later.

A third American, Henry Willsie, built a set of solar collectors for pumping water in the Arizona desert that cost more than coal-powered steam but was practical in remote areas.  Willsie’s struggle to commercialize solar power was fictionalized by his wife, Honore Willsie in the 1920 book The Forbidden Trail.  “It’s a big dream,” an engineering professor tells the protagonist, “too big for you or any other man to put over in a single generation.”




French history of solar energy on Knol

History of the greenhouse effect

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