Inventors unlocked the secrets of turning the sun's rays into mechanical power more than a century ago, only to see their dream machines collapse from lack of public support. Modern solar engineers must not be doomed to relive their fate.
Many of us assume that the nation's first serious push to develop renewable fuels was spawned while angry Americans waited in gas lines during the "energy crisis" of the 1970s. Held hostage by the OPEC oil embargo, the country suddenly seemed receptive to warnings from scientists, environmentalists, and even a few politicians to end its over-reliance on finite coal and oil reserves or face severe economic distress and political upheaval.
But efforts to design and construct devices for supplying renewable energy actually began some 100 years before that turbulent time--ironically, at the very height of the Industrial Revolution, which was largely founded on the promise of seemingly inexhaustible supplies of fossil fuels. Contrary to the prevailing opinion of the day, a number of engineers questioned the practice of an industrial economy based on nonrenewable energy and worried about what the world's nations would do after exhausting the fuel supply.
More important, many of these visionaries did not just provide futuristic rhetoric but actively explored almost all the renewable energy options familiar today. In the end, most decided to focus on solar power, reasoning that the potential rewards outweighed the technical barriers. In less than 50 years, these pioneers developed an impressive array of innovative techniques for capturing solar radiation and using it to produce the steam that powered the machines of that era. In fact, just before World War I, they had outlined all of the solar thermal conversion methods now being considered. Unfortunately, despite their technical successes and innovative designs, their work was largely forgotten for the next 50 years in the rush to develop fossil fuels for an energy-hungry world.
Now, a century later, history is repeating itself. After following the same path as the early inventors--in some cases reinventing the same techniques--contemporary solar engineers have arrived at the same conclusion: solar power is not only possible but eminently practical, not to mention more environmentally friendly. Alas, once again, just as the technology has proven itself from a practical standpoint, public support for further development and implementation is eroding, and solar power could yet again be eclipsed by conventional energy technologies.
The First Solar Motor
The earliest known record of the direct conversion of solar radiation into mechanical power belongs to Auguste Mouchout, a mathematics instructor at the Lyce de Tours. Mouchout began his solar work in 1860 after expressing grave concerns about his country's dependence on coal. "It would be prudent and wise not to fall asleep regarding this quasi-security," he wrote. "Eventually industry will no longer find in Europe the resources to satisfy its prodigious expansion. Coal will undoubtedly be used up. What will industry do then?" By the following year he was granted the first patent for a motor running on solar power and continued to improve his design until about 1880. During this period the inventor laid the foundation for our modern understanding of converting solar radiation into mechanical steam power.
Mouchout's initial experiments involved a glass-enclosed iron cauldron: incoming solar radiation passed through the glass cover, and the trapped rays transmitted heat to the water. While this simple arrangement boiled water, it was of little practical value because the quantities and pressures of steam it produced were minimal. However, Mouchout soon discovered that by adding a reflector to concentrate additional radiation onto the cauldron, he could generate more steam. In late 1865, he succeeded in using his apparatus to operate a small, conventional steam engine.
By the following summer, Mouchout displayed his solar motor to Emperor Napoleon III in Paris. The monarch, favorably impressed, offered financial assistance for developing an industrial solar motor for France. With the newly acquired funds, Mouchout enlarged his invention's capacity, refined the reflector, redesigning it as a truncated cone, like a dish with slanted sides, to more accurately focus the sun's rays on the boiler. Mouchout also constructed a tracking mechanism that enabled the entire machine to follow the sun's altitude and azimuth, providing uninterrupted solar reception. After six years of work, Mouchout exhibited his new machine in the library courtyard of his Tours home in 1872, amazing spectators. One reporter described the reflector as an inverted "mammoth lamp shade...coated on the inside with very thin silver leaf" and the boiler sitting in the middle as an "enormous thimble" made of blackened copper and "covered with a glass bell."
Anxious to put his invention to work, he connected the apparatus to a steam engine that powered a water pump. On what was deemed "an exceptionally hot day," the solar motor produced one-half horsepower. Mouchout reported the results and findings to the French Academy of Science. The government, eager to exploit the new invention to its fullest potential, decided that the most suitable venue for the new machine would be the tropical climes of the French protectorate of Algeria, a region blessed with almost constant sunshine and entirely dependent on coal, a prohibitively expensive commodity in the African region.
Mouchout was quickly deployed to Algeria with ample funding to construct a large solar steam engine. He first decided to enlarge his invention's capacity yet again to 100 liters (70 for water and 30 for steam) and employ a multi-tubed boiler instead of the single cauldron. The boiler tubes had a better surface-area-to-water ratio, yielding more pressure and improved engine performance.
In 1878, Mouchout exhibited the redesigned invention at the Paris Exposition. Perhaps to impress the audience or, more likely, his government backers, he coupled the steam engine to a refrigeration device. The steam from the solar motor, after being routed through a condenser, rapidly cooled the inside of a separate insulated compartment. He explained the result: "In spite of the seeming paradox of the statement, [it was] possible to utilize the rays of the sun to make ice." Mouchout was awarded a medal for his accomplishments.
By 1881 the French Ministry of Public Works, intrigued by Mouchout's machine, appointed two commissioners to assess its cost efficiency. But after some 900 observations at Montpelier, a city in southern France, and Constantine, Algeria, the government deemed the device a technical success but a practical failure. One reason was that France had recently improved its system for transporting coal and developed a better relationship with England, on which it was dependent for that commodity. The price of coal had thus dropped, rendering the need for alternatives less attractive. Unable to procure further financial assistance, Mouchout returned to his academic pursuits.
next page 2
solarenergy.com/info_history.html
