History of Solar Energy

Revisiting Solar Power's Past
By Charles Smith

Home Location: - Technology Review: July 95: Solar Power

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.

Charles Smith is an adjunct faculty member in the Department of Technology at Appalachian State University, and a doctoral candidate in the Department of Science and Technology Studies at Virginia Polytechnic Institute. His primary area of research is the history of energy.

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.

The Tower of Power

During the height of Mouchout's experimentation, William Adams, the deputy registrar for the English Crown in Bombay, India, wrote an award-winning book entitled Solar Heat: A Substitute for Fuel in Tropical Countries. Adams noted that he was intrigued with Mouchout's solar steam engine after reading an account of the Tours demonstration, but that the invention was impractical, since "it would be impossible to construct [a dish-shaped reflector] of much greater dimensions" to generate more than Mouchout's one-half horsepower. The problem, he felt, was that the polished metal reflector would tarnish too easily, and would be too costly to build and too unwieldy to efficiently track the sun.

Fortunately for the infant solar discipline, the English registrar did not spend all his time finding faults in the French inventor's efforts, but offered some creative solutions. For example, Adams was convinced that a reflector of flat silvered mirrors arranged in a semicircle would be cheaper to construct and easier to maintain. His plan was to build a large rack of many small mirrors and adjust each one to reflect sunlight in a specific direction. To track the sun's movement, the entire rack could be rolled around a semicircular track, projecting the concentrated radiation onto a stationary boiler. The rack could be attended by a laborer and would have to be moved only "three or four times during the day," Adams noted, or more frequently to improve performance.

Confident of his innovative arrangement, Adams began construction in late 1878. By gradually adding 17-by-10-inch flat mirrors and measuring the rising temperatures, he calculated that to generate the 1,200û F necessary to produce steam pressures high enough to operate conventional engines, the reflector would require 72 mirrors. To demonstrate the power of the concentrated radiation, Adams placed a piece of wood in the focus of the mirrored panes where, he noted, "it ignited immediately." He then arranged the collectors around a boiler, retaining Mouchout's enclosed cauldron configuration, and connected it to a 2.5-horsepower steam engine that operated during daylight hours "for a fortnight in the compound of [his] bungalow."

Eager to display his invention, Adams notified newspapers and invited his important friends--including the Army's commander in chief, a colonel from the Royal Engineers, the secretary of public works, various justices, and principal mill owners--to a demonstration. Adams wrote that all were impressed, even the local engineers who, while doubtful that solar power could compete directly with coal and wood, thought it could be a practical supplemental energy source.

Adams's experimentation ended soon after the demonstration, though, perhaps because he had achieved his goal of proving the feasibility of his basic design, but more likely because, as some say, he lacked sufficient entrepreneurial drive. Even so, his legacy of producing a powerful and versatile way to harness and convert solar heat survives. Engineers today know this design as the Power Tower concept, which is one of the best configurations for large scale, centralized solar plants. In fact, most of the modern tower-type solar plants follow Adams's basic configuration: flat or slightly curved mirrors that remain stationary or travel on a semicircular track and either reflect light upward to a boiler in a receiver tower or downward to a boiler at ground level, thereby generating steam to drive an accompanying heat engine.

Collection without Reflection

Even with Mouchout's abandonment and the apparent disenchantment of England's sole participant, Europe continued to advance the practical application of solar heat, as the torch returned to France and engineer Charles Tellier. Considered by many the father of refrigeration, Tellier actually began his work in refrigeration as a result of his solar experimentation, which led to the design of the first non-concentrating, or non-reflecting, solar motor.

In 1885, Tellier installed a solar collector on his roof similar to the flat-plate collectors placed atop many homes today for heating domestic water. The collector was composed of ten plates, each consisting of two iron sheets riveted together to form a watertight seal, and connected by tubes to form a single unit. Instead of filling the plates with water to produce steam, Tellier chose ammonia as a working fluid because of its significantly lower boiling point. After solar exposure, the containers emitted enough pressurized ammonia gas to power a water pump he had placed in his well at the rate of some 300 gallons per hour during daylight. Tellier considered his solar water pump practical for anyone with a south-facing roof. He also thought that simply adding plates, thereby increasing the size of the system, would make industrial applications possible.

By 1889 Tellier had increased the efficiency of the collectors by enclosing the top with glass and insulating the bottom. He published the results in The Elevation of Water with the Solar Atmosphere, which included details on his intentions to use the sun to manufacture ice. Like his countryman Mouchout, Tellier envisioned that the large expanses of the African plains could become industrially and agriculturally productive through the implementation of solar power.

In The Peaceful Conquest of West Africa, Tellier argued that a consistent and readily available supply of energy would be required to power the machinery of industry before the French holdings in Africa could be properly developed. He also pointed out that even though the price of coal had fallen since Mouchout's experiments, fuel continued to be a significant expense in French operations in Africa. He therefore concluded that the construction costs of his low-temperature, non-concentrating solar motor were low enough to justify its implementation. He also noted that his machine was far less costly than Mouchout's device, with its dish-shaped reflector and complicated tracking mechanism.

Yet despite this potential, Tellier evidently decided to pursue his refrigeration interests instead, and do so without the aid of solar heat. Most likely the profits from conventionally operated refrigerators proved irresistible. Also, much of the demand for the new cooling technology now stemmed from the desire to transport beef to Europe from North and South America. The rolling motion of the ships combined with space limitations precluded the use of solar power altogether. And as Tellier redirected his focus, France saw the last major development of solar mechanical power on her soil until well into the twentieth century. Most experimentation in the fledgling discipline crossed the Atlantic to that new bastion of mechanical ingenuity, the United States.

The Parabolic Trough

Though Swedish by birth, John Ericsson was one of the most influential and controversial U.S. engineers of the nineteenth century. While he spent his most productive years designing machines of war--his most celebrated accomplishment was the Civil War battleship the Monitor--he dedicated the last 20 years of his life largely to more peaceful pursuits such as solar power. This work was inspired by a fear shared by virtually all of his fellow solar inventors that coal supplies would someday end. In 1868 he wrote, "A couple of thousand years dropped in the ocean of time will completely exhaust the coal fields of Europe, unless, in the meantime, the heat of the sun be employed."

Thus by 1870 Ericsson had developed what he claimed to be the first solar-powered steam engine, dismissing Mouchout's machine as "a mere toy." In truth, Ericsson's first designs greatly resembled Mouchout's devices, employing a conical, dish-shaped reflector that concentrated solar radiation onto a boiler and a tracking mechanism that kept the reflector directed toward the sun.

Though unjustified in claiming his design original, Ericsson soon did invent a novel method for collecting solar rays--the parabolic trough. Unlike a true parabola, which focuses solar radiation onto a single, relatively small area, or focal point, like a satellite television dish, a parabolic trough is more akin to an oil drum cut in half lengthwise that focuses solar rays in a line across the open side of the reflector. This type of reflector offered many advantages over its circular (dish-shaped) counterparts: it was comparatively simple, less expensive to construct, and, unlike a circular reflector, had only to track the sun in a single direction (up and down, if lying horizontal, or east to west if standing on end), thus eliminating the need for complex tracking machinery. The downside was that the device's temperatures and efficiencies were not as high as with a dish-shaped reflector, since the configuration spread radiation over a wider area--a line rather than a point. Still, when Ericsson constructed a single linear boiler (essentially a pipe), placed it in the focus of the trough, positioned the new arrangement toward the sun, and connected it to a conventional steam engine, he claimed the machine ran successfully, though he declined to provide power ratings.

The new collection system became popular with later experimenters and eventually became a standard for modern plants. In fact, the largest solar systems in the last decade have opted for Ericsson's parabolic trough reflector because it strikes a good engineering compromise between efficiency and ease of operation.

For the next decade, Ericsson continued to refine his invention, trying lighter materials for the reflector and simplifying its construction. By 1888, he was so confident of his designs practical performance that he planned to mass-produce and supply the apparatus to the "owners of the sun burnt lands on the Pacific coast" for agricultural irrigation.

Unfortunately for the struggling discipline, Ericsson died the following year. And because he was a suspicious and, some said, paranoid man who kept his designs to himself until he filed patent applications, the detailed plans for his improved sun motor died with him. Nevertheless, the search for a practical solar motor was not abandoned. In fact, the experimentation and development of large-scale solar technology was just beginning.

The First Commercial Venture

Boston resident Aubrey Eneas began his solar motor experimentation in 1892, formed the first solar power company (The Solar Motor Co.) in 1900, and continued his work until 1905. One of his first efforts resulted in a reflector much like Ericsson's early parabolic trough. But Eneas found that it could not attain sufficiently high temperatures, and, unable to unlock his predecessor's secrets, decided to scrap the concept altogether and return to Mouchout's truncated-cone reflector. Unfortunately, while Mouchout's approach resulted in higher temperatures, Eneas was still dissatisfied with the machine's performance. His solution was to make the bottom of the reflector's truncated cone-shaped dish larger by designing its sides to be more upright to focus radiation onto a boiler that was 50 percent larger.

Finally satisfied with the results, he decided to advertise his design by exhibiting it in sunny Pasadena, Calif., at Edwin Cawston's ostrich farm, a popular tourist attraction. The monstrous machine did not fail to attract attention. Its reflector, which spanned 33 feet in diameter, contained 1,788 individual mirrors. And its boiler, which was about 13 feet in length and a foot wide, held 100 gallons of water. After exposure to the sun, Eneas's device boiled the water and transferred steam through a flexible pipe to an engine that pumped 1,400 gallons of water per minute from a well onto the arid California landscape.

Not everyone grasped the concept. In fact, one man thought the solar machine had something to do with the incubation of ostrich eggs. But Eneas's marketing savvy eventually paid off. Despite the occasional misconceptions, thousands who visited the farm left convinced that the sun machine would soon be a fixture in the sunny Southwest. Moreover, many regional newspapers and popular-science journals sent reporters to the farm to cover the spectacle. To Frank Millard, a reporter for the brand new magazine World's Work, the potential of solar motors placed in quantity across the land inspired futuristic visions of a region "where oranges may be growing, lemons yellowing, and grapes purpling, under the glare of the sun which, while it ripens the fruits it will also water and nourish them." He also predicted that the potential for this novel machine was not limited to irrigation: "If the sun motor will pump water, it will also grind grain and saw lumber and run electric cars."

The future, like the machine itself, looked bright and shiny. In 1903 Eneas, ready to market his solar motor, moved his Boston-based company to Los Angeles, closer to potential customers. By early the following year he had sold his first complete system for $2,160 to Dr. A. J. Chandler of Mesa, Ariz. Unfortunately, after less than a week, the rigging supporting the heavy boiler weakened during a windstorm and collapsed, sending it tumbling into the reflector and damaging the machine beyond repair.

But Eneas, accustomed to setbacks, decided to push onward and constructed another solar pump near Tempe, Ariz. Seven long months later, in the fall of 1904, John May, a rancher in Wilcox, Ariz., bought another machine for $2,500. Unfortunately, shortly afterward, it was destroyed by a hailstorm. This second weather-related incident all but proved that the massive parabolic reflector was too susceptible to the turbulent climactic conditions of the desert southwest. And unable to survive on such measly sales, the company soon folded.

Though the machine did not become a fixture as Eneas had hoped, the inventor contributed a great deal of scientific and technical data about solar heat conversion and initiated more than his share of public exposure. Despite his business failure, the lure of limitless fuel was strong, and while Eneas and the Solar Motor Company were suspending their operations, another solar pioneer was just beginning his.

Moonlight Operation

Henry E. Willsie began his solar motor construction a year before Eneas's company folded. In his opinion, the lessons of Mouchout, Adams, Ericsson, and Eneas proved the cost inefficiency of high-temperature, concentrating machines. He was convinced that a non-reflective, lower-temperature collection system similar to Tellier's invention was the best method for directly utilizing solar heat. The inventor also felt that a solar motor would never be practical unless it could operate around the clock. Thus thermal storage, a practice that lent itself to low-temperature operation, was the focus of his experimentation.

To store the sun's energy, Willsie built large flat-plate collectors that heated hundreds of gallons of water, which he kept warm all night in a huge insulated basin. He then submerged a series of tubes, or vaporizing pipes, inside the basin to serve as boilers. When the acting medium--Willsie preferred sulfur dioxide to Tellier's ammonia--passed through the pipes, it transformed into a high-pressure vapor, which passed to the engine, operated it, and exhausted into a condensing tube, where it cooled, returned to a liquid state, and was reused.

In 1904, confident that his design would produce continuous power, he built two plants, a 6-horsepower facility in St. Louis, Mo., and a 15-horsepower operation in Needles, Calif. And after several power trials, Willsie decided to test the storage capacity of the larger system. After darkness had fallen, he opened a valve that "allowed the solar-heated water to flow over the exchanger pipes and thus start up the engine." Willsie had created the first solar device that could operate at night using the heat gathered during the day. He also announced that the 15-horsepower machine was the most powerful arrangement constructed up to that time. Beside offering a way to provide continuous solar power production, Willsie also furnished detailed cost comparisons to justify his efforts: the solar plant exacted a two-year payback period, he claimed, an exceptional value even when compared with today's standards for alternative energy technology.

Originally, like Ericsson and Eneas before him, Willsie planned to market his device for desert irrigation. But in his later patents Willsie wrote that the invention was "designed for furnishing power for electric light and power, refrigerating and ice making, for milling and pumping at mines, and for other purposes where large amounts of power are required."

Willsie determined all that was left to do was to offer his futurist invention for sale. Unfortunately, no buyers emerged. Despite the favorable long-term cost analysis, potential customers were suspicious of the machine's durability, deterred by the high ratio of machine size to power output, and fearful of the initial investment cost of Willsie's ingenious solar power plant. His company, like others before it, disintegrated.

A Certain Technical Maturity

Despite solar power's dismal commercial failures, some proponents continued to believe that if they could only find the right combination of solar technologies, the vision of a free and unlimited power source would come true. Frank Shuman was one who shared that dream. But unlike most dreamers, Shuman did not have his head in the clouds. In fact, his hardheaded approach to business and his persistent search for practical solar power led him and his colleagues to construct the largest and most cost-effective machine prior to the space age.

Shuman's first effort in 1906 was similar to Willsie's flat-plate collector design except that it employed ether as a working fluid instead of sulfur dioxide. The machine performed poorly, however, because even at respectable pressures, the steam--or more accurately, the vapor--exerted comparatively little force to drive a motor because of its low specific gravity.

Shuman knew he needed more heat to produce steam, but felt that using complicated reflectors and tracking devices would be too costly and prone to mechanical failure. He decided that rather than trying to generate more heat, the answer was to better conserve the heat already being absorbed.

In 1910, to improve the collector's insulation properties, Shuman enclosed the absorption plates not with a single sheet of glass but with dual panes separated by a one-inch air space. He also replaced the boiler pipes with a thin, flat metal container similar to Tellier's original greenhouse design. The apparatus could now consistently boil water rather than ether. Unfortunately, however, the pressure was still insufficient to drive industrial-size steam engines, which were designed to operate under pressures produced by hotter-burning coal or wood.

After determining that the cost of building a larger absorber would be prohibitive, Shuman reluctantly conceded that the additional heat would have to be provided through some form of concentration. He thus devised a low-cost reflector stringing together two rows of ordinary mirrors to double the amount of radiation intercepted. And in 1911, after forming the Sun Power Co., he constructed the largest solar conversion system ever built. In fact, the new plant, located near his home in Talcony, Penn., intercepted more than 10,000 square feet of solar radiation. The new arrangement increased the amount of steam produced, but still did not provide the pressure he expected.

Not easily defeated, Shuman figured that if he couldn't raise the pressure of the steam to run a conventional steam engine, he would have to redesign the engine to operate at lower pressures. So he teamed up with E.P. Haines, an engineer who suggested that more precise milling, closer tolerances in the moving components, and lighter-weight materials would do the trick. Haines was right. When the reworked engine was connected to the solar collectors, it developed 33 horsepower and drove a water pump that gushed 3,000 gallons per minute onto the Talcony soil.

Shuman calculated that the Talcony plant cost $200 per horsepower compared with the $80 of a conventionally operated coal system--a respectable figure, he pointed out, considering that the additional investment would be recouped in a few years because the fuel was free. Moreover, the fact that this figure was not initially competitive with coal or oil-fired engines in the industrial Northeast did not concern him because, like the French entrepreneurs before him, he was planning to ship the machine to the vast sun burnt regions in North Africa.

To buy property and move the machine there, new investors were solicited from England and the Sun Power Co. Ltd. was created. But with the additional financial support came stipulations. Shuman was required to let British physicist C. V. Boys review the workings of the machine and suggest possible improvements. In fact, the physicist recommended a radical change. Instead of flat mirrors reflecting the sun onto a flat-plate configuration, Boys thought that a parabolic trough focusing on a glass-encased tube would perform much better. Shuman's technical consultant A.S.E. Ackermann agreed, but added that to be effective, the trough would need to track the sun continuously. Shuman felt that his conception of a simple system was rapidly disintegrating.

Fortunately, when the machine was completed just outside of Cairo, Egypt, in 1912, Shuman's fears that the increased complexity would render the device impractical proved unfounded. The Cairo plant outperformed the Talcony model by a large margin--the machine produced 33 percent more steam and generated more than 55 horsepower--which more than offset the higher costs. Sun Power Co.'s solar pumping station offered an excellent value of $150 per horsepower, significantly reducing the payback period for solar-driven irrigation in the region. It looked as if solar mechanical power had finally developed the technical sophistication it needed to compete with coal and oil.

Unfortunately, the beginning was also the end. Two months after the final Cairo trials, Archduke Ferdinand was assassinated in the Balkans, igniting the Great War. The fighting quickly spread to Europe's colonial holdings, and the upper regions of Africa were soon engulfed. Shuman's solar irrigation plant was destroyed, the engineers associated with the project returned to their respective countries to perform war-related tasks, and Frank Shuman died before the armistice was signed.

Whether or not Shuman's device would have initiated the commercial success that solar power desperately needed, we will never know. However, the Sun Power Co. can boast a certain technical maturity by effectively synthesizing the ideas of its predecessors from the previous 50 years. The company used an absorber (though in linear form) of Tellier and Willsie, a reflector similar to Ericsson's, simple tracking mechanisms first used by Mouchout and later employed by Eneas, and combined them to operate an engine specially designed to run with solar-generated steam. In effect, Shuman and his colleagues set the standard for many of the most popular modern solar systems 50 to 60 years before the fact.

The Most Rational Source

The aforementioned solar pioneers were only the most notable inventors involved in the development of solar thermal power from 1860 to 1914. Many others contributed to the more than 50 patents and the scores of books and articles on the subject. With all this sophistication, why couldn't solar mechanical technology blossom into a viable industry? Why did the discipline take a 50-year dive before again gaining a measure of popular interest and technical attention?

First, despite the rapid advances in solar mechanical technology, the industry's future was rendered problematic by a revolution in the use and transport of fossil fuels. Oil and coal companies had established a massive infrastructure, stable markets, and ample supplies. Also, besides trying to perfect the technology, solar pioneers had the difficult task of convincing skeptics to see solar energy as something more than a curiosity. Visionary rhetoric without readily tangible results was not well received by a population accustomed to immediate gratification. Improving and adapting existing power technology, deemed less risky and more controlled, seemed to make far more sense.

Finally, the ability to implement radically new hardware requires either massive commitment or the failure of existing technology to get the job done. Solar mechanical power production in the late nineteenth and early twentieth centuries did not meet either criterion. Despite warnings from noted scientists and engineers, alternatives to what seemed like an inexhaustible fuel supply did not fit into the U.S. agenda. Unfortunately, in many ways, these antiquated sentiments remain with us today. During the 1970s, while the OPEC nations exercised their economic power and as the environmental and "no-nuke" movements gained momentum, Americans plotted an industrial coup whose slogans were energy efficiency and renewable resources. Consequently, mechanical solar power--along with its space-age, electricity-producing sibling photovoltaics, as well as other renewable sources such as wind power--underwent a revival. And during the next two decades, solar engineers tried myriad techniques to satisfy society's need for power.

They discovered that dish-shaped reflectors akin to Mouchout's and Eneas's designs were the most efficient but also the most expensive and difficult to maintain. Low-temperature, non-concentrating systems like Willsie's and Tellier's, though simple and less sensitive to climatic conditions, were among the least powerful and therefore suited only to small, specific tasks. Stationary reflectors like those used in Adams's device, now called Power Tower systems, offered a better solution but were still pricey and damage prone.

By the mid-1980s, contemporary solar engineers, like their industrial-revolution counterparts Ericsson and Shuman, determined that for sunny areas, tracking parabolic troughs were the best compromise because they exhibited superior cost-to-power ratios in most locations. Such efforts led engineers at the Los Angeles-based Luz Co. to construct an 80-megawatt electric power plant using parabolic trough collectors to drive steam-powered turbines. The company had already used similar designs to build nine other solar electric generation facilities, providing a total of 275 megawatts of power. In the process, Luz engineers steadily lowered the initial costs by optimizing construction techniques and taking advantage of economies of buying material in bulk to build ever-larger plants until the price dropped from 24 to 12 cents per kilowatt hour. The next, even larger plant--a 300-megawatt facility--scheduled for completion last year, promised to provide 6 to 7 cents per kilowatt hour, near the price of electricity produced by coal, oil, or nuclear technology.

Once again, as with Shuman and his team, the gap was closing. But once again these facilities would not be built. Luz, producer of more than 95 percent of the world's solar-based electricity, filed for bankruptcy in 1991. According to Newton Becker, Luz's chairman of the board, and other investors, the demise of the already meager tax credits, declining fossil fuel prices, and the bleak prospects for future assistance from both federal and state governments drove investors to withdraw from the project. As Becker concluded, "The failure of the world's largest solar electric company was not due to technological or business judgment failures but rather to failures of government regulatory bodies to recognize the economic and environmental benefits of solar thermal generating plants.

Other solar projects met with similar financial failure. For example, two plants that employed the tower power concept, Edison's 10-megawatt plant in Daggett, Calif., and a 30-megawatt facility built in Jordan performed well despite operating on a much smaller scale and without Luz's advantages of heavy initial capital investment and a lengthy trial-and-error process to improve efficiency. Still they were assessed as too costly to compete in the intense conventional fuel market.

Although some of our brightest engineers have produced some exemplary solar power designs during the past 25 years, their work reflects a disjointed solar energy policy. Had the findings of the early solar pioneers and the evolution of their machinery been more closely scrutinized, perhaps by Department of Energy officials or some other oversight committee, contemporary efforts might have focused on building a new infrastructure when social and political attitudes were more receptive to solar technology. Rather than rediscovering the technical merits of the various systems, we might have been better served by reviewing history, selecting a relatively small number of promising systems, and combining them with contemporary materials and construction techniques. Reinventing the wheel when only the direction of the cart seems suspect is certainly not the best way to reach one's destination.

While the best period to make our energy transition may have passed and though our energy future appears stable, the problems that initiated the energy crisis of the 1970s have not disappeared. Indeed, the instability of OPEC and the recent success in the Gulf War merely created an artificial sense of security about petroleum supplies. While we should continue to develop clean, efficient petroleum and coal technology while our present supplies are plentiful, this approach should not dominate our efforts. Alternative, renewable energy technologies must eventually be implemented in tandem with their fossil-fuel counterparts. Not doing so would simply provide an excuse for maintaining the status quo and beg for economic disruption when reserves run low or political instability again erupts in oil-rich regions.

Toward that end, we must change the prevailing attitude that solar power is an infant field born out of the oil shocks and the environmental movement of the past 25 years. Such misconceptions lead many to assert that before solar power can become a viable alternative, the industry must first pay its dues with a fair share of technological evolution.

Solar technology already boasts a century of R&D, requires no toxic fuel and relatively little maintenance, is inexhaustible, and, with adequate financial support, is capable of becoming directly competitive with conventional technologies in many locations. These attributes make solar energy one of the most promising sources for many current and future energy needs. As Frank Shuman declared more than 80 years ago, it is "the most rational source of power."