Solar, Storage

Making Electricity Directly from Sunlight

Providing power to every satellite in space has made solar cells indispensable. Since the war in the Persian Gulf, solar-powered satellites have directed battle operations in all of America’s conflicts including the present one in Afghanistan. Information from GPS (Geographical Positioning Systems) satellites and spy satellites gathered and relayed to Command and Control by military satellite communication networks direct precision bombing.

On the ground, Special Forces depend on these satellites to carry out their missions. Spy satellites serve as the eyes and ears of Intelligence. Secure, high-speed communications via satellites between forces in the field and those in command allow for better-informed split-second battle decisions. In the words of General Lester Lyles, Air Force Material Command Commander, “No American military force could fight without the use of space based assets.” Satellites run much of civilian life as well. They control a multitude of disparate networks providing seamless wireless communication. Satellites have contributed to the increased use of electronic money by allowing companies to bypass slower and more tedious phone links. Mass transportation uses satellites to stay on course. Operators at fixed sites can stay in touch with mobile resources while data control by satellites keeps companies in intimate contact with their far-flung holdings throughout the globe. Live television footage from across the sea did not exist until communication satellites came of age. Now, all on-the-scene live TV reporting feeds into satellites. Satellites will soon speed up the internet by unclogging portions of the information highway prone to gridlock. PV in Space When you see an image of a satellite, look for the extended flat blue surfaces radiating from the payload – those are the solar modules. These modules consist of many solar cells, which convert sunlight directly to electricity. Thickness of the solar material ranges from several to a few hundred microns. Within this small area, photons – packets of energy from the sun – silently push electrons out of the cell and generate electricity. No moving parts come in to play. Here we have the first true quantum power device. New Yorker Charles Fritts built the world’s first solar electric module using selenium in 1883. He optimistically believed that his “photoelectric plate” would soon compete with Edison’s newly installed coal fired electrical generating plants. Though 117 have elapsed since Fritts made his bold challenge, solar cells have yet to economically compete with electricity produced from centralized power plants. Much has happened in the field of solar cells, though, turning Fritts’ lone module into a multi-billion dollar business producing the world’s most versatile means of generating electricity. Fritts’ published account of producing electricity by exposure of sunlight without combustion or movement of gears elicited much skepticism. His purported discovery ran counter to the physics of that day which still debated the reality of atoms and believed that the generation of power could only occur by consuming fuel and in the process, dissipating heat. A few of the best scientists realized that something significant had happened inside Fritts’ module that the science of their time could not explain. Werner von Siemens, whose reputation ranked alongside Edison’s among those studying electricity, remarked that the direct conversion of sunlight by selenium ranked as “scientifically of the most far-reaching importance.” James Clerk Maxwell, one of the great scientists of all time, wondered, “Is the radiation the immediate cause or does it act by producing some change in the chemical state?” Their bafflement regarding the conversion of light into electricity in selenium and related matters led to a whole new realm of physics called quantum mechanics. Its discoveries included the bold and novel description of light as containing packets of energy – called photons – and electrons and their behavior. These new concepts explained how solar cells worked. Scientists called the phenomenon the photovoltaic effect and the technology behind it photovoltaics.
Increased PV Research Scientific understanding of solar cells sparked a bevy of interest and research. But more thorough investigations in the 1920s and 1930s led experts like E.D. Wilson of Westinghouse Electric’s photoelectric division to dismiss selenium as a power converter of solar energy because it could only change about one tenth of one percent of the incoming sunlight into electricity. “The photovoltaic cell will not prove interesting to the practical engineer until the efficiency has been increased at least fifty times,” Wilson argued. A solar cell meeting Wilson’s criteria of changing enough sunlight into electricity for practical applications emerged in 1953 from semiconductor research at Bell Laboratories. Calvin Fuller, a Bell chemist, had developed the first working silicon transistor. He discovered how to control the introduction of impurities necessary to transform silicon from a poor to a superior conductor of electricity. Working on a hunch, a colleague, Gerald Pearson, hooked one of Fuller’s creations to an ammeter and then shined lamplight on it. The needle jumped significantly. Further investigations confirmed that Fuller had inadvertently constructed a very good solar cell. Pearson rushed down the hall where his good friend Daryl Chapin, working on remote power devices, struggled with little success to wring more power out of selenium. Handing Chapin the silicon solar cell he had just tested, Pearson advised Chapin, “Don’t waste another moment on selenium.” Tests confirming silicon’s superiority led Chapin to drop further research into selenium and concentrate on improving silicon’s efficiency. More than a year later and after untold hours of surmounting endless hurdles, Daryl Chapin, Calvin Fuller, and Gerald Pearson presented to the world on April 25, 1954 the first solar cell that could generate useful power. The New York Times rhapsodized that the work of the Bell scientists “may mark the beginning of a new era, leading eventually to the realization of one of mankind’s most cherished dreams – the harnessing of the almost limitless energy of the sun for the uses of civilization.” U.S. News & World Report speculated that the silicon solar cells discovered at Bell Laboratories “may provide more power than all the world’s coal, oil and uranium.” Despite such rosy expectations and the Bell team doubling cell efficiency over the following eighteen months, nothing of commercial significance transpired. And small wonder! Chapin calculated that with a one-watt cell costing US$286 a homeowner would have to pay US$1,430,000 for an array of sufficient size to power the average American house. Although Chapin despaired over the fate of the new device, a colleague, Gordon Raisbeck, offered a more realistic appraisal. “It would be a great mistake to jump to the conclusion, on the basis of such” a discouraging example, he wrote in a 1955 article in Scientific American, that the solar cell “would be of little practical use.” The Bell invention, according to Raisbeck, would first find use where power is needed “in inaccessible places where no lines go” and “in doing jobs the need for which we have not yet felt.” True to Raisbeck’s prophecy, Air Force and Army scientists eyed the Bell solar cell to power a top-secret item never before put to use – an earth-orbiting satellite – something for the 1950s more novel, and more remote from the power grid than ever thought of before. But when the Navy got the nod to launch America’s first satellite, it eschewed solar cells as “unconventional and not fully established” and chose, instead, limited-life chemical batteries to supply electricity for the satellite. The Navy’s decision enraged the Army’s lead researcher on power devices, Dr. Hans Ziegler. Ziegler fought the Navy’s decision and won the support of the nation’s preeminent civilian scientists overseeing America’s nascent space program. They, too, favored a power source that would last indefinitely so they and their colleagues could conduct meaningful experiments in space. Under pressure from these scientists, the Navy relented but skepticism of the solar element’s capability led for the launch of a dual-powered satellite. Nineteen days later the chemical batteries died and the solar took over. Its long life enabled geophysicist to discover our planet’s true shape. The stellar performance of the cells broke down the prejudice which existed against solar energy in space. By the 1960s both Americans and Soviets came to regard the solar cell as one of the critically important devices in their space programs. From milliwatts on the Vanguard to kilowatts for the International Space Shuttle, photovoltaics have powered almost every satellite ever launched. The urgent demand for solar cells above the earth opened an unexpected and relatively large business for companies manufacturing solar cells. Its unbridled success in space led many to ask why couldn’t the technology help on Earth. Addressing Costs The high price of solar cells remained the primary obstacle to terrestrial applications. Despite dropping in price from nearly US$300 per watt in 1956 to US$100 a watt in 1970, a survey taken in the late 1960s suggested that technologists had to shave another US$80 per watt for solar cells to compete against chemical batteries and generators for the off-grid market. Dr. Elliot Berman, an American industrial chemist, with the help of Exxon Corporation, found that he could drastically reduce the cost of modules without any major breakthroughs. Instead of competing with the semiconductor industry for the very expensive high-grade silicon, Berman and his team chose to purchase much cheaper reject wafers as they found that the discards worked perfectly well for generating power. Nor did a terrestrial photovoltaic manufacturer, Berman’s group proved, have to trim the cylindrical wafers into rectangles as they did for satellites. Changing their shape gave a more compact fit to lighten the payload and open up more area on the satellite for its mission, great concerns for space but having no relevance for power needs on Earth. Hence, Berman and his group could save a lot of expensive silicon by maintaining the wafer’s original form. Furthermore, the packaging of terrestrial cells did not demand the same rigor as those in space required contending with meteorites and radiation. Changes such as these reduced the price by early 1973 to the magical US$20 per watt for large orders, bringing to earth a formerly space-based enterprise. New Uses Berman’s company, Solar Power Corporation, began business selling modules to offshore oil rigs in the Gulf of Mexico. Pre-marketing research revealed that though the rigs required small amounts of electricity for warning lights and horns to prevent boats and ships from running into them, few had their own power. Instead, huge autonomous non-rechargeable batteries supplied the necessary electricity. Maintaining and replacing them every nine or so months proved expensive, labor intensive and time consuming. Much lighter, longer-lasting solar panels combined with smaller rechargeable batteries saved the oil industry time and money. For these reasons, by 1980 solar-powered navigation aides had become standard fare in the Gulf of Mexico, and because of the international nature of the oil business they soon became a common sight on off-shore rigs worldwide. The Coast Guard did not make the change to photovoltaics as quickly as did the oil industry even though the cost for periodically replacing the buoys’ batteries exceeded the purchase price of the buoys. The Coast Guard’s reluctance to make such an obviously positive change compelled a young lieutenant commander, Lloyd Lomer, to secretly initiate a photovoltaics program for that agency. Lomer established testing to develop design criteria for robust solar panels that would withstand the pummeling of waves and immersion in seawater. He then had a prototype built and placed it in one of the least sunny areas served by the Coast Guard. Though it operated successfully in the most trying of conditions, still, his superiors would not budge. Lomer than went above their heads, convincing their superiors to begin in earnest a photovoltaics program. By the 1980s, due to Lomer’s maverick efforts, the Coast Guard decided to convert all of its navigation aids to solar power. The rest of the world has followed suit. The availability of a relatively inexpensive module gained the attention of Telecom Australia, the quasi-public agency in charge of the nation’s communication networks. The government had ordered the telecom group to provide the most remotely situated Australians access to the same high quality telephone and television service those living in the urban centers enjoyed. Finding a reliable off-grid power supply became the chief obstacle to fulfilling the government mandate. Telecom Australia’s power engineers looked into windmills and generators but they proved too unreliable. Solar modules, in contrast, when attached to batteries did not demand refueling visits as did generators and unlike windmills or generators, which needed periodic upkeep, the solid-state construction of solar cells made them as long lasting as the transistorized phone transmitters and receivers they would power in the Outback. The solar phones connecting those in isolated situations with telephone exchanges tied to the national telephone system worked so well that by 1976 the government chose to run entire telecommunication networks with the sun. Multiple solar-driven repeater stations spanned thousands of miles so that people along the way had instantaneous long-distance calling and television programming. The Australian experience gave people all over the world greater confidence in photovoltaics. As one Australian Telecom engineer put it, “We showed the world how solar power could be used in a big way out in the field.” © John Perlin 2002 Used with Permission. About the Author The article is a synopsis of John Perlin’s book, “From Space to Earth: The Story of Solar Electricity,” which describes the step-by-step development of photovoltaics. The Oregon Museum of Science and Industry has agreed to produce a traveling outdoor exhibit based on the book. For more information on the book and/or exhibit, please contact John at [email protected]