Photovoltaic Cell
As far back as the 1800s scientists realized that, through certain chemical reactions, sunlight could be converted into electricity. The first experimenter to successfully accomplish this feat was A. E. Becquerel (1820-1891), who built a device that could measure the intensity of light by observing the strength of an electric current produced between two metal plates. Later scientists discovered that the metal selenium was particularly sensitive to sunlight, and during the 1880s Charles Fritts constructed the first selenium solar cell. Fritts's device was woefully inefficient, however, converting less than one percent of the received light into usable electricity.
The Fritts selenium solar cell was mostly forgotten until the 1960s when the drive to produce an efficient solar cell was renewed. It was known that the key to the photovoltaic cell was in creating a semiconductor that would release electrons when exposed to radiation within the visible spectrum. During this time researchers at the Bell Telephone Laboratories had been developing similar semiconductors to be used in communications systems. Quite by accident, Bell scientists Calvin Fuller and Daryl Chapin (who had been working independently on projects unrelated to solar cells) found the perfect semiconductor: a hybridized crystal called a "doped" cell made of phosphorous and boron. The first solar cells using these new crystals debuted in 1954 and yielded a conversion efficiency of nearly six percent. Later improvements in the design increased the efficiency to almost fifteen percent, a high mark by even today's standards.
In 1957 Bell Telephone used a silicon solar cell to power a telephone repeater station in Georgia. The process was considered a success, though it was still too inefficient to penetrate the general marketplace. The first real application of silicon solar cells came in 1958, when a solar array was used to provide electricity for the radio transmitter of Vanguard 1, the second American satellite to orbit the earth. Solar cells have been used on almost every satellite launched since.
Once space exploration had proven their efficacy, photovoltaic cells began to appear more and more frequently in homes. Just about any small appliance can be adapted to run on solar power, but by far the most successful have been watches and pocket calculators. These devices generally use a solar cell to charge a nickel-cadmium battery, so that they can be used even during periods of dim light.
Even in the early days of solar technology scientists envisioned vast photovoltaic arrays that could power entire cities. Those early dreams have been realized to a small extent by many homeowners who have installed solar panels in their homes. The usefulness of these panels is limited, however, by their relatively low rate of efficiency, as well as by the limited hours of available sunlight. It is unlikely that solar power will replace that gleaned from fossil fuels even in the distant future; still, the production of solar energy has increased steadily, approximately doubling each year. At that rate, it is conceivable that, by the year 2000, ten percent of the energy produced in the world will be produced by solar cells.
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