French physicist Edmond Becquerel first described the photovoltaic (PV) effect in 1839, but it remained a curiosity of science for the next three quarters of a century. At only 19, Becquerel found that certain materials would produce small amounts of electric current when exposed to light. The effect was first studied in solids, such as selenium, by Heinrich Hertz in the 1870s. Soon afterward, selenium PV cells were converting light to electricity at 1% to 2% efficiency. As a result, selenium was quickly adopted in the emerging field of photography for use in light-measuring devices.
Major steps toward commercialising PV were taken in the 1940s and early 1950s, when the Czochralski process was developed for producing highly pure crystalline silicon. In 1954, scientists at Bell Laboratories depended on the Czochralski process to develop the first crystalline silicon photovoltaic cell, which had an efficiency of 4%.
Although a few attempts were made in the 1950s to use silicon cells in commercial products, it was the new space program that gave the technology its first major application. In 1958, the U.S. Vanguard space satellite carried a small array of PV cells to power its radio. The cells worked so well that PV technology has been part of the space program ever since. Today, solar cells power virtually all satellites, including those used for communications, defence, and scientific research.
Figure 1. Even today, PV plays an important role in space, supplying nearly all power for satellites
The computer industry, especially transistor semiconductor technology, also contributed to the development of PV cells. Transistors and PV cells are made from similar materials and operate on the basis of similar physical mechanisms. As a result, advances in transistor research provided a steady flow of new information about PV cell technology. (Today, however, this technology transfer process often works in reverse, as advances in PV research and development are sometimes adopted by the semiconductor industry.)
Despite these advances, PV devices in 1970 were still too expensive for most "down to Earth" uses. But, in the mid-1970s, rising energy costs, sparked by a world oil crisis, renewed interest in making PV technology more affordable. Since then, the federal government, industry, and research organizations have invested billions of dollars in research, development, and production. Often, industry and the federal government work together, sharing the cost of PV research and development.
Today's commercial PV systems can convert from 7% to 17% of sunlight into electricity. They are highly reliable and last 20 years or longer. The cost of PV-generated electricity has dropped 15- to 20-fold, and PV modules now cost around $6 per watt (W) and produce electricity for as little as 25 to 50 cents per kilowatt-hour (kWh).