Introduction to Photovoltaic Systems

Photovoltaic (or PV) systems convert light directly into electricity.

The term photo comes from the Greek phos, which means “light.” The term volts a measure of electricity named for Alessandro Volta (1745-1827), a pioneer in the development of electricity. Photovoltaics literally means light–electricity.  
                     

Commonly known as solar cells, PV cells are already an important part of our lives. The simplest PV systems power many of the small calculators, wrist watches, and outdoor lights we see every day.                                                                                                

Larger PV systems provide electricity for pumping water, powering communications equipment, and even lighting homes and running appliances.                                            

In certain applications and remote settings, such as motorist aid call boxes on highways and pumping water for livestock, PV power is the cheapest form of electricity. Some electric utility companies are building PV systems into their power supply networks.                                                                      

History of photovoltaics 
                                                   French physicist Edmond Becquerel first described the photovoltaic effect in 1839, but it remained a curiosity of science for the next half century. At the age of 19, Becquerel found that certain materials would produce small amounts of electric current when exposed to light. In the 1870s, William Adams and Richard Day showed that light could produce an electric current in selenium. Charles Fritts then invented the first PV cell using selenium and gold leaf in 1883, which converted light to electricity at about one percent efficiency.                                                                           

The conversion efficiency of a PV cell is the proportion of radiant energy the cell converts into electrical energy, relative to the amount of radiant energy that is available and striking the PV cell.                                                                                                                               

 This is very important when discussing PV devices, because improving this efficiency is vital to making PV energy competitive with more traditional sources of energy, such as fossil fuels.                                                                                                                                  

During the second half of the 20th century, PV science was refined and the process more fully developed. Major steps toward commercializing photovoltaics were taken in the 1940s and 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 a conversion efficiency of four percent.                                                                                                                                    

As a result of technological advances, the cost of PV cells has decreased significantly over the past 25-30 years, as the efficiency has increased.                                                                                    

 Today’s commercially available PV devices convert 13 to 30 percent of the radiant energy that strikes them into electricity.                                                                                               

In the laboratory, combining exotic materials with specialized cell designs has produced PV cells with conversion efficiencies as high as 43 percent. The current expense of these technologies typically restricts their use to aerospace and industrial applications, where the unit cost of a solar array that powers, for example, a satellite is a minor concern.