Although a French physicist named Becquerel first reported the photovoltaic effect, the first solar cell was probably constructed by Charles Fritts in the early 1880’s. Fritts coated selenium with a very thin gold layer, but the efficiency of this first solar cell was abysmal. It wasn’t until 1941 when Russell Ohl patented the silicon solar cell that efficiency started to improve appreciably. Soon, other scientists had improved on Ohl’s silicon solar cell to achieve a 6 percent return on energy conversion in strong sunlight. Bell Laboratories produced the first crystalline silicon solar cell in 1954, but its efficiency was merely 4%.Because the first large-scale use for solar cells was space satellites, government funding began to power the research, which had a galvanizing effect on solar cell research. By the 1970’s, the USSR had created Gas heterostructure solar cells with a high efficiency, although production was very limited until equipment design caught up to design theory. By the 1980’s, the US had produced a cell with 20% efficiency for use in the space program. And by early in 2000, efficiency was up to 24%. As of 2007, solar cells with an efficiency of 28% are manufactured by the two companies that dominate world solar cell production, Spectrolab and Emcore Photovoltaics.

While silicon wafer-based first-generation solar cells make up almost 90% of the solar cell market for terrestrial applications, second generation or thin-film solar cells make up the same percentage of the space applications. While nowhere near as efficient as their first generation relatives, these thin-film cells are much lighter and more pliable, prime considerations for space flight. Other cells are being developed at the present time including some that are dye sensitized, and thus able to respond to all light frequencies, unlike the silicon-based cells. There are even cells that are capable of using infrared frequencies, which would allow them to operate at night to some extent. Solar cell technology now in the research stage includes nanocrystal solar cells, photo electrochemical cells and polymer solar cells. One emerging leader in the solar cell technology race is Nanosolar at http://www.nanosolar.com, a company that is partially owned by the founders of Google, Sergey Brin and Larry Page.

There is very little to wear out on photovoltaic cells. It’s reasonable to expect a well-designed and properly installed system to have a lifetime of three decades or more. The most common failure in a photovoltaic system are the other components that are needed to convert electrons to AC current. The inverter, the batteries, the wiring — all are subject to corrosion, wear and aging. Batteries will need to be replaced at proper intervals, for instance. The cells themselves, however, should need no maintenance over the course of their lifetime unless they’re exposed to unusually harsh weather conditions.

Something that needs to be taken into consideration is the amount of sunlight that falls on the solar cells. This can significantly affect the electrical output. Mechanical devices to assist the cells in “tracking” the sun are often built into solar modules and arrays. Before installing photovoltaic cells, contractors often research the sun’s irradiance at the latitude of the installation. Irradiance can be determined by consulting the Department of Energy’s charts or at Advanced Energy Group’s website at http://www.solar4power.com.

Modules are groups of solar cells connected in a series and attached to a panel. Modules are constructed to deliver a range of output. Depending on the application, output is measured in watts or kilowatts and is calculated using a formula that takes into consideration peak power usage and average power output of each cell. Arrays are groups of modules and several thousand may be used in an electrical generating plant designed to power hundreds or even thousands of houses. Solar power is extremely adaptable to a wide range of applications, which puts it at the forefront of renewable energy sources.