How Solar Energy Works
Commonly known as solar cells, PV systems are already an important part of our lives. The simplest systems power many of the small calculators and wrist watches we use every day. More complicated systems provide electricity for pumping water, powering communications equipment, and even lighting our homes and running our appliances. In a surprising number of cases, PV power is the cheapest form of electricity for performing these tasks.
The Photovoltaic Effect
In 1839 19-year old French physicist Edmond Becquerel first described the photovoltaic effect, finding that certain materials would produce small amounts of electric current when exposed to light. This was to remain a nothing more than a curiosity of science for the next three quarters of a century.
The PV effect was first studied in selenium by Heinrich Hertz in the 1870’s. Soon selenium photovoltaic cells were converting light to electricity at 1-2% efficiency. As a result, selenium was quickly adopted in the emerging field of photography for use in light-measuring devices.
Major steps toward the commercialization of photovoltaic cells began in the 1940s and early 1950s, when the Czochralski process had been developed for producing highly pure crystalline silicon. In 1954, scientists at Bell Laboratories depended on this process to develop a crystalline silicon photovoltaic cell, with an efficiency of 6%.
How Photovoltaic Cells Produce Electricity
The "photovoltaic effect" is the basic physical process through which a PV cell converts sunlight into electricity. Sunlight is composed of photons, or particles of solar energy. These photons contain various amounts of energy corresponding to the different wavelengths of the solar spectrum.
When photons strike a PV cell, they may be reflected or absorbed, or they may pass through it. Only the absorbed photons generate electricity. When this happens, the energy of the photon is transferred to an electron in an atom of the cell (which is actually a semiconductor) that then becomes part of the current in an electrical circuit. A built-in electric field in the PV cell provides the voltage needed to drive the current through an external load (such as a light bulb).