Photovoltaics

**Photovoltaics** (**PV**) is a method of [|generating electrical power] by converting [|solar radiation] into [|direct current][|electricity] using [|semiconductors] that exhibit the [|photovoltaic effect]. Photovoltaic power generation employs [|solar panels] composed of a number of [|solar cells] containing a photovoltaic material. Materials presently used for photovoltaics include [|monocrystalline silicon], [|polycrystalline silicon] , [|amorphous silicon] , [|cadmium telluride] , and [|copper indium gallium selenide] /sulfide. [|[1]] Due to the growing demand for [|renewable energy] sources, the manufacturing of solar cells and [|photovoltaic arrays] has advanced considerably in recent years. [|[2]][|[3]][|[4]] Solar photovoltaics is growing rapidly, albeit from a small base, to a total global capacity of 67,400 [|megawatts] (MW) at the end of 2011, representing 0.5% of worldwide electricity demand. [|[5]] The total power output of the world’s PV capacity run over a calendar year is equal to some 80 billion kWh of electricity. This is sufficient to cover the annual power supply needs of over 20 million households in the world. [|[5]] More than 100 countries use solar PV. [|[6]] Installations may be ground-mounted (and sometimes integrated with farming and grazing) [|[7]] or built into the roof or walls of a building ( [|building-integrated photovoltaics] ). Driven by advances in technology and increases in manufacturing scale and sophistication, the cost of photovoltaics has declined steadily since the first solar cells were manufactured [|[8]] and the levelised cost of electricity ( [|LCOE] ) from PV is competitive with conventional electricity sources in an expanding list of geographic regions. [|[9]] [|Net metering] and financial incentives, such as preferential [|feed-in tariffs] for solar-generated electricity, have supported solar PV installations in many countries. [|[10]] With current technology, photovoltaics recoup the energy needed to manufacture them in 1 to 4 years. Photovoltaics are best known as a method for generating electric power by using solar cells to convert energy from the sun into a flow of electrons. The [|photovoltaic effect] refers to photons of light exciting electrons into a higher state of energy, allowing them to act as charge carriers for an electric current. The photovoltaic effect was first observed by [|Alexandre-Edmond Becquerel] in 1839. [|[13]][|[14]] The term photovoltaic denotes the unbiased operating mode of a [|photodiode] in which current through the device is entirely due to the transduced light energy. Virtually all photovoltaic devices are some type of photodiode. Solar cells produce direct current electricity from sun light, which can be used to power equipment or to [|recharge a battery]. The first practical application of photovoltaics was to power orbiting satellites and other [|spacecraft], but today the majority of [|photovoltaic modules] are used for grid connected power generation. In this case an [|inverter] is required to convert the DC to AC. There is a smaller market for off-grid power for remote dwellings, [|boats], [|recreational vehicles] , electric cars, roadside emergency telephones, [|remote sensing] , and [|cathodic protection] of [|pipelines]. Photovoltaic power generation employs [|solar panels] composed of a number of [|solar cells] containing a photovoltaic material. Materials presently used for photovoltaics include [|monocrystalline silicon], [|polycrystalline silicon] , [|amorphous silicon] , [|cadmium telluride] , and [|copper indium gallium selenide] /sulfide. [|[1]] Due to the growing demand for [|renewable energy] sources, the manufacturing of solar cells and [|photovoltaic arrays] has advanced considerably in recent years. [|[2]][|[3]][|[4]] Cells require protection from the environment and are usually packaged tightly behind a glass sheet. When more power is required than a single cell can deliver, cells are electrically connected together to form photovoltaic modules, or solar panels. A single module is enough to power an emergency telephone, but for a house or a power plant the modules must be arranged in multiples as [|arrays]. A significant market has emerged in off-grid locations for solar-power-charged storage-battery based solutions. These often provide the only electricity available. [|[15]] The first commercial installation of this kind was in 1966 on Ogami Island in Japan to transition [|Ogami Lighthouse] from gas torch to fully self-sufficient electrical power. Due to the growing demand for renewable energy sources, the manufacture of solar cells and [|photovoltaic arrays] has advanced dramatically in recent years. [|[2]][|[3]][|[4]] Solar photovoltaics is growing rapidly, albeit from a small base, to a total global capacity of 67,400 [|megawatts] (MW) at the end of 2011, representing 0.5% of worldwide electricity demand. [|[5]] The total power output of the world’s PV capacity run over a calendar year is equal to some 80 billion kWh of electricity. This is sufficient to cover the annual power supply needs of over 20 million households in the world. [|[5]] More than 100 countries use solar PV. [|[6]] World solar PV capacity (grid-connected) was 7.6 GW in 2007, 16 GW in 2008, 23 GW in 2009, and 40 GW in 2010. [|[16]][|[17]] __ [|[18]] __ More than 100 countries use solar PV. [|[6]] Installations may be ground-mounted (and sometimes integrated with farming and grazing) [|[7]] or built into the roof or walls of a building ( [|building-integrated photovoltaics] ). Photovoltaic power capacity is measured as maximum power output under standardized test conditions (STC) in "Wp" (Watts peak). [|[19]] The actual power output at a particular point in time may be less than or greater than this standardized, or "rated," value, depending on geographical location, time of day, weather conditions, and other factors. [|[20]] Solar photovoltaic array [|capacity factors] are typically under 25%, which is lower than many other industrial sources of electricity. [|[21]] The EPIA/ [|Greenpeace] Advanced Scenario shows that by the year 2030, PV systems could be generating approximately 1.8 TW of electricity around the world. This means that, assuming a serious commitment is made to [|energy efficiency], enough solar power would be produced globally in twenty-five years’ time to satisfy the electricity needs of almost 14% of the world’s population.

