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Photovoltaics (PV) is a technique of producing electrical power by converting solar
radiation into direct current electricity using semiconductors and the photovoltaic
effect. Photovoltaic power generation uses solar panels composed of a number of
solar cells containing a photovoltaic material. Materials presently used for
photovoltaics include i.e. monocrystalline silicon, polycrystalline silicon, amorphous
silicon and cadmium telluride. Due to the increasing demand for renewable energy
sources, the manufacturing of solar cells has advanced considerably in recent years.
Solar photovoltaics is growing quickly to a total global capacity of 40,000 MW at the
end of 2010. More than 100 countries use solar PV. Installations may be ground-
mounted or built into the roof or walls of a building.
Driven by progress in technology and increases in manufacturing, the cost of
photovoltaics has declined steadily since the first solar cells were manufactured. Net
metering and financial incentives, such as preferential feed-in tariffs for solar-
generated electricity, have supported solar PV installations in many countries.
The photovoltaic effect is the creation of a voltage (or a corresponding electric
current) out of a material exposed to light. Though the photovoltaic effect is directly
related to the photoelectric effect, the two processes are different and should be
distinguished. In the photoelectric effect, electrons are ejected from a material's
surface upon exposure to radiation of sufficient energy. The photovoltaic effect is
different in that the generated electrons are transferred between different bands (i.e.,
from the valence to conduction bands) within the material, resulting in the build-up of
a voltage between two electrodes. The photovoltaic effect was first observed by
Alexandre-Edmond Becquerel in 1839.
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 term photovoltaic
stands for the unbiased operating mode of a photodiode in which current through the
device is entirely due to the transformed light energy.
Solar cells produce direct current electricity from sunlight, 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
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 many modules must be arranged together. Although the
selling price of modules is still too high to compete with grid electricity in most places,
significant financial incentives in different countries enforced a huge growth in
demand. Due to the growing demand for renewable energy sources, the manufacture
of solar cells and photovoltaic devices has advanced significantly in recent years.
Many of the PV-plants are integrated with agriculture and some use innovative
tracking systems that follow the sun's daily path across the sky to generate more
electricity than conventional fixed-mounted systems. There are no fuel costs or
emissions during operation of the power stations.
Photovoltaic production has been increasing by an average of more than 20 percent
each year since 2002, making it the world’s fastest-growing energy technology. At the
end of 2009, the cumulative global PV installations surpassed 21 GW. Roughly 90%
of this generating capacity consists of grid-tied electrical systems which pump the
PV-produced energy back into the public net. Germany installed a record 3.8 GW of
solar PV in 2009 and 7.4 GW in 2010. The German PV industry generated over
10,000 jobs in production, distribution and installation.
Vocabulary: valence: Ladungszahl (elek.); conduction band : Leitungsband (elek.);
radiation: Strahlung; electric current: Stromstärke; unbiased. unverfälscht; operating
mode: Betriebsart, Funktionsweise; grid connected: Anbindung an das öffentliche
Stromnetz; power generation: Stromproduktion; DC (direct current): Gleichstrom; AC
(alternating current): Wechselstrom; device: techn. Anlage, Gerät; net metering: