Solar Energy - General Information
History
The PHOTOVOLTAIC (PV) effect was discovered by a French physics
scientist, Alexandre Edmond Becquerel in 1839, when he discovered that
electric current can be generated when certain structures are exposed
to light (he dipped platinum plates into liquid electrolytes). The
Americans Adams and Day in 1876, using a selenium crystal, did
the demonstration of the effect. The efficiency in this case was only
slightly above 1%. In 1905 Albert Einstein formulated an explanation
of the PV effect (the photon hypothesis). In 1949 the Americans Shockley,
Bardeen and Brattain discovered the transistorp and n junctions in doped semiconductors
materials. The first solar cell with an efficiency of about 6% was
developed, and later, in 1956, a silicon solar cell was made with an
efficiency of 10%.
The rapid development of space exploration opened up excellent opportunities
for solar cells application. In 1958, 108 solar cells were sent for the first time to
space for trial. Serial production began soon
afterwards, albeit in small numbers. In 1970, began annual production of
solar cells for space applications with total surface 500 m2. Earth-bound use
of solar cells was given a boost during the '73/'74 oil crisis, and
this led to launch numerous research and development
projects. The most important aim in this field is to reduce the cost
of PV plants.
Solar cells and photovoltaic plants have since then become a common part
of everyday life. Their application spectrum is broadening all the
time and ranges from small - scale applications in pocket calculators
and watches to large electricity - generating plants with outputs
in the kW and MW ranges.
Principle of operation of the solar cell
A silicon solar cell is a specially made semiconductor diode (photodiode),
in which a charge transport is effected by light. When light strikes
the solar cell, photons are absorbed by the electrons. The photons
energy excites the electrons to a higher energetic state, so
they leave a hole their position. Thus every absorbed photon
generates an electron-hole pair. The electric field separates the
negative electrons from the positive holes and the voltage is 0.5-0.6
Volts. These light generated charge carriers can now flow through
the external closed circuit.
Applications
Solar cells, solar modules and large-scale solar power plants have
become part of every day life. Direct power generation from sunlight
is being increasingly used in many fields. PV systems stand for mobility,
flexibility, and remote-site energy supply. Their operation involves
no noise and is environment friendly. The only restriction to the
expansion of their use is their relative high cost. Depending on the
storage of the generated current, we distinguish between:
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Grid
connected plants on buildings roofs and facades
These plants use the electricity grid as their energy store. |
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Off
- grid electricity supply
Today, small systems such as telecommunications equipment, holiday
houses, alpine shelters, weather stations, beacon buoys are increasingly
being powered by PV. PV makes the system independent of electricity
grids. The battery takes over the job of storing energy. In case that
loads are AC, a DC-AC inverter must also be included in the system. |
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PV that are used widely today are the following: |
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The mono-crystalline
photovoltaics
The poly-crystalline photovoltaics
The amorphous silicon photovoltaics
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(Source: Heliocentris Handbook) |
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