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By
Alma Rosa López Martinez
Técnical Colaborator of RENOVETEC
The Solar Energy is not something new; it was
used for many centuries ago. But it was replaced for crude oil in the
Industrial Revolution.
Currently due to high crude oil costs and its
major environmental impact, has decided to return to the use of solar energy.
If crude oil did not exist, now we would have more technology about renewable
energy.
There are
a lot of kinds of Solar Energy; probably the most popular is the photovoltaic energy
which is a way to obtain electrical energy by photovoltaic panels. But there
are another ways to obtain electrical energy by solar light and probably with
better results.
One example is the Solar Thermal energy, which transforms the Solar
Energy into Electric Energy. The Solar Thermal Power Plants work by a
thermodynamic cycle, which consists of a set of mirrors (heliostats); located
on land and properly oriented to reflect sunlight that strikes them, all this
radiation is delivered to a receiver so all the energy is transported at the same
time.
History of Photovoltaic Solar Energy.
In 1893, Edmond Becquerel (French physicist) discovered the photovoltaic
effect, noted that some materials transforms the light into electric current.
In 1887, through several experiments, Heinrich Hertz was able to produce
photovoltaic cells which process light into electricity.
Albert Einstein could not miss in the history of Solar Energy; in 1905
he talked about the photo electric effect, associated with the generation of
electricity in solar cells.
The Czochralski process (method to obtain crystals of high purity
silicon) increased the PV Market. In 1954 scientist at Bell Laboratories
produced the first silicon solar cell capable of creating a controlled electric
current. During the Cold War took place solar cells on airplanes and
satellites.
In 2002, Japan installed 25, 000 solar panels on the roofs of houses
across all the country.
In 2003, investments in solar energy a wind energy exceeded 20 000
million per year.
In 2006, in the world are more than 25 0000 megawatts in photovoltaic
energy.
History of Solar Thermal Energy
In China and in the ancient Greece, people used the sunlight with
mirrors or glass for making fires. During war time, the same technique was used
to set fire to enemy ships. In the early twentieth century had already been
invented simple machines that could run from the concentration of heat from the
sun.
In 1931, Frank Shuman (American) developed the first solar thermal pumping
station in Meadi, Egypt. This system worked with 5 large reflectors, each one
had 62 meters long and contained glass mirrors forming a cylinder like parable.
The modern history of Solar Thermal Energy began in the crude oil crisis
of the 70s. Jimmy Carter, then president of the U.S., boosted the concentrated
solar power plants, SEGS and decided to install solar thermal collectors on the
roof to heat water from the White House.
In
1984, California built the first plant-1 SESGS (Solar Energy Generating
System). These kinds of plants operate with a parabolic trough
collector system. The SEGS consist of a solar field with parellel rows
of parabolic trough collectors connected in series to convert solar
energy into heat, warnind the oil passing throug the absorver tubes of
solar collectors. The hot oil is sent t a heat exchanger where it
generates superheated steam required to drive a turbo-alternador, and
that is how it produces electricity. SEGS
plants began with a power of 14MW and ended with an output of 80MW,
with a total installed capacity of 354 MW. These plants continue to
operate successsfully until 2003.
Diagram of a typical SEGS plant
The record with this type of
plants inspired Spain to continue with its investigations, opening in 2009 the
thermal plant in Aldeire Andasol-1, Granada.
The project aims Andasol-1
is to convert solar energy into electrical energy through a solar field of
parabolic trough collectors, a thermal storage system capacity of 6 hours plus
25% confidence based on molten salts and a steam cycle 49, 9 MV-building Andasol-1 process: when the
sun shines field collectors concentrate solar radiation on the absorber tubes
and heat the fluid to a temperature of 393 °. In the fluid are inorganic salts
such as sodium nitrate and potassium nitrate, when they reach the higher
temperature fluid is transported to a hot tank. At night, the hot tank to tank
transfers the cold fluid, hence the hot salt transfer energy to the fluid and
generate steam.
Andasol-1 achieved an
efficiency of 16% average annual conversion of solar radiation into electrical
energy.
We should also highlight the PS10 and PS20 solar
power plants created by the Abengoa Solar Company.
The PS10 is the first solar tower plant that
produces electricity in a stable way and commercial. It consists of 624
heliostats to focus solar radiation incident on the receptor that is found on
top of a tower 115 meters high.
The receiver is responsible for generating
saturated steam directly, consists of 4 vertical panels 5.5 m wide and 12 m in
height. PS10 contains 30 minutes of storage even at low irradiation. The solar
plant is capable of supplying 5500 homes and save 6700t of CO2 per year.
The PS20 is the second plant in the world with
this technological system. It consists of 1 255 heliostats to reflect solar
radiation received on the receiver on the tower of 165 meters of height which
produces steam to generate electricity in the turbine. The plant can power 10
000 homes and save 12 000t of CO2 per year.
Currently the researches
about solar thermal energy are growing, Maybe a Solar Thermal Plant
construction costs more than a typical thermal plant, but eventually they will
be the only alternative because we are killing our planet and we must act fast
to reverse.
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