By Alma Rosa López Martinez
RENOVETEC Technical Contributor
Translated by Beatriz Cantabrana
The Solar Energy use is not something new; it has been
used for several centuries
ago for different functions. But it was replaced for crude oil in the
Industrial Revolution.
Currently,
due to high crude oil costs and its great environmental impact, it has
decided to return to the use of solar energy. If crude oil had not
replaced the solar energy, surely that nowadays, we would have more
technology in renewable energy.
There
are many types of Solar Energy; probably the most popular is the
photovoltaic energy (PV) which is based on electrical energy production
by
photovoltaic panels. But there are other ways to obtain electrical
energy from sunlight with probably,better results.
An
example is the Solar Thermal Energy, which transforms the solar energy
into electricity. Solar Thermal Power Plants run trough a
thermodynamic cycle, which consists of a set of mirrors (heliostats);
located on land and properly oriented to reflect solar radiation that
comes into contact with them. All this radiation is directed to a
receiver so all the energy
is transported at the same time.
Photovoltaic Solar Energy History. Main Milestones.
In
1893, the French physicist Edmond Becquerel discovered the photovoltaic
effect, he noticed that some materials could convert light into
electricy.
In
1887, thanks to several experiments, Heinrich Hertz was able to
produce photovoltaic cells which process light into electricity.
Albert Einstein could not be missed in Solar Energy
history; because in
1905 he talked about the photo electric effect, associated with the
generation of electricity in solar cells.
The Czochralski process (method to obtain high purity
silicon crystals) increased the PV market. In 1954, scientist at Bell Laboratoires (Murray Hill, NJ D.M. Chapin,
C.S. Fuller, y G.L) made the first silicon solar cell capable of creating a
controlled
electric current. During the Cold War, solar cellars were installed on
airplanes and satellites.
In 2002, in Japan, 25000 solar panels were installed on
the roofs of houses all across the country.
In 2003, Solar and Wind Energy investements
exceeded 20000
million dollars a year.
In 2006, the Photovoltaic Energy in the world
exceeds 2500 megawatts .
Solar Thermal Energy History.
In China and in ancient Greece, people used mirrors or
glass to reflect the sunlight for makig fires.
During
wartime, the same technique was used to set fire to enemy
ships. In the early twentieth century, simple machines had already been
invented that could run from the concentration of the sun's heat.
In
1913, the american Frank Shuman developed the first solar thermal
pumping
station in Meadi, Egypt. This system worked with 5 large reflectors,
each one had 62 meters long and they contained glass mirrors making a
cylinder-like parabola. Each reflector focused the sunlight on a tube
along its length, heating the water that flowed inside them. In that
process, steam was generated and it was used to feed
a motor connected to a pump. This system was able to
distribute 6000 gallons of water per minute from the River Nile to
nearby places.
Solar
Thermal Energy modern history began on 70s crude oil crisis. Jimmy
Carter, then President of the U.S., boosted the SEGS (Solar Energy
Generating System) and decided to install solar
thermal collectors on the White House roof to heat water.
In
1984, in California the first plant SEGS-1 was built.
These kind of plants operate with a parabolic
trough solar collector system. The SEGS consist of a solar field with
parallel lines of parabolic trough solar collectors connected in series
to
convert solar energy into heat which warms the oil that flows through
the absorber tubes of solar collectors. Hot oil is sent to a heat
exchanger which generates superheated steam required to activate a
turbo-alternator, and that is how electricity is produced.
Storing Solar Thermal Power by Molten Salt Tanks.
SEGS
plants began with a 14 MW power and ended with a 80 MW power, with a
total installed capacity of 354 MW. These plants
continue to operate successfully until 2003.
The
record with this kind of plants inspired Spain to continued its
investigations which carry out the opening in 2009 the solar thermal
plant in Aldeire
Andasol-1, Granada.
The
aim of Andasol-1 project is to convert solar energy into electrical
energy through a solar field with
parallel lines of parabolic trough solar collectors, a 6 hours capacity thermal
storage system plus 25% of safety measures based on molten
salts and a 49,9 MW capacity steam cycle.
Andasol-1
procedure is as follows; when the sun shines, field collectors
concentrate solar radiation on the absorber tubes and this radiation
heats the fluid inside them until
393ºC. In the fluid are inorganic salts such as sodium nitrate and
potassium nitrate.When these inorganic salts reach the higher
temperature, fluid is
transported to a hot tank. At night, fluid is transferred from the hot
tank to the cold one, there is where energy transference takes place
and steam is generated.
Andasol-1 achieved an average annual efficiency of 16% on conversion
of solar radiation into electrical energy.
It should also emphasized the PS10 and PS20 solar power
plants created by Abengoa Solar Company.
The
PS10 is the first solar tower plant that produces electricity in a
steady and commercial way. It consits of 624 heliostats that
concentrate the
solar radiation incident on the receiver that is found on top of a
tower 115 meters high.
The
receiver is responsible for generating saturated steam directly,
it consists of 4 vertical panels 5,5 meters wide and 12 meters high.
PS10
contains 30 minutes of storage even at low irradiation conditions. The
solar plant
is capable of supplying 5,500 homes and save 6,700t 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 high.It produces
steam to generate electricity in the turbine. The plant can supply
10,000
homes and save 12,000 t of CO2 per year.
Currently
the researches about solar thermal energy are growing. Maybe a
Solar Thermal Plant construction cost 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 reserve it.
