Environmental Engineering Reference
In-Depth Information
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solar thermal power plants
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photolysis systems for fuel production
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solar collectors for water heating
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passive solar heating systems
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photovoltaics, solar cells for electricity generation.
Solar thermal power plants
Solar thermal power (power derived from the
thermal use of solar energy) can be used to generate electricity or to produce
high-temperature steam. Solar thermal power plants used for electricity
generation are:
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parabolic trough power plants
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solar thermal tower power plants
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solar furnace
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Dish-Stirling systems
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solar chimney power plants.
Parabolic trough power plants
were the first type of solar thermal power plant
technologies operating commercially. Nine large power plants called SEGS I to
IX (Solar Electric Generation System) were commissioned in California
between 1984 and 1991. These power plants have a nominal capacity of
between 13.8 and 80 MW each, producing 354 MW in total.
The parabolic trough collector consists of large curved mirrors, which
concentrate the sunlight by a factor of 80 or more to a focal line. A series of
parallel collectors are lined up in rows 300-600 metres long. Multiple parallel
rows form the solar collector field. The collectors moved on one axis in order
to follow the movement of the sun; this is called tracking. A collector field can
also be formed by long rows of parallel Fresnel collectors. In the focal line of
the collectors is a metal absorber tube, which usually is embedded into an
evacuated glass tube to reduce heat losses. A special selective coating that
withstands high temperatures reduces radiation heat losses.
In the Californian systems, thermo oil flows through the absorber tubes.
These tubes heat the oil to 400°C. A heat exchanger transfers the thermal
energy from the oil to a water-steam cycle (also called the Rankine cycle). A
pump pressurizes the water and an economizer, vaporizer and a superheater
jointly produce superheated steam. This steam expands in a two-stage turbine;
between the high- and low-pressure parts of this turbine is a reheater. The
turbine itself drives an electrical generator that converts the mechanical energy
into electrical energy; the condenser after the turbine condenses the steam back
to water, which allows the closing of the cycle by feeding this water back into
the initial pump.
Solar collectors can also produce superheated steam directly. This makes
the thermo oil superfluous and reduces costs due to savings associated with
not using the expensive thermo oil. Furthermore, heat exchangers are no
longer needed. However, direct solar steam generation is still at the prototype
stage.
