Technologies that use mirrors to reflect and concentrate
sunlight onto receivers collect solar energy and convert it to heat. This
thermal energy can then be used to produce electricity via a steam turbine or
heat engine that drives a generator. Concentrating solar power (CSP) systems
are not to be used for normal people in their homes; these can only be used on
a utility-scale, in big power plants where hundreds of thousands of megawatts
of electricity is produced. CSP plants produce electricity by using mirrors to
focus sunlight on a central point to heat water or another heat-carrying fluid.
Since the invitation of CSP the technology has developed to have more than just
one type, today there three different types of concentrating solar power systems
and those are categorized by the way they absorb solar energy, the three types
are Power Tower systems(PTS), Linear CSP
systems and the Dish/Engine CSP systems.
Power Tower Systems
The PTS system has a large tower where the top part if the
tower has a collector and around the large tower there are many large flat
mirrors that reflect the sunlight to the top of the tower to the collector,
these flat mirrors are equipped with sensors that change their direction with
the sunlight to assure best efficiency. The solar energy is collected by a
heat-carrying fluid on the top of tower; this fluid is used to produce
pressurized steam to rotate the turbine which in turn rotates the generator to
generate electricity. The top of tower is very hot and temperature reaches to
be more than 1000 degree Celsius. The fluid used in the system is molten
nitrate salt, the fluid can sustain and hold heat more than the water; the
fluid also has the ability to store the heat for prolonged use and save it for
later. The ability to store heat inside the fluid is very important when there
are clouds or at night time when there are no sun rays, this allows for a
continuous generation of electricity.
Linear CSP Systems
This system use parabolic mirrors to reflect
sun rays and focus the sunlight onto a receiver tube placed above the reflected
mirror, the receiver has a heat-carrying fluid which is heated by the reflected
sun rays, and then, the hot fluid passes through a heat exchanger to heat and
make a steam, the steam in turn turns the turbine and generates electricity. They
are 75% efficient, the oil inside the tubes can be heated up to 400 degree Celsius.
Just like the PTC systems, some systems using the linear CSP systems use molten
salt as the heated fluid to store the heat inside and use it in cloudy days.
The Linear CSP systems use a lot of land space where
kilometers of mirrors are placed inside, the numerous numbers of mirrors are
needed to generate enough electricity to be worth the building cost. The angle
of the mirrors is constantly adjusted to ensure the heat-collecting tube is
constantly exposed to the concentrated solar beam; one of the problems with the
mirrors is that the dust causes the mirrors to be less efficient so cleaning
the mirrors are necessary to ensure best possible efficiency, the cleaning
process is done by using a special modified truck that has a robotic tools
installed, then the truck goes along the mirrors in a constant speed to let the
robotic tools do the cleaning.
Dish/Engine CSP Systems
These stand-alone systems consist of a large parabolic dish,
similar to the older satellite TV dishes, but have reflective mirrors that
concentrate the solar energy to a focal point. A heat collector and engine is
mounted at this focal point to create electricity. The entire unit is
constantly adjusted to directly face the sun, the two-axis tracked mirror must
follow the sun with a high degree of accuracy in order to achieve high
efficiencies. The receiver is heated up to 650°C.
As a standalone system, these units produce less than 25 kW
of electricity. The heated fluid is used to move a piston a Sterling engine
which in turn can drive a crankshaft of a generator. No turbine is necessary.
These units are too small to heat molten nitrate salt and therefore only
produce electricity when the sun is shining.
Advantages of CSP Systems
•Solar farms can be placed in hot, dry inhospitable locations
where human and wildlife is sparse.
•The entire system uses established technology that is
readily available (mirrors, tubes and electrical generators).
•These units produce electricity during the day when
air-condition loading is high. These clean-running, daytime power plants help
supplement other primary electrical generation sources.
Disadvantages of CSP Systems
•Expensive transmission lines need to be installed in remote
desert locations to get the useful energy to market. Since electrical
production may not be continuous, it takes a longer time for CSP systems to pay
for themselves.
•These units are most efficient during the daylight hours and
cannot be relied upon as primary electrical sources. Even the systems that use
heat storage techniques may stop producing electricity if it's overcast for a
number of days.
•Small dish/engine systems cannot be economically used in a
backyard to power a house. It is currently too expensive to build a system with
a mirror alignment system and a Sterling engine.
Concentrating solar power plants have been around
since the 1980's. They proved that large installations can be efficient and can
pay for themselves if an economy of scale is achieved. Advances in system
design have made these power plants more efficient at producing electricity but
since they only collect solar energy when the sun is shining, they are not as
cheap to operate as conventional hydro, nuclear or coal-fired power plants. The
solar system power plants are being in use worldwide especially in Europe where
the perfect combination of good temperature and sunlight is. The United Arab
Emirates also is focusing on solar energy as an alternative energy source and
is developing the technology through Masdar institute and it has one of the
largest solar generated electricity in the western region.
