Before any discussion on the parabolic trough CSP, it is best if we first understand what the CSP Technology is all about. CSP (which is also known as the Concentrated Solar Power or Concentrating Solar Power) is a technology which gets its power from the direct radiation of the sun’s thermal energy. It is a renewable energy and does not involve the combustion of any particles. It is a clean form of energy which is today being gradually coming back nto the limelight. Various solar technologies are now being adopted and gradually replacing the fossils (especially in the Sun Belt regions).
The CSP technology was developed from the principle of converging and diverging of sun rays; the understanding of the principle of diverging and converging served as the door way to the invention of the technology.
The CSP technology can be further broken down into four. There are four different approaches to the CSP technology, all of which we shall be discussing in a moment.
The various approaches are:
- The Parabolic Dish CSP
- The Power Tower CSP
- The Compact Linear Fresnel Reflectors
- The Parabolic Trough CSP
In a cyber-lecture I held a few weeks back, I explained in details how the Parabolic Trough along the other CSP technologies work, there, I explained in details, how the other technologies work and their various components. In this post, we will be having a quick summary of the parabolic trough.
The Parabolic Trough Plant (PTPP) is made up of a field covered with arrays of parabolic troughs/giant U-shaped mirrors which direct all the incoming sunlight and heat unto a receiver tube position at its focal point.
that it can effectively concentrate all the incoming sunlight unto a receiver tube which passes through its focal point/line. The receiver tube contains a fluid which absorbs the energy and then processes it to another part of the plant where it is used to generate electricity, run water pumps or do some other work.
Looking at the Parabolic Trough in summary, it is a technology which comprises of three main components: The reflector, collector, and the component which utilizes the captured heat.
ENERGY STORAGE IN THE PARABOLIC TROUGH CSP.
Aside the Parabolic Dish CSP, every other CSP technology supports energy storage, every other CSP technology gives room for power generation at night and periods when the sun is behind clouds or during eclipse.
I earlier stated that in the PTPP, there is a collector tube which runs trough the focal line of the reflectors. In the heat collector tube, is a fluid which runs through it, absorbing the heat energy and passing it to another part of the plant where it is then used for power generation.
In the old CSP plants, there was no energy storage and as a result, water was passed through the collector tube in place of the Heat Transfer Fluid. Later, as technology advanced, energy storage was theb implemented and power can t be generated several hours into the dark.
The Heat Transfer Fluid (also known as the Heat Transfer Medium or HTF) is a fluid which can attain a very high temperature as liquid. It varies with the technology, different CSP technologies operate at different temperatures and as such, the same HTF may not be as efficient in the parabolic trough as it is in the power tower CSP, because they operate at different temperatures. In the parabolic trough CSP plant, the most commonly used Heat transfer fluid is the mineral, and the synthetic oils.
The absorbed energy then flows to the hot tank where it is stored and then used when the need arises. The hot tank is usually equipped to reduce or minimize the energy loss. It is properly insulated to ensure that much of the absorbed energy is not lost.
After storage, the hot fluid then flows to a heat exchanger where the heat is transferred to water to produce steam for power generation.
When the heat has been extracted from the fluid, it then flows back into the system to get heated again and on.
HOW THE POWER IS GENERATED
Just in case you don’t understand how the the heat is generated using the steam, what happens is that when the water has been heated to a very high temperature (has gotten to its boiling point) steam is then produced. The steam which runs at a very high pressure goes to power generation unit to do its work. As the steam runs at that high pressure, it forces its way through a steam engine, turning turbines as it tries to escape to the atmosphere. This continuous action (pushing the turbine) as it flows out then serves as the thrust to keep the turbine in constant motion. As the turbine moves, the mechanical energy is then converted to electrical energy by the copper coils in the engine.
A copper coil is a device which possesses both magnetic and electric properties. When it is fed with electric signals, in the presence of a magnet, it jerks. With the help of a split ring or slip ring cummutator and carbon brushes, the continuous movement can then be used to generate electrical signal. You may tend to ask, what connects this topic to Thermodynamics, well the answer is short, without it, power cannot be generated with the CSP technology.
When there is however, a thrust In the presence of a magnetic field, the coil tends to create electric charges which can then be captured and used to do electrical work.
THE PARABOLIC TROUGH REFLECTOR AND HEAT COLLECTOR
When ranking the most important components of the PTPP, the reflector and collector are one of the most important of all. There would be no reflected heat if there are no reflectors, in the same way, there would be no absorbed heat if your plant has no collectors – so you agree with me that these are the two most important components of the plant.
The reflector is generally composed of a bent glass mirror, with either a silver or aluminium coated on the backside of the glass (about 4mm thick) which is in iron thereby maximizing the reflectance of light (about 93.5%) with a silver coated protected by multilayer paint.
The receiver (or Heat Collector Element) is made up of a long metallic tube and mostly a glass covering it. In between the glass envelops and metallic tube is either air or a vacuum (this is done to minimize the loss of heat and to allow for thermal expansion). A glass-to-metal seal is crucial as well in the reduction of heat loss. The metallic tube is usually coated black to aid in the absorption of heat as black is a good absorber of heat (the black body principle). The HCE is the core part that enables the parabolic trough to acquire high efficiency , with only a 10% heat loss.
Other supporting structures include the:
- Pylons
- Controls
- Drive
- Collector interconnect
PYLONS: They are the foundations that hoist the mirrors.
DRIVE: The drive is responsible for the tracking of the sun’s movement. The drive enables the system to track the sun along a two way axis.
THE COLLECTOR INTER-CONNECT: The insulated hoses that link up the whole power cycle.
The collector inter-connect for each Solar Collector Assembly (SCA) is connected to the central computer where all the activities are being monitored and controlled. It keeps track of the drive and also watches out for any abnormal conditions
A SUMMARY OF THE PARABOLIC TROUGH CSP
The quick summary of the parabolic trough CSP is that, it is a form of CSP technology which Is made up of a parabolic mirror with a Heat absorber tube passing through its focal line. In the tube is a Heat Transfer Fluid which flows through it constantly, circulating the heat to the heat storage tank where it is kept until it is needed (in cases where heat storage medium is in place. In cases where the heat is being stored, the heat transfer fluid then flows to the heat exchanger where the absorbed heat is then transferred to water and used to produce steam. The steam is what is used in the steam engine to generate electrical power.
METRIKKS 
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