This document provides an overview of parabolic trough concentrating solar power (CSP) technology. It discusses the status and commercialization of CSP, with parabolic trough systems being the most widely used. Key components of parabolic trough plants include the solar field, power generation system, and thermal storage. The solar field, consisting of parabolic trough collectors, is the most expensive component. Research aims to reduce costs by improving collector structures, reflective surfaces, and heat transfer fluids. Thermal storage allows electricity production when the sun is not available. Parabolic trough CSP has progressed from early demonstration plants to commercial installations, with costs declining as the technology matures.

1. Concentrating
Solar Power
By
Sindu A Maiyya
Poondla Prashant
IIT Madras
For
Energy Alternatives India
This paper looks at Parabolic Trough Concentrating Power
Solar technologies from a technological perspective
and provides technology recommendations for each
component used in the system and current developments
in this area. It also provides an analysis of thermal storage
technologies and their degrees of success.

2. Foreword
2

3. Index
• Concentrating Solar Power
§ Status of CSP
• Parabolic Trough CSP
§ Level of Commercialization
§ Costs and Efficiencies
§ Key Components
○ Solar Field
○ Power Generation
○ Thermal Storage
• Key Barriers
• Opportunities for Indigenization
3
3
4
6
7
8
10
10
12
15
19
21

4. Concentrating Solar Power
Concentrating Solar Power is a renewable energy technology that uses the thermal
energy of incoming solar radiation to produce useful heat and power. CSP systems use lenses or
mirrors to concentrate a large area of Solar Radiation or solar thermal energy onto a small area
where this concentrated light is converted to heat and is used to drive a heat engine connected
to a generator to produce power.
There are four major forms of CSP Technology:
• Parabolic Trough
• Parabolic Dish
• Linear Fesnel
• Solar Power Tower
These four technologies differ mainly in how they concentrate and then use solar radiation.
Focus type
Towers (CRS)
Parabolic Troughs
Mobile
Collectors track the sun
along two axes and focus
irradiance at a single point
receiver. This allows for
higher temperatures.
LinearFresnel Reflectors
Fixed
Point focus
Collectors track the sun
along a single axis and
focus irradiance on a linear
receiver. This makes tracking
the sun simpler.
Receiver
type
Line focus
P arabolic Dishes
Fixed receivers are stationary
devices that remain
independent of the plant’s
focusing device.This eases the
transport of collected heat to
the power block.
Mobile receivers move
together with the focusing
device. In both line focus and
point focus designs, mobile
receivers collect more energy.
4

5. Status of CSP
Concentrated Solar Power is a proven technology that is currently spreading out into
the solar power generation market. Development started in the United States during the period
1984-91 in response to high fossil fuel prices, tax incentives, power purchase contracts and
federal funding. This resulted in a series of commercial scale experimental plants (SEGS Plants
1 to 9, with an installed capacity of 354 MW) that helped in proving and benchmarking Solar
CSP technology. A drop in fuel prices led to the supportive framework being dismantled and
commercial implementation of solar CSP came to a standstill though extensive research was
being done by labs worldwide.
Installed and Projected Capacity for CSP worldwide
Source: : http://www.emerging-energy.com/
The market has since re-emerged 2006 onwards in response to governmental measures,
renewable energy policy, public policy and mindset. Major installations and construction has
occurred in Spain and the united status with the current installed capacity of Solar CSP power
Plants being 697 MW. 1.2 GGW of Solar CSP projects are now in development with another
13.9 GW announced to be constructed by the year 2014 which will push the combined CSP
installed capacity to over 15 GW worldwide.
The CSP market is dominated by Parabolic Trough technology based power plants with
88% of installed capacity and 97.5% of projects under construction using this technology. This
demonstrated preference for Parabolic Trough comes from PTCs being the only commercially
5

6. proven CSP technology to perform for over 2 years on ground (Courtesy SEGS I-9) and none of
the others have undergone so much development. Innovations in Solar Field technology (60%
of the cost of a parabolic trough power plant ) over the next 5 years are estimated to provide a
15 to 28% decrease in LCOE for power generation from Parabolic Trough Power Plants.
Capacity breakdown projections by technology in 2014
Source: : http://www.emerging-energy.com/
Solar Power Tower technology is also making
headway in the CSP market with about 5% market
capacity now operating. Tower technology represents
the next big step in CSP technology and could bring
about significant cost reductions and increases in
efficiency and electricity yield. However a lack of
commercial testing and practical experience with utility
scale projects will hold back the technology for a while
to come.
Sources: http://www.desertec.org/ , The International
Energy Agency- CSP Roadmap
er
10
6

7. Parabolic Trough CSP
Parabolic Trough Concentrated solar power is the most mature and commercialized of
the four types of CSP technologies. It has enjoyed high commercial and scientific interest with
extensive research and implementation of the technology in test plants and now commercial
installations worldwide.
A parabolic trough CSP system uses a solar thermal collector in the form of long
parabolic mirrors that with a collector tube passing through their focal line. The mirrors
concentrate incoming solar radiation onto this tube by reflection to heat either a heat transfer
fluid such as organic oils or water to form steam directly. The troughs are generally aligned in
the north south direction and are rotated to track the sun as it moves across the sky.
Schematic of Current Commercial Parabolic Trough CSP Plants
A collector field generally consists of many parallel rows of troughs through which the
heat transfer fluid is pumped and heats up by absorption. Steam is then generated in a power
block by heat exchangers and as with conventional power plants, the steam is utilized in a
Rankine cycle steam turbine to generate electricity.
Some designs incorporate a hybrid design or thermal storage allowing the plant to
produce electricity over a longer period of time and during peak energy demand. Most current
plants are of the hybrid design, employing a natural gas/fossil fuel burner for steam generation
when solar energy is unavailable or insufficient. Thermal storage technologies store daytime
solar energy in thermal form in molten salt and use this stored energy during non-solar times to
keep electricity production on.
7

8. Level of Commercialization
Parabolic Trough Collector Solar Power Plants are the currently the most widely
deployed and commercialized CSP Systems . They are also the most mature and researched
technology in use. 11 of the current working commercial utility grade solar thermal power plant
installations worldwide are based on parabolic trough collectors. Likewise, 20 of the 27 Solar
Thermal Power Plants currently under construction are Trough based.
Commercial scale parabolic trough power plants stated with Luz Systems in a
government backed effort to build the first commercial SEGS (Solar Energy Generation System)
in the Mojave Desert, California in the year 1985. This extended to 9 commercial installations
SEGS 1 to 9 with a total capacity of 354 MW. Then after a lull in CSP exploration coupled with
lak in research or commercial funding for CSP, interest picked up again in the early 2000s in
Spain and the USA. Currently many projects are underway and many more are being started in
CSP, especially in Parabolic Trough Power Plants.
Currently there are 11 working installations using the Parabolic Trough Concentrator
technology amounting to a total production capacity of about 700 MW (689 MW). As opposed
to technologies like conventional power generation and PV plants. This technology is in relative
infancy and every new plant that is built will employ a fresh and developing technology for
some components of the plant, all aimed and bringing down the eventual cost of electricity
production.
The accepted standard for commercial power plants now is Parabolic Trough Collectors
with mineral oil Heat Transfer Fluids and a Rankine Cycle Steam Power Block coupled with some
form of molten salt storage.
Developmental work in Troughs, Receivers, HTFs and Storage Systems are now being
implemented in CSP Plants worldwide in order to reduce energy production costs and make
CSP more competitive vis-à-vis conventional power. Almost all of these have been
experimentally proven in the SEGS plants and are ready for commercial utilization:
• Combining storage and HTF media by using molten salt HTFs (Spain, Abengoa Solar)
• Metal troughs with reflective coating instead of mirrors (ReflecTech, Nevada Solar One)
• Evacuated collector tubes: Solel UVAC (EuroTrough)
• New Thermal Storage: Single Tank Thermocline Molten Storage
8

9. Costs and Efficiencies
Plant Costs:
The costs of setting up a Parabolic trough CSP Power Plant in comparison to the industry bench
mark and projection of costs in the next few years:
Case
Baseline
1984
Near Term
2010
Long Term
2020
Project
SEGS VI
SEGS LS-4
SEGS DSG
Factors
No Storage
10 Hr Storage
10 Hr Storage
Rated Power in MW
30
320
320
Capacity Factor
22/34 %
40%
50%
Area/MW
Solar Field
Overall
6266
21166
11223
39000
10545
34666
Solar To electric Efficiency
10.7%
14.6%
15.3%
Capital Cost (USD/KW)
3972
2999
2907
LEC (USD/MWh)
194
101
49
-In order to compare the costs and efficiencies of CSP and test the efficacy of fresh
technologies, the SEGS VI power plant was chosen as the baseline for all CSP technologies, and
every new technology has been tested there to compare cost and production efficiencies.
-All costs represented above are in USD.
-Plants taken for this cost comparison:
• Baseline Plant: SEGS VI
• Near Term Plant: SEGS LS 4: Also called SEGS X, this plant was built with LS 4 collectors
and 1 hours of molten salt storage in California.
• Long Term Plant: SEGS DSG: With the development of direct salt generation and ten
hour molten storage
9

10. Cost Breakdown:
Costs split across the subcomponents of a Parabolic Trough Power Plant:
Indicator
Baseline
Current
Project
SEGS VI
LS 4
Structures
54
62
60
Collector
3048
1327
1275
Storage
0
528
508
Heat exchanger and boiler sys
120
81
80
282
282
120
120
Enginr, Const , etc A*0.08
192
186
Process contingen B*0.15
389
377
Land
18
17
Elec generation
Balance of plant
750
2020
Total capital cost
3,972
2,999
2,907
Total O&M cost $/kW-yr
107
43
-All
34
costs are in USD per KW and O&M costs in KW-Year
-Land costs have been considered at 45943 USD/Hectare
-Engineering and consultancy costs have been considered at 8% of the project construction cost
-Process contingencies are considered at 15% of project cost
Current Break up of costs:
Current costs indicate that the solar field is the
single most expensive component in a solar field.
Most research in CSP technologies is conducted
in the area of solar fields. Recent advances in
collector technology which shall reach
commercial acceptance in the mid term shall
bring down field costs by almost 50%
Source: NREL
10

11. Key Components
Parabolic trough power plants use arrays of parabolic concentrators to transfer heat
from solar radiation to a heat transfer fluid. This heat transfer fluid is used in a steam generator
to power a conventional power plant to produce electrical energy.
The three main parts of any Parabolic Trough Solar Power Plant are:
● The Solar Field
● The Power Generation System
● Thermal Energy Storage
The Solar Field
A parabolic trough power plant’s solar field consists of a large array of sun tracking
trough solar collectors. Many parallel rows of these collectors, aligned usually in the north
south direction are placed over large areas to heat up the required heat transfer fluid.
The solar field is the single largest cost component of the power plant (6 % of capital
cost for parabolic trough power plants) and is the area where maximum research is going on
and cost reduction is expected to occur.
Subsystem
System Used
Current Choice
Future Choice
Collector Structure
LS 1,2,3; Eurotrough; Solargenix
EuroTrough
ReflecTech
Reflector Surface
Thick Glass; Thin Glass; Reflective
Film
Thick Glass
Reflective Film
Sun Tracker
Geared; Hydraulic
Geared
Hydraulic
Receiver Tubes
SchottPT; Solel UVAC; Luz Cermet
Schott PTR
Solel UVAC
Heat Transfer Fluid
Mineral Oil; Molten Salt; DSG
Mineral Oil
DSG
Collector
Interconnect
Flex Hoses; Ball Joints
Flex Hoses
Ball Joints
Overview of Sub-Components, available systems and the current technology of choice. The
future choice is the technology that we believe will reach commercial acceptance and cost
reductions in the mid term (2015)
11

12. The Solar Field’s primary component is the Solar Collector Assembly or SCA. Each SCA is
an independently tracking group of parabolic mirror reflectors, the metal support structure,
receiver tubes, and the tracking system including drives, sensors and controls.
Collector Structure:
The tracking availability, thermal performance and alignment are the three key features
to look at while selecting a collector structure. The backbone of the trough is made of either a
tube or a truss type box which take torsional loads and ensure alignment. Small stamped
trusses are attached to these to hold the mirrors. Tubes ensure lesser deflection but are high in
steel, new torque box designs cut down on a lot of steel consumption.
Key types are the Luz Systems 1,2(Tube) and 3, the EuroTrough consortium and
Solargenix(Box). Current choice is in the EuroTrough which has succeeded in reducing the
variety of parts, lessening the weight of the structure, and using more compact transport
leading to a cost savings of over 10% from conventional structures.
A new technology involving the torque box and a parabolic truss over which metal
sheets are simply bolted on is being rolled out which contains only 4 parts, is shipped fully flat,
and the reflecting surface is laminated on site cutting costs by over 60% is under testing.
Suppliers: LS2 Luz Systems, EuroTrough: EuroTrough, Reflective film based: Reflectech/NREL
Reflecting Surface:
The reflective surface in PCT must be parabolic and is made by the expensive sagged
mirror production method after which breakage rates in shipping and handling are high. The
only major supplier of these thick mirrors is Flabeg Solar of Germany but are the surface of
choice for current plants.
Recent developments have led to thin mirror technology which are lighter to make and
handle, but extremely fragile in shipping. The most promising technology and one that should
be exploited is the reflective film technology that is promoted by both the NREL/ReflecTech and
3M, which involves simply laminating a metal sheet with a reflective polymeric sheet and
assembling onto a shaped truss. These can shipped in rolls along with flat sheet and assembled
on site.
Suppliers: Normal Glass: FLabeg Solar, Thin Glass: SAIC, Film: 3M, ReflecTech.
Sun Tracker:
The sun tracker is the system used to track the sun and keep and maximum light focused
onto the receiver by rotating the assembly to face the sun. This is done by a tracking sensor
controlling either a geared motor drive or a hydraulic drive. The gear is simple while the
12

13. Subsystem
Systems Used
Current Choice
Future Choice
hydraulic the heavy and complicated is better in terms of load and accuracy. These systems are
not exactly proprietary and are simple to make, lending themselves to indigenization.
Thermal Storage
Direct; Indirect Single/
Indirect Double
Direct Molten
Systems
Double Tank; Solid Media;
Tank Molten Solar Salt; Direct Solid
Reciever:
Phase Change Media
Media
The receiver or heat collection element channels the Heat Transfer Fluid through the focal lines
of the mirrors to pick up heat. It is made up of a metal tube surrounded by a glass tube. The
Steam
Heat Exchangers; DSG
Heat Exchangers
DSG
metyal tube oldds the hcf, and is coated by a solar-selective absorber surface and is in vacuum
Generators
between the outer tube to minimize conduction losses. The selective surface ensuires high
Turbine
Rankine Cycle; OCR;
Rankine Cycle;
ISCCS
absorptivity and low emissivity to retain heat.
Combined Cycle
Combined Cycle
The current choice is either the Schott PTR or the Solel UVAC, both of which show high
efficiencies, low breakage rates and nearly the same Wet Cooling
costs.
Cooling Systems
Wet; Hybrid; Dry
Hybrid Cooling
Suppliers: Schott Glass Gmbh, Solel
Heat Transfer Fluid:
The heat transfer fluid or HTF is the fluid that picks up heat from the collectors and
transfers it to generate steam or into a molten salt storage system. This is accomplished by a
set of ehat exchangers. The ideal HTF would have a very low melting point and a high boiling
point to allow for larger heat transfer, but most organic oils are limited to about 500 oC. The
state of the art is Therminol VP 1 a synthetic organic mineral oil that boils upwards of 400 oC
Depending on technological advances, the oil HTFs will either be replaced by Direct Salt
of Direct Steam Generation. Direct Steam would present the highest cost improvement as
efficiencies would be higher, temperatures could be lower and there is no need for heat
exchangers.
Collector Interconnect:
Collectors were previously interconnected by flexible rubber hose to allow independent
tracking of the collectors but these had maintenance and sealing issues. New plants now use
piping and ball joints at the pivot point to allow for free motion and better sealing.
The Power Generation System and Thermal Storage System:
Power Generation in a CSP system is done through conventional steam turbine cycle
power plant. The key difference here being that solar radiation in the form of heat is used to
generate the steam. With the use of conventional mainstream power cycles, these plants can
be coupled/backed up or hybridized with conventional energy sources such as fossil fuels. As in
conventional power plants, a cooling system must also be implemented for the cooling of the
working fluid in the power cycle.
13

14. Turbine:
Rankine Turbine Cycles:
Almost all commercial trough based CSP systems employ the Rankine power cycle for electricity
generation. These systems use solar power to both generate high pressure steam and reheat
the steam . The system is ideally meant for large installations and power block cost/MW
reduces as the capacity increases.
Suppliers: GE, Schnieder, Arani Power
Organic Rankine Cycles:
Used in small capacity setups organic rankine cycle turbines run on an organic fluid such as
butane or pentane. This system can operate at lower temperatures and lower pressures,
reducing the cost of piping and seals. It also eliminates the need for maintaining a vacuum in
the condenser and further reducing operating costs. However these systems are usable and
efficient only at low power outputs in the order of .1 to 10 MWe.
Suppliers: Infinity Turbine, FreePower ORC
Combined Cycle power plants:
Some plants now integrate Solar Fields with an alternate energy source such as gas turbines to
ensure more constant production and sometimes even 24-hour steady operation.Turbine waste
heat is used for pre-heating or superheating the steam. Such systems can sometimes double
steam turbine capacity, but during non solar production, the large installed turbine will have
to run at part load, reducing efficiency. The cost of such a system is substantially lower than
the installation of a fresh standalone gas powered Rankine cycle station and it is the system of
choice with several new projects .
Cooling Systems:
A utility scale trough based CSP plant must use some form of cooling system for the steam
power generation system.
Wet Cooling: Most parabolic trough plants have used wet cooling towers for cooling generation
steam as this remains the only proven technology for cooling in such plants. Wet cooling is
implemented cooling towers and water consumption is equivalent to 3-5% of other power
generation methods and typically use about 3 Kiloliters per MWh.
14

15. Dry Cooling: Due to the emphasis on reduction in water consumption due to geographical
and other factors, fresh installations and experimental facilities are employing dry cooling
technologies. Dry cooling employs two major systems:
• Direct Dry System: Where the steam is directly condensed by air in a heat exchanger.
The cooling air required is blown by fans
• Indirect dry cooling: Where water is used to transfer heat from steam turbines to
cooling towers where it is dispersed in to air. This cooling water is then recycled.
Dry cooling is expensive and new to CSP and is used only when wet cooling is ruled out entirely.
15

16. Thermal Storage
Solar Concentration Power Plants convert solar radiation first into heat energy while
PV plants convert directly to electricity. Storing energy in the form of heat is significantly
simpler and cheaper than in the form of chemical energy (as it is stored in batteries, the current
standard for electricity storage) . This is the single largest factor that will eventually see the
advance of CSP as opposed to PV for utility grade Solar Power Plants.
Electricity storage as batteries is not suitable for utility grade power plants as there’s
too much energy to be easily stored in batteries. CSP plants can store vast amounts of energy
in thermal energy storage media and they can effectively create electricity in non-solar times,
effectively time shifting solar energy to non-solar times.
Overview
A common problem with solar plants is that they can only produce electricity during
sunlight hours, which is overcome by some sort of energy storage system. Batteries are
employed by small power systems, but are costly and ineffective in large utility grade power
plants because converting electrical energy into potential energy or chemical energy and then
back again, is inefficient and expensive.
CSP has a better and more efficient storage solution that retains the high grade heat
captured by collectors as heat, and can later be converted to electrical power as in the normal
system. Coupled with a thermal energy storage (TES) system allows a solar power plant to even
out production and dispatch power to peak load times, allowing utilities to “Power Shift”. TES
is also highly efficient (93% roundtrip efficiency) and can help raise project capacity factors to
higher than 50%.
CSP Storage Technologies
CSP thermal energy storage systems store heat in the form of thermal energy or heat.
This involves storage of heat in either a liquid/fluid heat transfer medium or in solid media like
ceramics or cement.
The only entirely proven and commercially employed technology is the two-tank molten
salt system. The cost of such a system could be reduced by using a therm cline based single
tank as this would reduce the amount of salt required.
16

17. Types
Method
Direct 2
Tank
Materials
Advantages
Cost Issues
HTF storage tanks
Mineral Oil; Molten
part of the loop, one Salt in towers and
hot one cold
experimental direct
salt systems
Simplest
System
Low storage time,
large volumes,
High pressure
storage needed
Indirect 2
Tank
HTF Heats
secondary material
stored in tanks
Molten Salt
Proven, Long
Term Storage
High Cost, Heat
loss in exchangers,
pumping costs
Indirect
Single Tank
Hot and cold media
stored in same tank,
form thermocline
Molten Salt
Reduces salt
requirement,
Lesser cost
Thermocline
spread, relatively
short term
Direct Solid
Media
Media heated by
Graphite Blocks in
radiation, HTF draws power towers
heat from it
Most
Efficient,
simple
Experimental,
small storage only,
high strength
tower required
Indirect
Solid
Media
Pipes pass through
solid, media stores
heat
Low cost of
media
Inefficient, high
volumes required
due to low ∆T
Cement, Ceramic
Direct Thermal Energy Systems:
Media that is heated up by the concentrator itself acts as the storage media.
2 Tank Direct Thermal Energy Storage:
Direct 2 Tank Storage systems directly store the heat transfer fluid in two tanks, one
cold and one hot. The fluid is cycle from hot to cold tanks to produce energy and vice versa to
heat and store. This eliminates the need for heat exchangers and loses across the processes.
However directly storing mineral oil provides short time and requires too large a volume to be
feasible. Hence these systems would be more useful and highly efficient in direct salt systems.
Direct Solid Thermal Storage
A different approach, under research in Australia involves a solar power tower with a
graphite block at its focal point. Steam is produced by running pipes thorugh the graphite block
(About 540 tonnes). The heat stored in the graphite block can then run the turbine during nonsolar hours. This system is in its early exprimental stages.
Indirect Thermal Energy Storage
17

18. Indirect Thermal systems heat an alternate medium to contain heat, including high
temperature fluids such as molten salts and solid media like cement and ceramics.
Solid Systems:
These systems pass heat from the HTF into solid blocks where it is stored. When cold
HTF is pumped in heat is released for energy production.
Concrete: Though only in experimental and in small scale commercial, high
temperature concrete and castable ceramics have been shown to be suitable thermal energy
storage mediums. This method is extremely simple and very low cost being even cheaper in the
case of concrete.
Phase Change Materials:
Phase change materials can store large amounts of heat in small volume due to latent heat,
resulting in one of the lowest costs for storage media in thermal storage systems. Cascaded
phase change materials with slightly varying melt points were considered that take up heat
and discharge upon flow reversal. While testing proved the feasibility of this concept, its
applications have been hindered due to:
● Highly complex solid state systems
● Thermodynamic penalty and loses due to interchange from sensible to latent heat and
back
● Lack of data on cycle time of the materials
Fluid/Salt Systems:
Use a mixture of molten salts with a low melting point and high heat capacity to contain
heat energy for future use. A heat exchanger heats up molten salt and stores thermal energy in
large hot salt reservoirs. Heat this way can be usefull stored for up to weeks (salt solution loses
heat at about one degree per day) . These systems have been used commercially in large scale
plants to store energy for upto 8 hours.This system is the most proven thermal storage system.
Some disadvantages of this system are its high capital expense and the low temperature
difference between its hot and cold fluid, necessitating high volumes.
Using molten salt directly in place of an oil based HTF eliminates the need for expensive
heat exchangers and gives higher efficiency as salts allows the solar field to be operated at
higher temperatures than organic oils (400 Degree limit) allow. Also heat exchangers are
eliminated and less salt is required, driving costs down. Some tower based CSP projects already
use salt as their working fluid and are at an advantage to solar trough systems where it is
currently infeasible to use. New salt mixtures are being developed with freezing points below
18

19. 100 C which will make their use in trough systems more manageable.
Single Tank Thermoclines:
A reduction in costs and storage tank volume is done by placing both the hot and cold
fluids in the same tank, with the less dense hot fluid floating atop the cold fluid. Cold fluid is
withdrawn from the bottom of the tank and heated, after which it is pumped in form the top of
the tank.
Thermocline energy systems have received much attention due to their reduced
tankage and media volume. Apart form this most of the fluid can also be replaced with a simple
and inexpensive filler layer which will take up energy from the fluid layers and form part of the
thermocline, further reducing storage media volume.
Future Storage:
Another fluid but non salt system involves using saturated water as a storage solution.
This uses peak production steam to charge a set of tanks in the storage system. At non-solar
hours, energy from this saturated water is recovered at high pressures to run the power block
at partial loads. This system will be most efficient and useful, and has been tried with direct
heating trough systems where steam is created in the trough system itself, allowing for a better
match between the phase change of heating and the phase change of storage.
19

20. Key Barriers
Major technological and technical barriers that retard the immediate commercialization
and large scale production of electricity through Parabolic Trough technology can be
categorized as follows:
Size of the Plant
As the size of the plant increases the
production cost of electricity decreases;
for instance Capital cost for power is
300USD /kW when plant size is 100MW
→ reduces to 260USD/kW for plant size
of 150MW → 230USD/kW for plant size
of 200MW. But larger size calls for large
scale investment, increases time,
resources and skill required for setting
up of the plant.
W
Reliability of components
Key components of a CSP Parabolic trough plant like mirrors, heat collector and
absorbers, heat exchangers, storage systems, transit pipes, etc. are liable to failure in short
term due to various factors like erratic loading fluctuations, high temperature and pressure,
clogging, etc. The annual reliability of components needs improvement.
Solution: Using different thickness for mirrors depending on the wind load at the position;
changing from metal heat exchanger and high pressure storage to immersed polymer heat
exchangers and low pressure polymer storage tanks; using improved designs of heat collectors
like Solel Uvac; Thorough and efficient installation procedures prevent failures.
Cumbersome and Expensive Storage
Heat collected using fluids like thermal oil has to be transferred to storage media
like molten salt. Heat exchangers are required between oil - hot salt and hot salt-cold salt
in two tank method of storage. This hikes up the cost and causes heat loss in the exchange
process. The storage system uses up a chunk of capital cost (18%) and it requires complicated
equipment and machinery which in turn adds to O&M burden. Pressurized metal Storage
system without heat exchanger costs $3/gallon and adding heat exchangers will increase the
20

21. cost substantially.
Solutions: One tank thermocline method instead of two tank molten salt reduces the cost
marginally; Direct Salt System where solar energy is directly transferred to salt is being
experimented; usage of solid storage media like concrete or graphite is being experimented.
Shipment and Installation
Installation density of a CSP parabolic trough plant is heavy – around 3lb/ft2 and
installation requires skilled labor, hi-tech installation equipment and tools. If the plant
installation is not sturdy the parts are liable to failure.
Most of the component manufacturers are situated in Europe or US. Shipping the parts
like reflector mirrors, storage system and heat exchangers will be difficult and expensive.
Solutions: Components like thin membrane mirror developed by Reflectech which are
modular and easy to ship should be used. The designs of trusses and support structures can
be purchased from leading companies and manufacturing can be done in India. Electronic
components, tracking systems, etc. can be designed and installed in India.
Geographical Location
The main limitation to expansion of CSP plants is not the availability of areas suitable for power
production, but the distance between these areas and many large consumption centres.
Solution: Technologies like HVDC address this challenge through efficient, long distance
electricity transportation.
Given the arid/semi-arid nature of environments that are well-suited or CSP, a key challenge is
accessing the cooling water needed for CSP plants.
Solution: Dry or hybrid dry/wet cooling under development now can be used in areas with
limited water resources.
21

22. Key Opportunities For Indigenization of
Technology
Due to the compartmentalized nature of PTCs and the large amount of academic literature, it
is relatively easy to replicate certain components of the Solar Parabolic Trough plant and not
have to depend on expensive international distributors. Other opportunities also abound in
surrounding fields.
Indigenous manufacture of:
• Steam Turbines: Are of conventional design not specially made for CSP
• Cooling systems: In areas where water supply is not a problem, they are again of a
conventional nature
• Heat Exchangers: Are of the shell and tube type and can be designed and cbuilt locally
by any fabrication center based on heat transfer required.
• Heat storage tanks: Are a matter of civil works and can be designed and built by anyone
• Collector Frames: Are again simple to design and build. Have relatively simple design
requirements and can be made and built relatively cheaply in India
•
Tracking System: Again simple to make and implement locally
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