BySindu A Maiyya

Poondla PrashantIIT Madras

For Energy Alternatives IndiaThis 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.

Concentrating Solar Power

Foreword

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Index

• Concentrating Solar Power 3§ Status of CSP 4

• Parabolic Trough CSP 6§ Level of Commercialization 7§ Costs and Efficiencies 8§ Key Components 10

○ Solar Field 10○ Power Generation 12○ Thermal Storage 15

• Key Barriers 19• Opportunities for Indigenization 21

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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 Line focus Point focus

Receiver type

Collectors track the sun along a single axis and

focus irradiance on a linear receiver. This makes tracking

the sun simpler.

Collectors track the sun along two axes and focus

irradiance at a single point receiver. This allows for

higher temperatures.

Fixed

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.

LinearFresnel Reflectors Towers (CRS)

Mobile

Mobile receivers move together with the focusing device. In both line focus and point focus designs, mobile receivers collect more energy.

Parabolic Troughs P arabolic Dishes

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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 worldwideSource: : 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

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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

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Parabolic Trough vs other Technologies in CSP. 2010

Source: NREL

Parabolic Trough CSPParabolic 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.

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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

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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:

-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

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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/MWSolar FieldOverall

626621166

1122339000

1054534666

Solar To electric Efficiency 10.7% 14.6% 15.3%

Capital Cost (USD/KW) 3972 2999 2907

LEC (USD/MWh) 194 101 49

Cost Breakdown:Costs split across the subcomponents of a Parabolic Trough Power Plant:

-All

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

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Indicator Baseline Current 2020

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

Elec generation 282 282

Balance of plant 750 120 120

Enginr, Const , etc A*0.08 192 186

Process contingen B*0.15 389 377

Land 18 17

Total capital cost 3,972 2,999 2,907

Total O&M cost $/kW-yr 107 43 34

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 FieldA 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)

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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

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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.

Reciever: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 metyal tube oldds the hcf, and is coated by a solar-selective absorber surface and is in vacuum between the outer tube to minimize conduction losses. The selective surface ensuires high absorptivity and low emissivity to retain heat. 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 costs.

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 500oC. The state of the art is Therminol VP 1 a synthetic organic mineral oil that boils upwards of 400oC

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.

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Subsystem Systems Used Current Choice Future Choice

Thermal Storage Systems

Direct; Indirect Single/Double Tank; Solid Media; Phase Change Media

Indirect Double Tank Molten Solar

Direct Molten Salt; Direct Solid Media

Steam Generators

Heat Exchangers; DSG Heat Exchangers DSG

Turbine Rankine Cycle; OCR; Combined Cycle

Rankine Cycle; Combined Cycle

ISCCS

Cooling Systems Wet; Hybrid; Dry Wet Cooling Hybrid Cooling

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.

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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.

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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.

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Types Method Materials Advantages Cost Issues

Direct 2 Tank

HTF storage tanks part of the loop, one hot one cold

Mineral Oil; Molten Salt in towers and 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 radiation, HTF draws heat from it

Graphite Blocks in power towers

Most Efficient, simple

Experimental, small storage only, high strength tower required

Indirect Solid Media

Pipes pass through solid, media stores heat

Cement, Ceramic Low cost of media

Inefficient, high volumes required due to low ∆T

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 StorageA 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 non-solar hours. This system is in its early exprimental stages.

Indirect Thermal Energy Storage

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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

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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.

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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.

Reliability of componentsKey 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 StorageHeat 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

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LEC vs Plant Capacity in MW

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 InstallationInstallation 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.

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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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