Tower

CRS BASED SOLAR TOWER POWER PLANT (Challenges in Indian Context)

Presented By: ANANTA JOSHIRefuelling Technology Division,BARC, Mumbai, India

___________________________________________________________National Workshop on “Solar Thermal Power Generation”at IIT Bombay on April 28, 2008 Organised by : IIT BombaySponsored by: MNRE, Govt of India, New Delhi

EARLIER INDIAN INITIATIVES

(1) MATHANIA SOLAR THERMAL POWER PLANT PROJECT (1996):

(RRECL, Rajasthan Renewable Energy Corporation LTD)

- Grid-connected, 140-megawatt (MW) hybrid power plant

- Parabolic trough solar-thermal field 35MW + 105 MW Natural Gas

- Finances - Cost Estimates: Rs 823.00 Crores - Global Environment Facility (GEF), USA - Rajasthan and Indian Government, Private Investors - Debt by the Kreditanstalt für Wiederaufbau, Germany, - EXECUTION: EPC Consortium, BHEL- Colel- Tahal- LI (Lahmeyer International, Germany) - Execution: 2001 - 2003


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MATHANIA SOLAR THERMAL POWER PLANT PROJECT (Contd.):

(RRECL, Rajasthan Renewable Energy Corporation LTD)

STATUS (as reported by Magazine “Project Monitor” on 3 rd April 2006)

- International Funds are transferred to some other project - Project needs revised techno-economic feasibility study

- RRECL has not been able to sign Gas Supply Agreement with GAIL(India)


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SUMMARY OF CRS DEMONSTRATION/ COMMERCIAL POWER PLANTS

Design stageDesign stageUnder Construction

1984-1985 1983-1986 1996 -1999 Period of Service

60 m150-200m120 m-100 m90 mTower Height

6.0 MWhe(3 hrs)(8 hours)

650 MWh, (16 hrs)

2.5 MWhe (3 hrs)

15 MWhe (6 hrs)

107 MWhth (3 hrs)

StorageCapacity

562600025902212011926No. ofHeliostats

Molten SaltMolten SaltMolten SaltMolten Salt Molten Salt Molten Salt HTF

27538 m2720000 m2298000 m27845 m2 10740 m2 81344 m2 ReflectorArea-Total

2.0 MWe100 MWe17 MWe0.75 MWe 2.5 MWe 10 MWe Electric Power

BARC(India)

ESKOM (SA)

Solar-TRES

(SPAIN)

MSEE (USA)

Themis (France)

Solar Two( USA )

Features


SOLAR TOWER POWER PLANT (1996):

- Capacity: 2.0 MWe

- Consortium of BARC, NTPC, TIFR and ECIL

- Central Receiver System based Solar Tower Technology

- 3 hrs of Thermal Storage

- HTF: Molten Salt (60% NaNO3 + 40% KNO3)


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ENERGY CONVERSION EFFICIENCY

6.5 %: Blocking & Shading67.3%

1 %: Tower Shadowing66.6%

10 %: Mirror Reflectance60 %

5 %: Atmospheric attn & Receiver Spill57 %

5 %: Receiver Reflectance54 %

15 %: Radiation & Convn.46 %

3 %: Line Losses45 %

73 %: T & G Losses

12 %

100 %28 %: Cosine Losses

72 %

SOLAR ENERGY

ELECTRICAL ENERGY

HeliostatField Layout

Receiver Coating


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MAIN SUB-SYSTEMS:- Collector System (CS) - Master Control System (MCS) - Receiver System (RS) - Electric Heat Tracing System (EHTS) - Steam Generation System (SGS) - Electric Power Generation System (EPGS) - Thermal Storage System (TSS)


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SITE SELECTION CRITERIA:

- Sufficient solar insolation throughout the year. (Direct normal insolation > 4 kWh/m2/day annual average)

- Weather conditions: atmospheric water, smoke, fogs, haze, airborne dust, etc) - High winds or wind amplification due to terrain features

- Availability of large area at a low cost sufficient to - site the SPT, Heliostat Field, and - provide clear safety zone for Glint, High concentration of UV Radiation, etc - Availability of Solar insolation data over a relatively long period.

- Additional requirement for deionized water for heliostat washing.

- Vicinity of airports (particularly airport low-altitude approach paths)

- Relatively low seismic risk


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HEAT TRANSFER FLUID: Molten Salt (Mixture of 60% NaNO3 and 40% KNO3 by weight )

Issues:

- High operating temperature between 260°C to 565°C

- Material Corrosion

- Abrasive nature

- Handling and Operational safety

- Localized freezing in the loop

- Compatibility with molten salt pump, Valves, instruments, etc.


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MOLTEN SALT PUMP: TYPE: Vertical cantilever type centrifugal pump

Specification (Typical for 2.0 MWe) Capacity : 35 Kg/sec Shut off Head : 25 Kg/cm² Motor (Main) : 100 HP, 3ø, Induction (Pony) : 13.5 HP Material : SS 316

Issues:

- Operating temp of molten salt about 300°C- Off-the-shelf availability - Needs customized design- Operation of bearings under molten salt at 300°C

- In Solar two long shafted pumps are used and tested


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MOLTEN SALT PUMP (Contd.):

Initiative by BARC:

Prospective vendors Identified: ( for customized design and manufacture)

1) M/s PPIL, Bangalore and 2) M/s KBL, Pune

The development plan includes

- Initial theoretical design - Design validation with FEA for Mechanical, Hydraulics and Heat transfer

analysis - Manufacture of prototype with - lesser shaft length and testing in water - actual shaft length and testing in water - Manufacture of actual pump and testing in water - Long term testing in molten salt at 300°C


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TESTING of

SALT PUMP, VALVES, INSTRUMENTS AND MATERIAL CORROSION: (in molten salt loop up to 600°C)

Initiative by BARC:

- Detailed test plan prepared - Principal Investigator : FCRI, Palakkad

- Objectives of test plan are to determine; - Suitability of different FCVs, PTs and flow meters - Corrosion behavior of various target materials - Changes in the salt chemistry - Long-term testing of salt pump to determine: - Operational characteristics of the pump and - Suitability of different components of the pump like, bearings,

seals, etc.


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ABSORPTIVE COATING for (RECEIVER PANEL)

Requirements:

- Temperature resistant: - Stable at elevated temperatures- High absorptivity - Low emissivity - Easy to apply - Commercially available

REFLECTIVE COATING: for

- Protection of Receiver non-absorbing structural elements exposed to focused insolation Requirements:

- High reflectivity for solar radiation


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INTERNATIONALLY USED COATINGS

ABSORPTIVE RECEIVER COATING

PYROMARK black paint coating by Tempil Inc, USA properties:

• 0.96 (new) solar absorptivity • 0.93 (effective over life time) solar absorptivity • 0.83 IR emissivity

REFLECTIVE COATING

PYROMARK white paint coating Tempil Inc, USA

Properties:

• 0.80 Solar reflectivity• 0.84 IR emissivity


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ABSORPTIVE RECEIVER COATING (Contd.) Initiative by BARC

(A) TEST PLAN prepared for the thorough investigation of PYROMARK black paint coating. The plan includes following tests and measurements:

1) Total Hemispherical Absorptivity (at ambient temp, at Temperatures from 50 to 800ºC) 2) Spectral Hemispherical Absorptivity 3) Directional Spectral Absorptivity 4) Total Hemispherical Emissivity (at ambient temp, at Temperatures from 50 to 800ºC) 5) Spectral Hemispherical Emissivity 6) Directional Spectral Emissivity 7) Repeating above tests after prolonged exposure at 1000ºC 8) Tests for different coating thicknesses

(B) INDIGENIZATION of black paint coatings

Various institutes like UICT, Mumbai, IICT, Hyderabad, NCL, Pune are identified


ABSORPTIVE RECEIVER COATING (Contd.) Initiative by BARC

(C) TEST PLAN for the thorough investigation of coating at elevated temperatures (up to 800ºC) in a SOLAR FURNACE

The CSMCRI, Bhavnagar, is identified to be the Principal Investigator:

The test plan includes;

- Building a 10 kW solar furnace using Paraboloidal Dish Concentrator with auto sun tracking- Flex sheet mirror over single piece molded FRP body with mosaic arrangement - A cavity type receiver at the focal plane of the concentrator to provide concentrated radiation to the receiver material test set up.- Direct measurement of solar absorptivity and thermal emissivity of samples using calorimetric techniques. - Validation of test data using a mathematical model based on heat transfer principles.


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COLLECTOR SYSTEM: Forms about 50% of Total Cost

HELOSTATS: Historically, heliostat drive failures occur more predominately than structural failures or facet failures.

The typical cost buildup of a heliostat from past experience is as follows:

• Drive : 40–50 % • Structure : 15–20% • Facets : 15–25 % • Foundation : 2% • Field wiring : 6% • HC and controls : 7%


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COLLECTOR SYSTEM

Design, fabrication and demonstration of sun-tracking Heliostats

Issues to be addressed

- Field Testing: Test program to qualify the heliostat structurally & optically.- Optical Performance: Heliostat stiffness and deflection - Effect of Wind on heliostat tracking and beam quality- Beam aberration of heliostats located other than North field - Structural sag due to gravity - Standby tracking point (along imaginary lines to prevent concentrating the image from more than one heliostat outside the plant boundaries).- Beam Characterization System (BCS): to compensate for errors due to electro-mechanical system wear, pedestal movements, errors in drive motor revolution counts, canting alignment errors, etc.- Mirror cleaning: provision for wash vehicle movement in the Heliostat field layout.


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HELIOSTATS (Issues):Float Glass Mirrors requirements

- Thickness 2 mm or less, - High Transmissivity (low absorptivity) - High reflectivity of mirror coating - Low iron content - Indian float glass manufacturers achieve (ASAHI float glass, etc)

- minimum float glass thickness 3 mm - Max Transmissivity of 0.88

- Min iron content of 0.11%- SOLAR-TWO

- 3 mm thick, low iron float glass - average reflectivity = 0.903 (clean), 0.82 (due to environmental dist)

Cost reduction: - Larger size, high reflectivity Glass-mirror Heliostats

- Stretched membrane technology (Silvered polymer film laminated to a thin metal foil stretched over a large diameter metal ring)

- Light weight- reflectivity = 0.92 - cost reduction by 30%


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HELIOSTATS

Initiative by BARC (for float glass and mirror coating requirements):

Test plan prepared for test and measurements of different float glass mfrs.:

Float glass:

- Total Hemispherical Absorptivity- Spectral Hemispherical Absorptivity- Directional Spectral Absorptivity

Mirror coating:

- Total Hemispherical Reflectivity- Total Hemispherical Diffuse Reflectivity- Total Hemispherical Specular Reflectivity- Spectral Hemispherical Reflectivity- Directional Spectral Reflectivity


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SECONDARY SYSTEM

Issues affecting the secondary steam cycle

- Need for high Plant Load Factor by

a) thermal storage for heat retention capacity of 24 hr operation b) use of another fuel (hybrid system) - Feeding the load radially or connecting to the grid

- Repetitive heating and cooling to be avoided. Thermal plant cannot be started and stopped random. - PLF for operation of 12 hrs a day, 9 month operation, and Energy required to keep the turbine warm is = 25%

CRS BASED SOLAR TOWER POWER PLANT CRS BASED SOLAR TOWER POWER PLANT (Challenges in Indian Context)(Challenges in Indian Context)

SOLAR TRES (Spain) to make use of SOLAR TWO experience.

FEATURES:

• Larger Heliostat field• Improved plant availability, 6% more overall annual plant efficiency.• 2493 Glass-Metal heliostats (120 m²) with higher-reflectivity glass • Simplified design, 45% reduction in costs• Larger thermal storage system (16 hours, 6250 T molten salt )• Advanced High-temperature long-shafted multi-stage vertical turbine

pump design with salt-lubricated bearings to pump salt directly from the storage tanks

• This pump arrangement eliminates the sump, level control valve and potential overflow of the pump sump vessels.

• Simplified molten-salt flow loop reducing the no. of valves by 50%, eliminates “dead legs” and allows fail-safe draining to avoid salt freezing.

• The larger heliostat field and thermal storage to operate the plant 24 hours

• Annual capacity factor of approximately 65%.

THANK YOU

Presentation By: Ananta Joshi RTD, BARC

Phone no.: 022-25591596, E-mail: [email protected]

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