Solar Thermal Power Generation

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Solar Thermal Power Generation

• Dr. Ashvini Kumar
• Ministry of New and Renewable Energy
• New Delhi 110 003
• ashvinikr_at_nic.in

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Solar Resource Availability in India

• 5000 trillion kWh solar radiation incident in a
  year over India
• Radiation data collected by India Meteorological
  Department and some other centres
• Daily solar radiation 4 - 7 kWh per sq. m.
• Most parts of the country receive solar radiation
  sufficient enough to effectively utilize solar
  energy systems
• Typically, 2.0 hectare of open space is required
  for one mega watt solar power plant

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Solar Radiation

• Solar radiation is the radiant energy emitted by
  the sun, particularly electromagnetic energy.
• About half of the radiation is in the visible
  part of the electromagnetic spectrum.
• Other half is mostly in the near-infrared part,
  with some in the ultraviolet part of the
  spectrum.
• The value of solar constant is 1367 W/m2.

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Solar Thermal Power Generation

• Has potential for decentralized as well as grid
  connected applications
• Also referred to as CSP (concentrating solar
  power) technologies for power generation
• Technology Options include
• Parabolic Troughs
• Central Receivers or Power towers
• Paraboloid dish systems
• Solar chimneys
• Some experience is available in the country on
  parabolic trough and dish Stirling technology

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Parabolic Trough Technology

• Parabolic troughs focus the sun onto a line.
• The parabolic troughs are used to track the sun
  and concentrate sunlight on to the thermally
  efficient receiver tubes placed in the trough
  focal line.

• They are used to harvest the sun to give
  typically a temperature of up to 400 deg C.
• Hot liquid is passed through a series of heat
  exchangers to generate steam, and to drive a
  turbine
• Rankine cycle configuration is used for power
  generation

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• Basic modular component is the solar collector
  assembly (SCA)
• Each SCA is an independently tracking unit
• Its main components are
• Parabolic Trough solar Collectors
• (parabolic reflectors, metal support structure
  and receiver tubes)
• Tracking system
• (Drive, sensors and controls)

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Parabolic Trough TechnologyCharacteristics

• Large thermal storage could be built to increase
  number of operating hours in a day
• Could be hybridized with power generation from
  fossil fuels
• Other alternatives for heat transfer fluid, such
  as water to produce DIRECT STEAM, and molten
  salts to produce higher temperatures are being
  tried out to increase the potential of the
  technology further.
• The parabolic trough technology is commercially
  available.

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Status

• In 1983, Southern California Edison signed an
  agreement with Luz International Limited to
  purchase power from Solar Electric generating
  Systems (SEGS).
• This resulted in the installation of nine
  commercial level plants during 1983-91 in the
  California Mojave Desert, with total aggregate
  capacity of 354 MWe.
• These plants have produced 11,000 GWh and more
  than 1.7 billion revenue over the last 22 years.
  The plants are still working.
• 1 MW capacity plant based on organic Rankine
  cycle with Pantene as the HTF, heated to 300 oC,
  at Saugaro, Arizona came up in 2006.
• In July 2007, another plant Nevada Solar One of
  64 MWe capacity has been commissioned in USA.
• In November 2008, Andasol 1 (50 MW) plant
  commissioned.

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Power block of the SEGS parabolic trough power
plant at Kramer Junction, US.
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Naveda Solar Power Plant
Commercial solar power plant after about 15
years Commissioned in July 2007
Capacity 64 MW Cost 250 M (Rs.1200 crores)
3.9 M/MW kWh 13 cent Schott vacuum
steel and glass receiver Liquid heating
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Characteristics of SEGS Plants
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Developmental IssuesReceivers

• Typically, it is 70 mm OD SS tube with cermet
  solar selective coating surrounded by 115 mm OD
  anti-reflective (both sides) evacuated glass tube
• Glass-to-metal seal to achieve vacuum and metal
  bellows to allow differing thermal expansion are
  used
• Vacuum 10- 4 torr (0.013 Pa)
• Getters, the metallic compounds, are installed in
  the vacuum space to absorb hydrogen and other
  gases which may permeate
• The following main reasons of failure are
  reported
• Glass-to-metal seal failures due to insufficient
  protection
• Hydrogen release related failures
• Bowing

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Developmental Issues Receivers (contd.)
The following selective coatings are already
available
Target Development of selective surfaces with e
lt 0.10 and temperature stability at gt 600 C.
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Developmental IssuesReflectors

• Presently, 4 mm thick glass mirror panels
  manufactured by Flabeg are used. Float glass
  with low iron content is used to produce
  parabolic shape.
• Present mirrors are back surface silver coated
  mirrors. Solar weighted specular reflectivity is
  93.5. Each panel is approximately 2 m2 in area.
• Performance has been good and high reflectivity
  levels could be maintained, bur suffer from
  breakages.

Target Development of reflectors with reduced
weight, cost and fragility, while maintaining
high solar transmittance values.
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Compact Linear Fresnel Reflector (CLFR)

• Similar to parabolic trough technology
• Has the advantage of lower production costs
• Require least amount of land per MW
  capacity among all solar technologies
• Developed to address the stiffness and wind
  loading challenges faced by the parabolic troughs

• Parabolic trough is sliced into individually
  tracking strips of mirrors and installed near the
  ground

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Linear Fresnel Reflector Technology

• Requires less structural rigidity, and
  incorporates less robust tracker gears and motors
  than parabolic troughs
• The individually tracking mirror strips, however,
  shade adjacent mirrors during times of low-angle
  light, making it less efficient and generate
  lower temperatures of about 280 to 350 C.
• 1-axis tracking is used, and one tracker motor
  typically drives an entire set of mirror slices.
  The mirror slices are slightly curved and
  typically use low-iron silvered glass.

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Linear Fresnel Reflector Technology
Preheats water for the coal fired power
plant. (2850C 70 bar steam)
Liddel power station, NSW, Australia
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Linear Fresnel Reflector Technology

• M/s AUSRA company has signed a deal with Pacific
  Gas Electric to build a 177 MW plant in San
  Luis Obispo by 2010.
• Expected cost of electricity generation in US is
  US 0.10/kWh for an installed capital cost of
  US 3250/kW
• The planned capacity utilization factor is 54
  with a special thermal storage.

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Direct Steam Generation

• Has the potential to reduce the overall cost
• Does not face the limitations of the thermal oil
  systems
• No realistic storage option exists presently.
• Initial studies indicate about 10 reduction in
  the solar portion of levelized cost of energy
• Faces serious challenges for safety and
  maintenance as large solar field is pressurized

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Central Receiver Systems

• These systems also use fields of mirrors to
  reflect the suns radiation to the top of a tower
• These contains a medium which heats up to very
  high temperatures (600 0C)
• Medium could be molten salt or saturated steam.
• The usable operating range of molten nitrate
  salt, a mixture of 60 sodium nitrate and 40
  potassium nitrate, matches with that of Rankine
  Cycles.

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Solar two Plant at California

• Molten salt as heat sink allowing it to run for
  24 hrs.

• Used 108 heliostats of 95 m2 each 1818
  heliostats of 39 m2 each.
• Overall peak conversion eff 13.5
• Receiver eff 88, Rankine cycle eff34, thermal
  storage system eff 97

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Experimental Central Receiver System at the
European Research Center, Plataforma Solar
deAlmería in Spain
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11-MW Power Plant for Southern Spain (PS 10)

• Annual radiation level
• 2063 kWh/sqm
• 90-m-high tower
• 624 heliostats (121 m² each)
• Volumetric wire-mesh
• receiver with tubular panels (680 C)

• Glass-metal heliostats
• Saturated steam cavity receiver producing steam
  at 40 bar and 250ºC
• Saturated water-steam heat storage (15 MWh) for
  50 minutes of plant operation at 50 load.

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Decentralized Tower Systems

• eSolar is developing a tower technology based on
  decentralized towers and small heliostats
• It allows reduced wind loading and inexpensive
  control system for heliostats reducing cost
• Can be installed in modular fashion and therefore
  in different sizes

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Paraboloid Dish Systems

• These systems use series of mirrors arranged in a
  concave plate to focus light onto a point
• Usually, a Stirling external combustion engine is
  placed at the focal point for collecting heat to
  drive pistons by continually expanding and
  condensing hydrogen gas
• With gas turbine, Brayton cycle may also be used.

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SES Solar-Dish Engine

• 88 facets are used in solar dish
• 1800 RPM 25 kWe engine
• Announced capacity is over 1700 MW

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Solar-Dish Engine

• Infinia Corporation, USA has developed 3 kW
  capacity free piston Stirling Engine along with a
  small solar dish

• System is under testing and commercialization
• Shortly will be tested in India also.

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Solar Thermal Power Projects Existing
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MNRE Demonstration Programme

• Demonstration Programme on Grid Interactive Solar
  Power Generation is being launched
• A provision is made to provide generation based
  incentive of a maximum of Rs. 12/kWh and Rs. 10
  /kWh for the electricity generated and fed to the
  grid through photovoltaic and solar thermal
  routes, respectively.
• The capacity of the plant should be greater than
  1 MW.
• Maximum cumulative capacity of 10 MW can be set
  up in one State.
• One developer is eligible to set up up to 5 MW
  cumulative capacity.
• The States, who have declared policy for solar
  power will get priority.
• Total target capacity of the demonstration
  programme is 50 MW up to a period ending March
  2010.

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Indian Solar Dish

• A large area solar dish of 160 m2 area has been
  developed and installed for milk pasteurization
  at Latur by IIT Bombay to provide heat at 160 deg
  C
• Automatic tracking system is used normal window
  glass has been used for reflector.
• Design of the dish has been upgraded for use in
  power projects. Aperture area is now 169 m2 .

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Thank you !