SOLAR THERMAL POWER!GEEN 4830 – ECEN 5007!

Manuel A. Silva Pérez!silva@esi.us.es!

6. Parabolic trough technology!

Main Concentrating Technologies

Central Receiver / Heliostats

Parabolic troughs

Parabolic dishes

Linear Fresnel Reflectors

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Solar Thermal Power Plant. Basic configuration

Beam irradiance

Concentrator

Receiver

Thermal Storage

Concentrated irradiance

Generator

Power conversion system

Thermal energy

Boiler Fossil fuel / Biomass

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Electricity

PT power plant configuration

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The collector

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Collector

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Types of collectors

Process heat STP plant

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Main elements of the collector

}  Reflector (mirror) }  Receiver tube }  Structure }  Tracking system }  Connecting elements }  Control system

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The reflector

Thin glass mirror (0.8 mm) Thick glass mirror (3 -5 mm)

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Alternative reflector materials: Reflectech mirror film

}  Specular Reflectance 94% At 25 mrad, 660 nm

}  Solar-Weighted Hemispherical Reflectance 94%

}  Durability: approx. 10 yrs.

}  Thickness: 0.1 mm

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Alternative reflector materials: Alanod Miro-SUN

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Structure

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Structure

 Bending  resistance   Torsional  resistance  

Torque  Tube  design    

LS3  Design    

Torque  Box  Design    

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The receiver tube

Selective coated steel tube

Glass envelope 'Getter‘ for vacuum maintenance

Expansion bellow

Glass pin for evacuation of gases Vacuum between glass and steel tubes Glass – metal welding

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Receiver tubes

Schott PTR-70 Solel UVAC-2 and UVAC-3

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Heat transfer fluid

}  Thermal oils }  Caloria (SEGS I and II, <300ºC) }  Therminol VP-1 (<400 ºC) }  Syltherm (Dow Chemical, >400ºC)

}  Water / Steam }  >400 ºC }  DISS Project

}  Molten salts }  ENEA facility

}  Gases }  PSA Research Facility

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Tracking mechanisms

Electrical motor - gearbox Hydraulic

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Connecting collectors

Flex hoses Rotating joints

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Control elements

Shadowband sensor

Controller

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Cleaning the mirrors

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Solar field configuration (I)

1 SCA 150 m 12 SCE 1 Drive Pylon 10 Middle Pylon 1 End Pylon 1 Shared Pylon (shared with next SCA)

Cold Oil

Hot Oil

End Pylon

Drive Pylon Middle Pylon

Shared Pylon SCE

150 m

150 m

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Solar field configuration (2)

Cross Over Pipes

1379 m

1248

m

Loop of 6 SCA’s

Headers SEGS Power Block 80 MW Rankine Cycle

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A) Direct return B) Inverse return

C) Central

h

h

h

h

D  Thermal losses D  Higher cost C  P balanced C  Lower consumption

C  Thermal losses D  unbalanced P D  Higher consumption

C  Shorter pipelines C  Better access to collectors D  unbalanced P

Solar field configuration (3)

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X

Y N

S E

O

Z

S C

Sol

X

Y N

S E

O

Z

S

C

Sol

b) N-S tracking a) E-W tracking

Solar Field Alignment

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Diámetro , D

Rayo solar

Angulo de apertura , f

Angulo de aceptancia , q Reflector Parabolic

External receiver diameter D

Sun rays

Aperture angle φ

Acceptance angle , Φ

b) Acceptance angle, ϕ b) Concentration ratio, C

Aperture, A

Absorber tube

C =.A /π.D

Basic parameters

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Beam irradiance interception factor, γ,

Selective-coated steel tube (Absortivity = α)

Glass envelope (Transmissivity = τ)

Parabolic mirror (Reflectivity = ρ)

ηo,peak = ρ·γ·τ·α

Energy balance. Optical losses

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Sun

Sun

Side view

Plant view Shaded area

φ Reflecting surface

Absorber tube

L = concentrator length φ = incidence angle

φ

F = focal length Sol

F

ED

L

b) Loss of effective collector length a) Shading losses

Af = W x ED = W x F x tan(φ)

Geometrical losses

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Loss of effective collector length

W

ED

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) ( )ambabsabs

conv-condabs,radabs,absL T - TLD

Q + Q=U

π[W/m2

abs ºC]

UL)col = UL)abs / C

Qv,abs.

Qabs,rad.

Qabs,cond/conv. Qamb,rad

Qamb,conv

Glass envelope

Absorber tube

Thermal losses

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eff eff

( )ϕcos⋅⋅= IAQ csol ( )inouteff hhMQ −⋅= thoptglobal K ηηη ⋅⋅= º0,

Energy balance (solar to thermal)

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95

96

97

98

99

100

Av

ail

ab

ilit

y -

%

1995 1996 1997 1998 1999

III IV V VI VII0%

10%

20%

30%

40%

50%

60%

70%

Effic

ienc

y [%

]

0

200

400

600

800

1000

1200

Dire

ct N

orm

al R

adia

tiom

[W/m²]

05:00 07:00 09:00 11:00 13:00 15:00 17:00 19:00 21:00

Solar to Electric Efficiency (gross)

Direct Normal Radiation

Thermal Solar Field Efficiency

-

Solar Efficiencies Measured at SEGS VI on July 1997 by KJC Operating Company

Typical operation curve (clear day, no thermal storage)

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Dispatchability of STP Plants

}  Integration of RES on the grid: }  Dispatchability is a key factor. }  STP Plants have the potential to be dispatchable by:

}  Including a Thermal Storage System (TES) }  Hybridization with fossil or renewable fuels.

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Andasol-type plants (thermal storage and auxiliary boiler)

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Dispatchable STP Plant

}  Continuous and stable operation is guaranteed by TES and / or hybridization

MW

0 2 4 6 8 10 12 14 16 18 20 22 24

Hours

50

40

30

20

10

0

50

40

30

20

10

0

50

40

30

20

10

0

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TES

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Hybridization options

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SEGS 30 MW

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Costs

}  Difficult to evaluate }  Confidentiality of contracts }  Volatility of prices }  Only 2 – 3 providers of key elements }  O&M experience restricted to US (SEGS Plants)

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Costs CCP – Spain. 8h TES

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Costs – Spain. No TES

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O&M Costs – Spain (8h TES)

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PT Technology today, pros & cons.

}  Pros: }  Mature technology;

}  Comercially proven, over 500 MW installed capacity; }  Extensive operational record: 9 plants operating for 15+

years

}  Easier to finance

}  Cons: }  Few manufacturers of key elements (recievers, mirrors…) ->

limited competence }  Limited maximum temperature -> limited efficiency }  Costly, hazardous HTF }  Limited TES options

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More…

}  http://www.nrel.gov/csp/troughnet/ }  Sargent & Lundy Assessment of CSP

http://www.nrel.gov/csp/troughnet/pdfs/34440.pdf }  Look for movies at youtube, e.g:

}  http://www.youtube.com/watch?v=ysDXwvNGHeM&feature=related

}  http://www.youtube.com/watch?v=3OLjooHY1VA }  http://www.youtube.com/watch?

v=mDWSW8BAM3U&feature=related }  And more…

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