Parabolic Trough

SOLAR THERMAL POWER!GEEN 4830 – ECEN 5007!

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

6. Parabolic trough technology!

12/7/10 1 GEEN 4830 – ECEN 5007

Solar Thermal Power Plant. Basic configuration

Beam irradiance

Concentrator

Receiver

Thermal Storage

Concentrated irradiance Electricity

Power conversion system

Thermal energy

Boiler Fossil fuel Biomass

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PT power plant configuration

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The collector

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Collector

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Main Concentrating Technologies

Central Receiver / Heliostats

Parabolic troughs

Parabolic dishes

Linear Fresnel Reflectors

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

  Thermal losses   Higher cost   ΔP balanced   Lower consumption

  Thermal losses   unbalanced ΔP   Higher consumption

  Shorter pipelines   Better access to collectors   unbalanced ΔP

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 orientation

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Diámetro , D

Rayo solar

Angulo de apertura , φ

Angulo de aceptancia , θ Reflector Parabolic

External receiver diameter D

Sun rays

Aperture angle φ

Acceptance angle , θ

b) Acceptance angle, θ 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 = γ·τ·α·ρ

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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[W/m2abs 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

Energy balance (solar to thermal)

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0%

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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