SOLAR THERMAL POWERGEEN 4830 – ECEN 5007

Manuel A. Silva Pérez

silva@esi.us.es

7. Central Receiver Systems

Central Receiver Systems - CRS

14/7/101 GEEN 4830 – ECEN 5007

Solar Thermal Power Plant.

Basic configuration

Beam irradiance

Concentrator

Receiver

Thermal

Storage

Concentrated irradianceElectricity

Power

conversion

system

Thermal energy

BoilerFossil fuel

Biomass

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Central Receiver System

http://www1.eere.energy.gov/solar/power_towers.html14/7/103 GEEN 4830 – ECEN 5007

CRS (Gema Solar, Molten salts)

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CRS

(Phoebus, Open air volumetric receiver)

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Collector System (concentrator)

14/7/10GEEN 4830 – ECEN 50076

Heliostat field

The concentrator is the “heliostat field”, a Fresnel

concentrator

Main elements

Heliostat

Control System

14/7/10GEEN 4830 – ECEN 50077

The heliostat

“an instrument consisting of a mirror mounted on an axis moved by clockwork by which a sunbeam is steadily reflected in one direction”

Basic components

Reflecting surface

Structure and tracking mechanism

Control system

Typology:

Glass - metal

Stretched membrane

Size: 1 m2 to 150 m2

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Heliostat

Back support

structure

Elevation drive

Azimuth drive

Reflecting surface

Reflected ray

Incident ray

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Burning mirror, Hoesen (18th century)

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Glass – metal heliostat

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Heliostat

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Glass – metal heliostat

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Glass – metal heliostats

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Stretched membrane heliostats

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Stretched membrane heliostats

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Stretched membrane heliostats

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Reflectivity

Reflectivity of a new, clean mirror ≈ 0.90 ÷ 0.94

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Mirror quality

Heliostat facets are spherically curved

For large focal distances, a parabolic surface can be approximated by

an spherical surface of radius r = 2f (f: focal distance).

14/7/10GEEN 4830 – ECEN 500719

Mirror quality

2222

cspSD

Ideal spherical curvature

Spherical curvature, with waviness

2222

cspSD

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Distortion

Spherical reflectors generate distortion of the image

Dependent on time (relative position sun-heliostat)

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Summer solstice, noon

Summer solstice, 7:30 a.m. Summer solstice, 7:30 p.m.

Heliostat field layout

Surround field

North (south) field

Secondary concentration

Secondary concentrator optics tower (SCOT)

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North field

0

200

400

600

800

1000

-600 -400 -200 0 200 400 600

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Surrounding field

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Geometrical performance of heliostats

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Cosine factor

Yearly average cosine factor for a

north heliostat field

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Shading and blocking

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Shading & blocking

Shading

Blocking

Air transmittance

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Air transmittance

Spillage

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Receiver system

Function

Components

Types of receivers

Working fluids

14/7/10GEEN 4830 – ECEN 500730

Receiver system

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Receiver types

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Cavity receivers

14/7/10GEEN 4830 – ECEN 500733

Cavity receivers

14/7/10GEEN 4830 – ECEN 500734

Molten salt cavity receiver

14/7/10GEEN 4830 – ECEN 500735

External, cylindrical receiver

14/7/10GEEN 4830 – ECEN 500736

External, cylindrical receiver

14/7/10GEEN 4830 – ECEN 500737

External, cylindrical receiver

14/7/10GEEN 4830 – ECEN 500738

Tubular receiver (boiler)

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Volumetric receivers

14/7/10GEEN 4830 – ECEN 500740

Volumetric receivers

14/7/10GEEN 4830 – ECEN 500741

Heat transfer characteristics of tubular and

volumetric receivers

14/7/10GEEN 4830 – ECEN 500742

Detail of a volumetric absorber (wire mesh)

14/7/10GEEN 4830 – ECEN 500743

Detail of a volumetric absorber

(ceramic cups)

14/7/10GEEN 4830 – ECEN 500744

Working fluids

14/7/10GEEN 4830 – ECEN 500745

Working fluids for CRS

Water / steam

Saturated steam

Superheated steam

Molten salts

Air

Pressurized

Atmospheric

Sodium

Thermal oils

14/7/10GEEN 4830 – ECEN 500746

Comparison of HTF’s

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Power conversion system

Rankine cycle (steam turbine)

Brayton cycle (gas turbine)

Combined cycle (gas turbine + steam turbine)

Stirling engines

(MHD)

14/7/10GEEN 4830 – ECEN 500748

CRS: pros and cons.

Pros:

Ability to achieve high temperatures

Wide industrial base for most components

Multiple technological options

Technologically proven

Multiple thermal energy storage options

High potential for improved effciency or cost reduction

Cons.:

Complexity

Short commercial record

Best technology still undefined

14/7/10GEEN 4830 – ECEN 500749

Energy Balance of Central Receiver

Systems

14/7/10GEEN 4830 – ECEN 500750

High concentration concepts

Secondary concentration

Increase flux density on the absorber

Reduce requirements for primary concentrator (heliostats)

Secondary Concentrator Optics Tower

The receiver can be placed at the ground level

Solar Furnaces

Very high concentration ratios

Combine a field of flat heliostats and a parabolic concentrator

Not for electricity generation

14/7/10GEEN 4830 – ECEN 500751

Secondary concentrators

REFOS Project (DLR)

14/7/10GEEN 4830 – ECEN 500752

SCOT (Secondary Concentrator Optics

Tower)

Weizmann Institute (Israel)

14/7/10GEEN 4830 – ECEN 500753

SCOT (Secondary Concentrator Optics

Tower)

14/7/10GEEN 4830 – ECEN 500754

Beam Down

14/7/10GEEN 4830 – ECEN 500755

Solar Furnaces

14/7/10GEEN 4830 – ECEN 500756

Solar Furnaces

14/7/10GEEN 4830 – ECEN 500757

CRS projects

14/7/10GEEN 4830 – ECEN 500758

CRS (PS10, sat. steam)

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PS10 and PS20 (Abengoa Solar, Spain)

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CRS (Gema Solar, Molten salts)

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Gema Solar (Torresol Energy, Spain)

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Gema SolarDesign Data

Total Reflective Area 285.200 m2

Number of heliostats 2480

Total Area covered by Heliostat Field 142.31 Ha

Thermal output of the Receiver 120 MWt

Tower height 120 m

Heat Storage Capacity (equivalent to turbine operation) 15 hours

Steam Turbine power 17 MWe

Natural Gas Thermal Power 16 MWt

Projected Operative Figures

Direct solar radiation over Heliostats 2062 kWh/m2

Annual Energy sales 96.400 MWhe

Contribution of Natural Gas 15%

Capacity utilization 65 %

CO2 savings 23.000 – 85.000 t/y

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Sierra Solar (e-Solar, USA)

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Unit #1 (100 kW hybrid GT) (Aora Solar,

Israel)

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