118910007 solar collectors

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1

CONCENTRATING SOLAR

COLLECTORSPortland State

University

Solar Engineering

Spring 2008

Carolyn Roos, Ph.D.

Washington StateUniversity

Extension Energy



2

OUTLINE

• A review of six concentratingsolar technologies and current

projects.• Basics of ray tracing.

• Sketch of a thermal analysis

example



3

Solar ConcentratingSystems

• Concentrate solar energy through use of mirrorsor lenses.

• Concentration factor (“number of suns”) may be

greater than 10,000.

• Systems may be small:

e.g. solar cooker

.... or large:- Utility scale electricity generation (up to 900

MWe planned)

- Furnace temperatures up to 3800oC (6800oF)



4

oncen ra ng o ar Power:

A Revived Industry• Utility Action on ~3,000 MW in

2005-06

• CSP for Commercial & IndustrialFacilities

Industrial Solar Tech’s Roof Specs

More planned since 2006



5

States Creating a

Market for CSP• AZ: 15% RE by 2025, 30% Distributed

Generation

• CA: 20% by 2010 & 33% by 2020 planned• CO: 10% by 2015

• NV: 20% by 2015, 5% Solar

• NM: 10% by 2011• TX: 4.2% by 2015



6

In a Carbon LimitedFuture…

• Carbon limits will close the cost gap.

• CSP can scale up fast without criticalbottleneck materials. (e.g. silicon)

• Costs will come down with increase incapacity

• expected to fall below natural gas in the

next few years.

• In the very near future, the CSP market in theSW US can grow to 1 to 2 GW per year.

From: http://www.nrel.gov/csp/troughnet/pdfs/2007/morse_look_us_csp_market.pdf



7

Examples of CSP Applications

Power Generation:

Utility Scale: 64 MW Nevada Solar One (2007) Buildings: 200 kW “Power Roof”

Thermal Needs: Hot Water and Steam (Industrial & Commercial Uses)

Air Conditioning – Absorption Chillers Desalination of seawater by evaporation

Waste incineration

“Solar Chemistry” Manufacture of metals and semiconductors Hydrogen production (e.g. water splitting)

Materials Testing Under Extreme Conditions

e.g. Design of materials for shuttle reentry



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r mary ypes o o ar Collectors

1. Parabolic Trough2. Compact Linear Fresnel Reflector

new

3. Solar Furnace

4. Parabolic Dish & Engine5. Solar Central Receiver

(Solar Power Tower)6. Lens Concentrators

Can be used in conjunction with PV:Use lenses or mirrors in conjunction with PVpanels to increase their efficiency.

(http://seattle.bizjournals.com/seattle/stories/2006/04/24/focus2.html)

http://seattle.bizjournals.com/seattle/stories/2006/04/24/focus2.html

http://seattle.bizjournals.com/seattle/stories/2006/04/24/focus2.html



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PARABOLIC DISH

& ENGINESOLAR FURNACE

CENTRAL RECEIVERSOLAR FURNACE

PARABOLIC DISH

PARABOLIC TROUGH

FRESNEL REFLECTOR

LENS CONCENTRATORS



10

Major Components of Solar Collector Systems• Concentrating mirror(s) May use primary & secondary

concentrators.

• Absorber within a Receiver

Receiver contains the absorber. It is theapparatus that “receives” the solar energy; e.g. evacuated tube. Absorber absorbs energy from concentrator andtransfers to process being driven (engine,

chemical reactor, etc.); e.g. the pipewithin an evacuated tube.

• HeliostatsFlat or slightly curved mirrors that track

the sun and focus on receiver or concentrator. Used with solar furnaces



11

Parabolic Troughs• Most proven solar concentrating

technology• The nine Southern California Edison

plants (354 MW total) constructed in

the 1980’s are still in operation



12

Parabolic Troughs - Operation

• Parabolic mirror reflects solar energy onto a receiver (e.g.a evacuated tube).

• Heat transfer fluid such as oil or water is circulatedthrough pipe loop. (250oF to 550oF)

• Collectors track sun from east to west during day.

• Thermal energy transferred from pipe loop to process.



13

Parabolic Trough System

- Can be hybrid solar / natural gas- New systems include thermal storage.



14

Thermal Storage

• Uses high heat capacity fluids asheat transfer storage mediums

• 12 to 17 hours of storage will allow

plants to have up to 60% to 70%capacity factors.

From: http://www1.eere.energy.gov/solar/pdfs/csp_prospectus_112807.pdf



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Thermal Outputof Hybrid Plant with Thermal Storage



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a ave een eTechnical Challenges?

Development of Materials

Heat transfer tubes that are less prone to sagging& breaking.

Improved surface material of heat transfer tubes.

High absorptivity, low emissivity and long-termstability in air.

Low cost mirrors that have reflectivity andwashability of glass.

Improved Components Flex hoses used to join sections of pipe loop were

prone to failure Replaced with ball jointdesign.

Ability to track on tilted axis

Improved Processes

e.g. Generate steam directly instead of runningheat transfer fluid throu h heat exchan er -



17

Saguaro Solar Generating Station (north of Tucson) 1MW - Compared to 395MW in natural gas fired

generating capacity at same site Broke ground March 24, 2004 and started generating

power December 2005

Built by Solargenix, subsidiary of ACCIONA Energyof Spain

Arizona has goal of 15% renewable energy by 2025. $6 Million Project

“First Solar Thermal Parabolic Trough

Power Plant Built in The U.S. In Nearly Two

Decades to Be Dedicated On Earth Day”

(2005)



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Saguaro Solar GeneratingStation

1MW - 2005



20

Nevada Solar One

64 MW - 2007



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Around the World

Granada, Spain.

• Two 50 MW plants

• Developed by Solar Millenium AG

Negev desert of Israel

• 150 MW facility to be expanded to 500

MW

• Developed by Solel (successor companyto Luz)

• Cost $1 billion

S ll S l



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Smaller Scale:SolarGenix “Power Roof”

(2002)• Parker Lincoln Building(demonstration)

• Design point of 176 kW

• Provides 50 tons of absorptioncooling



23

ara o c roug sLinks for More Info

http://www.iea-ship.org/index.html

http://www.solarpaces.org/solar_trough.pdf

http://www.nrel.gov/docs/fy04osti/34440.pdf

Heat Transfer Analysis:


Ball Joint Design:http://www.eere.energy.gov/troughnet/pdfs/moreno_sf_i

nterconnections_with_salt_htf.pdf





http://www.eere.energy.gov/troughnet/pdfs/moreno_sf_interconnections_with_salt_htf.pdf












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to Parabolic TroughProjects and Technology

Exampleshttp://www.solargenix.com/power_plant_tech.cfm http://www.solargenix.com/building_products.cfm http://www.us.schott.com/solarthermal/english/in

dex.html http://www.us.schott.com/solarthermal/english/pr oducts/receiver/details.html

http://www.inderscience.com/search/index.php?mainAction=search&action=record&rec_id=674

5 http://www.sete.gr/files/Ebook/2006/Hospitality_D

ay_Lokurlu.pdf http://www.eere.energy.gov/troughnet/pdfs/lewan

dowski_vshot.pdf

http://www.capitalsungroup.com/files/rmt.pdf

http://www.solargenix.com/power_plant_tech.cfm


http://www.solargenix.com/building_products.cfm

http://www.us.schott.com/solarthermal/english/index.html


http://www.us.schott.com/solarthermal/english/products/receiver/details.html





http://www.sete.gr/files/Ebook/2006/Hospitality_Day_Lokurlu.pdf


http://www.eere.energy.gov/troughnet/pdfs/lewandowski_vshot.pdf



http://www.industrialsolartech.com/













http://www.solargenix.com/building_products.cfm




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Preview…

• Sketch of thermal analysis anddesign for parabolic trough

system at the end of thispresentation.



26

Compact Linear Fresnel

Reflectors

Ausra, Inc.http://www.ausra.com/

Makes moot some of the design

challenges and weaknesses of

ompac near resne



27

ompac near resneReflectors

• A series of long, shallow-curvature mirrors

• Focus light on to linear receiverslocated above the mirrors.

Compact Linear Fresnel



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Compact Linear FresnelReflectors

Lower costs compared toparabolic troughs

• Several mirrors share the samereceiver

• Reduced tracking mechanism complexity

• Stationary absorber

• No fluid couplings required

• Mirrors do not support the receiver

• Denser packing of mirrors possible

• Half the land area



29

• 6.5-megawatt demonstration power

plant under construction in Portugal

(as of September 2007)

• Ausra and PG&E announce purchasing

agreement for 117 MW facility locatedin central California

(November 2007)

ReflectorsProjects



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Parabolic Dishes

- Plataforma Solar de Almeria – DISTAL I and II

- Dish with receiver for Stirling Engine



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Parabolic Dish/Engine -

Operation• Solar energy drives a Stirling engine

or Brayton cycle engine (gas

turbine.)

• Receiver absorbs solar energy andtransfers it to the engine’s working

fluid.

• Systems are easily hybridized since

Stirling engines can run on any



32

State of Dish Technology

Mature and Cost Effective Technology: Large utility projects

using parabolic dishes are now under development.

Technical Challenges Have Been: Development of solar materials and components Commercial availability of a solar-izable engine.

Advantage: High Efficiency Demonstrated highest solar-to-electric conversion efficiency

(still true with advances in CPV? No.)

Potential to become one of least expensive sources of

renewable energy. (still true with development of Fresnel reflectors?)

Advantage: Flexibility Modular - May be deployed individually for remote

applications or grouped together for small-grid (village power)systems.



33

Stirling Energy Systems,Inc.



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Stirling Engines

• Stirling engines are simple, have high efficiency(25% for industrial heat), operate quietly, have lowO&M costs (~$0.006/kWh)

• Waste heat can easily be recovered by the engine,as well as from the engine

• According to one manufacturer: $1000-2000/kW

installed

But• They have higher costs for materials and

assembly, are larger for same torque, have longer start up time (needs to warm up)

a ailable



35

available.e.g. Stirling Danmark

http://www.stirling.dk/default.asp?ID=121

… though these are designed for biopower



36

Infinia Corphttp://www.infiniacorp.com/applicatis/Prod_Spec.pdf

Stirling Engine



37

Stirling EngineManufacturers

• Stirling Denmark: http://www.stirling.dk/

• STM Power:http://www.energysolutionscenter.org/distgen/AppGuide/Manf/STMPower.htm

• QRMC

• Infinia: http://www.infiniacorp.com • Stirling Cycles has been acquired by Infinia.

• ReGen Power Systems: http://www.rgpsystems.com/

• Stirling Energy Systems: http://www.stirlingenergy.com/.• Currently manufacturers large utility-scale Stirling engines for use

with solar concentrating systems. Has plans to produce engines for use with combustible fuels in the future.

• Stirling Biopower: http://www.stirlingbiopower.com/.

• In the start up phase (as of July 2007)

http://www.stirling.dk/


http://www.energysolutionscenter.org/distgen/AppGuide/Manf/STMPower.htm



http://www.infiniacorp.com/

http://www.rgpsystems.com/

http://www.stirlingenergy.com/

http://www.stirlingbiopower.com/

http://www.stirlingbiopower.com/

http://www.stirlingenergy.com/

http://www.rgpsystems.com/

http://www.infiniacorp.com/






38

Receiver Tubes for Stirling Engine

Located at focus of dish to absorb heat.



39From: www1.eere.energy.gov/solar/pdfs/csp_prospectus_112807.pdf



40

rom , r ngSolar Dishes

in Imperial Valley, Southern

CA• San Diego Gas & Electric entered 20-year

contract with SES Solar Two, an affiliate of

Stirling Energy Systems in 2005.

• 12,000 Stirling solar dishes providing 300 MWon three square miles

• Two future phases possible that could add 600MW• At 900 MW would be one of the largest solar facilities

in the world.



41

500 MW from 20,000-Dish

Array

in Mojave Desert• Southern California Edison will

construct 500 MW solar generatingstation on 4500 acres:• Approved by CPUC in Dec 2005

• Using SES dishes

• First phase: 20,000-dish array to beconstructed over four years

• Option to expand to 850 MW.



42

A news story on these two

projects…

• SAN DIEGO, California, US, September 14, 2005 (RefocusWeekly) An electric utility in California will buy 300 MW of solarpower from a new facility that uses Stirling solar dishes.

• San Diego Gas & Electric will buy the green power under a 20-year contract with SES Solar Two, an affiliate of Stirling EnergySystems of Arizona. The 300 MW solar facility will consists of

12,000 Stirling solar dishes on three square miles of land in theImperial Valley of southern California.

SDG&E has options on two future phases that could add another 600 MW of renewables capacity and, if the plant grows to 900MW within ten years, it would be one of the largest solar facilities in the world. The utility also announced the purchase of

4 MW of energy from a local biogas landfill project.SES says the contract is the second record-breaking solar project it has signed in the past month, following a contract withSouthern California Edison for construction of a 4,500 acre solar generating station in southern California. That 20-year power purchase agreement, which also must be approved by the CPUC,calls for development of 500 MW of solar capacity in the MojaveDesert, northeast of Los Angeles.

The first hase will consist of a 20 000-dish arra to be

Salt River Landfill



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Salt River LandfillDemonstration Project

Four 22 kW SunDishes• Each 'SunDish' is 50' high.

• Stretched-membrane faceted dishes deflected to convexform by vacuum.

• Reflective surface is made of sheets of 1.0 mm low-ironglass.

• • Stirling engines and generators manufactured by STM

Corporation.

• Electricity is used by the landfill facilities.

• Efficiency is “20% higher than other solar systems of asimilar size.”

• Hybrid system: Stirling engines can run on solar energy,



44

STM’s Sun Dish System

From: http://www.energysolutionscenter.org/distgen/AppGuide/DataFiles/STMBrochure.pdf



45

Small Scale & Low TechParabolic Dish with Solar Cookers

Using parabolic dish concentrators on a smaller scale...



46

Solar Furnaces

• Centre National de Recherche Scientifique - Odeillo, France

• Largest solar furnace in the world (1 MWt)



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Solar Furnaces - Operation

Solar furnaces are used for:- High temperature processes “Solar Chemistry” - Materials testing

A field of heliostats tracks the sun and focusesenergy on to a stationary parabolic concentrator which refocuses energy to the receiver.

Receivers vary in design depending on process: Batch or continuous process Controlled temperature and pressure

Collection of product (gas, solid, etc.)



48

Why Run Processes in a Solar Furnace?

Higher Temperatures (up to 3800oC) Higher temperatures are possible in solar furnace

than in conventional combustion furnace or electric arc furnace.

Cleaner Processes e.g. Electric arc furnaces use carbon electrodeswhich often contaminate product.

Energy Sustainability Use of renewable energy for industrial processes.



49

Electricity through Solar Chemistry

Example: Water splitting: 2H2O → 2H2 + O2

S l F



50

Solar FurnacesTechnical Challenges

From test bench to commercial scale processes Development of continuous processes from

batch experiments

Material Development Materials suitable for very high temperatures.

Process Control e.g. Accurate measurement of high temperatures

Od ill F



51

Odeillo, France• Mirror is 10 stories high and forms one side of

the laboratory

• Maximum temperature is 3800oC



52

The Furnace

Inside the focal zone of the 1 MW mirror at Odeillo.



53

Receiver Example

Vaporization experiment with 2kW furnace at Odeillo.



54

Receiver and Attenuator

Plataforma Solar de Almeria:- Attenuator – Louvers control sunlight entering furnace



55

Other Solar Furnaces

Solar furnaces in Spain, Switzerland, Germany, Israel, France...

Paul Scherer Institute - Switzerland (45 kW)



56

Paul Scherer Institute, Switzerland

Stretched film concentrator

S l C t l R i



57

Solar Central Receivers

“Power Towers” Plataforma Solar de Almeria, Spain



58

Solar One

Located near Barstow, CaliforniaOperated from 1982 to1986



59

Solar One

Moonrise over the Solar One Heliostat Field

Photo from http://www.menzelphoto.com/gallery/big/altenergy3.htm



60

Solar Two

Solar Two improved the thermal storage of Solar One

Photo from http://ucdcms.ucdavis.edu/solar2/



61

Plataforma Solar de Almeria

• 1.8 MW steam generator

• Produces steam at 340oC and

to drive steam turbine

• Thermal storage: 18-tons of Al2O3

Notice the heliostat field and the

central tower reflected in this heliostat.

Concentrating Solar



62

Concentrating Solar

Photovoltaics

• 500 kW now installed in Arizona (APS)

• Concentrating sunlight 250x to 500x reduces cell cost

• Amonix CPV cells are 26% efficient.

•Most efficient in world for silicon until… (see next slides)

• With multi-junction cells, efficiency can be increased to

40%



63http://www.cc.state.az.us/utility/electric/EPS-USPAPS.pdf



64

Concentrators• In this example, energy is concentrated on to PVcells with lenses

(but lens systems don’t necessarily have PV cells.)

• 40% efficiency for CPV achieved.



65

Comparisonof Technologies

(2006)

http://tomkonrad.wordpress.com/2006/12/07/they-do-it-with-mirrors-concentrating-solar-power/



66

Environmental Impacts

Deserts have sensitive ecosystems and low water availability.

Land UseThe heliostat field occupies a large area of land, shading areas wherethe ecosystem is accustomed to full sun.

-

Water UseWet cooling towers used in power generation have high water consumption.



67

• Geometrical Optics:

• Law of Reflection and Refraction

are the only physical lawsrequired for geometrical optics.

• The rest is geometry Howrays of light are reflected off surfaces or refracted throughmaterials.

Ray Tracing

Reflection



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• Law of Reflection

• “The incident ray and reflected ray

lie in a plane containing theincident normal, and this normal

bisects the angle between the tworays.”

Reflection

Reference: “Modern Geometrical Optics”

by Max Herzberger, 1958

Refraction through a



69

Refraction through aLens• Snell’s Law

n is index of refraction of thematerial

2211sinsin nn

Ray Tracing Example



70

Ray Tracing ExampleSecondary concentrator to spread energy evenlyacross a cylinder.

…with a front that reflects reemitted radiation back

to the cylinder.

Reemission is not reallya single normal ray as shown,Normal is center of distributionof reemitted rays.

Miscellaneous



71

Reflection Examples

“Modern Geometrical Optics”, Max Herzberger, 1958

Miscellaneous



72

Refraction Examples

“Modern Geometrical Optics”, Max Herzberger, 1958



73

Edge Ray Analysis

• Edge ray analysis is used to doray tracing by hand.

• Select rays to establish bounds:

• Extreme angles

• With maximum error.

Analysis



74

y

Rays Enter CPC at ExtremeAngle• Perfect CPC:

• Conicalapproximation:• Some rays are reflected

back out withoutstriking the absorber.

• Select cone so rejection

of rays is acceptable.

A Compound ParabolicConcentrator focuses raysonto an absorber withouttracking.

Example of Secondary



75

p yConcentrator

• Rays from primary concentrator focus on a pipe

imperfectly.• Design secondary mirror so many of the rays that

miss the front will reflect back to the pipe.

• Select rays that represent the error of the primaryconcentrator.

Ray 1 strikes front. Ray 2 misses the front,

but is reflected back.

Ray 3 misses the front

and misses the back.

Ray Tracing by



76

Ray Tracing byComputer

• Ray tracing by hand, you arelimited to selecting a small

number of rays.• Ray tracing by computer, you

can send in many rays.

• Can look at distribution of raysacross a surface.

Example:



77

pFocal Point of an Imperfect

Primary Concentrator



78

Ray Tracing by Computer

Computer modeling:• Incoming rays created according to the profile of primary

concentrator.• Define surfaces of windows, reflectors and absorbers

mathematically.• Follow path of incoming rays to absorber

and reemission of rays from absorber back out of system• Determine surface temperatures and available process heat

from distribution of rays using energy balance.

Example design goals:• Minimize reflection out of receiver • Obtain even distribution across absorber surfaces

erma na ys sExample



79

Examplehttp://www.nrel.gov/docs/fy04osti/34169.pdf

• Consider a parabolic trough.

• Receiver - Pipe with and withoutevacuated tube.

From: “Heat Transfer Analysis and Modeling of a Parabolic Trough Solar Receiver

Implemented in Engineering Equation Solver”, R. Forristall, NREL, October 2003,


Thermal Analysis Example







80

y p

• Evacuated tube

ea a ance on ece ver ith d ith t



81

with and withoutevacuated tube

Heat Balance Equations



82

qon Receiver

Design



83

Design

In your thermal analysis, you may be interestedin considering:

• Length and cross-section of trough• Diameters of pipe and evacuated tube

• Velocity of heat transfer fluid• Optical properties of the pipe, glass and trough• Weather data: Temperature, Insolation, Wind• Temperatures of surfaces and heat transfer

fluid.• Energy absorbed by heat transfer fluid

Vary geometry, velocity and materials to meetyour design criteria cost effectively.

Thermal Analysis



84

Thermal Analysis

You may also want to include other

losses such as heat loss through supportbrackets.



85

Solar News Links

The Energy Blog’s Solar Thermal page:

http://thefraserdomain.typepad.com/energy/solarthermal_/index.html

FRESNEL REFLECTOR







PARABOLIC DISH

& ENGINESOLAR FURNACE

PARABOLIC DISH

PARABOLIC TROUGH

LENS CONCENTRATORS

The

End

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