1 CONCENTRATING SOLAR COLLECTORS Portland State University Solar Engineering Spring 2008 Carolyn Roos, Ph.D. Washington State University Extension Energy
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CONCENTRATING SOLAR
COLLECTORSPortland State
University
Solar Engineering
Spring 2008
Carolyn Roos, Ph.D.
Washington StateUniversity
Extension Energy
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OUTLINE
• A review of six concentratingsolar technologies and current
projects.• Basics of ray tracing.
• Sketch of a thermal analysis
example
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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)
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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
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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
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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
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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)
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PARABOLIC DISH
& ENGINESOLAR FURNACE
CENTRAL RECEIVERSOLAR FURNACE
PARABOLIC DISH
PARABOLIC TROUGH
FRESNEL REFLECTOR
LENS CONCENTRATORS
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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
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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
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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.
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Parabolic Trough System
- Can be hybrid solar / natural gas- New systems include thermal storage.
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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 -
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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
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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
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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:
http://www.nrel.gov/docs/fy04osti/34169.pdf
Ball Joint Design:http://www.eere.energy.gov/troughnet/pdfs/moreno_sf_i
nterconnections_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
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Preview…
• Sketch of thermal analysis anddesign for parabolic trough
system at the end of thispresentation.
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Compact Linear Fresnel
Reflectors
Ausra, Inc.http://www.ausra.com/
Makes moot some of the design
challenges and weaknesses of
ompac near resne
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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
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• 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
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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.
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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
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available.e.g. Stirling Danmark
http://www.stirling.dk/default.asp?ID=121
… though these are designed for biopower
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Infinia Corphttp://www.infiniacorp.com/applicatis/Prod_Spec.pdf
Stirling Engine
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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)
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Receiver Tubes for Stirling Engine
Located at focus of dish to absorb heat.
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39From: www1.eere.energy.gov/solar/pdfs/csp_prospectus_112807.pdf
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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.
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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.
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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,
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STM’s Sun Dish System
From: http://www.energysolutionscenter.org/distgen/AppGuide/DataFiles/STMBrochure.pdf
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Small Scale & Low TechParabolic Dish with Solar Cookers
Using parabolic dish concentrators on a smaller scale...
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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.)
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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.
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Electricity through Solar Chemistry
Example: Water splitting: 2H2O → 2H2 + O2
S l F
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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
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Odeillo, France• Mirror is 10 stories high and forms one side of
the laboratory
• Maximum temperature is 3800oC
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The Furnace
Inside the focal zone of the 1 MW mirror at Odeillo.
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Receiver Example
Vaporization experiment with 2kW furnace at Odeillo.
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Receiver and Attenuator
Plataforma Solar de Almeria:- Attenuator – Louvers control sunlight entering furnace
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Other Solar Furnaces
Solar furnaces in Spain, Switzerland, Germany, Israel, France...
Paul Scherer Institute - Switzerland (45 kW)
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Paul Scherer Institute, Switzerland
Stretched film concentrator
S l C t l R i
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Solar Central Receivers
“Power Towers” Plataforma Solar de Almeria, Spain
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Solar One
Located near Barstow, CaliforniaOperated from 1982 to1986
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Solar One
Moonrise over the Solar One Heliostat Field
Photo from http://www.menzelphoto.com/gallery/big/altenergy3.htm
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Solar Two
Solar Two improved the thermal storage of Solar One
Photo from http://ucdcms.ucdavis.edu/solar2/
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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
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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%
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63http://www.cc.state.az.us/utility/electric/EPS-USPAPS.pdf
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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.
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Comparisonof Technologies
(2006)
http://tomkonrad.wordpress.com/2006/12/07/they-do-it-with-mirrors-concentrating-solar-power/
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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.
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• 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
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Refraction through aLens• Snell’s Law
n is index of refraction of thematerial
2211sinsin nn
Ray Tracing Example
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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
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Reflection Examples
“Modern Geometrical Optics”, Max Herzberger, 1958
Miscellaneous
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Refraction Examples
“Modern Geometrical Optics”, Max Herzberger, 1958
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Edge Ray Analysis
• Edge ray analysis is used to doray tracing by hand.
• Select rays to establish bounds:
• Extreme angles
• With maximum error.
Analysis
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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
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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
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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:
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pFocal Point of an Imperfect
Primary Concentrator
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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
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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,
http://www.nrel.gov/docs/fy04osti/34169.pdf
Thermal Analysis Example
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y p
• Evacuated tube
ea a ance on ece ver ith d ith t
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with and withoutevacuated tube
Heat Balance Equations
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qon Receiver
Design
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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
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Thermal Analysis
You may also want to include other
losses such as heat loss through supportbrackets.
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Solar News Links
The Energy Blog’s Solar Thermal page:
http://thefraserdomain.typepad.com/energy/solarthermal_/index.html
FRESNEL REFLECTOR
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PARABOLIC DISH
& ENGINESOLAR FURNACE
PARABOLIC DISH
PARABOLIC TROUGH
LENS CONCENTRATORS
The
End