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1
CONCENTRATING SOLAR
COLLECTORS
Portland State
University
Solar Engineering
Spring 2008
Carolyn Roos, Ph.D.
Washington State
University
Extension Energy
2
OUTLINE
• A review of six concentrating
solar technologies and current
projects.
• Basics of ray tracing.
• Sketch of a thermal analysis
example
3
Solar Concentrating
Systems
• Concentrate solar energy through use of mirrors
or 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
Concentrating Solar
Power:
A Revived Industry
• Utility Action on ~3,000 MW in
2005-06
• CSP for Commercial & Industrial
Facilities
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 Limited
Future…
• Carbon limits will close the cost gap.
• CSP can scale up fast without critical
bottleneck materials. (e.g. silicon)
• Costs will come down with increase in
capacity
• expected to fall below natural gas in the
next few years.
• In the very near future, the CSP market in the
SW 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
8
Primary Types of Solar
Collectors
1. Parabolic Trough
2. Compact Linear Fresnel Reflector
new
3. Solar Furnace
4. Parabolic Dish & Engine
5. Solar Central Receiver
(Solar Power Tower)
6. Lens Concentrators
Can be used in conjunction with PV:
Use lenses or mirrors in conjunction with PV
panels to increase their efficiency.
(http://seattle.bizjournals.com/seattle/stories/2006/04/24/focus2.html)
9
PARABOLIC DISH
& ENGINE
SOLAR FURNACE
CENTRAL RECEIVER
SOLAR 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 the
apparatus that “receives” the solar
energy; e.g. evacuated tube. Absorber
absorbs energy from concentrator and
transfers to process being driven (engine,
chemical reactor, etc.); e.g. the pipe
within an evacuated tube.
• Heliostats
Flat 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 circulated
through 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 as
heat 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
15
Thermal Output
of Hybrid Plant with Thermal Storage
16
What Have Been the
Technical 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-term
stability in air.
 Low cost mirrors that have reflectivity and
washability of glass.
Improved Components
 Flex hoses used to join sections of pipe loop were
prone to failure  Replaced with ball joint
design.
 Ability to track on tilted axis
Improved Processes
 e.g. Generate steam directly instead of running
heat transfer fluid through heat exchanger -
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 Energy
of 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)
18
Saguaro Solar Generating
Station
1MW - 2005
19
Nevada Solar One
64 MW - 2007
• Now producing 64 MW on 140 hectares
• Located in Eldorado Valley (south of
Las Vegas)
• One of the world's largest CSP plants.
• Cost: $262 million
• Developed by Solargenix Energy.
SHOTT North America provided
receivers.
• Groundbreaking in February 2006
20
Nevada Solar One
64 MW - 2007
21
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 company
to Luz)
• Cost $1 billion
22
Smaller Scale:
SolarGenix “Power Roof”
(2002)
• Parker Lincoln Building
(demonstration)
• Design point of 176 kW
• Provides 50 tons of absorption
cooling
23
Parabolic Troughs
Links 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
24
Links
to Parabolic Trough
Projects and Technology
Examples
http://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?m
ainAction=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/lewand
owski_vshot.pdf
http://www.capitalsungroup.com/files/rmt.pdf
25
Preview…
• Sketch of thermal analysis and
design for parabolic trough
system at the end of this
presentation.
26
Compact Linear Fresnel
Reflectors
Ausra, Inc.
http://www.ausra.com/
Makes moot some of the design
challenges and weaknesses of
27
Compact Linear Fresnel
Reflectors
• A series of long, shallow-
curvature mirrors
• Focus light on to linear receivers
located above the mirrors.
28
Compact Linear Fresnel
Reflectors
Lower costs compared to
parabolic troughs
• Several mirrors share the same
receiver
• 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 located
in central California
(November 2007)
Compact Linear Fresnel
Reflectors
Projects
30
Parabolic Dishes
- Plataforma Solar de Almeria – DISTAL I and II
- Dish with receiver for Stirling Engine
31
Parabolic Dish/Engine -
Operation
• Solar energy drives a Stirling engine
or Brayton cycle engine (gas
turbine.)
• Receiver absorbs solar energy and
transfers 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.
34
Stirling Engines
• Stirling engines are simple, have high efficiency
(25% for industrial heat), operate quietly, have low
O&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)
35
available.
e.g. Stirling Danmark
http://www.stirling.dk/default.asp?ID=1
21
… though these are designed for biopower
36
Infinia Corp
http://www.infiniacorp.com/applicatio
/Prod_Spec.pdf
37
Stirling Engine
Manufacturers
• Stirling Denmark: http://www.stirling.dk/
• STM Power:
http://www.energysolutionscenter.org/distgen/AppGuide/M
anf/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)
38
Receiver Tubes for Stirling Engine
Located at focus of dish to absorb heat.
39
From: www1.eere.energy.gov/solar/pdfs/csp_prospectus_112807.pdf
40
300 MW From 12,000 Stirling
Solar 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 MW
on three square miles
• Two future phases possible that could add 600
MW
• 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 generating
station on 4500 acres:
• Approved by CPUC in Dec 2005
• Using SES dishes
• First phase: 20,000-dish array to be
constructed over four years
• Option to expand to 850 MW.
42
A news story on these two
projects…
• SAN DIEGO, California, US, September 14, 2005 (Refocus
Weekly) An electric utility in California will buy 300 MW of solar
power 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 Energy
Systems of Arizona. The 300 MW solar facility will consists of
12,000 Stirling solar dishes on three square miles of land in the
Imperial 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 900
MW 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 with
Southern 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 Mojave
Desert, northeast of Los Angeles.
The first phase will consist of a 20,000-dish array to be
43
Salt River Landfill
Demonstration Project
Four 22 kW SunDishes
• Each 'SunDish' is 50' high.
• Stretched-membrane faceted dishes deflected to convex
form by vacuum.
• Reflective surface is made of sheets of 1.0 mm low-iron
glass.
•
• Stirling engines and generators manufactured by STM
Corporation.
• Electricity is used by the landfill facilities.
• Efficiency is “20% higher than other solar systems of a
similar 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 Tech
Parabolic 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)
47
Solar Furnaces - Operation
Solar furnaces are used for:
- High temperature processes  “Solar Chemistry”
- Materials testing
A field of heliostats tracks the sun and focuses
energy 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 electrodes
which often contaminate product.
Energy Sustainability
 Use of renewable energy for industrial processes.
49
Electricity through Solar Chemistry
Example: Water splitting: 2H2O → 2H2 + O2
50
Solar Furnaces
Technical 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
51
CNRS Solar Furnace at
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
57
Solar Central Receivers
“Power Towers”
Plataforma Solar de Almeria, Spain
58
Solar One
Located near Barstow, California
Operated 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.
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%
63
http://www.cc.state.az.us/utility/electric/EPS-USPAPS.pdf
64
Lens
Concentrators
• In this example, energy is concentrated on to PV
cells with lenses
(but lens systems don’t necessarily have PV cells.)
• 40% efficiency for CPV achieved.
65
Comparison
of
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 Use
The heliostat field occupies a large area of land, shading areas where
the ecosystem is accustomed to full sun.
-
Water Use
Wet cooling towers used in power generation have high water
consumption.
67
• Geometrical Optics:
• Law of Reflection and Refraction
are the only physical laws
required for geometrical optics.
• The rest is geometry  How
rays of light are reflected off
surfaces or refracted through
materials.
Ray Tracing
68
• Law of Reflection
• “The incident ray and reflected ray
lie in a plane containing the
incident normal, and this normal
bisects the angle between the two
rays.”
Reflection
Reference: “Modern Geometrical Optics”
by Max Herzberger, 1958
69
Refraction through a
Lens
• Snell’s Law
n is index of refraction of the
material
2
2
1
1 sin
sin 
 n
n 
70
Ray Tracing Example
Secondary concentrator to spread energy evenly
across a cylinder.
…with a front that reflects reemitted radiation back
to the cylinder.
Reemission is not really
a single normal ray as shown,
Normal is center of distribution
of reemitted rays.
71
Miscellaneous
Reflection Examples
“Modern Geometrical Optics”, Max Herzberger, 1958
72
Miscellaneous
Refraction Examples
“Modern Geometrical Optics”, Max Herzberger, 1958
73
Edge Ray Analysis
• Edge ray analysis is used to do
ray tracing by hand.
• Select rays to establish bounds:
• Extreme angles
• With maximum error.
74
Analysis
Rays Enter CPC at Extreme
Angle
• Perfect CPC:
• Conical
approximation:
• Some rays are reflected
back out without
striking the absorber.
• Select cone so rejection
of rays is acceptable.
A Compound Parabolic
Concentrator focuses rays
onto an absorber without
tracking.
75
Example of Secondary
Concentrator
• 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 primary
concentrator.
Ray 1 strikes front. Ray 2 misses the front,
but is reflected back.
Ray 3 misses the front
and misses the back.
76
Ray Tracing by
Computer
• Ray tracing by hand, you are
limited to selecting a small
number of rays.
• Ray tracing by computer, you
can send in many rays.
• Can look at distribution of rays
across a surface.
77
Example:
Focal 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
79
NREL Thermal Analysis
Example
http://www.nrel.gov/docs/fy04osti/34169.pdf
• Consider a parabolic trough.
• Receiver - Pipe with and without
evacuated 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
80
Thermal Analysis Example
• Evacuated tube
81
Heat Balance on Receiver
with and without
evacuated tube
82
Heat Balance Equations
on Receiver
83
Design
In your thermal analysis, you may be interested
in 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 meet
your design criteria cost effectively.
84
Thermal Analysis
You may also want to include other
losses such as heat loss through support
brackets.
85
Solar News Links
The Energy Blog’s Solar Thermal page:
http://thefraserdomain.typepad.com/energy/solartherma
l_/index.html
86
PARABOLIC DISH
& ENGINE
SOLAR FURNACE
CENTRAL RECEIVER
SOLAR FURNACE
PARABOLIC DISH
PARABOLIC TROUGH
FRESNEL REFLECTOR
LENS CONCENTRATORS
The
End

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118910007-Solar-Collectors.ppt

  • 1. 1 CONCENTRATING SOLAR COLLECTORS Portland State University Solar Engineering Spring 2008 Carolyn Roos, Ph.D. Washington State University Extension Energy
  • 2. 2 OUTLINE • A review of six concentrating solar technologies and current projects. • Basics of ray tracing. • Sketch of a thermal analysis example
  • 3. 3 Solar Concentrating Systems • Concentrate solar energy through use of mirrors or 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. 4 Concentrating Solar Power: A Revived Industry • Utility Action on ~3,000 MW in 2005-06 • CSP for Commercial & Industrial Facilities Industrial Solar Tech’s Roof Specs More planned since 2006
  • 5. 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. 6 In a Carbon Limited Future… • Carbon limits will close the cost gap. • CSP can scale up fast without critical bottleneck materials. (e.g. silicon) • Costs will come down with increase in capacity • expected to fall below natural gas in the next few years. • In the very near future, the CSP market in the SW 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. 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
  • 8. 8 Primary Types of Solar Collectors 1. Parabolic Trough 2. Compact Linear Fresnel Reflector new 3. Solar Furnace 4. Parabolic Dish & Engine 5. Solar Central Receiver (Solar Power Tower) 6. Lens Concentrators Can be used in conjunction with PV: Use lenses or mirrors in conjunction with PV panels to increase their efficiency. (http://seattle.bizjournals.com/seattle/stories/2006/04/24/focus2.html)
  • 9. 9 PARABOLIC DISH & ENGINE SOLAR FURNACE CENTRAL RECEIVER SOLAR FURNACE PARABOLIC DISH PARABOLIC TROUGH FRESNEL REFLECTOR LENS CONCENTRATORS
  • 10. 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 the apparatus that “receives” the solar energy; e.g. evacuated tube. Absorber absorbs energy from concentrator and transfers to process being driven (engine, chemical reactor, etc.); e.g. the pipe within an evacuated tube. • Heliostats Flat or slightly curved mirrors that track the sun and focus on receiver or concentrator. Used with solar furnaces
  • 11. 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. 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 circulated through pipe loop. (250oF to 550oF) • Collectors track sun from east to west during day. • Thermal energy transferred from pipe loop to process.
  • 13. 13 Parabolic Trough System - Can be hybrid solar / natural gas - New systems include thermal storage.
  • 14. 14 Thermal Storage • Uses high heat capacity fluids as heat 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
  • 15. 15 Thermal Output of Hybrid Plant with Thermal Storage
  • 16. 16 What Have Been the Technical 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-term stability in air.  Low cost mirrors that have reflectivity and washability of glass. Improved Components  Flex hoses used to join sections of pipe loop were prone to failure  Replaced with ball joint design.  Ability to track on tilted axis Improved Processes  e.g. Generate steam directly instead of running heat transfer fluid through heat exchanger -
  • 17. 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 Energy of 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)
  • 19. 19 Nevada Solar One 64 MW - 2007 • Now producing 64 MW on 140 hectares • Located in Eldorado Valley (south of Las Vegas) • One of the world's largest CSP plants. • Cost: $262 million • Developed by Solargenix Energy. SHOTT North America provided receivers. • Groundbreaking in February 2006
  • 21. 21 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 company to Luz) • Cost $1 billion
  • 22. 22 Smaller Scale: SolarGenix “Power Roof” (2002) • Parker Lincoln Building (demonstration) • Design point of 176 kW • Provides 50 tons of absorption cooling
  • 23. 23 Parabolic Troughs Links 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
  • 24. 24 Links to Parabolic Trough Projects and Technology Examples http://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?m ainAction=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/lewand owski_vshot.pdf http://www.capitalsungroup.com/files/rmt.pdf
  • 25. 25 Preview… • Sketch of thermal analysis and design for parabolic trough system at the end of this presentation.
  • 26. 26 Compact Linear Fresnel Reflectors Ausra, Inc. http://www.ausra.com/ Makes moot some of the design challenges and weaknesses of
  • 27. 27 Compact Linear Fresnel Reflectors • A series of long, shallow- curvature mirrors • Focus light on to linear receivers located above the mirrors.
  • 28. 28 Compact Linear Fresnel Reflectors Lower costs compared to parabolic troughs • Several mirrors share the same receiver • 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. 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 located in central California (November 2007) Compact Linear Fresnel Reflectors Projects
  • 30. 30 Parabolic Dishes - Plataforma Solar de Almeria – DISTAL I and II - Dish with receiver for Stirling Engine
  • 31. 31 Parabolic Dish/Engine - Operation • Solar energy drives a Stirling engine or Brayton cycle engine (gas turbine.) • Receiver absorbs solar energy and transfers it to the engine’s working fluid. • Systems are easily hybridized since Stirling engines can run on any
  • 32. 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.
  • 34. 34 Stirling Engines • Stirling engines are simple, have high efficiency (25% for industrial heat), operate quietly, have low O&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)
  • 37. 37 Stirling Engine Manufacturers • Stirling Denmark: http://www.stirling.dk/ • STM Power: http://www.energysolutionscenter.org/distgen/AppGuide/M anf/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)
  • 38. 38 Receiver Tubes for Stirling Engine Located at focus of dish to absorb heat.
  • 40. 40 300 MW From 12,000 Stirling Solar 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 MW on three square miles • Two future phases possible that could add 600 MW • At 900 MW would be one of the largest solar facilities in the world.
  • 41. 41 500 MW from 20,000-Dish Array in Mojave Desert • Southern California Edison will construct 500 MW solar generating station on 4500 acres: • Approved by CPUC in Dec 2005 • Using SES dishes • First phase: 20,000-dish array to be constructed over four years • Option to expand to 850 MW.
  • 42. 42 A news story on these two projects… • SAN DIEGO, California, US, September 14, 2005 (Refocus Weekly) An electric utility in California will buy 300 MW of solar power 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 Energy Systems of Arizona. The 300 MW solar facility will consists of 12,000 Stirling solar dishes on three square miles of land in the Imperial 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 900 MW 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 with Southern 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 Mojave Desert, northeast of Los Angeles. The first phase will consist of a 20,000-dish array to be
  • 43. 43 Salt River Landfill Demonstration Project Four 22 kW SunDishes • Each 'SunDish' is 50' high. • Stretched-membrane faceted dishes deflected to convex form by vacuum. • Reflective surface is made of sheets of 1.0 mm low-iron glass. • • Stirling engines and generators manufactured by STM Corporation. • Electricity is used by the landfill facilities. • Efficiency is “20% higher than other solar systems of a similar size.” • Hybrid system: Stirling engines can run on solar energy,
  • 44. 44 STM’s Sun Dish System From: http://www.energysolutionscenter.org/distgen/AppGuide/DataFiles/STMBrochure.pdf
  • 45. 45 Small Scale & Low Tech Parabolic Dish with Solar Cookers Using parabolic dish concentrators on a smaller scale...
  • 46. 46 Solar Furnaces • Centre National de Recherche Scientifique - Odeillo, France • Largest solar furnace in the world (1 MWt)
  • 47. 47 Solar Furnaces - Operation Solar furnaces are used for: - High temperature processes  “Solar Chemistry” - Materials testing A field of heliostats tracks the sun and focuses energy 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. 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 electrodes which often contaminate product. Energy Sustainability  Use of renewable energy for industrial processes.
  • 49. 49 Electricity through Solar Chemistry Example: Water splitting: 2H2O → 2H2 + O2
  • 50. 50 Solar Furnaces Technical 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
  • 51. 51 CNRS Solar Furnace at Odeillo, France • Mirror is 10 stories high and forms one side of the laboratory • Maximum temperature is 3800oC
  • 52. 52 The Furnace Inside the focal zone of the 1 MW mirror at Odeillo.
  • 53. 53 Receiver Example Vaporization experiment with 2kW furnace at Odeillo.
  • 54. 54 Receiver and Attenuator Plataforma Solar de Almeria: - Attenuator – Louvers control sunlight entering furnace
  • 55. 55 Other Solar Furnaces Solar furnaces in Spain, Switzerland, Germany, Israel, France... Paul Scherer Institute - Switzerland (45 kW)
  • 56. 56 Paul Scherer Institute, Switzerland Stretched film concentrator
  • 57. 57 Solar Central Receivers “Power Towers” Plataforma Solar de Almeria, Spain
  • 58. 58 Solar One Located near Barstow, California Operated from 1982 to1986
  • 59. 59 Solar One Moonrise over the Solar One Heliostat Field Photo from http://www.menzelphoto.com/gallery/big/altenergy3.htm
  • 60. 60 Solar Two Solar Two improved the thermal storage of Solar One Photo from http://ucdcms.ucdavis.edu/solar2/
  • 61. 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.
  • 62. 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%
  • 64. 64 Lens Concentrators • In this example, energy is concentrated on to PV cells with lenses (but lens systems don’t necessarily have PV cells.) • 40% efficiency for CPV achieved.
  • 66. 66 Environmental Impacts Deserts have sensitive ecosystems and low water availability. Land Use The heliostat field occupies a large area of land, shading areas where the ecosystem is accustomed to full sun. - Water Use Wet cooling towers used in power generation have high water consumption.
  • 67. 67 • Geometrical Optics: • Law of Reflection and Refraction are the only physical laws required for geometrical optics. • The rest is geometry  How rays of light are reflected off surfaces or refracted through materials. Ray Tracing
  • 68. 68 • Law of Reflection • “The incident ray and reflected ray lie in a plane containing the incident normal, and this normal bisects the angle between the two rays.” Reflection Reference: “Modern Geometrical Optics” by Max Herzberger, 1958
  • 69. 69 Refraction through a Lens • Snell’s Law n is index of refraction of the material 2 2 1 1 sin sin   n n 
  • 70. 70 Ray Tracing Example Secondary concentrator to spread energy evenly across a cylinder. …with a front that reflects reemitted radiation back to the cylinder. Reemission is not really a single normal ray as shown, Normal is center of distribution of reemitted rays.
  • 73. 73 Edge Ray Analysis • Edge ray analysis is used to do ray tracing by hand. • Select rays to establish bounds: • Extreme angles • With maximum error.
  • 74. 74 Analysis Rays Enter CPC at Extreme Angle • Perfect CPC: • Conical approximation: • Some rays are reflected back out without striking the absorber. • Select cone so rejection of rays is acceptable. A Compound Parabolic Concentrator focuses rays onto an absorber without tracking.
  • 75. 75 Example of Secondary Concentrator • 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 primary concentrator. Ray 1 strikes front. Ray 2 misses the front, but is reflected back. Ray 3 misses the front and misses the back.
  • 76. 76 Ray Tracing by Computer • Ray tracing by hand, you are limited to selecting a small number of rays. • Ray tracing by computer, you can send in many rays. • Can look at distribution of rays across a surface.
  • 77. 77 Example: Focal Point of an Imperfect Primary Concentrator
  • 78. 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
  • 79. 79 NREL Thermal Analysis Example http://www.nrel.gov/docs/fy04osti/34169.pdf • Consider a parabolic trough. • Receiver - Pipe with and without evacuated 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
  • 81. 81 Heat Balance on Receiver with and without evacuated tube
  • 83. 83 Design In your thermal analysis, you may be interested in 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 meet your design criteria cost effectively.
  • 84. 84 Thermal Analysis You may also want to include other losses such as heat loss through support brackets.
  • 85. 85 Solar News Links The Energy Blog’s Solar Thermal page: http://thefraserdomain.typepad.com/energy/solartherma l_/index.html
  • 86. 86 PARABOLIC DISH & ENGINE SOLAR FURNACE CENTRAL RECEIVER SOLAR FURNACE PARABOLIC DISH PARABOLIC TROUGH FRESNEL REFLECTOR LENS CONCENTRATORS The End