This document provides an overview of six concentrating solar technologies: parabolic troughs, compact linear Fresnel reflectors, solar furnaces, parabolic dishes, solar central receivers, and lens concentrators. It discusses the operation and major components of these systems as well as examples of current projects using concentrating solar power technologies for electricity generation and industrial processes. Technical challenges in developing concentrating solar collectors are also reviewed.
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.
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
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
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
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)
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.
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
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
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.
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
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.
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