Evaluation of Electricity Storage versus Thermal Storage ...
Gould - Thermal Energy Storage
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THERMAL ENERGY STORAGE
Bill Gould
April 2010Chief Technology Officer
George Washington University
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2 INTE
RMIT
TANC
Y AN
D RE
NEW
ABLE
S Wind Generation Varies Day-to-Day : Hour-to-Hour
TEHACHAPI WIND GENERATION
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3
Wind Generation Out of Phase With DemandW
IND
ENER
GY G
ENER
ATIO
N PR
OFIL
E
Wind Generation July
MW
SCE Average Load July
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Just a Pretty Little Cloud
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• New Lower Freezing Point Heat Transfer Fluids
• Phase Change Materials,
• Thermo-chemical Storage,
• Sand Sifter,
• Nano Particles and Nano Tubes
• Graphite or Concrete Monoliths
Future Storage Concepts Being Studied
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Solid Media: Concrete, Ceramic, Alumina Manganese Oxide, Iron, etc.
Concrete Block
Pipe Filled w. Solid Media
• Concrete blocks and Solid Media containers might be paired with heated air, CO2 or liquid heat transfer fluids.
• Concrete can be inexpensive, but there is concern about concrete separating from the HTF tube after many thermal cycles. Tests underway at DLR look promising.
• Cost is still a question for other solid media.
• But steam turbines work best with constant high temperature steam.
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Two Tanks Capture More Energy Than a Single Tank
1000 Watts / M2
Receiver
200 Watts / M2
Hot Tank 566oC
566oC
Hot Tank566oC
Receiver
5:1 TURNDOWN CAPABILITY
Cold Tank288oc
Cold Tank288oc
288 to 566oC
Normal Operation
Low Insolation Operation
Single Tank Systems (Steam, Ceramic & Concrete) Cannot Capture Energy at Low Temperatures w/o Degrading the Hot Side Inventory.
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• Steam in Pressure Vessels
• Compressed Air – in Tanks or in underground caverns.
• Pumped Storage – using Water
• Concrete Monoliths.
• Other Solids: Ceramics, Alumina, Iron Oxides, etc.
• Molten Nitrate Salts:
– Single-Tank Thermocline
– Two-Tank System
Deployable Technologies
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Storing Steam in Large Pressure Vessels
ASME PRESSURE
VESSEL
• Should work well through short cloud transients.
• Requires an ASME stamped pressure vessel.
• Cannot support large scale:• Utility dispatch and curtail,• Dispatch over night or through a long storm,• Load Multiplying- for peaker duty,• Cannot efficiently collect energy at various
temperatures on hazy days or near sunset.
Primarily useful to provide grid stability through short cloud transients.
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Pumped Storage and Pressurized Caverns
Pumped StorageRequires a mountain and two reservoirs. Concepts
and costs are well understood.
Both Pumped Hydro and Compressed Air in Caverns work. Both require extensive infrastructure development!
Underground Salt Cavern requires the right
geological features, plus development.
Neither feature need be adjacent to the solar plant – as long as there is a transmission line to the geologic feature.
Underground Cavern
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Thermocline Thermal Storage Systems
•Thermoclines promise savings (one tank instead of two).
•Work best with tall, narrow cylinders (to keep the interface
zone from growing to fill the entire volume.
•Tall and narrow costs more than than short and fat.
• Does not scale to commercial sized plants. Which might
use 50 to 75 million pounds of salt.
HOT
COLD
INTERFACE
HOT
COLD
Thermoclines’ promised cost advantage does not scale.
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POWER TOWERSPower Towers Grew Out of Solar One & Solar Two
12Confidential and Proprietary
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How Does It Work?
HELIOSTATS
COLLECTOR FIELD
CONDENSER
POWER BLOCK
RECEIVER
MOLTEN SALT SYSTEM
Hot SaltReheater
ReceiverTower
Condensate Tank
Superheater
Steam Gen./Evaporator
Feedwater Preheaters
IP/LPTURBINEGENERATOR
HPTURBINE
Reheat Steam
HPSteam
Cold Salt
THERMAL STORAGE SYSTEM
STEAM GENERATION SYSTEM
MOLTEN SALT LOOP
STEAM TURBINE GENERATOR
288°C
565°C
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14
UTC
Prop
rieta
ryMOLTEN SALT THERMAL STORAGESEPARATES THERMAL ENERGY COLLECTION FROM ELECTRIC POWER PRODUCTION
Thermal EnergyStored in
Molten Salt
Noon
Sunlight
Midnight MidnightNoon
Ener
gy (M
wt-h
r)
Option 1 High PowerPeaker Plant
Option 2 Constant PowerBase-load Plant
Powe
r (M
we)
Sunlight
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15
Con
fiden
tial a
nd
Pro
prie
taryCLIENT SELECTS POWER USAGE
15
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TECHNOLOGY VALIDATED AT SOLAR TWO Technology Demonstrated at “Solar Two” Exceeded Performance Targets Demonstrated ability to produce power 24
hours/day
16Confidential and Proprietary
“…. The 10-megawatt Solar Two power tower pilot plant near Barstow, California, successfully completed operations in April 1999, having met essentially all of its objectives. It demonstrated the ability to collect and store solar energy efficiently and to generate electricity when needed by the utility and its customers. Based on the success of Solar Two, U.S. industry is actively planning the first commercial implementation of this technology….” SunLab SnapShot March 2000
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S0LAR ONE & SOLAR TWO COLLECTOR FIELDS
17Confidential and Proprietary
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RECEIVER IS THE HEART OF THE SYSTEM
18Confidential and Proprietary
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SOLARRESERVE’S TECHNOLOGY PARTNER
19Confidential and Proprietary
Sikorsky
Hamilton Sundstrand
Carrier UTC Fire & SecurityOtis
UTC Power Research Center
PW Rocketdyne
Pratt & Whitney
HS Rocketdyne
$59B Revenue
Rocketdyne3,500 Employees1,300 Technical Degrees
UTC
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RECEIVER: HIGH-TECH PORTION OF PLANT
Technology Leverage Engineered to withstand
extreme thermal cycles.
Hundreds of regeneratively cooled tubes.
Precision shapes, exotic alloys.
Instantaneous, severe temperature gradients
20Confidential and Proprietary
3,316˚C Rocket Flame-204˚C Hydrogen Coolant
650oC Tube Surface Temperature288oC Cold Salt Temperature
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MOLTEN SALT LOOP – RECEIVER SYSTEM
21Confidential and Proprietary
Upper Headerand
Tube Installation
Aerospace “mission critical” quality thermal, fluid flow and
structural analyses.
Stress Analysis of Tube-to-Header Joint
ANSYS Structural Analysis of Tube Clip
Larger system actually operates at lower risk conditions
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UPPER HEADER AND TUBE INSTALLATION
22Confidential and Proprietary
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UPPER HEADER AND TUBE INSTALLATION
23Confidential and Proprietary
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SALT PIPING
24Confidential and Proprietary
All Salt Piping is Enclosed and Sloped Downward
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STEAM GENERATOR LAYOUT
25Confidential and Proprietary
Two-tank system provides 10 to 16 hours of thermal storage
30-year design life Either tank safely able to hold total salt
inventory Tank heel volumes minimized 99% thermal storage efficiency
TANKS COLD HOT
SIDE WALL HEIGHT
12 m 12 m
INNER TANK DIAMETER
36 m 37 m
NOMINAL OPERATING TEMP
288°C 565°C
MAXIMUM BULK TEMP
316°C 593°C
SuperheatersPreheater
Reheater
Steam drum
Evaporators
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26
CON
FID
ENTI
AL
PLAN
T GE
NERA
L AR
RANG
EMEN
T
Receiver Tower
Cold Salt TankHot Salt
Tank
Steam Generator Building
Turbine Generator Building
Air Cooled Condenser
Control Building
Switchyard
Receiver Assembly Area
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Just a Pretty Little Cloud
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•Rocketdyne is one of the few companies who can say they have experience with both direct steam and molten salt.
•Solar One – 1979 – 1984 (Direct Steam)
•Solar Two – 1994-1999 (Molten Salt)
•Which fluid was best? Why?
Direct Steam
Direct SteamSALT
Direct Steam Versus Molten Salt
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0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
7:00 9:00 11:00 13:00 15:00 17:00 19:00
Time (hh:mm)
Sola
r Out
put (
% M
axim
um O
utpu
t)
CSP
PV
Steam Drum Limits
Solar PV Varies Minute-to-Minute: Second-to-SecondThe Advantages of Thermal
Storage
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0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
7:00 9:00 11:00 13:00 15:00 17:00 19:00
Time (hh:mm)
Sola
r Out
put (
% M
axim
um O
utpu
t)
CSP
PV
The Hot Tank is An Energy Integrator
The hot tank sums instantaneous energy flows.The turbine sees the integral of these flows.
So cloud passage never interrupts generation during peak periods, it only brings forward the shut down late at night.
Collection may be interrupted by cloud passage – but not generation.
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NaturalGasBoiler
Steam turbine
Electricity Generator
Condenser
Low pressure warmer
Degasification
Solar warmer
Solar pre-warmer
Solar warmer Water circuit pump
Solar steam generator
Expansion Tank
Thermal fluid pump
Heated collecting main pipeSolar field Steam Cycle
Euro
thou
gh C
olle
ctor
s
Cooled collecting main pipe
Typical Solar Thermal Trough System
Many solar plants need a gas boiler to maintain temperature on weak days.
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Optional Thermal Storage in a Trough
Transferring heat from oil to salt and back to Oil incurs a 7% round trip transaction cost.
Steam turbine
Electricity Generator
Condenser
Low pressure warmer
Degasification
Solar warmer
Solar pre-warmer
Solar warmer Water circuit pump
Solar steam generator
Expansion Tank
Thermal fluid pump
Heated collecting main pipeSolar field Steam CycleSalt Storage
Melted salts storage
Euro
thou
gh C
olle
ctor
s
Hot Salt Tank
Oil-Salt-Oil HEX
Cold Salt Tank
Cooled collecting main pipe
NaturalGasBoiler
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Stored Heat =∑ mCp ΔT
Large / Smaller ΔT ≈ 278°C/90°CLow Temperature Storage Requires ≈ 3X mass
Stored Heat is Proportional to ΔT
.Salt
566°C
288°C
~378°C
288°C Low Temperature Storage ~ 3X Cost per MWt
Therminol
At What Temperature Can You Store Heat?
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MODULAR - MULTI-PLANT SITE
Multiple plants share:• Control room,• Warehouse, and spare parts
inventory,• Administration building,• Operation and maintenance staff• Switchyard
Modular Multi-Plant Site
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What is the Optimum Receiver Size?
Relatively flat curve between 500 and 650 MWt receiver sizes
0 100 200 300 400 500 600 700 800THERMAL POWER (MW)
NORM
ALZI
DED
COST
($/M
W)
Results of Thousands of Monte Carlo Analyses Evaluating Plant Cost versus Receiver Size (MWt)
There Are Strong Economies of Scale!
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What is the Optimum Receiver Size?
Relatively flat curve between 500 and 650 MWt receiver sizes
0 100 200 300 400 500 600 700 800THERMAL POWER (MW)
NORM
ALZI
DED
COST
($/M
W)
Multiple Towers of an Inefficient Size Only Multiply the Inefficiencies
There Are Strong Economies of Scale!
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1GW : 24/7 Solar Park Layout12Place picture of ten tower station here.Control RoomAnd CommonFacilities2500 metersEach plant has standaloneTurbine and Steam Generator 1GW : 24/7 Solar Park Layout12
Control RoomAnd CommonFacilities2500 metersEach plant has standaloneTurbine and Steam Generator
Ten Towers Generate One Gigawatt (24x7)
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38Confidential and Proprietary38Confidential and Proprietary
Personal Experiences with Salt
Personnel Hazard: • No burns to exposed skin• Clothing not ignited• Paper in Trash Can Not Even Singed
Trash
ME
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39Confidential and Proprietary
Personal Experiences with Salt
Personnel Safety: • No burns to exposed skin• Clothing not ignited• Paper in trash can not discolored
Trash
Equipment Safety:• Salt washed off easily• No damage to paint• No burning, melting or chemical interaction with soft foam rubber gaskets or windshield wipers
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40Confidential and Proprietary
How to Clean Up a Salt Spill
Salt freezes within the top centimeter of soil, Therminol stays liquid and seeps up to 5’ meters into the sand.
• Wait ‘til the puddle freezes• Break up the frozen puddle with shovels• Load chunks of salt and sand into barrels• Haul barrels away
Molten Salt TankFrozen Salt Puddle
Salt from a small flange leak is recoverable. Operators simply break off the frozen stalactite and throw it back in the tank.
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41Confidential and Proprietary
How do you Decommission a Molten Salt System?
• Erect a tall scaffold & wrap with tarps• Pump salt through a shower head at the top• Salt cools, solidifies and “prills” as it falls• Laborers load the prills into shipping bags• Sell as fertilizer
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Two Tank Molten Salt Storage Systems
• Firm Dispatch – Enabling utility dispatch & curtail• Zero Fossil Fuel Combustion • Grid Stability – Stable output thru cloud transients. • Multiplied Peaking Capacity• Increased Annual Capacity Factor
– Low Insolation Collection – For Hazy Days • Equipment Elimination
– Eliminates Start Up Boiler– Eliminates Supplemental Firing for Superheat