Post on 27-Dec-2015
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The Role of Energy Storage in the Modern Low-Carbon Grid
Paul DenholmNational Renewable Energy Laboratory
Strategic Energy Analysis and Applications CenterJune 12, 2008
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Today’s Discussion: The Role of Storage in the Past, Present & Future
Grid
Fraction of Energy from Wind and Solar
0% 1% 20% 100%
Studied storage valuable but not necessary
PresentPast Near Future?
Less studiedstorage increasingly valuable and
at some point necessary
Low Carbon Future
Topics to Discuss:• Grid applications of storage & valuation• Potential changes in storage valuation created by renewable energy• Storage technologies
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Winter Spring Minimum
Summer Maximum
3 Weeks in Colorado (Xcel) 2003
The Challenge
Challenge is to meet this demand, increasingly with technologies that don’t behave the way we would like them
to behave
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Grid of the Past
Fraction of Energy from Wind and Solar
0% 1% 20% 100%
Challenges of meeting variations in demand provided early motivations for storage (<1980)
- Limited flexibility steam plants (no CTs)- Projected nuclear builds (100s of GW)- Fuels Act (no gas)
PresentPast Near Future?
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Early Storage Build Out
Conventional Pumped Hydro: ~ 20 GW
CAES: 1 Plant (110 MW)
Others (<100 MW total): A few batteries, SMES, mostly for local power quality issues
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Recent History (1980s-2000)
• Limited Activity– PHS sites mostly gone– Cheap natural gas– Limited nuclear build out – Exotic technologies remain
costly
• Cheaper and/or easier to meet variation in load and capacity requirements with conventional generation resources
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1970 1975 1980 1985 1990 1995 2000
Ele
ctri
c S
ecto
r N
atu
ral G
as P
rice
($/
tCF
)
Fuel Use Act
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Grid of the Present
Fraction of Energy from Wind and Solar
0% 1% 20% 100%0
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7
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1998 2000 2002 2004 2006E
lect
ric
Sec
tor
Nat
ura
l Gas
Pri
ce (
$/tC
F)
Renewed Interest in Storage- Emergence of energy and ancillary service markets- High natural gas prices
Present
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Potential Values of Energy Storage
• “Capturable” in existing markets– Energy Arbitrage– Capacity– Frequency regulation– Spinning and non-spinning reserve
• Less-Capturable / Regulated Services – Black start– T&D deferral– All of the above in regulated service territories
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0 6 12 18 24
Hour
Wh
ole
sale
Pri
ce (
$/M
Wh
)
Hold
Sell
Buy + Double Spin
Spin
Valuation of Energy Storage
8 MWh Purchased + 6 Hours of
Double Spin = 53.3
6 MWh Sold = $251.8
Daily Net Revenue (no O&M) = $369.2
8 Hours of Spin = $64
Revenues have increased 76% by combining services
1 MW, 6 MWh Device, 75%
efficiency
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Storage in Today’s Grid
• Can provide a variety of services• Proper valuation must consider multiple
services (energy + capacity)• Still economic, technical, regulatory &
institutional impediments to larger deployment• As with any potential solution it needs to meet
investment criteria and beat the competition• Storage is useful but not a required
component of the grid
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Grid of the Near Future
Fraction of Energy from Wind and Solar
0% 1% 20% 100%
• Growth in renewables- dominated by wind
• Perceived need/opportunities for “firming”• Concerns about adequate T&D
Near Future?
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Will Opportunities for Storage Increase with RE Deployment?
• Will there be increased opportunities for storage? – Increased variation in price – Increased need for capacity & ancillary
services– Greater need for T&D
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Characteristics of Wind
• Variable and uncertain output• Limited dispatchability (can curtail when
needed) • Significant ramp rates (but generally over hours
not minutes)• Wind output is not usually coincident with peak
load– Wind is an energy resource, not a capacity resource– Somewhat anti-correlated with load
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Possible RE Impacts that Increase Opportunities for Storage
• Increased need for ancillary services due to ramping and variability
• Increased variation in prices due to anti-correlation with load
• Increased T&D requirements due to low capacity factors
• How to evaluate???
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Utility Wind Integration Studies
• Simulate system with and without wind– Use expensive commercial software
that includes existing generation mix, transmission system
– Get lots of wind simulations from a commercial vendor
– Spend several 100ks to several M$
• Evaluate costs of forecast errors, additional reserves etc.
Ponnequin PeetzPonnequin Peetz
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Load Impacts
Greater Ramp Rates
Limited Capacity
Reduced Fuel Use
GE Study of ERCOT
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Forecast Error
Forecast error results in over- or under-commitment & increased costs
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Example Results (Arizona Public Service)
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Comparison of Cost-BasedU.S. Operational Impact Studies
* 3-year average; total is non-market cost** highest integration cost of 3 years; 30.7% capacity penetration corresponding to 25% energy penetration; 24.7% capacity penetration at 20% energy penetration*** found $4.37/MWh reduction in UC cost when wind forecasting is used in UC decision
Date Study Wind Capacity Penetra-tion (%)
Regula-tion Cost ($/MWh)
Load Following Cost ($/MWh)
Unit Commit-ment Cost ($/MWh)
GasSupplyCost($/MWh)
Tot Oper. Cost Impact($/MWh)
May ‘03 Xcel-UWIG 3.5 0 0.41 1.44 na 1.85
Sep ‘04 Xcel-MNDOC 15 0.23 na 4.37 na 4.60
June ‘06 CA RPS 4 0.45* trace na na 0.45
Feb ‘07 GE/Pier/CAIAP 20 0-0.69 trace na*** na 0-0.69***
June ‘03 We Energies 4 1.12 0.09 0.69 na 1.90
June ‘03 We Energies 29 1.02 0.15 1.75 na 2.92
2005 PacifiCorp 20 0 1.6 3.0 na 4.60
April ‘06 Xcel-PSCo 10 0.20 na 2.26 1.26 3.72
April ‘06 Xcel-PSCo 15 0.20 na 3.32 1.45 4.97
Dec ‘06 MN 20% 31** 4.41**
Jul ‘07 APS 14.8 0.37 2.65 1.06 na 4.08
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Load Impacts & Price Volatility
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Price/Load Relationship
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18000 20000 22000 24000 26000Load (MW)
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$/M
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More wind results in lower off-peak prices, and a
greater overall difference in on/off-peak prices…
..And sometimes $0 cost energy (curtailed
wind)
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Important Takeaways: How Does Wind Increase Opportunities for Grid Storage?
• Dedicated RE storage generally not justified– Integration cost penalties are not so high that they
themselves would pay for storage…Wind “adder” less than $5/MWh in cases up to 20% capacity (even 20% energy in some cases)
– existing flexible generation limits the impact– Spatial diversity smooths aggregated wind output
reducing short-term fluctuations to hour time scales
• What wind does do is add to the existing opportunities for energy storage
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Increased Opportunities for Storage
• Small increase in A/S market due to wind
• Increased arbitrage opportunities– Larger swings in prices– More hours of low cost electricity, including
zero cost energy from curtailment
• Increased opportunities for T&D deferment/alternative
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Storage in the Near Future Grid
• Applications still dominated by whole grid applications
• RE begins to have an impact– Increase in A/S requirements– Increase in short-term price volatility– More hours of low-cost energy
• Storage increasingly attractive but not yet a required component of the grid
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Grid of the Future
Fraction of Energy from Wind and Solar
0% 1% 20% 100%
• Carbon constraints & high priced fossil fuels• Massive growth of all RE sources including wind, solar
PV, CSP, geothermal- RE as the dominant electricity source
• Competition from non RE baseload technologies including IGCC/CCS & Nuclear
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What Happens When Extremely Large Amounts of RE is Deployed?
• More interaction between RE sources and baseload plants– More curtailment, perhaps significant– Need to evaluate whole new grid architectures– Enabling technologies become necessary
• Analysis can be challenging– Good wind data over large regions is limited
• An analysis of PV can provide and example of the potential need for storage or other enabling technologies…
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PV Coincidence With Load - Summer
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16 GW simulated PV system providing 11% of system’s energy
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PV Coincidence With Load - Spring
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Potentially curtailed PV
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Why is RE Curtailed?
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Hypothetical MinimumGenerator Loading
50% or more of a system’s energy is generated here
Price approaches
$0
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RE Curtailment
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IGCC, Nuclear
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PV Curtailment
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Fraction of Energy from PV
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Wind Curtailment
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PV Curtailment and Cost Impacts
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Supply Demand Coincidence
• Provides the ultimate limit to RE penetration• Generation does not occur when desired
– Too little supply during periods of high demand– Too much supply during periods of low demand
• Storage can effectively “shift” supply to demand– But so can other enabling technologies…
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Options for Increased Use of RE
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Load Shifting
Energy Storage
Increased Flexibility
AdditionalLoad
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Flexibility Supply Curve
Improved Pricing
Demand Response
Gas Generation
Coal Cycling
Existing Hydro
Pumped Hydro
Gas Storage
Increasing RE Penetration
LowCost
HighCost
The relative order of these is conceptual only.
Ice
Heat
Heating
Transportation
Demand Side
Flexibility
Supply Side
FlexibilityCSP
Markets
Thermal
Storage
New
Loads
Electricity
Storage
Electricity
Storage
Existing
Storage
RE
Curtailment
Thermal
Storage
Flexible
Generation
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Supply Side Storage Technologies
?
CSP Thermal
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Three Classes of Electricity Storage Devices
• Short-term storage for ancillary services• Distributed storage for local applications• Bulk energy storage
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Short-term Devices (30 min or less)
• Devices that can provide frequency regulation and spinning reserve
• Flywheels, batteries & capacitors
Beacon Flywheel for Frequency
Regulation
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Distributed Storage (<10 MW or so)
• Provide both capacity and energy services• Local T&D appears to be a primary
application• Primarily batteries
– Flow batteries– NaS– Other battery chemistries?
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Bulk Energy Storage
(Courtesy of TVA)
Compressed Air Energy Storage (CAES)
Limited growth opportunities for PHS
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What is CAES?
• Hybrid storage/generation system using gas turbine technology
• Requires natural gas– 4000-4400 BTU fuel per kWh out
• 0.7-0.75 kWh electricity in per 1 kWh out• Use of natural gas makes round trip efficiency difficult
to define, but 75% is a reasonable value• Requires underground storage
– Salt domes, aquifers, hard rockAlternative fuels possible including biofuels and “adiabatic” CAES using thermal energy storage
• Alternative configurations pursed by EPRI and others
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Proposed CAES Projects
Norton, OH 2700 MW (merchant plant – arbitrage and A/S)
Iowa Stored Energy Park~300 MW, $800-$900/kW
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Possible CAES Geology
Robert Haug (ISEP): “Suitable aquifer storage sites are
difficult to find…………..but not impossible”
Succar & Williams
2008
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Concentrating Solar & Thermal Storage
High-efficiency storage can be
added at relatively low cost
Huge resource- several times the nation’s electric
demand
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Parabolic Trough Power Plant w/ 6hr Thermal Storage
HX
HotTank
ColdTank
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End Use Storage
• Thermal Storage– Hot or Cold– Dispatchable– Low Cost
• Electric Transportation and PHEVs
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PHEVs as Dispatchable Load
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Storage in the Future Grid
• Inherent conflict between competing sources of low-carbon energy– Wind and solar need flexible generation– IGCC and nuclear reduces system flexibility
• Flexibility will have to come from a variety of sources on both the supply and the demand side
• Storage is one of a large number of enabling technologies that can increase the utilization of RE generation
• Still unclear at what point storage becomes the best option, but its probably less than 100%!
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Questions?