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NREL is a national laboratory of the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy operated by the Alliance for Sustainable Energy, LLC
Michael MilliganNational Renewable Energy Laboratory
Golden, Colorado USA
10 FAQs(Frequently Asked Questions)
About Wind Energy Integration
and Answers
State of the Electric
Industry
Missouri Public Service
Commission
August 24, 2009
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10 FAQs about Wind
1) How much wind is currently installedin the US?
2) What are the benefits of wind energyto the power system?
3) How can winds variability beincorporated into power systemoperations
4) Does wind plant output start/stopsuddenly?
5) Can wind be predicted?
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10 FAQs about Wind
6) Can the power system be reliablyoperated with wind energy?
7) Does wind need backup or storage?
8) Is there a limit to how much wind canbe accommodated on the grid?
9) Can wind power plants be controlled?
10)Can wind energy make effective useof transmission lines?
11)Bonus Question: How can more windbe accommodated on the grid?
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Where do the Answers Come From?
Extensive analysis
Power system simulations that mimic real-timeoperations
Statistical analysis of wind and load data Experience operating power systems with wind
International Energy Agency Task 25 Report:Design and operation of power systems with largeamounts of wind power State of the art report. http://www.vtt.fi/inf/pdf/workingpapers/2007/W82.pdf
Utility Wind Integration Group www.uwig.org
NREL Systems Integration http://www.nrel.gov/wind/systemsintegration/ http://www.nrel.gov/publications
http://www.vtt.fi/inf/pdf/workingpapers/2007/W82.pdfhttp://www.uwig.org/http://www.nrel.gov/wind/systemsintegration/http://www.nrel.gov/publicationshttp://www.nrel.gov/publicationshttp://www.nrel.gov/wind/systemsintegration/http://www.uwig.org/http://www.vtt.fi/inf/pdf/workingpapers/2007/W82.pdf8/9/2019 Milligan Faq Missouri Aug 2009 Converted
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1) How much wind is currently installed in the US?
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1) How much wind is currently installed in the US?
Colorado/Xcel:
Approx 20% windpenetration (wind
capacity/system peak)
Iowa: Approx 18%
wind penetration(wind energy/annual
demand, est. 2009)
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MW Installed End 2006 Installed 2007 End 2007
Total EU-12 419 263 675
Total EU-15 47,651 8,291 55,860
Total EU-27 48,069 8,554 56,535
1b) How much wind is currently installed in Europe?
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Wind energy displaces Fuel Emissions; carbon
Wind provides a hedgeagainst rising fuel prices
(natural gas, coal) Wind is an energy source
with limited capacitycontribution other
generation is also required Wind can be cost-competitive with otherforms of generation andmay reduce electricity cost
2) What are the benefits of wind energy to the
power system?
)
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3) How can winds variability be
incorporated into power system operations?
(Approximately 8 hours)National Renewable Energy Laboratory Innovation fo r Our Energy Future
1.6
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15 Turbines Stdev = 1.21, Stdev/Mean = .184
200 Turbines Stdev = 14.89, Stdev/Mean = .126215 Turbines Stdev = 15.63, Stdev/Mean = .125
3) H i d i bilit b i t d i t
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Electric load (without wind) varies considerably
Power system operating practices are built aroundmeeting the variable load with dispatchable generatorsthat can change their output level
Wind adds more variability to the system Existing operating practice can be used/expanded
upon with wind
3) How can winds variability be incorporated into
power system operations?
3) H i d i bilit b i t d i t
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Minnesota 25% wind energy penetration (by energy)causes an increase in variability that must be met bypower system operators and the non-wind generation fleet
5-minute variability does not increase as much as
variability over 10s of minutes to a few hours
14x103
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L
3) How can winds variability be incorporated into
power system operations?
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Comparison of Cost-Based Integration 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
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Large wind farmshave many individualwind turbines
The turbines arespread over many
miles and do notexperience the samewind at the sametime
TX event Feb 24,2007: drop of 1,500MW over 2 hours issimilar to behavior ofload
Total WIND
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2/24/07 9:00 2/24/07 9:28 2/24/07 9:57 2/24/07 10:26 2/24/07 10:55 2/24/07 11:24 2/24/07 11:52 2/24/07 12:21 2/24/07 12:50
Total WIND
2 Hours
www.osei.noaa.gov
4) Can wind power start and stop suddenly?
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5) Can wind be predicted?
Wind forecastsare derivedfrom weatherprediction
models Wind forecast
accuracy isimproving
Several windforecastingfirms in U.S.
Courtesy: WindLogics, Inc. St. Paul, MN
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Forecasts must be tuned to the needs of the system
operator and integrated in control room Forecasts of potentially large ramp events?
High-wind warning systems?
Aggregate wind forecast error is reduced with large
geographic aggregation Geographic dispersion can reduce forecast errors by
30-50% (WindLogics, UWIG Forecasting Workshop, Feb 2008)
Mean Absolute Error (Percent)
Next day hourly wind power forecast 10-14% of rated capacity
Next day total energy forecast 20% of energy delivered
Next 2-3 hour power schedule 5-7% of rated capacity
Are wind forecasts being used?
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UWIG/WindLogics RDF Xcel/CO
http://www.ercot.com/meetings/ros/keydocs/2008/0313/07._ERCOT_OPERATIONS_REPORT_EECP022608_pub
Wind Forecasts in the Control Room
6) C th t b li bl t d ith
http://www.ercot.com/meetings/ros/keydocs/2008/0313/07._ERCOT_OPERATIONS_REPORT_EECP022608_public.dochttp://www.ercot.com/meetings/ros/keydocs/2008/0313/07._ERCOT_OPERATIONS_REPORT_EECP022608_public.doc8/9/2019 Milligan Faq Missouri Aug 2009 Converted
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Yes additional flexible generation (operating reserves)
may be necessary at higher wind penetrations This additional operating reserve has a modest cost,
typically about 10% of the cost of the wind energy itself
Graph shows this level of operating reserve (blue) is a
relatively small, varying fraction of wind generation Split between spinning and non-spinning reserves
EnerNex: Minnesota 20% Wind study
6) Can the power system be reliably operated with
wind energy?
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Increased operating reserves may benecessary, but not dedicated backup
Although new storage has value, it maynot be cost effective
There is typically already storage on thesystem Natural gas in the pipeline or storage
facility
Controllable hydro A recent study by Xcel Energy in
Colorado found existing pumped storage provided
$1.30/MWh offset to wind integrationcost
Enlarging existing gas storage facilitywas economic at large wind penetration
Wind Penetration 10% 15%
$/ MWH Gas Impact No Storage Benefits $2.17 $2.52
$ / MWH Gas Impact With Storage Benefits $1.26 $1.45
EnerNex: Xcel ColoradoWind Integration Study
7) Does wind need backup or storage?
8) Is there a limit to how much wind can be
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Current studies in theU.S. have analyzed upto 25% of all electricenergy from wind
Based on work done sofar, the question is notwhetherwind can beaccommodated at high
penetrations, thequestion is howand atwhat cost of integration
8) Is there a limit to how much wind can be
accommodated on the grid?
8) Is there a limit to how much wind can be
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8) Is there a limit to how much wind can be
accommodated on the grid?
Recent International Energy Agency Report:
Design and operation of power systems withlarge amounts of wind power
http://www.uwig.org/IEA_Annex25-State_of_the_Art_Report.pdf
International Energy Agency Report: Wind Integration Studies
010
20304050
6070
8090
100
WDen
mark
Irelan
dESBNG UK
Portu
gal
USMinn
esota
2006
Nethe
rland
s
Spain
2011
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orwa
ySint
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any2
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Sweden
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04
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rman
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USMinn
esota
2004
USColo
rado
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d200
4
USNew
York
PercentPenet
ration
Peak Ene rg y
Lennart Sder,KTH, Sweden, presented at UWIG,Oct 23-25, 2006
Denmark has access to large export markets
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9) Can wind power plants be controlled?
New low-voltage ride-through (LVRT) grid codes in the U.S. willhelp wind turbines contribute to grid reliability
Wind turbines can be controlled but not to the extent thatconventional generation can be controlled Ramp rate limits Up-regulation (operate below potential so that wind output can be
increased if needed) [Kirby and Milligan, forthcoming] Curtailment, if necessary and economic, at low-load/high-wind
conditions
10) Can wind energy make effective use of
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10) Can wind energy make effective use of
transmission lines?
Conditional-firmtransmission tariff (recentFERC ruling)
Wind does not need
transmission all of thetime
Most transmission pathshave some open capacity
most of the time Adding wind can result in
more efficient usage ofexisting transmission
11) Bonus: How can more wind be accommodated
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11) Bonus: How can more wind be accommodated
on the grid?
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53045298529252865280
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ExcessRampingandRampPenalty(MW
/hr)
Operating separate balancing areas causesextra ramping compared to combined operations.Blue: up-rampGreen: down-rampYellow: combined ramp
Ramping that could be eliminated by combining operations
Some areas are ramping up nearly 1000 MW/hrwhile other areas are ramping down nearly 500 MW/hr
Utility balancing areas
can combine orcooperate largeelectricity markets
Example: Ramping, orchanging output of
generators that can beeliminated with largerbalancing areas
Milligan & Kirby 2007, Impact of Balancing AreasSize, Obligation Sharing, and Ramping Capabilityon Wind Integration .http://www.nrel.gov/docs/fy07osti/41809.pdf
11) Bonus: How can more wind be accommodated
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11) Bonus: How can more wind be accommodated
on the grid?
Power system operations
practices and wind farmcontrol/curtailment
Integration of windforecasting and real timemeasurements into controlroom operations ongoingwork at ERCOT, AESO
Coordination between BAs Bi-lateral agreement
Fast scheduling Pseudo-tie or dynamic
schedule
Virtual BA (ACE DiversityInterchange, Joint Initiative)
Responsive load
Hydro dispatch, pumpedhydro
Longer term: other storageand markets (plug-hybridelectric vehicles, hydrogen)
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Large-Scale Studies in Process
Western Wind & Solar Integration Study 30% wind + % solar in footprint, 20% in WECC
Eastern Wind Integration and Transmission Study,20-30% in study footprint
LEGEND
WestConnect LinesCalifornia Lines
LADWP LinesDC Lines
Control areas:
APS
El Paso
Nevada Power
PNM
Sierra Pacific
SRP
Tristate
Tucson
Xcel
WAPA
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IEEE Transactions on PowerSystems (2007)IEEE Power Engineering SocietyMagazine, November/December2005Updated in 2007 and upcoming
Nov-Dec issue in 2009Wind Power CoordinatingCommittee Wind Super-Session,Summer 2008Utility Wind Integration Group(UWIG): Operating Impacts and
Integration Studies User Group www.uwig.org
Increasing Attention in North America
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Discussion (if time/interest)
Impact of 25% Wind Energy Penetration:
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Ramp requirements increase with 25% wind energypenetration. The upper panel also shows theimportance of being able to achieve lower minimumloads by the conventional generation fleet.
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Impact of 25% Wind Energy Penetration:
5-minute data
T d i i d
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Lower Turn-down is required
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Load OnlyLoad and Wind
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3200
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2600
2400
4:00 AM 6:00 AM 8:00 AM 10:00 AM 12:00 PM 2:00 PM 4:00 PM 6:00 PM
Base Load - $10/MWh
Peaking -$90/MWh
Energy Price $10/MWhEnergy Price $10/MWh
Energy Price Increasesto $90/MWh becausebase unit can't rampfast enough
Can the non-wind fleet ramp quickly enough?
B tt f i ti fl ibilit
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Better use of existing flexibility
Tap into maneuverable
generation that may bebehind the wall1
Provide a mechanism(market, contract, other)that benefits systemoperator and generator
Fast energy markets helpprovide needed flexibility2
and can often supply load
following flexibility at nocost31Kirby & Milligan, 2005 Methodology for Examining Control Area Ramping Capabilities with Implications for Windhttp://www.nrel.gov/docs/fy05osti/38153.pdf2Kirby & Milligan, 2008 Facilitating Wind Development: The Importance of Electric Industry Structure.http://www.nrel.gov/docs/fy08osti/43251.pdf3Milligan & Kirby 2007, Impact of Balancing Areas Size, Obligation Sharing, and Ramping Capability on Wind Integration .http://www.nrel.gov/docs/fy07osti/41809.pdf
0%
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Hours/Year
PJM
CA ISO
CA ISO PJM WAPA
42,400 55,600 3,087 MW Peak Load Generation21,900 47,000 2,911 Fossil (measured)13,100 2,500 700 Hydro4,600 13,500 0 Nuclear3,700 600 11 Other
2002 Hourly Data and Generation Capacity
WAPA
A i dditi l fl ibilit BA
http://www.nrel.gov/docs/fy05osti/38153.pdfhttp://www.nrel.gov/docs/fy08osti/43251.pdfhttp://www.nrel.gov/docs/fy07osti/41809.pdfhttp://www.nrel.gov/docs/fy07osti/41809.pdfhttp://www.nrel.gov/docs/fy08osti/43251.pdfhttp://www.nrel.gov/docs/fy05osti/38153.pdf8/9/2019 Milligan Faq Missouri Aug 2009 Converted
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Reduce the need for ramping by combined BAs (real or virtual) Ramping capabilityadds linearly
Ramping needadds less than linearly
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Operating separate balancing areas causesextra ramping compared to combined operations.Blue: up-rampGreen: down-rampYellow: combined ramp
Ramping that could be eliminated by combining operations
Some areas are ramping up nearly 1000 MW/hrwhile other areas are ramping down nearly 500 MW/hr
Milligan & Kirby 2007, Impact of Balancing Areas Size, Obligation Sharing, and Ramping
Capability on Wind Integration . http://www.nrel.gov/docs/fy07osti/41809.pdf
Acquire additional flexibility across BAs
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BA Consolidation Reduces Ramp Requirements
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Excess ramping required by separate operations
Excess ramp durationHourly data
ns
Large infrequent 5
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ExcessRampComparison:Separatevs.
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This graph shows the difference in excess rampingrequirements between wind and no-wind cases.
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ExcessRampComparison:Separate
vs.CombinedOperations
100080060040020 00
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Milligan & Kirby 2008, An Analysis of Sub-Hourly Ramping Impacts
of Wind Energy and Balancing Area Size
Large, infrequent 5-
Minute Ramps can be
significantly reduced