cra spp witf wind integration study final report
TRANSCRIPT
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Final Report
Prepared For:
Southwest Power Pool
415 North McKinley, #140 Plaza West
Little Rock, AR 72205
SPP WITF Wind Integration Study
Prepared By:
Charles River Associates
200 Clarendon Street T-33
Boston, Massachusetts 02116
Date: January 4, 2010
CRA Project No. D14422
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Disclaimer
Charles River Associates (CRA) and its authors make no representation or warranty as to the
accuracy or completeness of the material contained in this document and shall have, and
accept, no liability for any statements, opinions, information or matters (expressed or implied)
arising out of, contained in or derived from this document or any omissions from this
document, or any other written or oral communication transmitted or made available to any
other party in relation to the subject matter of this document.
CRA Project Team
Project Manager:
T. Bruce Tsuchida ([email protected])
Engineering Lead:
Pablo A. Ruiz ([email protected])
Officer in Charge:
Aleksandr Rudkevich ([email protected])
Team Members:
Peter W. Sauer
Germn G. Lorenzn
Rodney Yeu
Richard Baxter
Jesse Cooper
Daniel Cross-Call
Scott L. Englander
John Goldis
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Acknowledgments
CRA would like to thank the dedicated SPP and WITF members for providing the opportunityto study the complex challenges addressed in this report, as well as for their invaluable
guidance throughout the process, insightful feedback on drafts of this report, and suggestions
for its improvement. It has truly been a pleasure to work with all of the stakeholders.
CRA would also like to express appreciation to the SPP engineers, not only for providing the
many gigabytes of data essential to this analysis, but also for the hours spent providing their
many keen insights on system planning and operation, without which the results of this study
would be much less rich.
Finally, the CRA Project Team extends its gratitude to the support staff at CRA, especially
software engineering for their timely handling of the programming requests, and ITS, whose
tireless efforts kept all servers in superb condition, greatly facilitating this simulation-intensive
analysis.
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TABLE OF CONTENTS
1. EXECUTIVE SUMMARY .............................................................................................1-11.1. OVERVIEW .......................................................................................................................1-1
1.2. STUDY APPROACH ...........................................................................................................1-1
1.3. MAJOR FINDINGS AND RECOMMENDATIONS .......................................................................1-2
2. INTRODUCTION..........................................................................................................2-1
2.1. BACKGROUND AND OBJECTIVES OF THE STUDY .................................................................2-1
2.2. THE SOUTHWEST POWER POOL........................................................................................2-2
2.3. WIND GENERATION POTENTIAL IN SPP AND NEIGHBORING REGIONS..................................2-4
2.4. KEY CHALLENGES OF WIND INTEGRATION .........................................................................2-6
3. SPP WIND RESOURCES: CASES ANALYZED AND THEIRCHARACTERISTICS ...................................................................................................3-1
3.1. WIND PENETRATION CASES FOR SPP AND NEIGHBORING REGIONS ...................................3-2
3.2. WIND PROFILE STATISTICAL CHARACTERISTICS...............................................................3-10
3.3. SPATIAL AND TEMPORAL DIVERSITY OF SPPWIND RESOURCES ......................................3-18
4. IMPACTS OF WIND INTEGRATION ON THE SPP TRANSMISSIONSYSTEM ......................................................................................................................4-1
4.1. OVERVIEW OF POWER FLOW CASES AND METHODOLOGY ..................................................4-2
4.2. BASE CASE ANALYSIS ......................................................................................................4-5
4.3. 10%CASE ANALYSIS .......................................................................................................4-6
4.3.1. Generation Dispatch in Power Flow Cases and Transmission Expansion ..................... 4-6
4.3.2. AC Contingency Analysis and Transmission Expansion ................................................ 4-9
4.3.3. Transmission Expansion Summary .............................................................................. 4-20
4.4. 20%CASE ANALYSIS .....................................................................................................4-21
4.4.1. Generation Dispatch in Power Flow Cases and Transmission Expansion ................... 4-21
4.4.2. AC Contingency Analysis and Transmission Expansion .............................................. 4-254.4.3. Transmission Expansion Summary .............................................................................. 4-35
4.5. VOLTAGE STABILITY ANALYSIS ........................................................................................4-36
4.5.1. PV Analysis / Transfer Characteristics ......................................................................... 4-37
4.5.2. dV/dQ Sensitivity Analysis............................................................................................ 4-42
4.5.3. VQ Analysis / Reactive Reserves................................................................................. 4-42
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4.6. TRANSIENT STABILITY ANALYSIS .....................................................................................4-44
4.6.1. Single Line Fault Transient Stability Analysis............................................................... 4-44
4.6.2. GGS Flowgate Limit Transient Stability Analysis.......................................................... 4-52
4.6.3. Critical Clearing Time ................................................................................................... 4-544.6.4. Transient Stability Conclusions .................................................................................... 4-55
4.7. ADDITIONAL SPPFLOWGATES FOR COMMITMENT AND DISPATCH.....................................4-56
4.8. WIND POWER DELIVERABILITY ........................................................................................4-61
4.8.1. 10% Case..................................................................................................................... 4-62
4.8.2. 20% Case..................................................................................................................... 4-65
4.9. AVAILABLE TRANSFER CAPABILITY IMPACTS OF INCREASED WIND PENETRATION ..............4-68
5. IMPACTS OF WIND INTEGRATION ON SPP OPERATIONS....................................5-1
5.1 OVERVIEW OF SPPOPERATIONS BY TIMEFRAME...............................................................5-3
5.2 WIND INTEGRATION AND RESERVE SERVICES NEEDS ........................................................5-5
5.2.1 Regulation-Up and Regulation-Down Requirements...................................................... 5-6
5.2.1.1 Updated Regulation Needs ................................................................................ 5-7
5.2.1.2 Wind Variability in the Regulation Timeframe................................................... 5-10
5.2.2 Load-Following Needs.................................................................................................. 5-15
5.2.2.1 Net Load Variability: Ramping Capability Needs.............................................. 5-17
5.2.2.2 Net-Load Uncertainty: Load-Following Reserve Needs.................................... 5-28
5.2.3 Contingency Reserve Requirements............................................................................ 5-42
5.3 MULTI-HOUR TIMEFRAME:WIND INTEGRATION IMPACTS ON UNIT COMMITMENT ................5-44
5.3.1 Effects of Wind Integration on Power Flows within SPP and Interchangeswith Neighboring Systems............................................................................................5-48
5.3.1.1 The Impact of Wind Penetration on Power Flows Between SPP andNeighboring Systems.......................................................................................5-49
5.3.1.2 The Impact of Wind Penetration on Power Flows within SPP ..........................5-53
5.3.2 Transmission Congestion and Wind Curtailments........................................................5-57
5.3.3 New Operational Patterns of Generating Units ............................................................5-78
5.3.3.1 10% Case Results ..................................................................................................... 5-78
5.3.3.2 20% Case Results ..................................................................................................... 5-84
5.3.4 Impacts of Wind Forecast Uncertainty..........................................................................5-90
5.3.4.1 Analysis Methods Overview ..................................................................................... 5-90
5.3.4.2 Results - Number of Starts and Capacity Factor While Up by Unit Type .......... 5-94
5.3.4.3 Results Wind Curtailment...................................................................................... 5-96
5.4 SUB-HOUR TIMEFRAME:WIND INTEGRATION IMPACTS ON GENERATION DISPATCHAND PROVISION OF ANCILLARY SERVICES......................................................................5-103
5.4.1. 20% Case................................................................................................................... 5-103
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5.4.1.1 Impcts of Minimum-Generation Constraints ................................................... 5-104
5.4.1.2 Impacts of Reserve Requirements ................................................................. 5-105
5.4.1.3 Impacts of Transmission Congestion ............................................................. 5-106
5.4.1.4 Impacts of Forecasting Errors ........................................................................ 5-1085.4.2. 10% Case................................................................................................................... 5-110
6. IMPACTS OF WIND INTEGRATION ON SPP MARKETS..........................................6-1
6.1. IMPLICATIONS OF WIND INTEGRATION FOR SPPDAY 2MARKET DESIGN ANDOPERATIONS....................................................................................................................6-1
6.1.1. SPP and the Day 2 Market ............................................................................................. 6-1
6.1.2. Benefits of Being a Single Balancing Authority .............................................................. 6-5
6.1.3. Change in Market Clearing Price.................................................................................... 6-6
6.1.4. Increase in Net Load Forecast Error .............................................................................. 6-86.2. PROPOSAL FOR ADDRESSING WIND AND LOAD FORECAST ERRORS ...................................6-8
6.2.1. Comprehensive and Consistent Wind and Load Forecasts for Operations .................... 6-9
6.2.2. Enforcement of Load-Following Reserve Requirements .............................................. 6-11
6.2.3. Stochastic Methods for Unit Commitment .................................................................... 6-13
6.3. OVERVIEW OF BEST PRACTICES OF WIND INTEGRATION IN THE UNITED STATESAND ABROAD..................................................................................................................6-1 4
6.4. POLICY RECOMMENDATIONS FOR SPP............................................................................6-1 6
6.4.1. Interconnection Requests............................................................................................. 6-17
6.4.2. Transmission................................................................................................................ 6-18
6.4.3. Regulation Requirements............................................................................................. 6-18
6.4.4. Wind Forecasting ......................................................................................................... 6-19
6.4.5. Unit Commitment and Dispatch.................................................................................... 6-19
6.4.6. Market Updates............................................................................................................ 6-20
6.4.7. Additional Recommendations....................................................................................... 6-22
7. METHODOLOGY.........................................................................................................7-1
7.1. OVERVIEW OF THE STAKEHOLDER PROCESS .....................................................................7-1
7.2. MAJOR ANALYTICAL TASKS AND THEIR ROLES IN THE STUDY .............................................7-1
7.3. DEVELOPMENT OF WIND PROFILES ...................................................................................7-4
7.4. POWER FLOW ANALYSIS...................................................................................................7-4
7.4.1. Contingency Analysis and Transmission Expansion...................................................... 7-4
7.4.2. PV Analysis Methodology............................................................................................... 7-6
7.5. ANALYSIS OF REGULATING RESERVE REQUIREMENTS........................................................7-7
7.6. UNIT COMMITMENT ANALYSIS .........................................................................................7-12
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7.6.1. Analytical Approach...................................................................................................... 7-13
7.6.2. Input Assumptions and Data Sources .......................................................................... 7-14
7.6.3. Software Tools ............................................................................................................. 7-16
7.7. REAL-TIME SIMULATIONS OF ECONOMIC DISPATCH ..........................................................7-16 7.7.1. Input Assumptions and Data Sources .......................................................................... 7-17
7.7.2. Software Tools ............................................................................................................. 7-18
7.8. OVERVIEW OF WIND INTEGRATION PRACTICES IN THE U.S. AND ABROAD..........................7-18
8. GLOSSARY .................................................................................................................8-1
9. REFERENCES.............................................................................................................9-1
APPENDIX A: TRANSMISSION ANALYSIS ................................................................................A-1
APPENDIX B: SEASONAL DATA FROM SECTION 5.3: PRODUCTION SIMULATION......................B-1
APPENDIX C: OVERVIEW OF WIND INTEGRATION PACTICES IN THE U.S. ANDINTERNATIONALLY ....................................................................................................... C-1
APPENDIX D: ENERGY STORAGE AND WIND ..........................................................................D-1
APPENDIX E: SPP FLOWGATES .............................................................................................E-1
APPENDIX F: LOAD DATA - INTRA-HOUR AND FORECAST PROFILES....................................... F-1
APPENDIX G: GE MAPS .........................................................................................................G-1
APPENDIX H: POWERWORLD SIMULATOR .............................................................................H-1
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LIST OF FIGURES
1. EXECUTIVE SUMMARY
2. INTRODUCTION
2.2-1: SPP footprint ...................................................................................................2-3
2.3-1: Wind potential in the United States .................................................................2-5
2.4-1: Wind turbine power curve................................................................................2-7
3. SPP WIND RESOURCES: CASES ANALYZED AND THEIR CHARACTERISTICS
3.1-1: Wind plant sites and clusters ..........................................................................3-8
3.1-2: Base Case wind nameplate capacity distribution by cluster ...........................3-9
3.1-3: 10% Case wind nameplate capacity distribution by cluster ............................3-9
3.1-4: 20% Case wind nameplate capacity distribution by cluster ..........................3-10
3.2-1: Wind power output: histograms by case .......................................................3-12
3.2-2: Wind power output: autocorrelation by case.................................................3-13
3.2-3: Hourly change in available wind power output: histograms by case ............3-14
3.2-4: Hourly change in available wind power output: autocorrelations bycase ...............................................................................................3-15
3.2-5: Histograms of deviations from day-ahead wind forecasts by case ...............3-16
3.2-6: Base Case average daily wind output by season .........................................3-17
3.2-7: Base Case range of daily wind output...........................................................3-18
3.3-1: Wind output cross-correlation between wind penetration cases...................3-19
3.3-2: Wind output cross-correlation between clusters ...........................................3-19
3.3-3: Standard deviation of hourly available wind power increments bycluster ............................................................................................3-20
3.3-4: Correlation factor between NREL site 394 and the remainingNREL sites in SPP.........................................................................3-21
3.3-5: Maximum correlation factor between NREL site 394 and theremaining NREL sites in SPP........................................................3-22
3.3-6: Time-shift for maximum correlation factor between NREL site 394and the remaining NREL sites in SPP: 3-year time series............3-23
3.3-7: Time-shift for maximum correlation factor between NREL site 394and the remaining NREL sites in SPP: 16 March 2004(high ramp down event).................................................................3-24
4. IMPACTS OF WIND INTEGRATION ON THE SPP TRANSMISSION SYSTEM
4.2-1: Base Case transmission topology above 200 kV............................................4-5
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4.2-2: Base Case generation dispatch in the four seasonal power flowcases ...............................................................................................4-6
4.3.1-1: 10% Case generation dispatch in the four seasonal power flowcases ...............................................................................................4-7
4.3.1-2: 10% Case transmission expansions above 200 kV included toeliminate pre-contingency violations ...............................................4-8
4.3.1-3: Initial 10% Case transmission topology above 200 kV ................................4-9
4.3.2-1: Contingencies that cause violations in the Spearville - Wichitacorridor in the 10% Case spring power flow..................................4-11
4.3.2-2: Contingencies that caused violations in the Spearville - Wichitacorridor in the 10% Case fall power flow.......................................4-13
4.3.2-3: Contingencies that caused violations in the SPS - OKGE corridorin the 10% Case spring power flow ...............................................4-15
4.3.2-4: Contingencies that caused violations in the SPS - OKGE corridor
in the 10% Case fall power flow ....................................................4-18
4.3.3-1: Final 10% Case transmission topology above 200 kV...............................4-21
4.4.1-1: 20% Case generation dispatch in the four seasonal power flowcases .............................................................................................4-22
4.4.1-2: 20% Case transmission expansions above 200 kV included toeliminate pre-contingency violations .............................................4-24
4.4.1-3: 20% Case transmission topology above 200 kV........................................4-24
4.4.2-1: 20% Case contingency analysis of the E Manhattan - Concordiaregion.............................................................................................4-26
4.4.2-2: 20% Case contingency analysis of northeast Nebraska............................4-27
4.4.2-3: 20% Case contingency analysis of west Kansas.......................................4-28
4.4.2-4: 20% Case contingency analysis of the Wichita area .................................4-29
4.4.2-5: 20% Case contingency analysis of Roman Nose - El Reno ......................4-31
4.4.2-6: 20% Case contingency analysis of west Oklahoma City ...........................4-32
4.4.2-7: 20% Case contingency analysis of SPS ....................................................4-34
4.4.3-1: Final 20% Case transmission topology above 200 kV...............................4-35
4.5.1-1: Voltage contour for the maximum post-contingency transfer fromSPS to SPP; Tuco-OKU line outaged, fall 10% Case ...................4-38
4.5.1-2: Voltage contour for the SPS to SPP pre-contingency transfer
and minimum voltage of 0.9 p.u.; fall 20% Case...........................4-41
4.5.3-1: VQ curve for the Riley 161 kV bus in the 10% Case summerpower flow, pre-contingency case.................................................4-44
4.8.2-1: Bus voltage contour for the maximum wind power injection in thesummer 20% Case........................................................................4-67
4.9-1: ATC for selected transfers by case...............................................................4-69
4.9-2: Net export for each seller for selected transfers by case..............................4-70
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4.9-3: Net import for each buyer for selected transfers by case .............................4-71
5. IMPACTS OF WIND INTEGRATION ON SPP OPERATIONS
5.1-1: Operations timeframes for SPP Day 2 market design ....................................5-45.1-2: Recommended SPP operations timeframe.....................................................5-4
5.2.1.1-1: Winter regulation requirements as a function of the total windnameplate capacity for different daily load levels............................5-8
5.2.1.1-2: Spring regulation requirements as a function of the total windnameplate capacity for different daily load levels............................5-8
5.2.1.1-3: Summer regulation requirements as a function of the total windnameplate capacity for different daily load levels............................5-9
5.2.1.1-4: Fall regulation requirements as a function of the total windnameplate capacity for different daily load levels............................5-9
5.2.1.2-1: Short-term wind variability as a function of the total nameplatewind capacity.................................................................................5-10
5.2.1.2-2: Wind variability down as a function of the total nameplate windcapacity by season........................................................................5-11
5.2.1.2-3: Wind variability up as a function of the total nameplate windcapacity by season........................................................................5-11
5.2.1.2-4: Wind variability down as a function of the total wind nameplatecapacity by day-ahead wind forecast level....................................5-12
5.2.1.2-5: Wind variability up as a function of the total wind nameplatecapacity by day-ahead wind forecast level....................................5-13
5.2.1.2-6: Wind variability down as a function of the day-ahead wind
forecast level by wind penetration level.........................................5-145.2.1.2-7: Wind variability up as a function of the day-ahead wind
forecast level by wind penetration level.........................................5-14
5.2.2-1: Net load profiles for increased wind penetration levels (April 14,2010, based on 2004 historical profiles)........................................5-16
5.2.2-2: Net load 4-hour-ahead forecast uncertainty by wind penetrationcase ...............................................................................................5-16
5.2.2.1-1: Net load ramps as a function of time for 6 - 7 am in the BaseCase ..............................................................................................5-17
5.2.2.1-2: Net load ramps as a function of time for 6 - 7 am: a) upper-bound, b) lower-bound...................................................................5-18
5.2.2.1-3: Upper-bound net load ramps as a function of time for eachhour of the day...............................................................................5-19
5.2.2.1-4: Lower-bound net load ramps as a function of time for eachhour of the day...............................................................................5-19
5.2.2.1-5: Net load hourly ramp range as a function of the hour of the day............5-20
5.2.2.1-6: Net load hourly ramp as a function of the installed windcapacity .........................................................................................5-21
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5.2.2.1-7: Net load hourly ramp range as a function of the hour of the dayin winter .........................................................................................5-22
5.2.2.1-8: Net load hourly ramp range as a function of the hour of the dayin spring.........................................................................................5-23
5.2.2.1-9: Net load hourly ramp range as a function of the hour of the dayin summer......................................................................................5-24
5.2.2.1-10: Net load hourly ramp range as a function of the hour of theday in fall .......................................................................................5-25
5.2.2.1-11: Net load hourly ramp range as a function of the hour of theday: high positive wind ramp forecast ...........................................5-26
5.2.2.1-12: Net load hourly ramp range as a function of the hour of theday: high negative wind ramp forecast..........................................5-27
5.2.2.1-13: Net load hourly ramp range as a function of the hour of theday: low wind ramp forecast..........................................................5-28
5.2.2.2-1: Day-ahead wind and load forecast uncertainty up: evolutionwith time ........................................................................................5-30
5.2.2.2-2: Day-ahead wind and load forecast uncertainty down: evolutionwith time ........................................................................................5-31
5.2.2.2-3: Day-ahead net load forecast uncertainty: evolution with time.................5-32
5.2.2.2-4: Changes between day-ahead and 4-hour-ahead load and windforecasts........................................................................................5-33
5.2.2.2-5: Changes between day-ahead and 4-hour-ahead load and windforecasts as a function of the time of day......................................5-34
5.2.2.2-6: Changes between day-ahead and 4-hour-ahead net load
forecasts as a function of the time of day......................................5-355.2.2.2-7: 4-hour-ahead load and wind forecast uncertainty up: evolution
with time ........................................................................................5-37
5.2.2.2-8: 4-hour-ahead load and wind forecast uncertainty down:evolution with time.........................................................................5-37
5.2.2.2-9: 4-hour-ahead net load forecast uncertainty by hour of the day ..............5-38
5.2.2.2-10: 4-hour-ahead net load forecast uncertainty up: time evolution.............5-39
5.2.2.2-11: 4-hour-ahead net load forecast uncertainty down: timeevolution ........................................................................................5-40
5.2.2.2-12: Evolution of 10-minute-ahead persistence wind forecastuncertainty (range of deviation from 10-minute-aheadwind forecasts as a function of time) .............................................5-41
5.2.2.2-13: Persistence wind forecast uncertainty as a function of theforecast lead time ..........................................................................5-42
5.3-1: SPP hourly load for Wednesdays during summer 2010 ...............................5-44
5.3.1.1-1: Base Case annual average RTC SPP import/export flows, inMW ................................................................................................5-51
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5.3.1.1-2: 10% Case annual average RTC SPP import/export flows, inMW ................................................................................................5-51
5.3.1.1-3: 20% Case annual average RTC SPP import/export flows, inMW ................................................................................................5-51
5.3.1.2-1: Base Case annual average (RTC) intra-SPP flows, in MW....................5-54
5.3.1.2-2: 10% Case annual average (RTC) intra-SPP flows, in MW.....................5-54
5.3.1.2-3: 20% Case annual average (RTC) intra-SPP flows, in MW.....................5-54
5.3.2-1: 10% Case summer binding constraints......................................................5-59
5.3.2-2: 10% Case fall binding constraints .............................................................. 5-60
5.3.2-3: 10% Case winter binding constraints .........................................................5-60
5.3.2-4: 10% Case spring binding constraints.........................................................5-61
5.3.2-5: Wind sites 52 and 64..................................................................................5-63
5.3.2-6: Wind sites 52 and 64 (enlarged) ................................................................5-635.3.2-7: Wind site 52 and NF8 constraint................................................................5-64
5.3.2-8: 20% Case summer binding constraints......................................................5-67
5.3.2-9: 20% Case fall binding constraints .............................................................. 5-68
5.3.2-10: 20% Case winter binding constraints .......................................................5-69
5.3.2-11: 20% Case spring binding constraints.......................................................5-70
5.3.2-12: Wind sites curtailed in excess of 2% .......................................................5-73
5.3.2-13: NF8 constraint and wind site 52...............................................................5-75
5.3.2-14: FG6140 constraint and wind site 28.........................................................5-77
5.3.3.1-1: Non-wind generation by unit type (annual total) .....................................5-80
5.3.3.1-2: Average hours running per start for non-wind generation byunit type (annual average).............................................................5-81
5.3.3.2-1: Non-wind generation by unit type (annual total) .....................................5-86
5.3.3.2-2: Average hours running per start for non-wind generation byunit type.........................................................................................5-87
5.3.4.1-1: Spring 2004 Case....................................................................................5-91
5.3.4.1-2: Fall 2005 Case ........................................................................................5-92
5.3.4.1-3: Fall 2006 Case ........................................................................................5-92
5.3.4.3-1: Forecast direction and wind curtailment for all 20% Cases....................5-975.3.4.3-2: 4-hour-ahead forecast direction and wind curtailment for
Spring 2004 20% Case..................................................................5-98
5.3.4.3-3: Day-ahead forecast direction and wind curtailment for Spring2004 20% Case.............................................................................5-98
5.3.4.3-4: 4-hour-ahead forecast direction and wind curtailment for Fall2005 20% Case.............................................................................5-99
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5.3.4.3-5: Day-ahead forecast direction and wind curtailment for Fall2005 20% Case.............................................................................5-99
5.3.4.3-6: 4-hour-ahead forecast direction and wind curtailment for Fall2006 20% Case...........................................................................5-100
5.3.4.3-7: Day-ahead forecast direction and wind curtailment for Fall2006 20% Case...........................................................................5-100
5.3.4.3-8: Wind curtailment as a function of the forecast error .............................5-102
5.4.1.1-1: Intra-hour profiles with perfect foresight, no transmissioncongestion, and no reserve requirements for Nov 1,2010 (based on 2006), 20% Case...............................................5-104
5.4.1.2-1: Intra-hour profiles with perfect foresight and no transmissioncongestion with reserve requirements enforced for Nov1, 2010 (based on 2006), 20% Case...........................................5-105
5.4.1.3-1: Wind power dispatch with perfect foresight, compared to the
case with no transmission congestion for Nov 1, 2010(based on 2006), 20% Case........................................................5-106
5.4.1.3-2: Wind power dispatch with perfect foresight and fixed hourlyunit commitment, compared to the case with updatedintra-hourly commitment for fast-start units; Nov 1, 2010(based on 2006), 20% Case........................................................5-107
5.4.1.4-1: Wind forecasts and available wind power for Nov 1, 2010(based on 2006), 20% Case........................................................5-108
5.4.1.4-2: Wind power dispatch with commitment performed using day-ahead and 4-hour-ahead wind forecasts, compared tothe case with perfect foresight for Nov 1, 2010 (based on2006), 20% Case.........................................................................5-109
5.4.2-1: Wind power dispatch with perfect foresight with and withoutreserve requirements, compared to the available windpower for Nov 1, 2010 (based on 2006), 10% Case ...................5-111
6. MARKET IMPACT STUDY
6.1.1-1: SPP generation stack with 1,000 MW of wind .............................................6-3
6.1.1-2: SPP generation stack with 2,500 MW of wind .............................................6-4
6.1.1-3: SPP generation stack with 5,000 MW of wind .............................................6-4
6.1.2-1: Standard deviation of hourly wind generation increments ...........................6-5
6.2.2-1: Operational timeframe for load following reserves.....................................6-11
6.2.2-2: Load-following reserves example...............................................................6-12
6.2.3-1: Scenarios for stochastic unit commitments: high wind cut-outexample.........................................................................................6-13
6.2.3-2: Scenarios for stochastic unit commitments: 20% - 80% forecastexample.........................................................................................6-14
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7. METHODOLOGY
7.2-1: Flow of CRA tasks for the Wind Integration Study..........................................7-3
7.5-1: Wind deviations from the wind short-term forecast versus loaddeviations from the load short-term forecast ...................................7-9
7.5-2: Frequency of occurrences of joint load and wind deviations for thesix days analyzed ..........................................................................7-10
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LIST OF TABLES
1. EXECUTIVE SUMMARY
2. INTRODUCTION
3. SPP WIND RESOURCES: CASES ANALYZED AND THEIR CHARACTERISTICS
3.1-1: Wind generation capacity by penetration level ...............................................3-2
3.1-2: Base Case wind from SPP GI queue as of February 2009.............................3-4
3.1-3: 10% Case wind from SPP GI queue as of February 2009..............................3-5
3.1-4: 20% Case wind from SPP GI queue as of February 2009..............................3-6
3.1-5: 40% Case wind from SPP GI queue as of February 2009..............................3-7
3.2-1: Summary of the wind power statistics by case .............................................3-11
4. IMPACTS OF WIND INTEGRATION ON THE SPP TRANSMISSION SYSTEM
4.1-1: SPP load and wind power dispatch in the power flow cases..........................4-3
4.1-2: Wind power dispatch in the power flow cases by power flow area,in MW...............................................................................................4-4
4.3.3-1: Transmission lines added to the 10% Case...............................................4-20
4.4.3-1: Transmission lines added to the 20% Case...............................................4-36
4.5.1-1: PV study results for SPS to SPP transfers in the 10% Case.....................4-39
4.5.1-2: PV study results for SPS to SPP transfers in the 20% Case.....................4-41
4.5.3-1: Nodes with VQ characteristics analyzed....................................................4-43
4.6.1-1: Single line fault transient stability results for Base Case fall......................4-46
4.6.1-2: Single line fault transient stability results for Base Case spring.................4-46
4.6.1-3: Single line fault transient stability results for Base Case summer .............4-46
4.6.1-4: Single line fault transient stability results for Base Case winter.................4-47
4.6.1-5: Single line fault transient stability results for 10% Case fall.......................4-47
4.6.1-6: Single line fault transient stability results for 10% Case spring..................4-48
4.6.1-7: Single line fault transient stability results for 10% Case summer ..............4-48
4.6.1-8: Single line fault transient stability results for 10% Case winter..................4-49
4.6.1-9: Single line fault transient stability results for 20% Case fall.......................4-49
4.6.1-10: Single line fault transient stability results for 20% Case spring ...............4-50
4.6.1-11: Single line fault transient stability results for 20% Case summer ............4-51
4.6.1-12: Single line fault transient stability results for 20% Case winter................4-52
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4.6.2-1: Base Case GGS flowgate limit...................................................................4-53
4.6.2-2: 10% Case GGS flowgate limit....................................................................4-54
4.6.2-3: 20% Case GGS flowgate limit....................................................................4-54
4.6.4-1: Summary of single-line fault results ...........................................................4-55
4.7-1: Newly identified constraints for the 10% Case (Part 1 of 2)..........................4-56
4.7-2: Newly identified constraints for the 10% Case (Part 2 of 2)..........................4-57
4.7-3: Newly identified constraint limits for the 10% Case (Part 1 of 2) ..................4-57
4.7-4: Newly identified constraint limits for the 10% Case (Part 2 of 2) ..................4-58
4.7-5: Newly identified constraints for the 20% Case (Part 1 of 2)..........................4-58
4.7-6: Newly identified constraints for the 20% Case (Part 2 of 2)..........................4-59
4.7-7: Newly identified constraint limits for the 20% Case (Part 1 of 3) ..................4-59
4.7-8: Newly identified constraint limits for the 20% Case (Part 2 of 3) ..................4-60
4.7-9: Newly identified constraint limits for the 20% Case (Part 3 of 3) ..................4-61
4.8.1-1: Critical constraints for wind power output increases in thesummer 10% Case........................................................................4-63
4.8.1-2: Critical constraints for wind power output decreases in thesummer 10% Case........................................................................4-64
4.8.2-1: Critical constraints for wind power output increases in thesummer 20% Case (Part 1 of 2) ....................................................4-65
4.8.2-2: Critical constraints for wind power output increases in thesummer 20% Case (Part 2 of 2) ....................................................4-66
4.8.2-3: Critical constraints for wind power output decreases in the
summer 20% Case........................................................................4-67
5. IMPACTS OF WIND INTEGRATION ON SPP OPERATIONS
5.2.1.1-1: Total regulation requirements for seasonal peak loads, in MW................5-7
5.2.2.2-1: Day-ahead load and wind forecast uncertainty.......................................5-29
5.2.2.2-2: Day-ahead net load forecast uncertainty ................................................5-31
5.2.2.2-3: 4-hour-ahead load and wind forecast uncertainty...................................5-36
5.2.2.2-4: 4-hour-ahead net load forecast uncertainty ............................................5-38
5.2.2.2-5: 4-hour-ahead net load forecast error by season, in MW.........................5-39
5.3-1: Seasonal definitions ......................................................................................5-47
5.3.1-1: SPP regions for flow pattern analysis ........................................................5-48
5.3.1.1-1: SPP and neighboring areas annual average flows (RTC), inMW ................................................................................................5-52
5.3.1.1-2: SPP and neighboring areas annual average flows (on-peak), inMW ................................................................................................5-52
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5.3.1.1-3: SPP and neighboring areas annual average flows (off-peak), inMW ................................................................................................5-53
5.3.1.2-1: SPP area annual average flows (RTC), in MW.......................................5-56
5.3.1.2-2: SPP area annual average flows (on-peak), in MW.................................5-56
5.3.1.2-3: SPP area annual average flows (off-peak), in MW.................................5-57
5.3.2-1: Binding constraints and hours binding by season......................................5-58
5.3.2-2: Average wind curtailment for the 10% Case..............................................5-62
5.3.2-3: Wind curtailment by season and profile year for the 10% Case ................5-62
5.3.2-4: Binding constraints and hours binding by season 20% Case.................5-66
5.3.2-5: Average wind curtailment for the 20% Case..............................................5-72
5.3.2-6: Wind curtailment by season and profile year for the 20% Case ................5-73
5.3.2-7: Curtailment for wind site 31........................................................................5-74
5.3.2-8: Curtailment for wind site 52........................................................................5-74
5.3.2-9: Curtailment for wind site 73........................................................................5-75
5.3.2-10: Curtailment for wind site 88......................................................................5-76
5.3.2-11: Curtailment for wind site 28......................................................................5-76
5.3.3.1-1: Non-wind generation (GWh) by unit type (annual total)..........................5-80
5.3.3.1-2: Average hours running per start for non-wind generation byunit type.........................................................................................5-81
5.3.3.1-3: Minimum average hours running per start for non-windgeneration by unit ..........................................................................5-81
5.3.3.1-4: Generation (GWh) by SPP area..............................................................5-825.3.3.1-5: Generation difference (GWh) between Base Case and 10%
Case ..............................................................................................5-83
5.3.3.1-6: Capacity factors while up for the Base Case and 10% Case..................5-83
5.3.3.1-7: Number of starts for the Base Case and 10% Case for summer............5-84
5.3.3.2-1: Non-wind generation (GWh) by unit type................................................5-86
5.3.3.2-2: Average hours running per start for non-wind generation byunit type.........................................................................................5-87
5.3.3.2-3: Minimum average hours running per start for non-windgeneration by unit ..........................................................................5-87
5.3.3.2-4: Generation (GWh) by SPP area..............................................................5-88
5.3.3.2-5: Generation difference (GWh) between Base Case and 20%Case ..............................................................................................5-89
5.3.3.2-6: Capacity factors while up for the Base Case and 20% Case..................5-89
5.3.3.2-7: Number of starts for the Base Case and 20% Case ...............................5-90
5.3.4.1-1: SPP load for selected weeks ..................................................................5-91
5.3.4.1-2: MAPS runs performed for forecast error analysis...................................5-93
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5.3.4.2-1: Number of starts by unit type for 20% Cases .........................................5-94
5.3.4.2-2: Capacity factors while up by unit type for 20% Cases ............................5-95
5.3.4.2-3: Number of starts by unit type for 10% Cases .........................................5-95
5.3.4.2-4: Capacity factors while up by unit type for 10% Cases ............................5-95
5.3.4.3-1: Direction of forecast errors for 20% Cases .............................................5-97
5.3.4.3-2: Forecast direction and wind curtailment for all 20% Cases....................5-97
5.4.1-1: Scenarios analyzed for the 20% Case intra-hour simulations .................5-103
5.4.1.4-1: 10-minute deviations from hourly wind averages and windforecasts for the 20% Case for Nov 1, 2010 (based on2006), in MW ...............................................................................5-108
6. MARKET IMPACT STUDY
6.1.3-1: Count of marginal hours by unit type ...........................................................6-66.1.3-2: Ratio of marginal hours by unit type.............................................................6-6
6.1.3-3: Market clearing price using assumptions from table 6.1.3-4........................6-7
6.1.3-4: Fuel price and heat rate assumptions .......................................................... 6-7
7. METHODOLOGY
7.5-1: Load and wind deviations from their short-term forecasts forrepresentative days, in MW.............................................................7-9
7.6.1-1: 36 MAPS model simulations ......................................................................7-14
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1. EXECUTIVE SUMMARY
1.1. OVERVIEW
The Southwest Power Pool (SPP) selected Charles River Associates (CRA) in early 2009 to
conduct a study to determine the operational and reliability impact of integrating wind
generation into the SPP transmission system and energy markets. The study required an
intensive effort to perform a detailed engineering analysis and then interpret the findings and
associated policy implications in the context of a regional market. To achieve the objectives,
the study assessed the impacts of wind generation on three different aspects of SPP:
transmission, operation, and markets.
1.2. STUDY APPROACH
The study was performed for the year 2010 with the assumption that SPP operates as a
single balancing authority (BA) with a co-optimized energy and ancillary service market (Day
2 Market). Three wind penetration levels were studied and each was compared to the current
system conditions (Base Case, with approximately 4% wind penetration). The three
penetration levels were 10%, 20%, and 40% by annual energy (10% Case, 20% Case, and
40% Case, respectively). Detailed studies were performed on the 10% and 20% Cases; the
40% Case was examined in those portions of the study that related to wind characteristics.
The goal of the study was to identify the challenges of integrating high levels of wind
penetration into the SPP transmission system. In order to meet that objective, it wasnecessary to identify transmission upgrades needed to accommodate the studied wind power
additions with minimal curtailment. This was not an economics study; no economic
optimization, such as an analysis of the tradeoff between building transmission upgrades and
curtailing wind, was performed. Furthermore, the transmission upgrades implemented in the
study were based on the assumed wind plant locations and sizes.
To begin the study, SPP selected a set of wind plants from the SPP Generation
Interconnection (GI) queue as of February 2009 to encompass the full range of wind capacity
needed for the Base Case through the 40% Case.1 CRA then analyzed the characteristics of
the selected wind plants, including probabilistic output and geographic correlation
characteristics, as discussed in Section 3.2 Next, CRA assessed the power flow models
1 It is important to note that this study was not intended to address the impact of any individual wind plant and
therefore the results should not be tied to, or used to evaluate, any individual wind plant or its operations.
2 The study results may have been different if future wind generation sites were based on wind resource assessment
that showed greater geographical diversity, rather than the GI queue. Greater geographical diversity helps mitigating
the variability of aggregate wind generation.
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provided by SPP representing four seasons for the Base, 10%, and 20% Cases. This
assessment led to the identification of transmission upgrades needed to accommodate the
wind plant additions associated with each penetration level.3
The transmission upgrades were studied using several different approaches, including
voltage analysis, dynamic stability analysis, and available transfer capability (ATC) analysis,
as discussed in Section 4. The results of the wind characteristics analysis (Section 3) and
transmission analysis (Section 4) were then used to analyze the impact of wind power on
ancillary services (reserves in particular), as well as their impact on the dynamic system
operations via a production simulation. The production simulation analyzed the effects of
increased wind power on congestion patterns, unit commitment and dispatch decisions, and
forecasting errors. Additionally, intra-hour simulations were performed for a selected day to
address the challenges of wind variability. The implications of these simulation results are
discussed in Section 5. Finally, Section 6 synthesizes the findings of Section 3 through
Section 5 in order to examine the implications of wind power for the SPP market. It alsoprovides recommendations ranging from methods for addressing forecast errors to policy
reform. Methodological details are provided in Section 7.
1.3. MAJOR FINDINGS AND RECOMMENDATIONS
SPP wind generation resources are primarily located in the western portion of the SPP
footprint, mostly in transmission-constrained locations away from load and non-wind
generation centers. For this reason, increase in the wind penetration level causes changes in
the power flow patterns, requiring upgrades and/or reconfigurations to the transmission
system. In particular, the power flows from western SPP to eastern SPP increase
significantly. To accommodate the increased west-to-east flows while meeting the reliabilitystandards of the SPP Criteria, a number of transmission expansions were required. These
included new transmission lines totaling 1,260 miles of 345 kV and 40 miles of 230 kV lines
for the 10% Case, and an additional 485 miles of 765 kV, 766 miles of 345 kV, 205 miles of
230 kV, and 25 miles of 115 kV lines for the 20% Case.
With the aforementioned transmission expansions, current voltage and thermal transfer
limitations in the areas of greatest wind expansion were eased. For example, voltage-driven
transfer limitations from SPS to SPP were increased from 529 MW in the Base Case to 1,200
MW and 3,090 MW in the 10% and 20% Cases, respectively. The contingency analysis that
CRA performed on this expanded grid identified new flowgates that should be monitored
during operations. No voltage stability issues were found, mainly due to the transmissionexpansions.
3 Transmission upgrades were selected based on their projected impact on SPP transmission system capabilities;
no consideration was made of the estimated cost of any of the upgrades.
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No transient stability issues were found for the 10% or 20% Cases, supporting the conclusion
that increasing wind penetration levels, along with appropriate transmission expansions, does
not adversely affect the transient stability of the power system.
Based on the findings of this study, several transmission-related recommendations are made.
First, major transmission reinforcements are needed to accommodate increased wind
penetration levels, starting as low as 10%. Considering that the lead times of transmission
projects are longer than those of wind plant projects, it is recommended that SPP take
definitive steps to reinforce its transmission network, especially west to east, and that
economic analyses of the needed transmission expansions be undertaken. Second, the
addition of high voltage lines requires the installation of voltage control devices to prevent
over-voltages under low-flow conditions due to contingencies or low wind power availability.
Third, dynamic voltage support becomes increasingly important for higher wind penetration
levels, in which several conventional generators may become displaced in the dispatch order
by wind generators. Therefore, it is recommended that new reactive capability of the samenature as that provided by the displaced thermal units (i.e., continuously and instantaneously
controllable) be added as wind penetration increases.4
The study found that, with all needed transmission upgrades in place, integrating the levels of
wind studied in the 10% and 20% Cases could be attained without adversely impacting SPP
system reliability. Although localized voltage issues and transmission congestion were
observed, wind curtailment levels, on average, were around 1% for both the 10% Case and
the 20% Case. Even with the transmission upgrades, however, operational complexity would
increase and lead to economic challenges.
Consolidating SPP into a single BA, as is planned, should reduce overall needs for reserves
and flexible resources. To accommodate higher wind penetration levels, however, more
operational flexibility (more start-ups and cycling of units) is required. The need for flexible
units increases as the forecast error increases. A robust transmission system could reduce
local generation requirements. Additionally, as the operational needs for non-wind units
change, resulting changes in the commitment and dispatch bring about new flow patterns.
Coordinated planning between wind and transmission is therefore essential. SPP should
proceed with the cluster approach for generation interconnection evaluations, and explicitly
account for the diversity and correlation of wind resources in generation interconnection and
planning studies. If possible, SPP should explore ways to increase diversity in the wind
resource base by encouraging wind power investment in areas without significant wind
development.
Ancillary service requirements depend on the wind penetration level. The increase of wind
power leads to a need for increased regulation capability. The regulation requirement
increase accelerates as the wind penetration level increases. Wind regulation needs are time-
4 The quantity of voltage support provided by individual units was not assessed in this study.
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varying and can be reduced by improvements in forecast accuracy. The study findings show
that regulation-up and regulation-down requirements are not symmetric and could differ
significantly from one another. Furthermore, wind may be able to provide regulation down
during high-wind periods. Therefore, CRA recommends that these two ancillary services beseparated. A new type of ancillary service, such as load-following reserves, which are not
currently defined or required in SPP, may become highly beneficial as the net load forecast
variability increases with higher wind penetration levels.5 As with regulation, the need for
these reserves is also time-dependent and not symmetric in each direction.
The study found that forecast errors increase startups of flexible units and reduce generation
of less flexible units, which typically have lower marginal costs. Forecast errors were
observed to have different impacts depending on whether the deviation from the forecast was
positive or negative. Wind under-forecasts tend to exacerbate wind curtailments and small
forecast errors lead to increased curtailment levels. Wind over-forecasts have a much smaller
impact on curtailment but could lead to reliability issues if not enough non-wind resources arecommitted. Primary causes for wind curtailments observed in the study include minimum
generation requirements of committed thermal units, the need to dispatch units capable of
providing reserves (especially regulation down), and transmission congestion. Minimum
generation challenges arise when minimum generation is higher than net load (which
decreases as the wind penetration level increases). Given the high correlation in output
observed among wind sites within SPP, the implementation of a centralized forecasting
system would be advantageous. It is recommended that specific-purpose forecasts be
procured for difficult operational situations, such as high magnitude ramps.
The needs for operational flexibility, enhanced ancillary services, and accommodation of
forecast error all lead to the conclusion that unit commitment capabilities are key to windintegration. Efficient wind integration requires a sophisticated unit commitment process that
explicitly addresses the uncertainty associated with forecast errors. Based on the operational
impacts observed and the wind characteristics analyzed, it is recommended that the day-
ahead unit commitment be supplemented with an intra-day unit commitment (e.g., 4-hour-
ahead).6
The study identified four major implications of wind integration under the Day 2 Market, which
will operate as a single BA. First, the Day 2 Market will lead to different unit commitment and
dispatch decisions than are currently observed, even without high wind penetration level and
additional transmission. Second, a single BA would greatly facilitate the integration of wind.
Third, higher penetration levels of wind do not immediately guarantee a lower market clearing
price for energy. Fourth, error in the net load forecast will increase.
5 Net load is defined as load minus wind generation.
6 The Day 2 Market is assumed to have a day-ahead commitment schedule.
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This study contains an overview of existing policies pertaining to wind integration in other
markets, both in North America and Europe. CRA has reviewed these policies in conjunction
with the findings of the analyses performed and has provided recommendations for policy
implementation. These recommendations are presented and discussed in Section 6.
The analytical results of the study show that there are no significant technical barriers to
integrating wind generation to a 20% penetration level into the SPP system, provided that
sufficient transmission is built to support it. The study, however, did not include an
optimization of the level of transmission expansion required to support wind integration. The
findings of this study could be used as the basis of such an optimization, which along with
further analyses using actual SPP wind plant operating data (when available), is
recommended as a follow-up study.
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2. INTRODUCTION
2.1. BACKGROUND AND OBJECTIVES OF THE STUDY
The Southwest Power Pool (SPP) selected Charles River Associates (CRA) in early 2009 to
conduct a study to determine the operational and reliability impact of integrating wind
generation into the SPP transmission system and energy markets. The study required an
intensive effort to perform a detailed engineering analysis correctly and then interpret the
findings and associated policy implications in the context of a broad regional market. To
achieve the overall objective, the study assessed the impacts of wind generation on three
different aspects of SPP: transmission, operation, and markets. The three aspects and the
analyses associated with each are summarized below.
Transmission Impact Study
Steady-state thermal and voltage analysis: pre- and post-contingency
Voltage stability analysis: PV, VQ, and dV/dQ analyses
Transmission expansion requirements to facilitate the wind projects including transient
stability, voltage stability, and VAR requirements
Impacts of wind generation on ATC
Recommendations on generation interconnection (GI) analysis, procedures, and
requirements for wind generation
Operational Impact Study
Impacts on both operations and markets in the regulation, load-following, and unit
commitment timeframes
Time-synchronized load and wind data
Impacts on ancillary services
Market Impact Study
Impact of the additional wind generation on the Energy Imbalance Market and
identification of potential policy changes required to accommodate the additional windgeneration
Review of the practices of other markets that have successfully integrated large amounts
of wind generation and identification of best practices
Propose method to incorporate day-ahead wind and load forecasting error in the unit
commitment and dispatch processes
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The study was performed for the year 2010 with the assumption that SPP operates as a
single balancing authority (BA) with a co-optimized energy and ancillary service market (Day
2 Market). The goal was to identify the challenges of high wind penetration levels and the
infrastructure required to accommodate the integration of wind into the SPP transmissionsystem. One of the objectives was to identify the transmission upgrades needed to
accommodate wind power without curtailment. This was not an economics study and
therefore economic optimization, such as determining an appropriate balance between
building transmission upgrades and curtailing wind was not performed. Another important
note is that the study was not intended to address the impact of any individual wind plant and
therefore the analyses results should not be tied to, or used to evaluate, any individual wind
plant and its operations.
The analyses were performed in the following order. First, SPP selected the set of wind
plants to be included in the study. Analysis of these select wind plants characteristics was
performed. This is discussed in Section 3. Then, transmission expansions needed to
accommodate these wind plants were identified band added to the current system. These
needs were based on the application of the SPP Criteria to a set of power flows with
increased wind penetration without any consideration for cost. Transmission related analysis
was performed for the upgraded system and discussed in Section 4. The results from the
wind characteristic analysis (Section 3) and transmission analysis (Section 4) were then used
to analyze the impact of wind on ancillary services, reserves in particular, and on system
operation over time by running a production simulation. The production simulation analyzed
additional congestion not observed in the transmission analysis in Section 4, unit commitment
and dispatch issues, and the impact of forecast errors. These impacts to operations are all
discussed in Section 5. Finally Section 6 translates findings from Section 3 through Section 5
to market impacts, and provides policy recommendations including methods to addressforecast errors.
Details of the methodologies used for this study are described in Section 7.
2.2. THE SOUTHWEST POWER POOL
SPP, originally founded in 1941, is a Regional Transmission Organization (RTO) approved by
the Federal Energy Regulatory Commission (FERC). As an RTO, SPP ensures reliable
supply of power, adequate transmission infrastructure, and competitive wholesale pricing of
electricity. SPP currently serves parts or all of eight states (Arkansas, Kansas, Louisiana,
Missouri, Nebraska, New Mexico, Oklahoma, and Texas) and has members in nine states(Mississippi in addition to the eight states listed above), with over five million customers. It
covers a footprint of over 370,000 square miles with 47,000 miles of transmission lines
(nearly enough to circle the earth twice). SPP is interconnected heavily with Entergy,
Associated Electric Cooperative Incorporated (AECI), the Midwest Independent System
Operator (MISO), Mid-Continent Area Power Pool (MAPP), and through limited DC ties with
Electric Reliability Council of Texas (ERCOT) and Western Electricity Coordinating Council
(WECC). SPP is also a North American Electric Reliability Corporation (NERC) Regional
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Entity, overseeing compliance enforcement and reliability standards development. Figure 2.2-
1 [52] shows the geographic footprint of SPP.
Figure 2.2-1: SPP footprint
As of December 2008, the forecasted 2009 peak demand for SPP was approximately 50 GW
and the annual energy consumption was 240 TWh. As of December 2008, SPP had nearly 66
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GW of installed capacity with a generation portfolio of approximately 40% coal, 42% gas, 4%
nuclear, 4% hydro, 2% wind, and 8% other generation technologies. The wind power
component (nameplate) of the portfolio was approximately 1.8 GW in December 2008, and
approaching 3 GW in December 2009.
Since 2007, SPP has been operating an Energy Imbalance Service Market in which
participants can buy and sell wholesale electricity in real time. This market is currently
operated under 13 BAs. The definition of SPP used for the purpose of this study is limited to
the SPP members that are part of the SPP market. These members are American Electric
Power West (AEPW), Empire District Electric Company (EMDE), Grand River Dam Authority
(GRDA), City of Independence, Missouri (INDN), Kansas City Board of Public Utilities
(KACY), Kansas City Power and Light (KACP), Westar (WERE), Lincoln Electric System
(LESY), Midwest Energy Incorporated (MIDW), Missouri Public Service (MIPU),1 Nebraska
Public Power (NPPD), Oklahoma Gas and Electric Company (OKGE), Omaha Public Power
District (OPPD), Southwestern Public Service Company (SPS), Sunflower Electric Power
Corporation (SUNC), and Western Farmers Electric Cooperative (WFEC). SPP plans to
implement the Day-Ahead Market and Ancillary Services Market by December 2013 under a
single BA (Day-2 Market). For this study, it is assumed that these markets were already in
service.
2.3. WIND GENERATION POTENTIAL IN SPP AND NEIGHBORING REGIONS
Figure 2.3-1 [55] shows the wind potential of the entire United States, as provided by 3Tier
Inc.
As seen in Figure 2.3-1, high wind potential exists on either side of the Rocky Mountains,including a significant portion of the SPP footprint (most of Nebraska and Kansas, the
western half of Oklahoma, and the portions of New Mexico and Texas in SPP), along with the
upper Midwest region of the Eastern Interconnection (EIC), including MAPP, Western Area
Power Administration (WAPA), and MISO. Significant penetration of wind has an enormous
potential to displace generation from existing thermal units, leading to reduced emissions
(NOx, SO2, and CO2) and to reduce overall energy production costs. As of December 2009,
the SPP GI queue contains approximately 48,000 MW of wind generation (nearly 80% of all
generation projects in the queue).
This high wind potential region is sure to play a key role in evolving national energy policy.
Even in the absence of a national requirement, many states are considering or requiring
Renewable Energy Standards (RES), mandating that utilities generation portfolios must
1 Missouri Public Service (MIPU) is now KCP&L Greater Missouri Operations Company (GMOC). However it will be
referred to as Missouri Public Service or MIPU throughout this report. This is to avoid unnecessary confusion as the
data received from SPP, including the power flow cases, historical load data, and load forecast data, were all using
the MIPU nomenclature.
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contain a minimum amount of renewable sources. Of the states within the SPP footprint,
Missouri, New Mexico, and Texas already require RES, and Kansas2 has recently
established renewable portfolio standard although the rules and regulations that administer
this portfolio standard has not yet been established at the time of preparing this report. Of therenewable resources available, wind is in the most advanced stage of development in the
SPP region.
Figure 2.3-1: Wind potential in the United States
Under pending federal and state policies, states that lack renewable resources may need to
seek imported power generated by renewable resources. SPP has the potential to become a
large exporter of wind power to neighboring states with little wind potential. As discussed in
Section 2.4, however, SPP faces significant operational considerations at all levels.
2 House Bill 2369 that established the renewable portfolio standard for Kansas was enacted in May 2009. The
Kansas Corporation Commission is now given 12 months to establish rules and regulations to administer the portfolio
standard, which requires states investor owned utilities and larger corporative utilities to generate or purchase
certain amount of generation capacity from eligible renewable resources.
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2.4. KEY CHALLENGES OF WIND INTEGRATION
Integrating wind power into an existing portfolio does not pose significant operational
challenges when the wind penetration level is low, especially in portfolios with abundant
flexible resources with high response rates. As the wind penetration level increases, however,
challenges arise due to the unique characteristics of wind.
The most apparent challenge is that wind is a variable resource and cannot be controlled in
the same manner as traditional generators. The variability leads to a greater need for
reserves; disturbances of the generation-to-load balance due to high ramp events require
supplementation by responsive resources, including generation and demand. Additional
reserves have additional costs and increase operational challenges, especially in a market
like that of SPP, in which the generation is primarily thermal with few hydro resources.
Furthermore, the peak hours for wind generation usually occur in the early morning, just
before sunrise, and do not coincide with the peak hours for load, which typically occur mid- to
late-afternoon.3 As a result, net load (load minus wind generation) exhibits more significant
fluctuations between off-peak and on-peak periods. This leads to more operational
challenges in controlling non-wind generators serving the net load. For a primarily thermal
generation portfolio like that of SPP, this means that additional challenges arise during the
off-peak hours because of minimum generation requirements.
The variation of wind output and forecast errors have a significant impact on non-wind unit
commitment. Under-forecasting wind generation leads to over-commitment of non-wind
generation and over-forecasting wind generation leads to under-commitment. Over-
commitment can result in a suboptimal economic dispatch and high uplift costs as well as
wind generator curtailment. Under-commitment can result in shortage of supply, a reliability
concern. In order to avoid these commitment problems, the uncertainty introduced by wind
power in the unit commitment timeframe must be minimized and explicitly modeled in the unit
commitment decisions, especially with high wind power penetration levels.
Another factor affecting wind integration is the output characteristic of a wind plant power
curve. Figure 2.4-1 [53] shows a representative power curve. The power curve is unique to
each turbine type and location and represents the relationship between wind speed and
electric power output for a given unit at a given site. As seen in Figure 2.4-1, the forecast
error can vary greatly depending on the wind speed. If the wind speed is in the range shown
as S2 (in between the two red lines), a small forecast error in wind speed leads to a large
error in wind generation output. If wind speed is in the S3 range but near the border of the S3
and S4 range, there is a risk of a cutoff event, which shuts down the wind turbine to avoid
mechanical failure. These differing potential forecasting errors will lead to different reserves
needs.
3 This is typically not true for off-shore wind, but there are no planned off-shore wind additions for SPP.
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S1 S2 S3 S4S1 S2 S3 S4
Figure 2.4-1: Wind turbine power curve
Apart from the unique characteristics of wind power, it is important to note that wind
generation is usually located far from load centers; therefore, advanced transmission
planning is required. The topology and technology of the transmission overlay is critical to
integrating high wind power penetration levels. This is especially true for SPP because the
areas of highest wind potential are in the west, but the load centers are in the east. Another
transmission-related concern is that SPP has limited DC connections with ERCOT (to the
south) and WECC (to the west). Therefore, if SPP were to export wind power, the best option
would be to export to neighboring areas east and southeast of SPP, requiring additional
transmission expansion.
Finally, the geographic characteristics of the SPP footprint lead to another challenge.Because the SPP footprint is primarily flat terrain, the correlation of output among wind plants
is relatively high compared to that of regions like PJM, where most wind plants are sited on
ridge tops. Therefore, as this report will illustrate, the stochastic properties of wind and load
time series become critical.
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3. SPP WIND RESOURCES:CASES ANALYZED AND THEIR CHARACTERISTICS
This section describes the wind penetration cases modeled in this study, including a
specification of the wind plants considered in each case, and analyzes their statistical
characteristics. The focus of the analysis in this section is on the characteristics of wind
resources that have large impacts on operations, such as average wind profiles and the
deviations from those averages, and spatial and temporal wind profile diversity. The insights
gained in this part of the study were used to shape and inform the transmission analysis
described in Section 4 and the operations analysis described in Section 5.
Four wind penetration cases defined by SPP were analyzed: the power system as it currently
exists (approximately 4% wind penetration), and three levels of higher wind penetration
10%, 20%, and 40% (10% Case, 20% Case, and 40% Case, respectively). The level of
penetration in each scenario signifies the percentage of annual energy generated by wind in
SPP. Most wind plants in each case are concentrated in the western part of SPP.
The statistical analysis performed by CRA and described in this section revealed high
variability in the available wind power outputs. In fact, the maximum and minimum observed
available output for the aggregate wind generating resources in SPP ranges from less than
1% to 92% of the nameplate wind capacity. On average, available wind generation depends
on the season and time of day, among others factors. The overall capacity factor 1 of the wind
plants is about 39%. SPP wind resources exhibit geographic diversity in their profiles, so for
this reason, consolidating BAs in SPP should reduce overall needs for reserves and flexible
resources. For the wind cases analyzed, however, increasing wind penetration yielded little
gain in diversity, because the geographic spread of wind plants in the higher wind penetration
cases is similar to that of the existing wind plants. Greater geographic diversity mitigates the
variability of aggregate wind generation. The study results might have been different,
therefore, had different assumptions for wind generation siting been used, e.g., based on
wind resource assessments instead of the current generation interconnection queue.
Based on the findings in this section, CRA makes the following recommendations to enable
high levels of wind integration in the SPP power system:
Proceed with the consolidation of SPP into a single BA.
Proceed with the cluster approach for GI evaluations.
1 Capacity factor is the average output as a percentage of the total nameplate capacity.
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Explicitly account for the diversity and correlation of wind resources in planning and
interconnection studies, e.g., through the use of historical wind data in the determination
of wind power dispatch for the cluster studies mentioned above.
Explore ways to increase diversity in the wind resource base by encouraging wind power
investment in areas without significant development.2
The remainder of this section is organized into three portions. Section 3.1 describes the wind
penetration cases modeled in the study; Section 3.2 provides the statistical characteristics of
wind profiles; and Section 3.3 discusses the spatial and temporal diversity of wind resources
in SPP.
3.1. WIND PENETRATION CASES FOR SPP AND NEIGHBORING REGIONS
For the purposes of this study, four scenarios defined by SPP were analyzed: the power
system as it currently exists (Base Case, 4% wind penetration), and three levels of wind
penetration 10%, 20%, and 40%. The level of penetration in each scenario signifies the
percentage of annual energy generated by wind in SPP; because the capacity factor of wind
generation is below the fleet average, the wind generation proportions of total installed
nameplate capacity for each scenario were higher than the corresponding penetration levels.
Detailed analysis was done for the Base, 10%, and 20% Cases, while partial analysis was
done for the 40% Case. Table 3.1-1 shows the wind generation capacity for each wind
penetration level.3
Table 3.1-1: Wind generation capacity by penetration level
Penetration Scenario Base Case 10% Case 20% Case 40% Case
Number of farms 40 69 100 142
Installed Nameplate
Wind Capacity (MW)2,877 6,840 13,674 25,003
Wind/Non-Wind
Nameplate Capacity0.046 0.109 0.217 0.397
2 Western Nebraska is one example of a region in SPP with good wind potential and low wind profile correlation
with the areas where most of the wind sites in this study ar