CRA SPP WITF Wind Integration Study Final Report

7/31/2019 CRA SPP WITF Wind Integration Study Final Report

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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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January 4, 2010 Charles River Associates

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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



6.1.2-1: 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


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



3.2-1: 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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Final Report Page xv

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


4.7-3: Newly identified constraint limits for the 10% Case (Part 1 of 2) ..................4-57







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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Final Report Page xvi

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



5.3.2-10: 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


5.3.3.1-3: 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


5.3.3.2-3: 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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Final Report Page xvii

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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Final Report Page 1-1


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

CRA SPP WITF Wind Integration Study Final Report

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