1. http://nodal.ercot.com 1 Market Trials Open Market Participant Call Weekly Kick Off October 04, 2010

2. http://nodal.ercot.com 2 Antitrust Admonition ANTITRUST ADMONITION ERCOT strictly prohibits Market Participants and their employees who are participating in ERCOT activities from using their participation in ERCOT activities as a forum for engaging in practices or communications that violate the antitrust laws. The ERCOT Board has approved guidelines for members of ERCOT Committees, Subcommittees and Working Groups to be reviewed and followed by each Market Participant attending ERCOT meetings. If you have not received a copy of these Guidelines, copies are available at the Client Relations desk. Please remember your ongoing obligation to comply with all applicable laws, including the antitrust laws. DISCLAIMER All presentations and materials submitted by Market Participants or any other Entity to ERCOT staff for this meeting are received and posted with the acknowledgement that the information will be considered public in accordance with the ERCOT Websites Content Management Operating Procedure.

3. http://nodal.ercot.com 3 General Updates / Reminders October October 1, 2010 through October 11, 2010: ERCOT will be performing system maintenance and verifications of production systems During this time, ERCOT Nodal Production systems will not be guaranteed to be available Market Participants may receive communication or application level exceptions when trying to interact with the ERCOT systems Exceptions to this outage are as follows (these systems will remain operational and available unless otherwise communicated via a Market Notice up until and beyond Go-Live): Outage Scheduling NMMS Telemetry October 11, 2010 through October 17, 2010: ERCOT systems will be available, but no markets or scheduled events will occur during this period October 18, 2010 through October 30, 2010: ERCOT will be performing the following Market Facing Tests Day Ahead Market runs up to daily (minimum Monday – Friday) until 10/30/2010 DRUC runs up to daily (minimum Monday – Friday) until 10/30/2010 HRUC runs up to hourly 7 days / weekly (minimum based on operator availability) SCED will publish LMPs and base points every five minutes during this period Additionally: October 27, 2010 through October 28, 2010 Full System Market and Reliability test will take place for a total of 24 hours Full details and start/stop times will be shared on the upcoming Friday Market calls During the October testing with the Market, it is strongly encouraged that Market Participants participate in this testing Participation during the Full System Test is required for QSEs with Resources ERCOT will not be performing any detailed analysis of market solutions and/or prices except during the Full System Market and Reliability test Note that Settlements, CRR Ownership, Credit and Outages will not be integrated into this test ERCOT may “stub” this data as a close representation of what MPs might expect to see These systems will be involved with their transition plans

4. http://nodal.ercot.com 4 General Updates / Reminders November November 23, 2010 through November 29, 2010, Non-Binding: Day Ahead Market, HRUC and DRUC per protocol timelines SCED will continue to publish base points and LMPs Note that this testing will occur in parallel to the open submission window for the first binding Operating Day in Nodal (12/1/2010) Note that ERCOT is evaluating the request from the Market to start this November testing as early as November 15, 2010 Note that Settlements, CRR Ownership, Credit and Outages will not be integrated into this test ERCOT may “stub” this data as a close representation of what MPs might expect to see These systems will be focused on their transition to Go-Live plans Go-Live Sequence will be reviewed as part of the Cutover review

5. http://nodal.ercot.com 5 COMS/Settlements

6. Settlements Note that details of Daily Settlements is included in today’s appendix COMS Known Issues TELHSLFLAG Bill Determinant (Defect): The exemption logic for units during startup is inaccurately exempting resources, based on the data being provided to settlements TWTG Bill Determinant (Defect): the calculation for TWTG is not built per protocol; it is performing a simple average of the telemetered generation over the settlement interval, rather than doing a time-weighted average based on SCED intervals COMS Closed Issues No New Closed Issues Reminder: ERCOT will post known issues every Friday to the readiness center at: http://nodal.ercot.com/readiness/markettrials/coms/index.html http://nodal.ercot.com/readiness/markettrials/coms/index.html http://nodal.ercot.com 6

7. http://nodal.ercot.com 7 RTM / LFC

8. Standing Reports and Updates: General Reminders / Updates http://nodal.ercot.com 8 Reminders/Updates Updates to Tracking Artifacts The updated Known Issues tracking sheet is available on the Readiness Center at http://nodal.ercot.com/readiness/markettrials/rtm/index.htmlhttp://nodal.ercot.com/readiness/markettrials/rtm/index.html GREDP Results for the 36-Hour Test Results will be distributed to QSEs the week of Oct 4 th

9. Real Time Market / LFC Update http://nodal.ercot.com 9 SCED Week 35 (9/23 – 9/29) System Lambda at $2250 offer cap for 4 intervals on 9/24 9/25 SL 4 intervals ~$1000 New System Wide Offer Cap of $180 took effect on 9/27 One interval had SL above new offer cap on 9/28 No high prices during closed loop test (9/29 – 9/30); prices between $20-$40 throughout test

10. Real Time Market / LFC Update http://nodal.ercot.com 10 SCED Week 36 (9/30 – 10/6) As Energy Offer Curves are no longer required to be submitted (and may not even be possible to submit), the majority of dispatchable MW available to SCED will be at the offer cap (proxy) price of $180 Starting on 10/2, majority of intervals have SL of $180 Frequency of $3001 intervals (power balance constraint shadow price) is independent of EOC submissions

11. http://nodal.ercot.com 11 Real Time Market / LFC Update Notes - Significant drop in “SUSPECT TEL HDL=LDL=MW,” “INVALID HSL SUM,” and “TEL HSL BELOW 0” during the 36 hour LFC test. - Reminder that HSL and LSL should represent the physical capabilities of the resource regardless of resource status (even when resource is “OFF”).

12. http://nodal.ercot.com 12 36-Hour Full-System Market and Reliability Test (Sep 29 – 30) Stacy Bridges

13. http://nodal.ercot.com 13 36-Hour Test Update 36-Hour Full-System Test –ERCOT conducted the 36-Hour Test from Sep 29 th, 8 AM (CDT), through Sep 30 th, 8 PM (CDT) –No Non-Spin was deployed during the test –ERCOT performed a nodal database load during the test EMS failover occurred at approximately 11:57 pm on Sep 29 th MMS switchover completed approximately 12:02 am on Sep 30 th –Issue was observed by MPs that UDBPs were inconsistent during the timeframe of the database load –ERCOT SMEs are discussing ways to minimize inconsistencies in UDBPs during nodal database loads –Conducted first test of Inc/Dec Offers from DSRs ERCOT is investigating the Offer Curves used by SCED for DSRs

14. http://nodal.ercot.com Test Timeline – DAY ONE (SEP 29) DateTimeEvent 9/2905:30Pre-test meeting for Nodal Support Staff 06:00Hotline call by ERCOT Operators to announce the start time Kick-off of the Market WebEx Market Notice to be sent out with the test start time Operators to start using OC3s to manage congestion 08:00Hotline call to QSEs/TOs to announce the start of the test ERCOT Operators begin switching QSEs to Nodal control 08:45All participating QSEs switched to Nodal control Hotline call to announce that all participating QSEs are on Nodal control 17:00-17:30ERCOT staff transitions from day shift to evening shift 20:00Close Market WebEx for Day One EMS failover occurred at approximately 11:57 pm on Sep 29 th MMS switchover completed approximately 12:02 am on Sep 30 th

15. http://nodal.ercot.com Test Timeline – DAY TWO (SEP 30) DateTimeEvent 9/305:00- 5:30 ERCOT staff transitions from evening shift to day shift 06:00Re-Open Market WebEx 15:00- 15:30 ERCOT staff transitions from day shift to evening shift 19:15Hotline call to announce that ERCOT will begin switching QSEs back to Zonal control ERCOT Operators begin switching QSEs back to Zonal control 19:52All QSEs on Zonal control Hotline call to QSEs/TOs to announce that the test has concluded 20:00End Test

16. http://nodal.ercot.com 36-Hour Test Update Overview – Completion Criteria –CPS1 Scores: –Zonal Commercially Significant Constraints (CSCs) and Closely Related Elements (CREs) managed below thermal limits: No CSCs or Stability Limits activated during the test –Local Congestion managed below thermal limits: One constraint was activated both days with no issues –Stability limits managed below transfer limits : No CSCs or Stability Limits activated during the test –No NERC Disturbance Control Standard (DCS) failure if applicable: None –No LFC-SCED system issues that result in termination of the test : None –Procedural and software fixes have been verified to address lessons learned from previous rounds of testing : None Average Hourly CPS1 Score140 Max. Hourly CPS1 Score169 Min. Hourly CPS1 Score100

17. http://nodal.ercot.com 17 Market Trials DAM/RUC/SASM Weekly Update October 4, 2010

18. http://nodal.ercot.com 18 Market Overview

19. http://nodal.ercot.com 19 Submission Overview for Friday September 24 DAM submission overview 175 QSEs participated for Op Day 9/25 Energy Bids totaled 18,482 to 30,287 MW/hr Cleared 13,683 to 23,519 MW energy bids/hr Cleared 27,438 to 38,321 MW net energy transactions per hr, 78% to 98% of forecasted load Cleared 14,993 to 20,929 PTP bids per hr Four major Load Zone prices ranged from $18.88 to $42.00

20. http://nodal.ercot.com 20 Submission Overview for Saturday September 25 DAM submission overview 159 QSEs participated for Op Day 9/26 Energy Bids totaled 16,483 to 23,853 MW/hr Cleared 11,453 to 20,233 MW energy bids/hr Cleared 24,251 to 32,727 MW net energy transactions per hr, 74% to 95% of forecasted load Cleared 11,140 to 14,094 PTP bids per hr Four major Load Zone prices ranged from $10.00 to $38.81

21. http://nodal.ercot.com 21 Submission Overview for Sunday September 26 DAM submission overview 160 QSEs participated for Op Day 9/27 Energy Bids totaled 17,525 to 24,420 MW/hr Cleared 12,510 to 20,606 MW energy bids/hr Cleared 24,417 to 32,616 MW net energy transactions per hr, 80% to 100% of forecasted load Cleared 10,725 to 13,464 PTP bids per hr Four major Load Zone prices ranged from $21.38 to $41.32

22. http://nodal.ercot.com 22 Submission Overview for Monday September 27 DAM submission overview 201 QSEs participated for Op Day 9/28 Energy Bids totaled 20,172 to 30,982 MW/hr Cleared 14,031 to 23,305 MW energy bids/hr Cleared 27,618 to 38,136 MW net energy transactions per hr - 88% to 129% of forecasted load Cleared 13,127 to 20,670 PTP bids per hr Four major Load Zone prices ranged from $5.78 to $47.86

23. http://nodal.ercot.com 23 Submission Overview for Tuesday September 28 DAM submission overview 204 QSEs participated for Op Day 9/29 Energy Bids totaled 18,230 to 30,908 MW/hr Cleared 14,378 to 23,209 MW energy bids/hr Cleared 28,251 to 38,510 MW net energy transactions per hr - 83% to 124% of forecasted load Cleared 14,403 to 22,057 PTP bids per hr Four major Load Zone prices ranged from $19.03 to $40.40

24. http://nodal.ercot.com 24 Submission Overview for Wednesday September 29 DAM submission overview 199 QSEs participated for Op Day 9/30 Energy Bids totaled 17,305 to 29,979 MW/hr Cleared 12,615 to 24,228 MW energy bids/hr Cleared 27,500 to 37,564 MW net energy transactions per hr - 75% to 112% of forecasted load Cleared 14,388 to 21,380 PTP bids per hr Four major Load Zone prices ranged from $23.43 to $40.40

25. http://nodal.ercot.com 25 Submission Overview for Thursday September 30 DAM submission overview 187 QSEs participated for Op Day 10/1 Energy Bids totaled 17,800 to 28,923 MW/hr Cleared 14,563 to 23,644 MW energy bids/hr Cleared 22,585 to 32,594 MW net energy transactions per hr - 73% to 99% of forecasted load Cleared 10,867 to 17,052 PTP bids per hr Four major Load Zone prices ranged from $21.10 to $36.54

26. RUC Update http://nodal.ercot.com 26

27. Update on prior special topics Update on self-commitment –Previous slides presented on the market call noted that the HSL constraint was ignored by the DAM engine in addition to LSL when a resource is self- committed. This is incorrect – HSL is respected in the same way as for a normal TPO http://nodal.ercot.com 27

28. Update on prior known issue Update on RUC start/notification time –Known issue reported on 5/28 market call was later deemed invalid –RUC only considers start time when the Resource is initially offline based on EMS at the time of the RUC study, and not when they are initially online. For an initially online resource (at the start of the HRUC study period), RUC can commit a resource a couple of hours into the study period while respecting the Minimum Off-line time. Some QSEs had interpreted the protocols such that the minimum number of hours offline enforced within the unit commitment would include the warmth-dependant start time. –For Resources which are initially online even though HRUC considers lead time as zero, it enforces minimum offline time if the Resource is committed later in the study period. Hence if Minimum Off-line time is greater than or equal to the Hot Start Time then the Resource will get at least a lead time greater than or equal the Hot Start Time before getting committed by HRUC. http://nodal.ercot.com 28

29. http://nodal.ercot.com 29 Appendix

30. http://nodal.ercot.com 30 State Estimator Convergence Update State Estimator Daily Convergence Statistics (these percentages are graphed in the next slide) MonthDay% Convergence (Including Solved w/ Mismatch) SEPT2098.63% SEPT21100.00% SEPT2299.65% SEPT2394.59% SEPT24100.00% SEPT2596.53% SEPT2699.65% SEPT2799.65% SEPT2899.65% SEPT2999.31% SEPT3097.63%

31. http://nodal.ercot.com 31 State Estimator Convergence Update

32. http://nodal.ercot.com 32 DAM Settlement Overview for September 22 Statement and Invoice Overview 143 Statements/Invoices posted to QSEs 61 Statements/Invoices posted to CRRAHs 1 QSEs received Statements/Invoices for $0 CRR Overview CRRs not derated There were no CRR Shortfall Charges General Reminders/Updates Submit any questions/issues about statements, invoices, extracts or calculations to markettrials@ercot.commarkettrials@ercot.com

33. http://nodal.ercot.com 33 DAM Settlement Overview for September 23 Statement and Invoice Overview 142 Statements/Invoices posted to QSEs 61 Statements/Invoices posted to CRRAHs 2 QSEs received Statements/Invoices for $0 CRR Overview CRRs were not derated There were no CRR Shortfall Charges General Reminders/Updates Submit any questions/issues about statements, invoices, extracts or calculations to markettrials@ercot.commarkettrials@ercot.com

34. http://nodal.ercot.com 34 DAM Settlement Overview for September 24 Statement and Invoice Overview 154 Statements/Invoices posted to QSEs 61 Statements/Invoices posted to CRRAHs 4 QSEs received Statements/Invoices for $0 CRR Overview CRRs were not derated There were no CRR Shortfall Charges General Reminders/Updates Submit any questions/issues about statements, invoices, extracts or calculations to markettrials@ercot.commarkettrials@ercot.com

35. http://nodal.ercot.com 35 DAM Settlement Overview for September 25 Statement and Invoice Overview 147 Statements/Invoices posted to QSEs 55 Statements/Invoices posted to CRRAHs 1 QSEs received Statements/Invoices for $0 CRR Overview CRRs were not derated There were CRR Shortfall Charges General Reminders/Updates Submit any questions/issues about statements, invoices, extracts or calculations to markettrials@ercot.commarkettrials@ercot.com

36. http://nodal.ercot.com 36 DAM Settlement Overview for September 26 Statement and Invoice Overview 144 Statements/Invoices posted to QSEs 55 Statements/Invoices posted to CRRAHs 0 QSEs received Statements/Invoices for $0 CRR Overview CRRs were not derated There were no CRR Shortfall Charges General Reminders/Updates Submit any questions/issues about statements, invoices, extracts or calculations to markettrials@ercot.commarkettrials@ercot.com

37. http://nodal.ercot.com 37 DAM Settlement Overview for September 27 Statement and Invoice Overview 137 Statements/Invoices posted to QSEs 60 Statements/Invoices posted to CRRAHs 3 QSEs received Statements/Invoices for $0 CRR Overview CRRs were not derated There were no CRR Shortfall Charges General Reminders/Updates Submit any questions/issues about statements, invoices, extracts or calculations to markettrials@ercot.commarkettrials@ercot.com

38. http://nodal.ercot.com 38 DAM Settlement Overview for September 28 Statement and Invoice Overview 137 Statements/Invoices posted to QSEs 60 Statements/Invoices posted to CRRAHs 3 QSEs received Statements/Invoices for $0 CRR Overview CRRs were not derated There were no CRR Shortfall Charges General Reminders/Updates Submit any questions/issues about statements, invoices, extracts or calculations to markettrials@ercot.commarkettrials@ercot.com

39. http://nodal.ercot.com 39 RTM Settlement Overview for Sept 14 (168 hour Test Date) Statement Overview 204 Statements posted to QSEs 6 Statements posted to CRRAHs 3 QSEs received Statements for $0 General Reminders Submit any questions/issues about statements, invoices, extracts or calculations to markettrials@ercot.commarkettrials@ercot.com

40. http://nodal.ercot.com 40 RTM Settlement Overview for Sept 15 (168 hour Test Date) Statement Overview 208 Statements posted to QSEs 6 Statements posted to CRRAHs 8 QSEs received Statements for $0 General Reminders Submit any questions/issues about statements, invoices, extracts or calculations to markettrials@ercot.commarkettrials@ercot.com

41. http://nodal.ercot.com 41 RTM Settlement Overview for Sept 16 Statement Overview 192Statements posted to QSEs 5 Statements posted to CRRAHs 9 QSEs received Statements for $0 General Reminders Submit any questions/issues about statements, invoices, extracts or calculations to markettrials@ercot.commarkettrials@ercot.com

42. http://nodal.ercot.com 42 RTM Settlement Overview for Sept 17 Statement Overview 167 Statements posted to QSEs 65 Statements posted to CRRAHs 3 QSEs received Statements for $0 General Reminders Submit any questions/issues about statements, invoices, extracts or calculations to markettrials@ercot.commarkettrials@ercot.com

43. http://nodal.ercot.com 43 RTM Settlement Overview for Sept 18 Statement Overview 195 Statements posted to QSEs 5 Statements posted to CRRAHs 4 QSEs received Statements for $0 General Reminders Submit any questions/issues about statements, invoices, extracts or calculations to markettrials@ercot.commarkettrials@ercot.com

44. http://nodal.ercot.com 44 RTM Settlement Overview for Sept 21 Statement Overview 191 Statements posted to QSEs 6 Statements posted to CRRAHs 9 QSEs received Statements for $0 General Reminders Submit any questions/issues about statements, invoices, extracts or calculations to markettrials@ercot.commarkettrials@ercot.com

45. http://nodal.ercot.com 45 RTM Settlement Overview for Sept 22 Statement Overview XXX Statements posted to QSEs X Statements posted to CRRAHs X QSEs received Statements for $0 General Reminders Submit any questions/issues about statements, invoices, extracts or calculations to markettrials@ercot.commarkettrials@ercot.com