1. ERCOT Load Research Sampling Round 2 Model Coefficient Updates Additional Evaluations Presented to the PWG on July 28, 2010

2. Overview Outcomes from last month’s PWG meeting Plots of scaled LRS means and backcasts and for selected 4CP days Plots of scaled LRS means, backcasts and UFE for selected high UFE days Summary MAPE’s by Profile Type and Weather Zone for 4CP and high UFE days Summary and Conclusions Discussion points from June 24 PWG conference call. Discussion points from June 24 PWG conference call. 2

3. Outcomes from the May PWG Meeting There was no interest in building completely “new” models. There was some interest in updating the coefficients in the existing models for selected Profile Type/Weather Zone combinations. PWG requested that ERCOT evaluate: Coincident peaks (4CP) during the study period High UFE days during the study period. 3

4. 4CP DAYS 4

5. Summary of 4CP Days The 4CP days are as follows. 2008 – June 16 interval ending 16:45 (Not in study period.) – July 31 interval ending 16:45 – Aug 4 interval ending 17:00 – Sept 2 interval ending 16:45 2009 – June 25 interval ending 16:15 – July 13 interval ending 17:00 – Aug 5 interval ending 16:00 – Sept 3 interval ending 16:00 5

6. 4CP Day August 4, 2008 BUSMEDLF COAST 6 4CP at interval ending 17:00

7. 4CP Day August 4, 2008 BUSMEDLF NCENT 7 4CP at interval ending 17:00

8. 4CP Day August 4, 2008 BUSLOLF COAST 8 4CP at interval ending 17:00

9. 4CP Day August 4, 2008 BUSLOLF NCENT 9 4CP at interval ending 17:00

10. 4CP Day August 4, 2008 RESLOWR COAST 10 4CP at interval ending 17:00

11. 4CP Day August 4, 2008 RESLOWR NCENT 11 4CP at interval ending 17:00

12. 4CP Day June 25, 2009 BUSMEDLF COAST 12 4CP at interval ending 16:15

13. 4CP Day June 25, 2009 BUSMEDLF NCENT 13 4CP at interval ending 16:15

14. 4CP Day June 25, 2009 BUSLOLF COAST 14 4CP at interval ending 16:15

15. 4CP Day June 25, 2009 BUSLOLF NCENT 15 4CP at interval ending 16:15

16. 4CP Day June 25, 2009 RESLOWR COAST 16 4CP at interval ending 16:15

17. 4CP Day June 25, 2009 RESLOWR NCENT 17 4CP at interval ending 16:15

18. HIGH UFE DAYS 18

19. Summary of High UFE Days The UFE days were selected from the UFE Analysis Report 2009 19

20. BUSMEDLF COAST High Negative UFE – Actual Load Less Than Estimated Load December 23-24, 2009 20

21. BUSMEDLF NCENT High Negative UFE – Actual Load Less Than Estimated Load December 23-24, 2009 21

22. BUSLOLF COAST High Negative UFE – Actual Load Less Than Estimated Load December 23-24, 2009 22

23. BUSLOLF NCENT High Negative UFE – Actual Load Less Than Estimated Load December 23-24, 2009 23

24. High Negative UFE – Actual Load Less Than Estimated Load December 23-24, 2009 RESHIWR COAST 24

25. RESHIWR NCENT High Negative UFE – Actual Load Less Than Estimated Load December 23-24, 2009 25

26. BUSMEDLF COAST High Positive UFE – Actual Load Greater Than Estimated Load March 1, 2009 26

27. BUSMEDLF NCENT High Positive UFE – Actual Load Greater Than Estimated Load March 1, 2009 27

28. BUSLOLF COAST High Positive UFE – Actual Load Greater Than Estimated Load March 1, 2009 28

29. BUSLOLF NCENT High Positive UFE – Actual Load Greater Than Estimated Load March 1, 2009 29

30. High Positive UFE – Actual Load Greater Than Estimated Load March 1, 2009 RESHIWR COAST 30

31. RESHIWR NCENT High Positive UFE – Actual Load Greater Than Estimated Load March 1, 2009 31

32. Summary for All Intervals 32

33. Summary for 4CP and High UFE Days 33

34. Summary MAPE’s for scaled Round 2 Means by Profile Type and Weather Zone range between 2.8 % (BUSHILF, NCENT) and 27.9% (BUSNODEM, COAST) with the mean for all profile types and weather zones = 8.5%. MAPE’s for 2008-2009 4CP days by Profile Type and Weather Zone range between 2.1 % (BUSHILF, COAST) and 33.9% (BUSNODEM, COAST) with the mean for all profile types and weather zones = 6.7%. MAPE’s for selected 2009 high UFE days by Profile Type and Weather Zone range between 2.9 % (BUSHILF, NORTH) and 17.4% (BUSLOLF, NCENT) with the mean for all profile types and weather zones = 9.3%. 34

35. Conclusions The average MAPE for the 2008-2009 4CP days (6.7%) is less than the MAPE for the study period (8.5%) because the current models were designed and perform best during summer high-load days. Profiling error is a significant part of UFE so it is expected that the average MAPE for selected 2009 high UFE days (9.3%) would be greater than MAPE for the study period (8.5%). 35

36. Discussion points from June 24 PWG ERCOT suggested updates of the model coefficients for the Coast and North Central weather Zones for all Profile Types. Coast and North Central were selected because those weather zones contain the greatest percentages of TNMP’s load. TNMP has the latest timeline for advanced meter installation. Should other weather zones be included whose advanced meters will be deployed later? How could the value from updating the model coefficients be estimated? 36

37. Discussion points from June 24 PWG How might MAPE’s and UFE change with the implementation of new model coefficients? Due to the nodal code freeze, notification and transition to new models, the earliest new models could be implemented is July 2011. If a new model transition is required, it will be necessary to create a project that would go through the prioritization process. ERCOT is neutral on the issue of updating the model coefficients. 37

38. Discussion points from June 24 PWG ERCOT suggested three model transition options: straight cutover to new models—no transition; linearly interpolate from current models to new models; cutover to new models based on start date of meter read. The PWG Chair will poll market participants on whether PWG should pursue updating the model coefficients. An updated timeline is presented on the next slide. 38

39. Updated Timeline 39

40. Questions and Discussion 40