UFE ANALYSIS Old – New Model Comparison

1. UFE ANALYSISOld – New Model Comparison Compiled by the Load Profiling Group ERCOT Energy Analysis & Aggregation May 03, 2007

2. Sources of UFE include: ■ Generation Measurement Errors ■ Load - Missing/Erroneous Usage Data - Model Error - Load Profile ID Assignment Error ■ Losses - Model Error - Loss Code Assignment Error UFE Basics • UFE (unaccounted for energy) is computed as follows: UFE = Generation – (Load + Losses) • UFE % is computed as follows: UFE % = UFE / Generation • Negative UFE indicates load/losses are overestimated

3. UFE Net Generation forSettlement Interval GAP - - - - - - > Losses: Transmission & Distribution Profiled Energy Usage Non-Interval Data Non-Metered Accounts Net Generation Compared to Load Buildup Interval Data Energy Usage UFE Basics

4. Analysis Overview • Objective: Estimate UFE impact for the 48 new profiles models • Analyze UFE impacts on an annual basis and across seasons, day-types and time-of-day • Winter (Dec, Jan, Feb) Spring (Mar, Apr) • Summer (May – Sep) Fall ( Oct, Nov) • Analysis based on current profile type assignments • Analysis window January 1, 2005 – July 31, 2006 • Analysis limited to the most recent settlement run for trade date • Create a dataset of usage-sum values • Compute the sum of all meter readings with the same Profile Type, Weather Zone, read start date, and read stop date. • Based on usage data available and Profile ID assignments in December 2006

5. Analysis Overview(continued) • Create daily profile kWh for new and old models by summing the profile intervals for each day of the analysis window • Apply the daily profile kWh values to the usage-sum data to allocate the usage-sum across the days in the meter reading period • Result is daily kWh based on new and old profiles • Assumed usage records spanning trade days within the analysis window were completely loaded • Apply new and old profiles to the daily kWh to allocate it to intervals within the day • Sum the profiled interval values across all 48 profile type and weather zone combinations for each interval • Result is an old and new version of the total profiled load (for the 48 combinations) for each interval

6. Analysis Overview(continued) • Compute the difference between the old and new versions of the total profiled load for each interval • Difference = Profiled Loadold – Profiled Loadnew • Add the difference above to UFE (Old UFE) in the interval from the latest settlement run • New UFE = Old UFE + Difference • All other settlement values thus are held constant • Losses were not recalculated … they were also held constant as a simplifying assumption • Proceeded with comparison analysis following the patterns of previous UFE Analysis Reports

7. UFE on Ercot Peak Day August 23, 2005Old Models vs New Models

8. UFE │UFE│ UFE MWh by Month New Models vs Old Models Abs. UFE MWh for New Models is 13% lower than Old Models

9. UFE Cost │UFE Cost│ UFE Cost by Month New Models vs Old Models UFE Cost for New Models is 40% lower than Old Models Abs. UFE Cost for New Models is 19% lower than Old Models

10. Statistical Comparisons – Study PeriodNew Models vs Old Models

11. Statistical Comparisons - MonthlyNew Models vs Old Models

12. Statistical Comparisons - MonthlyNew Models vs Old Models

13. Statistical Comparisons - MonthlyNew Models vs Old Models

14. Statistical Comparisons - MonthlyNew Models vs Old Models

15. Statistical Comparisons - MonthlyNew Models vs Old Models

16. Statistical Comparisons - MonthlyNew Models vs Old Models

17. Statistical Comparisons - MonthlyNew Models vs Old Models

18. Statistical Comparisons - MonthlyNew Models vs Old Models

19. Statistical Comparisons - MonthlyNew Models vs Old Models

20. Statistical Comparisons - MonthlyNew Models vs Old Models

21. Distribution of UFE MWNew Models vs Old Models

22. Distribution of UFE CostNew Models vs Old Models UFE Cost = ∑(MCPE × UFE_MWh)

23. UFE % by Day of Week New Models vs Old Models Medians, 5th and 95th Percentiles compiled over entire analysis period

24. UFE % - Average Weekday New Models vs Old Models Medians, 5th and 95th Percentiles compiled over entire analysis period

25. UFE Cost by Day of Week New Models vs Old Models Medians, 5th and 95th Percentiles compiled over entire analysis period

26. UFE Cost - Average WeekdayNew Models vs Old Models Medians, 5th and 95th Percentiles compiled over entire analysis period

27. UFE % vs Load New Models vs Old Models

28. UFE % – Average WeekdayNew Models vs Old Models

29. UFE Cost vs Load New Models vs Old Models

30. UFE Cost – Average Weekday New Models vs Old Models

31. UFE % vs Load by Season New Models vs Old Models

32. UFE % Average Weekday by SeasonNew Models vs Old Models

33. UFE Cost vs Load by Season New Models vs Old Models

34. UFE Cost – Average Weekday by SeasonNew Models vs Old Models

35. UFE % vs ERCOT Load New Models Medians, 5th and 95th Percentiles compiled over entire analysis period

36. UFE % vs ERCOT Load Old Models Medians, 5th and 95th Percentiles compiled over entire analysis period

37. UFE Cost vs ERCOT Load New Models Medians, 5th and 95th Percentiles compiled over entire analysis period

38. UFE Cost vs ERCOT Load Old Models Medians, 5th and 95th Percentiles compiled over entire analysis period