ERCOT Managers Working Group Discussion

In this discussion, the ERCOT Managers Working Group reviewed Loss of Load Probability, years used for Mu and Sigma calculations, hourly blocks and seasons data, and Security Constrained Economic Dispatch. The process includes determining the ORDC for upcoming seasons based on historic data and ensuring its accuracy. Different seasons and hour blocks are analyzed for Mu and Sigma calculations to understand system conditions and ORDC prices. Consideration is given to potential hour-to-hour differences and the need for representative data. The use of blended values is also addressed for more stable results.

• ERCOT
• Mu and Sigma
• ORDC
• System Conditions
• Economic Dispatch

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1. ORDC Curve Discussion ERCOT QSE Managers Working Group 9/4/2015 1

2. Discussion Outline Review of Loss of Load Probability Review of years used for the Mu and Sigma calculation Review of hourly blocks and seasons Data used for Mu and Sigma calculation 6.5.7.3 Security Constrained Economic Dispatch (14) At the end of each season, ERCOT shall determine the ORDC for the same season in the upcoming year, based on historic data using the ERCOT Board-approved methodology for implementing the ORDC. Annually, ERCOT shall verify that the ORDC is adequately representative of the loss of Load probability for varying levels of reserves. Twenty days after the end of the Season, ERCOT shall post the ORDC for the same season of the upcoming year on the MIS Public Area. 2

3. Years used in Mu and Sigma calculations If the methodology to calculate the Mu and Sigma stays the same then over time the curve change year over year will be very small what data will be used to get the Mu & Sigma for the season 1,2 3,4,5 6,7,8 9,10,11 12 Jan/Feb Spring Summer Fall Dec 2011 2012 2011 2012 2011 2012 2010 2011 2012 2013 2014 2015 2010 2011 2012 2013 2014 2015 2016 2010 2011 2012 2013 2014 2015 2016 2017 2014 2011 2012 2013 2014 2011 2012 2013 2014 2011 2012 2011 2012 2015 2011 2012 2013 2014 2015 2011 2012 2013 2014 2015 2011 2012 2013 2014 2015 2011 2012 2013 2014 2015 2016 2011 2012 2013 2014 2015 2016 2011 2012 2013 2014 2015 2016 2011 2012 2013 2014 2015 2016 2011 2012 2013 2014 2015 2016 2017 3

4. Seasons and Hour Blocks used for Mu and Sigma Anytime blocks of data are used The high intervals will be lowered The low intervals will be raised Block to block, Identical system conditions can have different ORDC price Same with season to season and the combination of the two This will happen inherently no matter how small or large the blocks are Potential Hour to Hour difference can be reduced the smaller the time blocks The smaller the time blocks the more data is required for representative results Month Season Hour Ending Hour_block 1 WINTER 1 1 2 WINTER 2 1 3 SPRING 3 2 4 SPRING 4 2 5 SPRING 5 2 6 SUMMER 6 2 7 SUMMER 7 3 8 SUMMER 8 3 9 FALL 9 3 10 FALL 10 3 11 FALL 11 4 12 WINTER 12 4 13 4 14 4 15 5 16 5 17 5 18 5 19 6 20 6 21 6 22 6 Would a blended value give more stable results? 23 1 24 1 25 1 4

5. Seasons and Hour Blocks used for Mu and Sigma 97 Hourly Curves; smoothed within the seasons LOLP Distribution as of March season hour_block mean sd Hour Block Factor Block Hour WINTER 1 -105.82 1261.06 1 0.75 3 WINTER 2 -44.89 1238.87 1 0.5 4 WINTER 3 -44.89 1238.87 2 0.5 1 WINTER 4 16.04 1216.67 2 0.75 2 WINTER 5 18.22 1284.81 2 0.75 3 WINTER 6 -40.53 1375.14 2 0.5 4 WINTER 7 -40.53 1375.14 3 0.5 1 LOLP Distribution as of March WINTER 8 -99.28 1465.48 3 0.75 2 season hour_block mean sd WINTER 9 -294.93 1550.85 3 0.75 3 WINTER 1 -166.75 1283.26 WINTER 10 -431.83 1545.89 3 0.5 4 WINTER 2 76.97 1194.47 WINTER 11 -431.83 1545.89 4 0.5 1 WINTER 3 -158.03 1555.81 WINTER 12 -568.72 1540.93 4 0.75 2 WINTER 4 -705.62 1535.97 WINTER 13 -633.66 1502.64 4 0.75 3 WINTER 5 -417.76 1402.66 WINTER 14 -561.69 1469.32 4 0.5 4 WINTER 6 -287.31 1138.72 WINTER 15 -561.69 1469.32 5 0.5 1 WINTER 16 -489.73 1435.99 5 0.75 2 WINTER 17 -385.15 1336.68 5 0.75 3 WINTER 18 -352.54 1270.69 5 0.5 4 WINTER 19 -352.54 1270.69 6 0.5 1 WINTER 20 -319.92 1204.71 6 0.75 2 WINTER 21 -257.17 1174.86 6 0.75 3 WINTER 22 -227.03 1210.99 6 0.5 4 WINTER 23 -227.03 1210.99 1 0.5 1 WINTER 24 -257.17 1174.86 1 0.75 2 In this example Hour Block 4 values would become 4 separate hourly values with Hours 1 and 2 of the block smoothing with the previous hour block Hours 3 and 4 of the block smoothing with the next hour block 5

6. QUESTIONS / COMMENTS??? 6

7. Appendix 7

8. Mu and Sigma Posting The Summer 2016 (effective 6/1/2016) values will be posted in September http://www.ercot.com/mktinfo/rtm/index.html The Mu and Sigma values will be recomputed using most recently approved methodology; NPRR 710 Approved on August 11, 2015 8

9. Mu and Sigma Posting Calendar 6.5.7.3 Security Constrained Economic Dispatch (14) At the end of each season, ERCOT shall determine the ORDC for the same season in the upcoming year, based on historic data using the ERCOT Board-approved methodology for implementing the ORDC. Annually, ERCOT shall verify that the ORDC is adequately representative of the loss of Load probability for varying levels of reserves. Twenty days after the end of the Season, ERCOT shall post the ORDC for the same season of the upcoming year on the MIS Public Area. The historical data will be recomputed using most recently approved methodology This means if there are to be changes they need to be made >=9 months before change is to take effect Values are posted 9 months prior to being used by SCED (e.g. Summer 2016 posted Sep-2015 and used on Jun-2016) Season Jun-2014 Posted/In Use Sep-2014 Dec-2014 Mar-2015 Jun-2015 Sep-2015 Dec-2015 Mar-2016 Jun-2016 Sep-2016 Dec-2016 In Use In Use In Use post In Use post In Use post post post Summer Fall Winter Spring Summer Fall Winter In Use In Use In Use post In Use post In Use 9