1. Severe Winter Weather Resource Outage Analysis Chad Thompson Operations Working Group September 24 2014

2. 2 ROS and WMS have been tasked with evaluating early RUC activity in anticipation of severe winter weather and observed unit start-up failures, trips, and derates WMS created a RUC Task Force to also investigate early RUC instructions ERCOT was asked to look at the data to determine if correlations to temperature and unit outages exists ERCOT believes there is a need to procure additional online generation capacity in anticipation of severe winter weather Background

3. 3 Lesson Learned from Feb 2011 Event was to bring units on-line before freezing weather hits (Jan 23) Alternative fuel commitments need to be made as early as possible (preparation for gas curtailments) (Feb 6) Some fuel restrictions cannot be predicted (Feb 7) Brief History

4. 4 ERCOT investigated concepts with input from stakeholders –New Forced Outages* VS Wind Chill –New Forced Outages* VS Daily Wind Chill changes –New Forced Outages* VS Daily Min Temperature changes Data used is for the 2013/2014 Winter Season (Dec-Feb) Given the geographic diversity of the ERCOT Grid, results were separated based on Load Areas ERCOT Assessment *Note: Data used is from ERCOT Outage Scheduler

5. 5

6. 6 Background on Data –Daily Maximum MW that were forced out –Coldest observed Wind Chill –Lowest observed Air Temperature Note that these 3 items may not have been coincidental ERCOT Assessment

7. 7 Forced Outages VS. Wind Chill

8. 8 Forced Outages VS. Daily Wind Chill Change

9. 9 Forced Outages VS. Daily Air Temperature Change

10. 10 Aggregated Values

11. 11 Comparing air temperature or wind chill changes does not show much correlation Daily min wind chill does show an increase in new forced outages as wind chill decreases Observations

12. 12 When the wind chill is expected to be below freezing, a minimum of 600 MW of additional online generation capacity should be procured –1300 MW, when wind chill is expected to be below 20 0 F This accounts for the average amount of new generation forced outages, and is not intended to account for extreme events like Jan 6 or Feb 6 Conclusions