ST4. ERCOT, Update to April 6, 2021 Preliminary Report on Causes of Generator Outages and Derates During the February 2021 Extreme Cold Weather Event. ERCOT Public April 27, 2021. PDF slides 2, 3, 8-9. Original: https://www.ercot.com/files/docs/2021/04/28/ERCOT_Winter_Storm_Generator_Outages_By_Cause_Updated_Report_4.27.21.pdf

[Slide 2, Overview]
This report provides aggregated information about the causes of generator outages and derates during the February winter storm event based on information provided in response to ERCOT Requests for Information.

[Slide 3, Important Notes]
The information in this document is preliminary and subject to change.
For the purposes of this document, an “outage” is the complete unavailability of a generator’s capacity, and a “derate” is the partial unavailability of that capacity.
All generator outage and derate values reflected in the graphs are based on generator nameplate capacity—i.e., the maximum possible MW output specified by the generator manufacturer. Because wind and solar output is typically much lower than the specified nameplate capacity, the outage and derate MW values used for those units to develop this report are generally much higher than the actual amount of power that would have been available in the absence of the outage or derate.

[Slide 8, Generator Outage and Derates: Maximum Unavailability; chart labels with original values]
The highest amount of unavailable capacity during the period of February 14-19, 2021 occurred on February 16 at ~8:00 AM and was 52,037 MW.
Existing Outages (7,650 MW, 15%)
Weather Related (27,567 MW, 53%)
Fuel Limitations (6,130 MW, 12%)
Equipment Issues (7,457 MW, 14%)
Transmission Loss (1,459 MW, 3%)
Miscellaneous (512 MW, 1%)
Frequency Related (1,262 MW, 2%)
Note that the total outaged and derated capacity at this time is different than what was previously reported (52,277 MW) due to additional information received in response to the RFIs.

[Slide 9, Outage Cause Categories]
Existing Outages: Generator outages or derates that started before the issuance of the Operating Condition Notice on February 8, 2021; includes ongoing planned and forced outages as well as seasonally mothballed units.
Fuel Limitations: Generator outages or derates due to lack of fuel, contaminated fuel, fuel supply instability, low gas pressure, or less efficient alternative fuel supply.
Weather Related: Generator outages or derates explicitly attributed to cold weather conditions in the RFI responses.
