NOTICE DATE: October 3, 2019

NOTICE TYPE: M-A100319-01 Operations

SHORT DESCRIPTION: Potential Price Correction – Modeling of Withdrawn Outages in the Day-Ahead Market and Reliability Unit Commitment

INTENDED AUDIENCE: All Market Participants

DAYS AFFECTED: September 16-23, 2019

LONG DESCRIPTION: On September 24, 2019, ERCOT became aware of an issue concerning the modeling of withdrawn Outages in the Day-Ahead Market (DAM) and Reliability Unit Commitment (RUC) for various Operating Days (ODs) in August and September. On May 30, 2019, ERCOT deployed a system enhancement for modeling Outages in DAM and RUC. The enhancement was intended to only model withdrawn Outages in DAM and RUC for instances where out-of-service equipment was in the process of being restored. However, ERCOT identified that its systems inadvertently modeled all withdrawn Outages for DAM and RUC—i.e., not just those undergoing restoration. ERCOT has identified erroneously modeled Outages in DAM and RUC for ODs August 20-21, 2019, and September 16-25, 2019. ERCOT immediately implemented an emergency fix, and began investigating prices for the affected ODs. ERCOT has determined that DAM clearing was impacted for all of the affected ODs.

Although ERCOT has determined that ODs August 20-21, 2019, were affected by the above-referenced software implementation error, ERCOT will not seek ERCOT Board review for prices on those ODs, as the timeline under ERCOT Protocol Section 4.5.3(5) precludes ERCOT Board review.

ERCOT corrected prices for ODs September 24, 2019 and September 25, 2019 in accordance with ERCOT Protocol Section 4.5.3(4).

ERCOT is continuing to investigate prices for ODs September 16-23, 2019. ERCOT has made a preliminary determination that prices for some, if not all, of the affected ODs are in need of correction. ERCOT will provide an updated Market Notice to inform the market of the specific ODs for which ERCOT intends to seek ERCOT Board review (at its December 2019 meeting) of prices in need of correction.

While this modeling issue also affected models used by RUC, ERCOT has reviewed RUC instructions for the ODs at issue and does not believe any were associated with transmission congestion or other system conditions that may have arisen out of this modeling issue. Moreover, this issue did not affect pricing outcomes in the Real-Time market, as ERCOT System topology in Real-Time is based on telemetry, rather than information from the Outage Scheduler.

CONTACT: If you have any questions, please contact your ERCOT Account Manager. You may also call the general ERCOT Client Services phone number at (512) 248-3900 or contact ERCOT Client Services via email at ClientServices@ercot.com.

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