NOTICE DATE: July 27, 2011

NOTICE TYPE: M-C072711-01 Settlements

SHORT DESCRIPTION: Correction of Electrical Bus LMPs

INTENDED AUDIENCE: QSE and CRRAH Settlement Personnel

DAYS AFFECTED: Operating Days April 6 – 20, 2011

LONG DESCRIPTION: Due to a software error, ERCOT performed a manual workaround to re-calculate certain Day-Ahead Market (DAM) Settlement Point Prices (SPPs) for Operating Days April 6 – 20, 2011. The software error was related to the DAM price calculation for a specific scenario where a single Point-to-Point (PTP) Obligation bid was placed between an energized Settlement Point and a de-energized Settlement Point and no PTP Obligation bids were placed on the energized Settlement Point and another energized Settlement Point. This software error caused the price for the energized Settlement Point to be set to system lambda. However, this workaround did not allow ERCOT to re-calculate the underlying Electrical Bus LMPs for those SPPs.

As part of the analysis related to the recent Board approved price correction (December 3, 2010 – April 5, 2011), ERCOT was able to re-calculate these Electrical Bus LMPs during the period of manual SPP corrections. To coincide with the already corrected SPPs, ERCOT has posted the supporting price files for the LMPs of the Electrical Buses which were not accurate in the original published solutions for April 6 – 20, 2011.

ADDITIONAL INFORMATION: The corrected Electrical Bus LMPs have been posted in both CSV and XML formats in the DAM Price Corrections folder located at http://www.ercot.com/mktinfo/prices/.

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 [log in to unmask].

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