Texas Staff Updates Estimate of ERCOT Capacity Used for Small Fish Swim Free Rule

Staff of the Public Utility Commission of Texas have filed an updated estimate of installed generation capacity in ERCOT.

The amount of installed generation capacity is a factor in determining (1) the 20 percent limit on installed generation capacity established in PURA § 39.154 and (2) the 5 percent wholesale market power exemption established in P.U.C. Subst. R. 25.504(c).

For purposes of the 20% limit, the estimated total installed generation capacity is 88,840 MW.

For purposes of the 5% exemption, the estimated total installed generation capacity is 81,765 MW.

Staff reported that there were a few changes in methodology this year that affect the total capacity estimates:

1. The capacity credit for wind facilities in the ERCOT Coastal region increased from 58% of the nameplate capacity of the facility to 59%. This change was made to be consistent with the Summer Peak Average Capacity Contribution Percentages used by ERCOT in the December 2017 CDR. The capacity credit for wind facilities in the Non-Coastal region remained at 14% of the nameplate capacity of the facility.

2. The capacity credit for solar facilities decreased from 77% of the nameplate capacity of the facility to 75%. This is consistent with the Summer Peak Average Capacity Contribution Percentage that ERCOT reported in the December 2017 CDR.

3. On previous versions of this spreadsheet, switchable generation facilities were given full credit for the capacity listed in the CDR, minus the capacity ERCOT listed as "Switchable Capacity Unavailable to ERCOT". However, Subst. R. 25.401(e)(1)(D) states that installed generation will include "generating facilities that are located on the boundary between two power regions and are able to deliver electricity directly into either power region, except that the capacity of such facility shall be allocated between the power regions based on the share of its total electric energy that the facility sold in each power region during the preceding year." [Emphasis by Staff]. To better align with this rule, Staff will now utilize information provided in the most recent Generating Capacity Report filed by each of the switchable generation owners under PUC Docket 23730. Table 1 of the Generating Capacity Report lists the annual wholesale energy sales into each power region. The capacity reduction will be based on the percentage of energy that is sold into the non-ERCOT power regions.

Furthermore, several generation units are included on the "Adjustments" tab of the spreadsheet containing Staff's calculation this year. Reasons for these units having their reported capacity adjusted include (with a more thorough explanation provided in Staff's filing):

1. The capacity for switchable generation facilities is reduced in accordance with Subst. R. 25.401(e)(1)(D).

2. The capacity for the battery storage facilities that are given zero capacity in the ERCOT CDR is added. This aligns with PURA Section 35.152(a), which provides that "Electric energy storage equipment or facilities that are intended to be used to sell energy or ancillary services at wholesale are generation assets."

3. The capacity for generating facilities with a nameplate rating of 1 MW or less is removed, aligning with Subst. R. 25.401(e)(2)

4. The December 2017 ERCOT Generator Interconnection Status Report, which provides the information for the New Capacity tab of the spreadsheet, stated that a couple of generation facilities had achieved commercial operation since the December 2017 CDR was released. Thus, the capacity for those facilities was added.

The definition of installed generation capacity includes capacity that is currently not available to the ERCOT market but could be potentially marketable, such as mothballed capacity and "behind-the-fence" capacity. Therefore, the estimate in the spreadsheet file should not be used for purposes of resource adequacy, Staff said