FERC has accepted SPP’s revisions to its Western Energy Imbalance Service (WEIS) market’s tariff related to the residual supply index (RSI) and ensuring that affiliated market participants’ resources are evaluated together (ER24-2208).

In its Aug. 15 letter order, the commission found the revisions will help identify and address structural market power in the WEIS market by ensuring a market participant affiliate’s online resource capacity is evaluated in the RSI calculation. It said the proposed revisions modify the market’s existing definition of “affiliate” by incorporating FERC’s regulations and require market participants to affirmatively identify affiliates when they register in the WEIS market and on an ongoing basis.

SPP’s Market Monitoring Unit determined in 2020 that the WEIS market had a high level of structural market power when viewed through the RSI, or the ratio of residual supply to total market demand. The RTO said that under the calculation, affiliated market participants’ total capacity is not evaluated together and creates a situation in which an entity can split its fleet of resources into multiple market participant registrations to avoid any one of the market participants failing the RSI calculation.

The grid operator’s proposal addressed FERC’s concerns when it rejected SPP’s first attempt in December. The commission found that allowing the MMU to exclude affiliated capacity from the RSI calculation if the monitor determined there were sufficient safeguards and corporate controls was not just and reasonable. The MMU, which supported SPP’s revisions, now can exclude affiliated capacity from the RSI calculation.

The RTO still must make an informational filing notifying FERC of the revisions’ actual effective date no less than 30 days prior to their implementation.

SPP has administered the WEIS market on a contract basis since February 2021. It serves 12 participants.