FERC accepts SPP tariff creating Montana, Rocky Mountain transmission cost subregions
- Two new subregions in SPP's western footprint
- Revisions take effect Nov. 9, 2026
- Montana and North subregions to share combined rate
Photo: Wikimedia Commons - Rsparks3What changed The order changes the basis for an affected system interconnection customer's queue position from the SPP interconnection customer's receipt of the ICS study results to whether a cluster has started its ICS study.
WASHINGTON, Nov. 6 — The Federal Energy Regulatory Commission (FERC) on Nov. 6 accepted Southwest Power Pool, Inc. (SPP) tariff revisions that establish two new subregions in its Western Interconnection footprint, effective Nov. 9, 2026, and bring that region into its Consolidated Planning Process.
The new Montana Subregion and Rocky Mountain Subregion in the SPP West Region will be used to allocate a portion of the costs of future Base Plan Upgrades between 100 kV and 300 kV, known as Byway facilities, according to the order in Docket No. ER26-3740-000.
FERC found that SPP's technical analyses show the zones grouped in each subregion are significantly integrated and that their transmission customers use and benefit from Byway facilities. The order says the Rocky Mountain Subregion includes zones for Colorado Springs Utilities, Platte River Power Authority, Tri-State Generation and Transmission Association, the Colorado River Storage Project and the Loveland Area Projects transmission pricing zone in the Western Interconnection.
Under the revisions, subregional charges for the Montana and North subregions will be calculated jointly. SPP said the SPP Regional State Committee determined the two subregions should pay a combined rate due to concerns that the Montana Subregion's relatively small load could result in disproportionate rate impacts.
The order also accepts separate GRID-C rates, a per-megawatt charge reflecting interconnection customers' share of network upgrade costs, for the East and West regions in the first planning cycle. The initial interconnection cluster window for both regions will close 60 days after SPP posts the first GRID-C rates for the East Region.
SPP said West Region interconnection customers will have to provide a financial security deposit of $8,000/MW of requested interconnection service before that window closes.
SPP filed the proposal on Sept. 9, 2026. FERC accepted SPP's subregion cost allocation for its eastern footprint on Dec. 30, 2025, and accepted the Consolidated Planning Process on March 13, 2026.
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