By Suzanne Herel

FERC last week approved MISO’s rate schedules for the system support resource agreements at three aging power plants on Michigan’s Upper Peninsula but directed the RTO to revisit its general cost allocation methodology to address concerns over how it might be applied to future SSR units.

The order conditionally approved the allocation of SSR costs at Presque Isle, Escanaba and White Pines (ER14-2952-003). The commission had rejected a prior cost allocation plan in an order in February.

FERC found that MISO’s proposed cost allocation methodology “generally complies” with the February order “in that it assigns SSR costs directly to load-serving entities (LSEs) serving loads that would contribute to thermal or voltage reliability violations in the absence of the Presque Isle, Escanaba and White Pine SSR units under conditions that are representative of actual manual and/or automatic responses taken during reliability events.”

But it rejected MISO’s filing as a generally applicable rate schedule, instructing the RTO to address the commission’s remaining concerns in a compliance filing.

FERC said the proposed methodology does not explain how MISO will calculate load distribution factors and does not justify how it selects load buses in identifying SSR beneficiaries.

The commission also said MISO did not provide an adequate explanation of the terms “daily load weighting factor” and “aggregate distribution factor” and failed to justify its proposal to allocate SSR costs at commercial pricing nodes based on their non-coincident monthly peak volumes.

“We find that this approach does not represent the actual conditions studied that caused the constraints, because MISO’s Attachment Y study identifies constraints during the coincident system peak volume, as this is when the SSR unit is most likely needed for reliability purposes,” the commission said.

FERC’s February order prompted rehearing requests from the Michigan Public Service Commission and other stakeholders. (See FERC Faulted, Asked to Reconsider Presque Isle SSR Ruling.)

In last week’s order, FERC dismissed the Michigan commission’s “generic criticism” that MISO’s new methodology is based only on how load contributes to thermal constraints and voltage violations in the absence of the SSR unit. The PSC said MISO failed to consider other factors that could be used to identify LSEs that require the SSR units.

“The Michigan commission has not made a showing that these two factors are insufficient to identify LSEs that benefit from the operation of the SSR units, nor has it identified other factors that MISO should have considered,” FERC said.