Four environmental nonprofits insist MISO’s recently approved capacity accreditation is incomplete unless the RTO details how it will conduct its loss of load modeling the new approach relies upon. 

The Sierra Club, Natural Resources Defense Council, Sustainable FERC Project and Fresh Energy on Nov. 25 sought rehearing of MISO’s accreditation, saying FERC seemed to miss a key piece of the puzzle when it authorized MISO’s new capacity accreditation method without forcing the RTO to codify and then update its loss of load expectation modeling process in its tariff (ER24-1638). 

FERC in late October approved MISO’s capacity accreditation, which blends the historical performance of individual generators with a probabilistic performance during simulated loss-of-load events. (See FERC Approves New MISO Probabilistic Capacity Accreditation.) The RTO plans to draw on its loss of load expectation (LOLE) analysis to estimate the hours across a year that the system is likely to experience a deficit or dwindling margins and compare those to when its resource classes are expected to be available.  

The four nonprofits contend that FERC failed to appreciate how significant MISO’s LOLE modeling will be to the accreditation.  

“The key inputs and assumptions that MISO uses for the LOLE model have major effects on accreditation outcomes and rates. Neither the commission nor stakeholders can determine whether the RTO’s accreditation scheme will actually produce just and reasonable rates without reviewing those significant modeling choices,” the groups argued.  

They also said the consequences of not vetting LOLE modeling stand to be “severe,” with FERC potentially “abdicating” its responsibility to ensure reasonable rates and MISO wielding “unchecked discretion to alter … key components to change rate outcomes without commission scrutiny.” 

The groups disagreed with FERC that MISO including a description of its LOLE modeling process is merely an “implementation detail.” They said the RTO’s LOLE modeling process contains “several discretionary judgments” and could alter accreditation and significantly affect rates. 

For instance, MISO’s LOLE modeling at present includes a cold weather outage adder, they said, which attempts to capture thermal resources’ outage risks in winter and could dent those resources’ accreditation values. They also said it is working on a new LOLE model for its storage resources, and staff so far in public stakeholder meetings have presented modeling approaches that produce wildly different outcomes.  

The four further argued that the inputs and assumptions to MISO’s LOLE model “are not generally understood in any contractual arrangement such that recitation would be superfluous.” They pointed to the RTO’s existing reference to its LOLE modeling in its tariff and said that “barebones” description “implies nothing about how MISO generates probability distributions for variables such as demand, generator performance, storage availability or external import availability.” They also said MISO doesn’t specify how it assesses “potential load growth or expected changes in the installed resource mix prior to a given delivery year” to influence the modeling.  

“As a direct result of its accreditation choices, MISO has ensured that LOLE modeling choices are specifiable practices that significantly affect rates. Yet MISO’s tariff implies almost nothing about what discretionary modeling methods MISO will adopt within the very complex LOLE analytical space,” the groups summed up. “To facilitate just and reasonable rates, FERC should ensure that stakeholders have full visibility into MISO’s LOLE model as soon as possible so that they can work with MISO to refine the model toward optimized predictive power.”