CARMEL, Ind. — MISO said it will push back a contentious filing for a new, marginal approach to capacity accreditation into early next year.

MISO originally was trying to file for FERC permission for the new accreditation by year’s end. But persistent stakeholder opposition means the RTO will wait and hold more public discussions to sell stakeholders on its proposal.

MISO maintains a direct loss-of-load-style accreditation will directly link generators’ accreditation to their contribution during risky periods.

The direct loss of load approach is set to replace MISO’s current use of unforced capacity values in accreditation and will be based on a combination of individual past performance and a class average performance during risky hours for different types of generation. Most MISO resources will see their capacity values decrease under the new method. (See MISO Strengthens Resolve on Marginal Capacity Accreditation, Stakeholders Displeased.)

MISO hopes to use the new accreditation by the 2028/29 planning year.

Speaking during an Oct. 4 Resource Adequacy Subcommittee, MISO’s Davey Lopez said MISO now will use an expanded set of hours in the accreditation beyond the loss of load hours MISO’s annual study produces. The grid operator also will use all the hours when generation supply comes within 3% of load to base accreditation values on.

Lopez said that even using the expanded set of sample hours, the direct-loss-of-load-expectation accreditation will naturally produce more volatile accredited values year over year. But he also said the accreditation will solve some of the “disconnect” between capacity values and actual generator performance in the system’s riskiest periods.

Still, stakeholders continue to push MISO to use even more sample hours in the accreditation process, insisting the 3% margin expansion produces an accreditation that uses too few hours. However, Lopez said MISO will not increase the 3% reserve margin threshold further. He said including hours where MISO comes within 5% or 10% of load would defeat the purpose of what MISO’s accreditation is trying to accomplish.

“You would continue to further deviate from where the risk in the model is. You’re effectively approaching [unforced capacity] at that point,” Lopez said.

Stakeholders continue to call MISO’s class average accreditation values mysterious and said understanding how MISO arrived at them is difficult.

“I don’t know how any members will meet their fiduciary responsibility ensuring their customers and their shareholders that they’re going to get the value they need,” Customized Energy Solutions’ David Sapper said.

MidAmerican Energy’s Dehn Stevens requested MISO delay its planned implementation beyond 2028. He predicted the “shock of resource planners not being able to get new resources online” would offset accreditation losses and pointed out that regulatory approvals for new generation are lengthy.

MISO Independent Market Monitor David Patton recently said a marginal accreditation style is necessary to reflect the diminishing reliability value of intermittent renewables as more are added to the system. He said MISO could have as much as 30 GW of solar power in its fleet by 2030.

“I recognize that marginal accreditation is extremely unpopular, particularly with the environmental community because it results in lower accreditation for most intermittent renewables. But it also would result in lower accreditation for other types of units,” Patton explained at a Gulf Coast Power Association Virtual Forum on Sept 15.

Notably, MISO’s gas unit class average accreditation drops from the current 84% accreditation in winter to 70% and from 88% in spring to 72% under the new accreditation. Coal unit class average accreditation also drops similarly in winter and spring.

Patton said as MISO’s reliability risk shifts to wintertime in the coming years, MISO could dole out smaller capacity values to gas units in winter to reflect gas pipeline issues and the reliability issues that play out when gas-only units have difficulties securing nonfirm gas.

He said the new accreditation will be applied to all resources in a “non-discriminatory fashion.”