CARMEL, Ind. — Stakeholders remain frustrated with MISO’s plan to enact a marginal capacity accreditation as staff insist the approach will measure the true value of capacity.

MISO is dedicated to a new accreditation plan directly based on a combination of individual past performance and a class average performance during risky hours for different types of generation. The grid operator hopes to file the plan with FERC in November. (See MISO Intent on Marginal Accreditation and Requirements Based on Risky Hours.)

At an Aug. 23 Resource Adequacy Subcommittee meeting, MISO adviser Davey Lopez said the RTO is working to pin down more risky hours to base capacity credits on. MISO may consider adding more hours throughout the year when margins dipped to around 3% or lower, he said.

The accreditation will apply to most MISO classes of resources, including gas, coal, hydro, nuclear, storage, wind and solar. MISO’s load-modifying resources still need an accreditation plan. MISO said it also intends eventually to determine LMRs’ accreditation based on their availability during the times of highest need on the system. It said it will make a separate LMR filing next year.

Most resource accreditations will take a hit using the direct loss of load approach versus MISO’s existing accreditation calculation based on unforced capacity and availability during risky hours.

Under MISO’s new accreditation method, the class average for gas-fired resources will range from 89% to 70% based on the time of year, coal will be anywhere from 91% to 72%, hydro will receive 99% to 69%, nuclear 91% to 80%, pumped storage 98% to 57%, solar 37% to 1%, wind 18% to 12%, energy storage 95% to 94% and run-of-river resources 100%.

Lopez said MISO will prepare other loss of load modeling sensitivities that consider higher solar penetration on the system.

But Minnesota Power’s Tom Butz called for more “fully developed” future fleet mix assumptions in MISO’s loss of load modeling before MISO pursues the new accreditation.

“To say you’re not going to do that before the filing, I don’t feel that’s responsible,” he said. “That’s a shortfall of the modeling.”

Lopez said MISO plans include more factors in its future loss of load modeling. But he said MISO will not use its second planning future — the same one MISO’s long-range transmission planning currently relies on — in loss of load modeling.

“To match Future 2, that would take a significant amount of time and resources, and we have already begun analysis,” he said.

Other stakeholders asked for MISO to hold off on making a FERC filing until it can conduct more comprehensive modeling that includes future system changes.

Executive Director of Market and Grid Strategy Zak Joundi committed to sharing future projections of accreditations with stakeholders before filing for FERC approval.

Lopez said MISO already has conducted extensive modeling analysis, involving hundreds of millions of rows of data. He promised to share more findings in October.

Constellation Energy’s John Orr said MISO’s analysis seemed too “assumption-driven,” and asked for more details behind MISO’s performance assumptions by resource class.

“We’re struggling with, ‘how can this be real?’ We’re trying to understand these dramatic changes,” Orr said.

Orr said it doesn’t seem fair that other generators’ outage scheduling practices will affect the accreditation of other, similar resources.

Other stakeholders warned that MISO won’t be able to satisfactorily defend its proposal in front of FERC because resources won’t be given a fair crack at accreditation.

MidAmerican Energy’s Dehn Stevens said the direct loss of load approach is “extraordinarily complex” and makes it impossible for load-serving entities to anticipate capacity credits and plan resource additions.

“We’re really struggling with how we’re going to translate this,” Stevens said.

WEC Energy Group’s Chris Plante suggested MISO split its resource classes by age of plants so newer units aren’t grouped with outage-prone, older units.

“Maybe we shouldn’t be lumping those all in the same class,” he said.

Lopez said accreditation boils down to a simple reflection of contribution during loss of load hours in modeling. He said an accreditation based on loss of load is in the same currency as MISO’s reserve margin requirements. He said the new accreditation will resolve an existing “disconnect” in MISO’s resource adequacy construct.

“If resources perform better during those risky hours, they’re going to get a bigger slice of the credit,” Lopez said.

Xcel Energy’s Kari Hassler said stakeholders need to better understand how MISO arrived at its class average percentages.

“MISO is asking us to dive in, but that’s difficult when we don’t understand,” Hassler said. She also said MISO should refrain from making changes to its loss of load modeling during its proposed three-year transition to the new accreditation. Others agreed MISO already should have a new loss of load modeling that’s more reflective of actual operations in place before it switches to the new accreditation style.

Lopez said MISO plans a September workshop to explain its loss of load modeling under the new accreditation.

Wisconsin Public Service Commissioner Tyler Huebner said he was frustrated that MISO’s modeling is so poorly understood among stakeholders that NextEra Energy and Invenergy enlisted Astrapé consulting to try to make sense of it.

With the help of Astrapé, NextEra and Invenergy concluded MISO should expand the window of risky hours it will use in the accreditation beyond the loss of load hours MISO’s annual study produces. They said, “expanding the definition of loss of load to include more critical reliability hours per season provides a more consistent signal to resources.”

Chris Miller, FERC liaison to MISO, said FERC already is examining publicly available information on MISO’s possible new accreditation method, even though it hasn’t been filed.

MISO to Change LSEs’ Reserve Responsibility in Accreditation Filing

MISO’s new accreditation proposal now contains changes to how it allocates what share of the planning reserve margin requirements load-serving entities will be responsible for. The amendment represented a change from last month’s version of the proposal.

MISO said it now will dole out a share of the PRMR to LSEs based on their local resource zones’ load during loss of load events. The move is another step away from MISO’s once-pervasive use of unforced capacity values.

MISO said it needs the change because loss of load risk occurs in extreme conditions, or during 90/10 load probability events; however, it said LSEs’ obligations are based on the expected 50/50 load probability.

Lopez said MISO’s proposal “seeks to allocate the planning reserve margin requirement to load-serving entities more commensurate to their contribution to reliability risk.”

The announcement seemed to be an unwelcome addition and visibly took stakeholders by surprise, though staff said they’d been signaling since last month they would adjust LSEs’ reserve obligations with the new accreditation style.

“It’s really scary not to have a feel for what we’re going to be responsible for,” Orr said. He argued that although MISO plans to fully implement the accreditation by 2028, that’s “already here” for some market participants. Orr pointed out that states like Michigan require resource planning four years in advance.

MISO will spend more time discussing accreditation at the next Resource Adequacy Subcommittee meeting Oct. 3-4.