MISO will evaluate the merits of defining new seasonal reliability criteria and implementing a sub-annual capacity construct, stakeholders learned Wednesday.

The new evaluation stage is another, more formal step toward creating a seasonal capacity construct. The RTO has repeatedly said it is considering defining unique system reliability requirements for the footprint because of analyses that signal an emerging wintertime loss-of-load risk.

The move could have MISO issuing sub-annual reserve margins based on seasons, beyond NERC’s annual reliability standards. The RTO plans to publish a white paper on reliability needs in the third quarter.

Brattle Group Principal Sam Newell told stakeholders that supply shortage risks are shifting from the summer peak.

“As MISO looks to a future with more wind and solar and less coal and seasonal mothballing, the risks will continue to shift,” Newell said during a Resource Adequacy Subcommittee conference call Wednesday.

Some stakeholders have said seasonal reliability criteria could infringe on states’ jurisdiction over resource adequacy and told MISO the existing annual local clearing requirements and planning reserve margins it provides are sufficient. (See Stakeholders Split on Potential MISO RA Requirements.)

But on Tuesday, 11 utilities and power organizations urged MISO in a letter to move ahead with a sub-annual capacity construct. The group — including Xcel Energy, Ameren, DTE Energy, Consumers Energy and WEC Energy Group — said the RTO should pursue a segmented capacity auction and capacity resource accreditation changes based on seasons or months.

“The reliability risks facing the MISO footprint have been plainly identified, appropriately articulated to stakeholders and demonstrated by the significant number of emergency actions taken by MISO operators since June 1, 2016,” the group wrote. “The transition to a sub-annual capacity construct would provide MISO and stakeholders with the ability to procure more tailored capacity commitments to address non-summer capacity risk.”

MISO also added another maximum generation emergency event to its tally Tuesday for its Northern and Central regions, as much of MISO Midwest was gripped by a persistent heat wave.

This year’s resource adequacy survey conducted by MISO and the Organization of MISO States indicated that the RTO could face a 400-MW capacity shortfall as early as 2022, and the next five years could contain surpluses as high as 12.5 GW or deficits as steep as 6.8 GW. (See OMS-MISO Survey Sees Uncertain Supply Future.)

MISO Executive Vice President of Market and Grid Strategy Richard Doying said change in some form is inevitable for the Planning Resource Auction. He said the capacity auction needs to send signals to buy or build generation when appropriate.

“I don’t believe we can say, ‘Most load is covered, so we’re good,’” Doying said. “It’s a varied landscape that we need to navigate here.”