The seasonal accreditation of MISO capacity resources continues to be a point of contention among the RTO, its Market Monitor and the stakeholder community.

MISO restored some of the bite to its accreditation proposal when it announced Wednesday that the riskiest 3% of hours will be assigned an 80% weight in accreditation, while the non-risky hours will have the remaining 20% weight. MISO’s Independent Market Monitor recently warned board members that MISO’s leniency in the accreditation proposal would do nothing to strengthen resource availability.

MISO last month softened its accreditation proposal to include availability during non-risky hours in addition to the tightest 3% of hours in a year as the basis for accreditation. (See MISO Softens Capacity Accreditation Proposal.) The RTO wants to file in September to introduce a seasonal capacity accreditation based on generators’ availability over the last three years. The seasonal accreditation will be used in a four-season capacity auction and corresponding reserve margin targets. The RTO plans to begin holding four independent seasonal auctions by the 2023/24 planning year.

“We’re very motivated for a September filing,” Executive Director of Market Strategy and Design Scott Wright told stakeholders during a Resource Adequacy Subcommittee teleconference on July 7. However, MISO agreed to a stakeholder request to collect a round of stakeholder feedback on the 80/20 weighting.

MISO selected the riskiest 3% of hours for the Midwest and South regions separately. Included were hours that contained maximum generation events and warnings and other hours across seasons with tight operating conditions. The RTO excluded all hours that contained a more than 25% supply margin. The 25% threshold means some seasonal accreditation will be based on fewer than the 65 hours that make up 3% of a season.

“Stakeholders need to be personalizing the impact on their portfolios as a result of the changes,” Wright said.

Monitor has Harsh Words

During a July 8 Market Subcommittee meeting, Monitor chief David Patton said he will likely register a protest with FERC over MISO’s accreditation filing, which he said would award a bloated capacity credit to inflexible and slow-moving resources.

“It’s important to provide adequate credit to resources that can respond with short lead times or are always on,” he said. “It’s one of the reasons we’re unhappy with MISO’s filing.”

Patton said generators with up to two-hour lead times are “probably close enough” to the response time of an online unit. He also proposed a sliding scale for the capacity credits of units with lead times up to 12 hours.

The Monitor said MISO’s current proposal is risking creating a system that doesn’t reward the most efficient contributors to reliability.

“It’s such an important proposal that we ought to be doing the right thing, not the popular things,” he said. “I’m concerned that stakeholders are worried that this accreditation proposal is going to harm them. … If you own gas resources or pumped storage or anything that’s flexible, you should really be advocating for a more principled accreditation.”

Patton added that MISO’s proposed suite of resource adequacy solutions is “a poor way to deal with the fact” that MISO’s Planning Resource Auction provides paltry compensation for capacity. He repeated his longstanding recommendation that the RTO use a sloped demand curve instead of a vertical demand curve in the PRA.

MISO Analysis Shows Less Capacity, Lower Requirements

The grid operator said an analysis of the new accreditation method showed a system-wide reduction in accredited capacity, which is offset by lower seasonal reserve margin requirements. It said nearly all local resource zones should have adequate capacity to cover seasonal clearing requirements. Senior Manager of Resource Adequacy Coordination Lynn Hecker said the only exception is wintertime in Mississippi’s Zone 10, which stands to face a smaller seasonal capacity supply and lower capacity import limits. MISO said Zone 10 could find itself about 700 MW short of its winter requirement.

Mississippi Public Service Commission counsel David Carr called for a special meeting between MISO and the PSC to discuss the RTO’s transfer limit analysis using the seasonal values and the potential shortfall it found. Hecker said MISO could schedule such a meeting.

He said the RTO found that thermal capacity resources will see the biggest changes in wintertime under the seasonally adjusted accreditation. It also found that about 35% of thermal capacity units in the winter experience an increase in accreditation, while 65% have their accreditation decreased.

MISO is still deciding whether it will still use its effective load carrying capability (ELCC) values for intermittent generation in a seasonal capacity paradigm. Wright said ELCC already gets at some of what the grid operator is trying to accomplish for thermal generation in its seasonal capacity filing.

The RTO also took stakeholders by surprise by including September back in its fall definition, rather than summer. Stakeholders have said warmer Septembers coupled with fall maintenance outages are a breeding ground for maximum generation emergencies.

Hecker said MISO may reevaluate the merits of a September in the summertime categorization.

Stakeholders also asked how the RTO will split up calls for load-modifying resources by season. Beginning in the 2022/23 planning year, demand response resources receive a 100% credit if they can be available within six hours or less to 10 calls or more in a planning year, while resources that can respond to five to nine calls receive an 80% accreditation. Until then, LMRs must respond the requisite five times per year.

Hecker said MISO is considering dividing a minimum of “10 or so” calls for LMRs by season.