MISO has expanded its availability-based capacity accreditation proposal for generation resources by including hours that aren’t so risky.

The grid operator originally proposed that a resource’s accreditation would hinge solely on availability during “resource adequacy hours,” or the year’s top 5% of hours that MISO believes contain reliability risks. The plan will now include unremarkable hours in addition to RA hours, leading to more lenient accreditations.

MISO will use a resource’s availability “across all hours with a two-tiered weighting structure between tight condition hours and non-tight hours.” Risky hours will carry more weight than other hours. The grid operator will use the top 3% of tight hours and retain a rolling three-year period to define a resource’s availability for accreditation.

“Resources that tend to offer their full availability and don’t miss tight hours receive full credit,” staff said.

During a special May 21 teleconference, Scott Wright, the RTO’s executive director of market strategy and design, said staff will soon prepare numbers for the weighting.

The decision comes a month after MISO said it would wait until September to file with MISO Places 4-month Hold on Seasonal Auction, Stricter Accreditation.)

Stakeholders denounced the RTO’s first resource adequacy hours selection as too random to be helpful. Some have said it’s too difficult to pin down when maximum generation events are likely to occur. Other stakeholders have said MISO has not provided enough data-driven results to justify a new accreditation process.

“This should reduce year-over-year volatility in accreditation values, and allow for better planning,” Kevin Vannoy, director of market design said of MISO’s revisions.

He said staff would “continue to monitor this as the resource mix evolves.”

Vannoy also said the accreditation will necessitate improvements in managing outages. “MISO’s going to have to enhance our tools and processes for outage coordination,” he said.

24-Hour Exemption

An accreditation exemption provision has drawn the most attention from MISO stakeholders and its Independent Market Monitor.

The grid operator is providing a 24-hour exemption for offline resources during tight condition hours. If the offline resources rumble to life in a 24-hour window of the identified tight conditions, the inaction won’t count against a resource’s capacity accreditation.

IMM staffer Michael Chiasson said the 24-hour lead time seems too long. He said the grace period makes some resources “totally unavailable” for a perilous morning or midday peak.

The IMM’s David Patton said many emergencies occur with as little as 15 minutes’ advance notice.

“You’re proposing something here that doesn’t seem to differentiate” flexible resources from inflexible resources, he said. “At the end of the day, the resources that help you make it through these emergencies are the flexible ones.”

Patton said that while he recognized MISO was “trying to make stakeholders happy,” it probably wasn’t doing what is best for reliability.

“You need to prioritize where your principles are over just minimizing stakeholder concerns,” he told MISO staff.

Customized Energy Solutions’ Ted Kuhn argued that many emergency weather conditions are foreseen and take place over multiple days.

“The winter event and summer heat waves last for days,” he said. “Planning for only a two-hour event seems ill-advised.”

MISO Executive Director of Market Operations Shawn McFarlane said the grid operator first needs to address the generation fleet’s growing unplanned and forced outages.

“When we’ve needed generation and resources the most, they haven’t been there as much as we’re forecasting,” he said.

McFarlane acknowledged that MISO may need to eventually drop the 24-hour grace period.

Kuhn said using MISO’s exemption, some generators could be spared from any performance measurement during resource-adequacy (RA) hours in their accreditation.

MISO market design adviser Dustin Grethen said “it is a risk” that generators could be exempted for all RA hours. “We’d probably need some protection in place there.”

Grethen asked stakeholders for ideas on how MISO might allocate a limited number of RA hours exemptions.

Clean Grid Alliance’s Natalie McIntire said she was unsure how the new accreditation will help on an “unexpectedly warm day … that we don’t see weeks in advance.”

“It’s a hot topic,” Vannoy agreed, saying that outage planning will continue to evolve as more is learned about climate change and extreme weather.

Still 4 Seasons

MISO is still planning for four separate seasonal-capacity auctions. The proposal is premised on a four-month summer season, a two-month fall, and three months apiece for spring and winter. Staff said warmer Septembers are better categorized among summer load shapes.

The grid operator plans to use its current annual loss-of-load expectation analysis to set seasonal reserve requirements. Reliability targets will be rounded up to a minimum one-day-in ten-years standard, even if minimal or no risk is identified during shoulder seasons.

MISO will also conduct four separate analyses so transfer limits between its resource-adequacy zones vary with the seasons.

Patton said he doesn’t agree with the proposed four-season accreditation. He said MISO should instead focus on separate winter and summer accreditations.

“I don’t think you’re going to have a lot of tight hours in spring and fall,” he said.

Grethen said a seasonal division will account for special attributes, such as winter weatherization, and remove a year-round higher must-offer requirement to allow some units to take seasonal outages.