Stakeholders continue to ask MISO to crunch hypothetical auction clearing prices absent the RTO’s new sloped demand curve that sent prices past $660/MW-day for summer.
During a May 21 Resource Adequacy Subcommittee meeting, multiple stakeholders asked MISO staff to publish 2025/26 hypothetical auction clearing prices through a simulation with the old, vertical curve. The exchange led Independent Market Monitor David Patton to chime in to defend MISO’s installment of a sloped demand curve.
The 2025/26 planning year auction marked the first time MISO used a sloped demand curve, meant to procure more capacity than strictly necessary to meet MISO’s one-day-in-10-years reliability standard. MISO ultimately cleared 137.5 GW, more than the 135.3 GW it designated prior to the auction to meet its one-day-in-10-years reliability standard, at a cost of $666.50/MW-day for the upcoming summer. (See MISO Summer Capacity Prices Shoot to $666.50 in 2025/26 Auction.)
“Given that we just switched from a vertical demand curve to a sloped demand curve,” it’s appropriate for MISO to show what the clearing would have been with a vertical curve, WEC Energy Group’s Chris Plante said during the meeting.
WPPI Energy’s Steve Leovy said he failed to see how MISO could claim that its sloped demand curve “enabled MISO to secure more capacity at a significantly lower price,” as the RTO claimed in its presentation. He asked which alternate reality MISO used as a comparison.
MISO Resource Adequacy Manager Andy Taylor said MISO’s comparison “is not a counterfactual to” the old, vertical demand curve, but a counterfactual to other sloped demand curve designs.
MISO develops its sloped curves by assessing the value of additional capacity beyond the one-day-in-10-years standard relative to its price. If the cost isn’t too steep, MISO shapes the slopes with the OK to clear extra megawatts.
MISO said had the auction cleared only to its initial planning reserve margin requirement of 135.2 GW, prices would have been $846/MW-day based on the sloped curve it ultimately used.
Plante said MISO’s comparison is “very confusing to a casual observer.”
Clean Grid Alliance’s David Sapper said he didn’t believe MISO’s auction clearing process as described in its business practice manual makes sense. He asked MISO to redraft a process that could be more readily understood.
Sapper said he also was “dismayed” that FERC Chair Mark Christie, whom he said is consequential in RTOs’ capacity auction changes and “a scholar and a gentleman,” didn’t seem to understand auction clearing processes.
“He seems to have thrown up his hands that they’re impenetrable,” Sapper said.
Minnesota Power’s Tom Butz said prices this year “rocketed up to CONE-like values” and it seems they will be there for the foreseeable future.
But IMM David Patton said, “for the first time,” auction clearing prices in MISO reflected the marginal value of capacity. Patton said the auction clearing an additional 2% in capacity is a good thing despite what stakeholders might think.
“I know this is a shock with prices being high, but we do find that this is going to set up for a much more reliable system,” he said. Patton said prices should compel utilities and regulators to make more informed decisions in integrated resource plans and selecting resource retirement dates.
Patton estimated summer prices would have been about $20/MW-day under the old, vertical curve. But he cautioned that hypothetical, low prices aren’t as attractive as they appear.
“What you should take away from that is: Our previous market was flawed and wouldn’t have produced prices in line with reliability,” Patton said.
Had inexpensive capacity prices held court for another planning year, Patton said it wouldn’t meet any “fundamental objectives of the capacity market to set prices this way.”
During the April 29 auction results call, Taylor said had MISO used its vertical curve, the auction would have produced “extreme, very low or very high” pricing outcomes as it has in years past.
At the time, Clean Grid Alliance’s David Sapper asked if MISO would commit to re-running the auction if it’s discovered the RTO drew on incorrect inputs in its sloped curve. MISO counsel Michael Kessler said it would be “highly unusual” for FERC to order any capacity auction to be rerun.
The 2025 auction results are poles apart from auction results a decade ago, when Southern Illinois’ Zone 4 clearing price of $150/MW-day sparked concerns that pivotal supplier Dynegy manipulated capacity availability to raise prices. (See FERC Sets Dynegy’s MISO Market Manipulation Case for Hearing.)
MISO to Allow Resources with Provisional Agreements to Provide Capacity
At the same resource adequacy meeting, MISO said it will take steps to allow resources with provisional generator interconnection agreements (GIAs) to offer capacity in MISO’s seasonal capacity auctions if they can deliver.
MISO’s tariff expressly prohibits resources with provisional GIAs from participating in capacity auctions. MISO announced it will pursue a turnaround on its longstanding policy and open the auction to the resources with the provisional agreements starting with the 2026 seasonal capacity auction.
“We would like these resources to participate in the planning resource auction as well, provided they’ve procured deliverability,” Taylor said.
Taylor said the “current length and state” of MISO’s interconnection queue might have influenced MISO’s rethinking of the nearly complete resources’ ability to furnish capacity.
