NYISO has proposed to stop using “winter to summer” and “summer to winter” ratios to determine maximum clearing and reference point prices in its seasonal demand curves.
Their use is no longer necessary for the demand curves because NYISO is developing distinct seasonal minimum installed capacity requirements, ISO staff says.
“If NYISO were to move to the seasonal requirement structure without removing these availability adjustments, the seasonal [installed capacity] ICAP demand curves would be adjusted for seasonal differences twice,” Alexis Drake, a NYISO senior market design specialist, said during an Aug. 19 meeting of the ISO’s ICAP Working Group.
The two ratios are adjustments to seasonal capacity availability the ISO uses to account for seasonal differences in ICAP availability on the spot market.
During the last demand curve reset, the ISO looked into using seasonal ICAP demand curves to reflect differences in winter/summer reliability risk. During the current capability year (2025/26), NYISO used the ratios to calculate separate demand curves for each season.
Drake said that method more accurately reflects future New York grid needs in upcoming spot market auctions.
What Happened to Seasonal CAFs?
In a previous meeting, the ISO unexpectedly dropped seasonal capacity accreditation factors (CAFs) from its winter reliability enhancements project. (See NYISO Drops Seasonal CAFs from Winter Reliability Project.) Stakeholders had asked the ISO to walk through its internal analysis and discussions of seasonal CAFs.
“This presentation is about correcting that oversight,” said Mike Swider, NYISO capacity and new resource integration market designer.
CAFs represent the marginal reliability contribution of resources in the ICAP market counted toward New York State Reliability Council resource adequacy requirements. None of the calculations on the ISO or NYSRC end incorporate seasonality. The Installed Reserve Margin and the Locational Minimum Installed Capacity Requirement cases represent reliability risk annually across both seasons. Annual CAFs are calculated using the final, annual LCR case.
Swider said there is no “stable criteria” to calculate marginal reliability values for each season. Using the installed reserve margin as the ultimate basis for modeling seasonal reliability risks creating situations where certain resource classes have no, or almost no, CAF value.
“If there is only summer risk, some resources, even the perfect resources conceptually, receive zero CAF value in the winter,” Swider said. “We have concern about large resources entering and exiting and changing the seasonal risk from year to year and the volatility that’s entailed.”
A resource that isn’t compensated for its capacity contribution might pull out of the market, introducing reliability risks even in months — such as November — where those risks aren’t ordinarily forecasted.
Swider said the ISO also looked into using weighted CAFs using seasonal CAF values and attribute payments to potentially mitigate these issues. He said there was “no basis” for setting weights and no “clear cost basis” for attribute payments as a service.
In response to a stakeholder question about whether NYISO had examined what other RTOs do with respect to seasonal values, Swider said the ISO had looked at MISO and SPP’s processes.
“[MISO] had to do some interesting gymnastics to calculate seasonal CAFs,” Swider said. “In the end it wasn’t useful for us.”
Swider said another issue is that, unlike other RTOs, NYISO does not select its own reliability criteria, a task that falls to the NYSRC. Even if the ISO was able to pick its own reliability criteria, its winter risk modeling wouldn’t need to adopt MISO’s modeling techniques, he said, because MISO is modeling a lot of terrestrial wind, for example — a resource not prevalent in New York.
The ISO also went over tariff and manual revisions, respectively, for the Firm Fuel project and for Certain New Resource Entry, the latter intended to handle the Champlain Hudson Power Express.
