ISO-NE kicked off discussions on the second phase of its capacity auction reform (CAR) project at the NEPOOL Markets Committee on Sept. 10, beginning long-awaited talks on accreditation and seasonal capacity auction changes.
Changes to capacity accreditation would directly affect the capacity market revenues available to resources in the region, which makes it a particularly hot topic for New England stakeholders.
The second phase of the CAR project also includes a proposal to split ISO-NE’s annual capacity commitment period (CCP) into six-month summer and winter seasons with separately procured capacity.
ISO-NE is aiming to finalize and file the CAR seasonal and accreditation (CAR-SA) changes by the end of 2026. The RTO is nearing the end of its work on the first phase of the CAR project (CAR-PD), which is focused on transitioning from a forward to a prompt capacity auction, along with resource retirement changes. (See Stakeholders Mixed on ISO-NE Prompt Capacity Market Proposal.) Both phases of the CAR project are intended to take effect for the 2028/2029 CCP.
The RTO’s CAR effort began in 2022, but it paused the work for an extended period to expand the scope of the project to include changes to the auction format.
The proposed accreditation reforms would base each resource’s capacity value on “how an increment of capacity from the resource would reduce the total amount of expected unserved energy.”
Steven Otto, manager of economic analysis at ISO-NE, said this approach should better account for resources’ actual contributions to regional reliability, improving market efficiency and providing more accurate signals for resource entry and exit.
“The [marginal reliability impact] framework, in conjunction with the other elements of the CAR proposal, will help the capacity market meet its core objectives of reliability, sustainability and cost effectiveness by accrediting resources based on their expected performance during simulated hours where additional available capacity would mitigate or prevent load shed,” Otto said.
In the new format, each resource’s accreditation would be subject to change as the resource mix evolves, which could incentivize a more diverse resource mix. For example, as the proliferation of solar generation reduces reliability risks during early evening hours in the summer, incremental additions of solar capacity would reduce the accreditation of all solar resources.
Under the existing rules, “resources’ [qualified capacity] values are largely static, which may cause disparities between resources’ capacity market compensation and their resource adequacy contributions as system conditions evolve,” Otto said.
One key component of the accreditation reform proposal will be the calculation of the winter gas constraint, intended to reflect the region’s limited access to gas during cold periods.
Otto noted that ISO-NE plans to develop a “market-based gas constraint for the winter season,” which would be based on separate demand curve for gas resources that lack firm fuel contracts.
ISO-NE wrote in a 2024 memo that the approach “would decrease the amount of gas capacity procured in the winter… and would pay that capacity a lower price.”
Though the details of this market constraint have yet to be developed, the mechanism will likely reduce accreditation values for gas resources that do not have firm fuel arrangements, creating incentives for generators to secure their fuel supply.
Stakeholder Proposals
Also at the MC, stakeholders proposed several changes to ISO-NE’s CAR-PD proposal.
Andrew Gillespie, director of governmental and regulatory affairs at Calpine, made the case for ISO-NE to change its formula for calculating the capacity offer price threshold (COPT) in the capacity market. Market participants that bid above this threshold are subject to market power review by the Internal Market Monitor and must submit a detailed cost workbook.
For the 2028/2029 CCP, ISO-NE plans to base the threshold on the average of the clearing price from previous Forward Capacity Auction (FCA) and a clearing price forecast for the upcoming auction.
Gillespie argued that relying on the clearing price from previous capacity auction, which would have been held about four years earlier, inadequately accounts for the recent spike in capacity scarcity hours.
Elaborating on a proposal outlined at the MC in August, he said the RTO should instead rely on the opportunity costs, as defined by a formula multiplying the balancing ratio by the performance payment rate by the expected number of capacity scarcity hours. (See “Seller-side Market Power,” NEPOOL Nears Vote on 1st Phase of ISO-NE Capacity Auction Reforms.)
Relying on this formula would significantly increase the threshold price, Gillespie said. He estimated that the threshold price for the past three auctions would have been more than double the auction clearing price for the past three FCAs.
He said recent FCAs have underestimated the number of scarcity hours and added that, “without modification to the threshold price, suppliers that submit an offer based on ‘opportunity costs’ may be mitigated by IMM.”
Ben Griffiths, vice president of wholesale market policy for LS Power, offered an alternative proposal for the threshold, proposing to rely on the most recent annual reconfiguration auction clearing price instead of the most recent FCA clearing price.
He said this proposal should be applied solely to the 2028/2029 CCP and would serve as a “one-time, targeted fix that it preserves the broader tariff framework and leaves the general COPT formula unchanged for future auctions.”
Griffiths added that the annual reconfiguration auction clearing price would be a “reasonable substitute” for the FCA clearing price, since annual reconfiguration auctions “are deliberately designed to mirror the FCA in many of their mechanics.”
Also at the meeting, FirstLight Power’s Tom Kaslow proposed tariff changes to impose Pay-for-Performance charges on exports during capacity scarcity events. ISO-NE also advocated for this change in its annual report, published earlier in 2025. (See ISO-NE Monitor Discusses Market Trends, Energy Transition.)
In response to the proposal, some stakeholders have advocated for explicit language exempting capacity-backed exports from performance charges.


