ISO-NE outlined its methodology for analyzing potential effects of its capacity auction reform (CAR) project at the NEPOOL Markets Committee meeting Jan. 14, detailing resource mix and load inputs for the near- and longer-term base cases and potential factors to be considered in sensitivity analyses.
The RTO plans to present the initial results of the impact analysis starting in March and will work with stakeholders to develop sensitivities building on the two base cases.
“This analysis will provide stakeholders with a better understanding of how CAR may impact how much capacity they can sell, and wholesale market revenues and costs under specific scenarios, as well as other key parameters,” said Chris Geissler, director of economic analysis at ISO-NE.
The near-term base case “seeks to use assumptions that are broadly in line with expected system conditions for CCP [capacity commitment period] 19,” said Fei Zeng, manager of planning services at ISO-NE.
CCP 19 will procure capacity for the 2028/29 commitment period; ISO-NE aims to implement both phases of the CAR project for this period. The first phase of CAR, filed with FERC at the end of 2025, centers around implementing a prompt capacity auction and resource deactivation reforms. The second phase centers around resource capacity accreditation and the development of seasonal capacity commitment periods. (See NEPOOL Supports First Phase of ISO-NE Capacity Market Reform.)
The RTO plans to rely on resource mix modeling assumptions from the most recent annual reconfiguration auction, adjusting the mix based on planned deactivations, under-development resources that have withdrawn from critical path schedule monitoring and resources that qualified in the 2025 interim qualification process. The resource mix assumptions result in about 37,500 MW of non-intermittent qualified capacity and about 2,000 MW of intermittent qualified capacity.
To estimate demand, ISO-NE will use the 2028/29 load forecast from its 2025 capacity, energy, loads and transmission (CELT) report.
For the longer-term modeling base case, ISO-NE plans to use the 2025 CELT demand forecast for 2035. The RTO plans to approximate the resource mix for 2035 by adding 2,000 MW of offshore wind, 200 MW of utility solar and 200 MW of two-hour batteries. These resource additions “may be aligned with a conservative approximation on progress toward the states’ public policy by this time frame” and are meant to serve as a “starting point to build from,” Geissler said.
Some stakeholders expressed concern that the longer-term base case includes too little storage at too short of a duration. In response, ISO-NE emphasized that conservative assumptions should help provide a good point of comparison for subsequent sensitivity analyses evaluating increased levels of storage and renewable penetration.
For both base cases, the impact analysis will provide information on estimated effects on the net installed capacity requirement, marginal reliability impact demand curves, and seasonal relative MRI values and MRI capacity by resource type, he said.
ISO-NE previously presented initial impact analysis results associated with its resource capacity accreditation project, which the RTO incorporated into the broader CAR project in 2024. These results indicated significant capacity revenue boosts for imports, energy efficiency, non-intermittent hydropower, dual-fuel generators and nuclear plants, along with revenue declines for energy storage, oil-only resources, hybrid resources and active demand response. (See ISO-NE: RCA Changes to Increase Capacity Market Revenues by 11%.)
Building on the base case modeling, ISO-NE plans to run sensitivity analyses based on stakeholder recommendations. Potential sensitivities could alter factors related to heating and transportation electrification, behind-the-meter generation, renewable and storage development, and retirements of oil-fired generators.
Because ISO-NE’s proposed MRI accreditation approach is intended to compensate resources for their reliability contributions during the hours with greatest shortfall risk, changes to the load profile or resource mix could significantly affect resource accreditation by shifting when these hours occur.
One stakeholder expressed concern that the 2025 CELT report does not include large loads expected to come online and urged the RTO to consider running a sensitivity analysis that considers the effects of this potential demand. ISO-NE indicated this may be challenging due to the lack of “well-established evaluation frameworks.”
ISO-NE plans to give a follow-up presentation on the impact analysis in February and has requested stakeholder feedback on its proposed approach.
Gas Capacity Demand Curve
Also at the Markets Committee meeting, ISO-NE continued discussion on its proposal for a new gas capacity demand curve intended to account for generators’ limited access to pipeline gas during cold-weather periods. (See ISO-NE Talks CAR Gas Constraints, Seasonal Risk Split, Impact Analysis.)
The current rules, which do not account for the region’s gas constraint, create a “money for nothing problem” by fully accrediting gas-only resources that may not be able to run when pipeline access is limited, said Stephen Otto, manager of economic analysis at ISO-NE.
While ISO-NE initially proposed to account for gas constraints within the accreditation process, it has shifted its approach due to concerns about how gas would be allocated to different resources. Under the current accreditation proposal, the RTO would model gas-only resources without fuel limits.
“When gas availability is constrained, the inclusion of the gas capacity demand curve in the winter capacity market would affect the quantity of gas capacity procured and its settlement price in the same way that an export-constrained capacity zone demand curve affects the procurement and settlement price of export-constrained capacity zone capacity,” the RTO noted in a Jan. 7 memo.
Otto said the changes are essential for sending accurate market signals, procuring the most cost-effective mix of capacity, and preventing reliability issues associated with relying on gas capacity that is unable to perform during cold weather. The proposal likely would provide an incentive for gas resources to enter firm fuel arrangements that would exempt the resources from the gas capacity demand curve.
Intermittent Resource Accreditation
ISO-NE also discussed its proposed approach to accrediting intermittent resources. It plans to use hourly profiles for all intermittent resources; it would construct hourly wind and solar profiles based on resource characteristics and historical weather patterns; and it would construct profiles for run-of-river hydropower, landfill gas, municipal solid waste, wood and biogas generation based on historical output data.
The RTO plans to model all non-settlement-only intermittent resources on an individual basis and model settlement-only intermittent resources on an aggregated basis, “grouped by load zone and IPR type,” said Hannah Johlas of ISO-NE. This aggregation would apply only to solar and intermittent hydro resources, and the RTO would not rely on aggregates for groups made up of fewer than 10 resources, Johlas added.
ISO-NE plans to continue discussions on intermittent resource modeling and accreditation at the Markets Committee meeting in February.



