As ISO-NE undertakes major capacity market accreditation reforms, New England storage developers are voicing concerns that potential flaws in the RTO’s modeling methodology could discourage new investments in storage resources. 

The resource capacity accreditation (RCA) project has been in motion for more than two years, and the development process could continue into 2027 following the RTO’s three-year delay of its 19th capacity auction, which applies to the 2028/29 capacity commitment period. (See NEPOOL Markets Committee Restarts Work on Capacity Market Changes.) 

The RCA project is intended to better align the capacity procurements with real-world reliability benefits, mirroring similar reform efforts in MISO, NYISO and PJM.  

Prior to FERC’s approval of the full three-year delay — which will give ISO-NE time to reform the timing of the capacity auction process along with accreditation — the RTO published RCA impact analysis results that painted a dire picture for storage resources. (See FERC Approves Additional Delay of ISO-NE FCA 19.) 

While the analysis indicated that the accreditation changes would increase the overall pool of capacity revenue by 11%, it showed a 37% revenue reduction for storage resources, equivalent to about $58 million. (See ISO-NE: RCA Changes to Increase Capacity Market Revenues by 11%.) 

While these results are subject to change as ISO-NE refines the methodology and accounts for the transition from a forward annual capacity market to a prompt-seasonal capacity market, the analysis served as a wakeup call for many of storage companies participating in the capacity market. (See ISO-NE Moving Forward with Prompt, Seasonal Capacity Market Design.) 

The concerns about storage accreditation derating come as several New England states are looking to rapidly ramp up the deployment of storage resources; Connecticut, Massachusetts, Maine and Rhode Island all have storage targets in the hundreds of megawatts. 

State programs also are a key revenue component for storage developers, as the current levels of revenue from ISO-NE wholesale markets alone are not enough to support the resources, said Alex Chaplin of New Leaf Energy, adding that “storage provides significant reliability benefits to New England which need to be adequately measured and compensated for in the ISO-NE markets.” 

Chaplin noted that most storage in the region is concentrated in Connecticut and Massachusetts due to their state incentives for storage. Massachusetts’ clean peak energy standard, which is aimed at cutting emissions and air pollution from fossil peaker plants, is a key revenue source for storage resources in the state. (See Panel Provides Update on Energy Storage in Mass.) Decreasing capacity revenue could lead to more pressure on states to support the resources to hit their storage deployment goals and cut emissions. 

“Capacity market revenues are typically an irreplaceable and indispensable source of revenue for the financeability and viability of resources, and storage is no exception,” said Alex Lawton of Advanced Energy United. He added that the energy market and ancillary services market do not provide “the scale or certainty needed for investors to back storage projects.” 

The crux of the issue, Lawton said, appears to stem from how ISO-NE is artificially scaling up load in its model to evaluate the reliability benefits of different resource types, which ultimately will determine how much capacity each resource can sell into the market. This modeling shows capacity scarcity events that significantly exceed the duration of events historically experienced in the region.  

While the longest capacity scarcity condition New England has experienced since the implementation of pay-for-performance rules in 2018 lasted two hours and 40 minutes, the RCA project is modeling events that typically exceed four hours, and — according to a March presentation — 36% of modeled shortfall events lasted more than eight hours.  

“As soon as you exceed four hours in duration — because most storage is between two and four hours — the marginal reliability impact (MRI) of storage just tanks,” Lawton said. 

There is broad consensus that the region’s power grid will face longer-duration periods of shortfall risk in the future as it trends toward a winter peaking system, but there is uncertainty around when these longer-duration risks will show up, and how they should be weighed against higher-likelihood, shorter-duration events.  

Over the long term, ISO-NE has stressed the need for dispatchable resources that can balance intermittent generation over extended periods of time. (See ISO-NE Outlines Economic Challenges of Decarbonization.) 

Frank Swigonski of Jupiter Power said the weighting of extreme winter storms in the methodology compared to more frequent, shorter-duration events “is an open question … that stakeholders should explicitly discuss in this process.” 

Swigonski noted the stakeholder engagement process for PJM’s accreditation reforms did not spend significant time discussing this question, which led to rehearing requests with FERC. 

“It ultimately had a massive impact on the final accreditation numbers,” Swigonski said. “We’re hoping that we don’t have the same experience in New England.” 

Swigonski also disagreed with the notion that shorter-duration storage resources are unable to provide significant resource adequacy benefits during longer-duration events. Storage resources likely still will be able to recharge off-peak during extended events, and operators eventually will gain experience with dispatching storage to avoid depleting all available storage in the first hours of an event, he said. 

Responding to questions about the RCA methodology, ISO-NE spokesperson Mary Cate Colapietro emphasized that the methodology is still a work in progress and that stakeholder engagement is ongoing. ISO-NE recently solicited comments on the scope of its Capacity Auction Reform (CAR) project, which included requests from storage companies for ISO-NE to evaluate the underlying modeling methodology. 

“Establishing a durable capacity market that provides the necessary reliability services as the power system evolves is a vital component of New England’s clean energy transition,” Colapietro said. “While we plan to continue pursuing an accreditation design based on capacity’s marginal reliability impact, the additional time afforded by the delay gives us time to work with stakeholders on possible improvements to that design.” 

Bruce Anderson of the New England Power Generators Association declined to comment on the treatment of specific resource types but stressed the need for ISO-NE to prioritize implementing a “sound market design” that provides efficient signals for resources to enter and exit the market.