To: Al McBride, Vice President, System Planning
From: NESCOE (Contact: Sheila Keane)
Date: September 8, 2026
Subject: Transitional Cluster Study and Forward-Looking Enhancements
The efficient and timely interconnection of new resources is crucial to ensure electric reliability and affordability for New England households and businesses. The purpose of ISO New England’s (ISO-NE) recent Order 2023 compliance changes is to improve the interconnection process and thereby reduce uncertainty around the timing and cost of interconnecting to the transmission system. These improvements represent a foundational shift in how resources are studied and interconnected to the transmission system—the region has moved from a “first-come, first-served” serial process to a “first-ready, first-served” cluster process, with energy and capacity interconnection service studied together in a single study.
The Transitional Cluster Study (TCS), finalized by ISO-NE on August 6, 2026, represents the first study completed under this new paradigm.[1] While the TCS is unique—intended to serve as a bridge to the new cluster study process—it offers early insight into the benefits and challenges of the new interconnection paradigm.
The TCS has made clear that ISO-NE can accelerate interconnection timelines compared to previous studies. ISO-NE completed the TCS on time, studying ~4,800 MW of capacity in approximately eight months.[2] NESCOE recognizes the significant effort undertaken by ISO-NE to keep this study on time. Continuing to maintain study timelines will provide the region with a regular, predictable cadence of interconnection studies.
However, the TCS also highlights the need for further work to reduce uncertainty around interconnection costs. Speed without a reasonable degree of predictability delivers certainty about timing but not about viability. This could undermine the reforms’ promise to reduce both dimensions of interconnection risk.
To be clear, NESCOE recognizes that interconnection customers are likely to bear some interconnection costs depending on the size and location of their projects. However, it is also reasonable to expect an interconnection process that provides sufficient information to allow project developers to proceed with a reasonable expectation of the interconnection upgrades and costs that their projects may face. The upgrades and costs identified in the TCS were significant and far exceeded what many developers anticipated.
NESCOE appreciates ISO-NE’s commitment to engaging in a lessons learned and study improvements process.[3] There is specific interest in better understanding the key drivers of the TCS costs and whether and how targeted process and study methodology changes could improve the interconnection process going forward. These discussions are scheduled to occur in parallel with the interconnection process so as not to introduce unnecessary pauses or delays. NESCOE intends to conduct an independent comparative assessment of Regional Transmission Organization interconnection processes and methodologies to further inform these discussions.
In the nearest term, ISO-NE should improve transparency and predictability ahead of the first full cluster study process expected to begin in October 2026. NESCOE appreciates that ISO-NE launching its heatmap tool ahead of schedule to inform the upcoming cluster study.[4] We strongly encourage ISO-NE to evaluate whether any additional changes can be made within its current authority to improve transparency and information access to interconnection customers going into the first full cluster study. Ultimately, the October 2026 cluster study cannot replicate the TCS model without addressing this gap. The valuable timeline gains that ISO-NE has achieved have to work within an interconnection process that allows developers to reasonably predict whether their projects are financially viable.
***
NESCOE looks forward to continuing to work with ISO-NE and stakeholders to improve the transparency and efficiency of the region’s interconnection process.