ISO New England tells committee nuclear remains a major zero‑carbon resource, urges investment in flexible balancing resources

ISO New England officials told the House Energy and Digital Infrastructure committee on April 23 that nuclear power continues to supply a large share of the region's zero‑carbon energy and reliability capacity, and that the system will need more fast, flexible balancing resources as demand shifts toward winter peaks.

Sarah Adams, senior state policy adviser for ISO New England, and Eric Johnson, head of external affairs, said nuclear plants operate as base‑load, price‑taking resources and that their high availability makes them central to reliability planning. "Nuclear remains one of our largest zero‑carbon contributors to actual energy production," Adams said, explaining that nuclear's consistent output and long run times differ from variable resources such as wind and solar.

ISO staff warned the committee that electrification of heating is expected to move the system from a summer peak to a winter peak in coming years, raising concerns about fuel availability for natural‑gas‑fired generators during extreme cold. Johnson explained that local distribution contracts for home heating typically get winter priority, which reduces the gas available for electricity generation and can tighten imports from neighboring regions.

The ISO also described operational limits of nuclear plants: while they are under ISO dispatch control, they are not as nimble as fast‑start peaking units and they typically schedule long run times and refuel at multi‑month intervals. Johnson noted operators plan refueling outages in spring and fall to minimize reliability impacts and stressed that pump‑storage hydro built near nuclear stations provides daily storage and fast backup capacity (roughly eight hours) to cover large outages.

Committee members pressed ISO on state contracts that support nuclear plants outside the wholesale market. ISO said Connecticut has a 10‑year long‑term agreement with Millstone (the Connecticut station) and that part of Seabrook in New Hampshire has been included in interstate discussions; ISO staff said that contract had no automatic renewal clause and that Connecticut would seek other state participation before renewing.

On grid modernization and standards, ISO urged the committee to adopt additional inverter language the ISO had proposed for S.202. Adams said the UL standard cited in testimony describes inverters' capabilities but does not guarantee those safety and ride‑through features are enabled at installation; she recommended adding the additional standard referenced in ISO's letter to ensure those settings are enabled at install.

Adams and Johnson closed by urging investment in flexible, dispatchable balancing resources — batteries, demand response and other fast‑responding assets — to manage steep evening ramps and ensure fuel security during winter peaks. They noted the interconnection queue now contains many battery and renewable projects but relatively little new dispatchable generation, which raises longer‑term reliability questions.

Next steps: committee members agreed to insert the ISO‑recommended language into S.202 and to continue oversight as states consider out‑of‑market contracts and future reliability investments.