Paul Hibbard, vice president of The Analysis Group, expressed concern about New England’s ability to meet its carbon-reduction goals if nuclear plants continue to leave the generation fleet and are only replaced by natural gas. Entergy’s 680-MW Pilgrim plant may retire as early as next year.

“The scary part here is that Pilgrim is the smallest of the nuclear generation within New England [behind Seabrook and Millstone] and all of them continue to be economically stressed,” he said. “How do we let this resource mix evolve in a way that’s going to help meet the states’ carbon reduction requirements?”

As gas plants race to replace retiring coal and nuclear generation, “The question we are being asked is ‘are we in an overbuild situation?’” said Paul Flemming, director, power and gas services for ESAI Power. The question is “especially [relevant] in PJM, but also to some extent in New England.”

Dan Allegretti, vice president of energy policy for Exelon, said that although expanding the Regional Greenhouse Gas Initiative would create more liquidity and increase efficiency, it also faces challenges. “There are legal problems, there are political problems … so the discussion should really center around being trading-ready. So rather than join the compact, I think there’s going to be a future for RGGI to expand … with the other states who have adopted a similar mass-based program for Clean Power Plan compliance.”

David Littell, a principal with the Regulatory Assistance Project, said states’ conflicting rules on clean energy resources are hurting investment.

“Fixing this Balkanized [renewable portfolio standard] system would be beneficial to the whole region. It just makes no sense for everybody starting a [legislative] season going for changes in what qualifies in each state,” he said. “That’s not sending an investment signal that the commercial community can respond to.”

David Alward, Canada’s consul general to New England, addressed fears that large hydropower imports would crowd out smaller solar and wind projects. “In 2014, Canada supplied 13.2% of New England’s electricity, mostly from hydro … this is third behind natural gas and nuclear. It’s hardly oversized.”

“Even though administrations have changed, from Democratic Gov. [Deval Patrick] in Massachusetts to Republican Gov. [Charlie Baker], the commitment to bring in more imports has stayed the same,” said Josh Bagnato, vice president of project development for Transmission Developers Inc. The company has proposed projects to import Canadian hydropower under Lake Champlain into Vermont and New York.

Aleksandar Mitreski, a senior director of regulatory affairs for Brookfield Renewable Energy, warned that power imports into New England don’t have firm contracts. “So … if Quebec or New York or New England has a reliability constraint, they may cut those transactions because they have no requirement to deliver,” he said.

Greg Cunningham, vice president of clean energy and climate change for the Conservation Law Foundation, explained why his group opposes the Massachusetts Department of Public Utilities’ decision to allow electric distribution companies to negotiate supply contracts with natural gas pipeline operators and pass costs to electric ratepayers.

“There are concerns that we have, both from a public policy and legal approach … if it’s going to involve any cross-border interaction between Marcellus shale natural gas and Canada. This is unprecedented — literally never before been done in this country, let alone this region,” he said. “This could result in an overbuild of natural gas that will undermine our public policy goals, the principal of which is our climate goals.”