A new report promoted by conservative New England think tanks warns that the region’s decarbonization plans could add as much as $815 billion in electricity costs by 2050.

The analysis, produced by Always On Energy Research and backed by groups including the Fiscal Alliance Foundation and Americans for Prosperity, contends that current clean energy mandates — focused heavily on solar, onshore and offshore wind, and battery storage — would be far more expensive than alternatives centered on nuclear and natural gas.

Except for New Hampshire, the report notes, each New England state has adopted aggressive clean energy requirements alongside mandates to sharply reduce natural gas use within the ISO New England power system.

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Supporters say the shift will fight climate change, improve aid quality and create a base of local jobs.

According to the report, those policies also require widespread electrification of home heating and transportation, a transition that would “nearly double peak electricity demand on the ISO-NE system and increase overall electricity demand by 106 percent.”

The analysis argues that meeting this demand while moving away from dispatchable resources like natural gas toward wind, solar and batteries would “cause electricity prices to skyrocket” and raise the risk of rolling blackouts.

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The analysis estimates that meeting decarbonization and electrification policies could cost annual household electricity costs to rise from about $2,100 in 2024 to $4,600 in 2050.

The report evaluates three alternative scenarios — nuclear, natural gas and a blended “happy medium” of the two sources — and concludes that all would be cheaper and more reliable than a renewables-dominant pathway, though still more expensive than today’s grid.

Under the nuclear scenario, which would lead to the most greenhouse gas reductions, New England costs would rise by $415.3 billion through 2050. The natural gas scenario is the least expensive, adding $106.9 billion while reducing greenhouse gas emissions by 24.5% across the electric, heating and transportation sectors. The hybrid approach would cut emissions by 50% at an added cost of $195.8 billion.

Massachusetts is the region’s largest electricity consumer. Under the renewable-heavy scenario, cumulative energy costs for the state rise to $405.1 billion by 2050, compared with $206.4 billion under the nuclear scenario, $97.4 billion under the hybrid approach, and $53.1 billion under the natural gas scenario, according to the study.

Environmental advocates dispute the report’s assumptions and cost modeling, arguing it overstates the expense of renewables while understating both fossil fuel risks and climate impacts.

Amy Boyd Rabin, vice president of policy and regulatory affairs at the Environmental League of Massachusetts, said the analysis inflates renewable energy needs well beyond ISO New England’s own projections while assuming the existing fossil-fuel-heavy grid remains stable.

“The report is doing three things incorrectly,” Boyd Rabin said. “Rather than trusting ISO-NE — which has every incentive to keep our grid reliable — it inflates the amount of renewable energy we would need by over twice what ISO estimates, and also assumes the current electric grid is going to remain healthy and free, with no new maintenance, no new generators and no fossil fuel price increases.”

She also criticized the report for excluding the social cost of carbon.

“There are billions, or trillions, of dollars in damages headed our way if we don’t take action on the climate crisis,” Boyd Rabin said, adding that health and safety impacts are routinely left out of fossil fuel cost comparisons.

Kyle Murray, Acadia Center’s director of state program implementation and Massachusetts program director, said no grid planning “would put all power generation eggs in just one or two baskets.”

“Any low cost grid mix is going to include a portfolio of many resource categories, and we know that renewables are poised to anchor the most cost-effective portfolio for the region,” Murray said.

State lawmakers face decisions on an energy affordability bill that has exposed tensions between cost concerns and the state’s legally binding 2030 emissions target. House leaders in November paused a proposal that would weaken the mandate under certain conditions, amid opposition from climate and environmental groups.

House Ways and Means Chairman Aaron Michlewitz said leadership was not prepared to reopen the 2030 mandate at the time but acknowledged the issue remains unsettled.

“We are probably going to have to have a conversation at some point related to whether we can meet our goals for 2030,” he told reporters, citing federal actions that have complicated state climate efforts.

During a press conference about the report on Tuesday morning, Drew Cline, president of the Josiah Bartlett Center in New Hampshire, framed the study in broader political terms.

“Affordability is the number one political issue in the United States right now as we head into 2026,” Cline said. “Any New England politician who wants to actually make substantial progress on affordability really needs to read this report.”

Cline also emphasized New Hampshire’s role as a net exporter of electricity, noting the state generates roughly 150% to 170% of its needs. If the rest of New England adopted a similar mix centered on nuclear and natural gas, he argued, the region could save hundreds of billions of dollars while avoiding energy shortages.

Massachusetts, by contrast, consumes roughly 25 times more energy than it produces, though it ranks among the five states with the lowest per capita energy consumption, according to the US Energy Info Administration.

Greg Moore of Americans for Prosperity raised concerns about rising electricity demand from data centers, warning New England could lose competitiveness if they can’t host the energy-intensive industry. He pointed to recent New Hampshire legislation allowing private electric grids and exploring an exit from ISO New England, suggesting such a move could have serious implications for neighboring states.

Paul Craney of the Fiscal Alliance Foundation said energy costs are increasingly shaping political debate, pointing to Gov. Maura Healey’s past opposition to natural gas pipeline expansion, to a shift in rhetoric when she has recently claimed she has never stopped gas pipelines from entering the state.

Craney said the report is meant to offer clearer cost data for lawmakers considering whether to soften the state’s zero-emissions mandates.

Boyd Rabin countered that affordability concerns strengthen — rather than weaken — the case for clean energy.

“Affordability is a chief concern, and that’s why getting off the roller coaster of fossil fuel price spikes is a necessity for Massachusetts consumers,” she said.

More than 100 climate and environmental organizations, including ELM, have urged lawmakers to reject any effort to weaken the 2030 mandate or reduce Mass Save funding, warning that abandoning climate commitments would be a “grave misstep.”

“Across the country, and in the Northeast, states with higher natural gas penetration have higher electricity rates – whereas states that have added more renewables have seen smaller electric rate hikes over the past two-plus decades,” Murray said.

As lawmakers prepare to revisit the stalled affordability bill, the report is likely to be embraced by critics of the region’s clean energy strategy — and challenged by those who argue the long-term economic, health and climate costs of fossil fuel dependence are even higher.