Hours before a much-anticipated public hearing on the merits of a new transmission line through western Maine, an analysis released Wednesday by environmental and renewable energy interests concluded that the New England Clean Energy Connect project would not reduce carbon pollution and therefore do nothing to offset climate change.

The analysis claims the line would only redirect existing hydroelectricity generated by Hydro-Québec to Massachusetts, while allowing the Canadian utility to sell gas and oil-fired power elsewhere.

The analysis was conducted by the consulting firm Energyzt Advisors of Boston, on behalf of the Natural Resources Council of Maine, the Sierra Club, and the Maine Renewable Energy Association.

The charges are not new. They mirror arguments made by Energyzt on behalf of competing power plant owners in testimony at the Maine Public Utilities Commission, which held a public hearing on the project Wednesday evening at its offices in Hallowell. These charges and countercharges were first reported in the Press Herald in May. 

They conclude that the line wouldn’t really lower carbon emissions that accelerate climate change because no new hydropower facilities would be built. That implies that fossil-fuel power plants outside New England would be called on to backfill demand in New York state and elsewhere created by the diversion of power to Massachusetts.

These accusations have been refuted by both Hydro-Québec and Avangrid, the parent company of the line’s builder, Central Maine Power. In a column last month in CommonWealth magazine, CMP and Hydro-Québec accused the Sierra Club and the NRCM of forming an alliance with power-plant interests to kill the project.

Avangrid spokesman John Carroll, in a written statement Wednesday, said environmental advocacy groups were recycling arguments paid for by Calpine Corp., which owns a natural gas-fired power plant in Westbrook. 

“These were largely rebutted months ago in the case before the Maine Public Utilities Commission, and coming this late in the proceeding, anything that might be news won’t have any bearing on the outcome,” Carroll said.

In an email last month to the Portland Press Herald, Lynn St. Laurent, a spokeswoman for Hydro-Québec, said the provincial utility was in fact building new hydro generating stations.

“Thanks to our build-out and efficiency measures,” St. Laurent said, “HQ is fully capable of increasing its total clean energy exports in support of the Massachusetts contract. The claim that HQ would dispatch fossil fuel generation to offset the energy earmarked energy for NECEC makes absolutely no sense.”

Project opponents say they’ve seen no evidence to back up these claims, so debate over the issue continues. But coming on the day of the PUC hearings, a new report about a project that’s labeled clean energy ­— but may actually be a dirty enterprise — is bound to create more uncertainty.

The proposed $950 million project would be built to satisfy ambitious clean-energy goals in Massachusetts, and utility customers there ultimately would pay the entire cost. The 1,200 megawatts of capacity is enough power to run more than 1 million homes.

To win approval, Maine regulators must find that the project will benefit Maine residents, even though none of the electricity carried by the line would be sold in the state.

CMP has said the project will save Maine ratepayers roughly $40 million a year by lowering wholesale electricity costs in New England. Communities along the transmission corridor will share $18 million a year in new tax revenue, and nearly 1,700 direct and indirect jobs will be created during construction, CMP says.

But the NRCM and renewable generators point out that the line’s technical design makes it unfeasible to connect Maine-based wind and solar projects, which they say could provide greater economic benefits and offset carbon-based power.

The Energyzt analysis examined electricity generation and consumption within Quebec, and power transmission into and out of the province. It included areas that rely heavily on fossil fuels, such as New Brunswick and New York. 

The analysis also looked at public records that document Hydro-Québec’s financial incentive to maximize profits from exports at the expense of accurate carbon accounting.

It also points out that Hydro-Québec has declined to participate as a party in the PUC review. 

“As a result,” the NRCM notes, “the evidence provided to the Maine PUC has come in the form of secondhand statements by CMP.”

According to the NRCM, evidence at the PUC clearly shows that Hydro-Québec would not undertake any construction of new generation facilities or equipment in order to provide power for NECEC. Because NECEC would not result in any new generation capacity, it asserts, the power would come largely from reducing exports to other markets. 

The study found that additional generation in those markets would be, at best, as dirty as the power being displaced in New England, making for no net carbon reduction.  

“This report makes clear that CMP and Hydro-Québec still haven’t answered the key question: Is this Canadian power going to help reduce harmful polluting power?” said Jeremy Payne, executive director for the Maine Renewable Energy Association. “In fact, it seems to create more questions than answers, and unfortunately HQ has chosen to hide behind CMP rather than being forthcoming.”