Maine’s nine wood-fired power plants may be threatened by a new study that concludes that cutting trees to generate electricity can release more greenhouse gases than burning coal.

The study says the net emissions of greenhouse gases from biomass would be 3 percent greater than from coal by 2050. The conclusion is based on the amount of carbon dioxide released from harvesting and burning the wood, and the amount of the gas that’s absorbed from the atmosphere by living trees.

The controversial findings are in a study done by the Manomet Center for Conservation Sciences for the Massachusetts Department of Energy Resources. The agency is preparing new sustainability rules for the state’s Renewable Portfolio Standard, the policy by which power plants are paid more for generating power from renewable sources.

The role of biomass in the policy is being debated in Massachusetts, where four wood-fired power plants have been proposed in the western part of the state. It also could have effects in Maine, where nine power plants in rural areas sell power to Massachusetts and depend on above-market rates from the renewable-energy incentive.

Besides power, the Maine plants create $108 million a year in economic value and employ 1,000 people in direct operations, wood harvesting and other jobs, says the Portland-based Biomass Power Association.

The trade group, which represents 80 plants in 20 states, pushed back against the study Friday, calling it “misleading and irresponsible.”

Bob Cleaves, the group’s president and chief executive officer, said the Manomet study focused on Massachusetts, which doesn’t have a big forest products industry and would need to harvest standing timber to feed biomass plants.

The conclusions don’t apply to states such as Maine, he said, which is heavily forested and where biomass plants are fueled largely by waste wood and thinnings.

Most of Maine’s free-standing biomass plants are in the northern part of the state: Greenville, Ashland, Fort Fairfield, Sherman and Stratton. Others are in Livermore, West Enfield, Jonesboro and Old Town.

Together, they have a capacity of roughly 230 megawatts and burn more than 1.5 million tons of wood a year, according to industry estimates.

Most of the plants were built two decades ago, in an era of high oil prices. They have had volatile histories — running when oil and natural-gas prices have risen, and struggling when prices have collapsed.

No new plants are planned in Maine because of the economics, Cleaves said. The existing investments were based on the renewable-energy incentives in New England. If Massachusetts were to change its policy, Cleaves said, it could threaten to put some of the plants out of business.

“We’re obviously very concerned about that,” he said.

The largest biomass owner in Maine, Boralex Inc. of Montreal, operates five plants. It declined to comment specifically on any risk to its business, but issued this statement: “Boralex has monitored this study and endorses the position of the Biomass Power Association, of which we are a member.”

The Maine plants compete for wood supply, to varying degrees, with some paper and lumber mills that use wood to generate heat and electricity. The Manomet study estimated that burning biomass for combined heat and power would reduce greenhouse gas emissions by 25 percent, relative to oil.

The study looks out 40 years because of a state law that requires Massachusetts to cut greenhouse emissions 80 percent by then.

The Manomet study also projected a 25 percent cut in greenhouse gases from burning biomass for heat, rather than using oil. That conclusion was welcomed by the Maine Pellet Fuels Association, which has four manufacturing plants in Maine.

“We would agree with the conclusion that generating electricity from wood is a poor use,” said Bill Bell, the group’s spokesman.

Beyond Maine and Massachusetts, the study is likely to expand debate on the role of bioenergy in combating climate change.

Last month, 90 scientists sent a letter to congressional leaders who are contemplating federal rules to cut greenhouse gas emissions.

The experts made similar points about the release of carbon dioxide when forests are cut to feed power plants. The letter underscores an evolving view among environmental groups that biomass isn’t a “carbon-neutral” fuel, as supporters sometimes claim.

“Calling it carbon-neutral is extremely inaccurate,” said Dylan Voorhees, clean energy director for the Natural Resources Council of Maine.

The contribution of biomass to greenhouse gas emissions depends on several variables, he said, including whether trees are replanted and the efficiency of the power plants.

Beyond climate change, policymakers must wrestle with whether the trade-offs of burning wood are trumped by goals of cutting the region’s dependence on imported oil.

“That’s a better question,” Voorhees said.

The Massachusetts energy office plans a series of public hearings in July to discuss the study.

 

Staff Writer Tux Turkel can be contacted at 791-6462 or at:

[email protected]