MA biomass study finds complex carbon impact

By Lisa Gibson
Posted June 10, 2010, at 4:30 p.m. CST

Woody biomass energy production is commonly thought to be carbon neutral, but a Manomet Center for Conservation Sciences study shows a more complex picture of biomass energy's carbon footprint. The study, however, may have one fundamental flaw, as it bases its analyses on new forest biomass instead of the waste wood and residues most plants would use.

"Biomass Sustainability and Carbon Policy Study" examines three main aspects of biomass energy in Massachusetts: feedstock availability; impacts of increased harvest on forest ecosystems; and carbon accounting implications. The study was commissioned and funded by the state Department of Energy Resources (DOER), which suspended all new applications for renewable portfolio standard (RPS) qualification, awaiting the results.

The six-month study, commissioned largely in response to citizen opposition of four proposed biomass facilities in the state, shows that using forest biomass for energy results in "carbon debt" because burning wood releases more carbon dioxide into the atmosphere per unit of energy than coal, oil or natural gas. Unlike fossil fuels, however, forests can grow back and recapture carbon dioxide from the atmosphere, paying off the carbon debt. After the debt is paid off, if the forest continues to grow, a "carbon dividend" is realized and the use of wood then becomes increasingly beneficial for greenhouse gas (GHG) mitigation, according to the Manomet Center for Conservation Sciences. As a result, using forest wood for energy can lead to lower atmosphere GHG levels than fossil fuels, but only after the time when the carbon debt has been paid off. Whether or not full carbon neutrality can be achieved will depend on if, when and how the forest is harvested in the future, the study found.

In addition, combined-heat-and-power (CHP) facilities and biomass heating operations reach carbon dividends much sooner than forest biomass power plants because of greater efficiency, the study says. Replacing oil-fired CHP and thermal capacity yields benefits within a decade and when replacing natural gas thermal, taking between 20 and 30 years. Dividends from the replacement of coal-fired electricity with forest biomass begin approximately 20 years later, and when biomass replaces natural gas electricity capacity, carbon debts are still not paid off 90 years later, according to the study.

The work also determined that forest biomass availability depends heavily on prices that bioenergy facilities are able to pay for wood. At present, landowners in the region typically receive between $1 and $2 per green ton of biomass. Under that scenario, the estimate for new biomass that can be harvested annually from forests in the state is only between 150,000 and 250,000 green tons, only enough to generate 20 megawatts of power. Those estimates could potentially increase 50 to 100 percent when out-of-state forest biomass resources are taken into account. If prices were to increase to $20 per green ton, availability from combined in-state and out-of-state forest biomass could total between 1.2 million and 1.5 million green tons per year, but the study says that scenario is unlikely.

"There are wood supplies from forest biomass and nonforest biomass," said Peter Bos, developer with Russell Biomass, which plans to build a 50 MW power plant in Russell, Mass., which would use nonforest biomass such as residues, stumps and other debris not considered new forest biomass. "Manomet estimated forest biomass conservatively, but that's probably OK because that will be taken into account when DOER establishes its new wood sustainability policies for each biomass plant." Nonforest biomass has substantially lower global warming impacts than forest biomass because it does not require cutting new wood, he said. At least 1 million tons per year of nonforest wood is available in the state and surrounding areas, he said, adding that estimate is conservative, as well.

A 2002 report found that 2.5 million tons of nonforest biomass is available in the state, the Manomet report cites, adding that the potential and value of these sources may be substantial and is worthy of further investigation. This point seems crucial to feedstock availability for Massachusetts biomass plants, as none of the proposed facilities have included cutting new forest biomass in their plans. "They're making a fundamental assumption that is not correct," said Bob Cleaves, president and CEO of the Biomass Power Association, in reference to the Manomet study. "I think they missed the point that the overwhelming feedstock for biomass projects in the country is tops and limbs from the forest products industry, rice hulls, orchard prunings, all byproducts of another process." When taking that point into consideration, biomass power is absolutely carbon neutral, he added. "The report's authors appear to focus primarily on growing and harvesting trees for use in the generation of energy." Biomass was recently deemed exempt from California's cap-and-trade program, Cleaves emphasizes, and respected scientific and environmental groups such as the Union of Concerned Scientists and the Forest Guild have expressed strong support for biomass power.

Bos is not concerned that the DOER might rule out biomass altogether for RPS qualification, saying the only way that would happen is if there was no waste wood available at all. "I think DOER in Massachusetts now has a framework they can use for allowable sources of wood supply," he said.

As far as forest sustainability and biomass harvests, the study shows that harvesting rates would not increase from current levels in the low-price scenario. The combined volume of timber and biomass harvests in the scenario represents less than half of the annual net forest growth across the state's operable forest land base. In the high-price scenario, however, the total harvested approaches the total amount of wood grown each year on the operable private forest land base, the report states.

A public comment period of one to two months follows the June 10 release of the findings, after which time, the DOER will carry out a redrafting process. "We will create standards, taking into account the study," said David Cash, assistant secretariat for policy at the Massachusetts Executive Office of Energy Environmental Affairs, which has a secretariat umbrella over six line agencies including the DOER. Cash said it's too early to speculate as to what the new standards will include and exclude. "It's clear from the findings that … long-term GHG balance on biomass electricity doesn't work," he said. Creating the standards could take another one to two months after the comment period, which Cash said will be an important aspect of final decisions. RPS qualification applications will remain suspended until new standards are finalized. The study can be viewed in its entirety at