Growth of wood biomass power stokes concern on emissions
Across the U.S., companies are planning scores of projects to burn trees and wood waste to produce electricity, claiming such biomass plants can be carbon-neutral. But critics contend that combusting wood is not really a form of green energy and are urging a go-slow approach until clear guidelines can be established.
It seems modest, as power plants go — a 29-megawatt facility, situated just north of the Vermont-Massachusetts line, that will burn woody biomass to generate enough power for 25,000 to 30,000 homes. But like many proposed plants in the recently reborn biomass power industry — a supposedly renewable and clean energy source — the Vermont project is encountering significant opposition.
“We live in a wooded, hilly part of New England, so it’s easy to sweep your arm around and say, ‘Look at all these trees. How can there not be enough biomass to operate this plant?’” says Charley Stevenson, co-director of a citizens group in the area that is opposing the plant. “But when you start to look at the scale of the proposed plant, the answer to that becomes less clear.”
The Pownal plant, one of two that Beaver Wood Energy has proposed in Vermont, faces the types of concerns confronting the entire industry. Biomass proponents have long claimed the power source can be carbon neutral — that the amount of carbon dioxide released into the atmosphere by burning trees and wood waste in a biomass plant will be offset by the growth of new trees to replace the old ones. However, evidence has accumulated that although biomass has the potential for some carbon benefit compared to fossil fuels, burning wood isn’t as simple a climate solution as many thought.
Combusting wood to produce heat and energy is not a new concept. In fact, whoever first rubbed two sticks together tens of thousands of years ago was an early biomass proponent. And biomass power plants are certainly not new — most of the several-hundred existing plants were built decades ago. But in recent years, as interest in renewable energy has grown, the industry has awakened and dozens, if not hundreds, of new plants have been proposed in the U.S. or are at some stage of a permitting process. Although some of the more intense battles over biomass power plants have taken place in New England, biomass projects are being proposed across the U.S., from the Pacific Northwest to the Southeast.
The awakening can be pegged directly to two developments: the growth of state renewable portfolio standards, which require that a certain percentage of a state’s electricity be generated by green energy, and federal policies that provide large incentives for renewable energy projects. Biomass is listed right alongside wind, solar, and other carbon-free power sources in various regulations, a fact that can be traced to a single questionable idea: that burning biomass for power generation is carbon neutral.
“People are waking up to the fact that this is not such a good deal,” says William Moomaw, director of the Center for International Environment and Resource Policy at Tufts University. “We could decide we’re going to do it, but right now we’re giving these huge subsidies and carbon credits for something that is not carbon neutral.”
Among the first to call attention to the problem of simply labeling it all carbon neutral was a paper in Science in 2009. The paper, written by Princeton University’s Timothy Searchinger and colleagues, pointed out that when all biomass is considered beneficial in carbon accounting terms, the economics tend to favor converting large amounts of land into forests planted solely to be cut down and burned, thus increasing CO2 emissions.
The only way that biomass achieves carbon neutrality is if growing forests sequester — that is, absorb from the atmosphere — as much or more carbon dioxide than is released in the burning process. If those forests get burned and none spring up to replace them, there is clearly a net addition of carbon to the atmosphere. And even if there is a one-to-one ratio of burned trees to growing trees, there is a timing problem. It takes only seconds to burn a tree’s worth of wood, and decades for that tree to grow back and sequester the same amount of carbon.
In fact, a study commissioned by the state of Massachusetts and conducted by the Massachusetts-based Manomet Center for Conservation Sciences suggested that for at least 30 years from the initial cutting of trees for biomass, there is actually a “carbon debt” compared to the burning of coal. It is only after several decades of tree regrowth that biomass power can start to show an emissions advantage over the dirtiest of fuels.
Still, biomass burning can approach carbon neutrality if forests are carefully managed and biomass power sources are restricted to waste wood products and material that would otherwise decompose on the forest floor and emit greenhouse gases anyway.
Because of the confusion surrounding biomass’s carbon neutrality, the EPA last month announced a plan to defer for three years the greenhouse gas permitting requirements for biomass facilities, ostensibly to allow time for better research into the proper ways to use biomass. This comes at the start of the agency’s effort to regulate carbon emissions from large sources around the country, and biomass proponents are happy for the deferral.
The biomass power industry says it does not want to cut down whole trees — let alone whole forests — just to produce electricity. Instead, the power plants will use wood residues from paper and timber mills and woody waste taken from other forestry practices.
“We would never defend the proposition that it is carbon neutral to take an acre of trees, burn those trees in a boiler, and pave that acre over for a Walmart,” says Bob Cleaves, president of the Biomass Power Association.
Though Tufts’ Moomaw and other experts seem to agree that at its absolute best, practices involving waste wood probably come close to carbon neutrality, they disagree on whether enough of the waste exists. Mary Booth — a scientist who in 2009 helped found the Massachusetts Environmental Energy Alliance, which opposes biomass burning — says that Massachusetts has only about 100,000 green tons (meaning, with the substantial moisture content included in the weight) of woody waste material available for use each year. She says that an average biomass plant needs about 13,000 tons of wood to produce 1 megawatt of electricity for one year; with biomass plants that average about 40 to 50 megawatt capacities, the state would run out of megawatts quickly.
Take the proposed Pownal plant, as well as its sister plant in Fair Haven, Vermont. They each would need about 350,000 tons of wood annually to produce at the stated capacity of 29 megawatts. Thomas Emero, one of the founding partners of Beaver Wood Energy, says that analyses have shown that taking half of the available waste wood from forest floors within 50 miles of Pownal would be enough to power the plant. The waste — otherwise unusable tops of trees, branches, and the like — would be created by existing logging operations, though a small portion would be added from a wood pellet plant connected to the Pownal power generating station.
“Within that same 50-mile radius, tree growth exceeds harvest by 2.4 million tons per year,” Emero says. “If that isn’t sustainable, then I don’t know what is.”
With so many other plants proposed, though, opponents see the equations differently. “There is no way that they aren’t harvesting more trees that would not otherwise be harvested,” Booth says.
Elsewhere in New England, similar issues have arisen. One proposed plant in Berlin, New Hampshire, has seen substantial opposition from within its own industry. A number of existing, small biomass facilities have argued against the Laidlaw Energy Group’s proposal for a 65-megawatt plant because it would substantially raise fuel prices. In other words, there isn’t enough wood in the region to go around.
As a result of the Manomet and other studies, Massachusetts will become the first state to actually put restrictions on types of biomass that can be included under the renewable portfolio standard. The changes are not yet finalized, but the draft regulation would limit biomass fuel to “non-forest derived and forest derived residues, forest salvage, and energy crops.”
Some say, though, that Massachusetts could be setting a standard that limits even truly beneficial biomass utilization. “We do see a danger of throwing out the baby with the bathwater, because the draft regulation would essentially do away with stand-alone biopower facilities,” says John Rogers, a senior energy analyst with the Union of Concerned Scientists. “There's a concern, if we’re setting the bar too high, that we’re cutting out biomass resources that the science says can be beneficial.”
Yet with every state except Massachusetts still using a generic biomass definition that doesn’t set limits, there could be substantial dangers. Booth helped conduct a study with the Environmental Working Group that made some stark estimates: Given the relatively modest projected growth of wind and solar power in the near future, to generate 25 percent of all U.S. electricity from renewable sources by 2025 would require an increasing dependence on biomass, and subsequently the need to clear-cut 46,000 square miles of forests over the next 15 years. That’s an area bigger than Pennsylvania.
The rush of studies and research in the last several years highlights a growing understanding that one cannot simply build a biomass plant, throw some wood in the boiler, and claim to be saving the planet. There are, however, circumstances and specific places where it can be done well.
Renewable energy resources in the southeastern U.S. don’t compare with wind in the Midwest or solar resources in the Southwest. As a result, biomass has long been suggested as a potential renewable energy option in the South. And though the same caveats remain in terms of determining carbon neutrality, there are differences. For one, the warm Southeastern climate means trees will grow back faster, lessening the period before neutrality is achieved.
Still, opposition has arisen to some proposed biomass plants in the Southeast. One 40-megawatt plant proposed in Lowndes County, Georgia, is being challenged by local environmental groups concerned about where the wood will come from and local health impacts.
Biomass proponents contend that the EPA’s decision to defer greenhouse gas permitting regulations for biomass plants will give the industry time to prove its environmental worth.
“I think it’s a good thing,” says Samuel Jackson, a biomass researcher at the University of Tennessee. “I think it will encourage industry investment and innovation in biomass utilization.” Jackson, who studies both woody biomass material as well as energy crops like switchgrass, is also involved with a startup biomass company called Genera Energy.
While some biomass energy skeptics, such as Booth and Moomaw, say the delay is political and a bad idea, other analysts are more optimistic about biomass’s potential.
“Biomass is a resource that can be tapped well or it is a resource that can be tapped badly, and we need policies that drive development of the good stuff but keep out the bad stuff,” says Rogers. “It can be done right, and we should find ways to do that, not just say no to it.”
ABOUT THE AUTHOR
Dave Levitan is a freelance journalist based in Philadelphia who writes about energy, the environment, and health. His articles have been published by Reuters, SolveClimate, IEEE Spectrum, and Psychology Today. In previous articles for Yale Environment 360, he wrote about the potential of vehicle-to-grid technology and whether biochar can help slow global warming.
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