Biomass, a renewable energy source derived from organic matter such as wood, crop waste, or garbage, makes up 4.8 percent of total U.S. energy consumption and about 12 percent of all U.S. renewable energy. Wood is the largest biomass energy source. In the U.S., there are currently 227 biomass plants operating. In the U.K., 35 are operating, 15 are under construction and 17 have been proposed.
There are several ways to produce energy from biomass, including burning biomass to generate heat or run steam turbines that produce electricity, burning biomass to produce heat in thermal systems (when combined with electricity generation, it’s called “combined heat and power”), turning feedstocks into liquid biofuels, and harvesting gas from landfills or anaerobic digesters. Biomass can consist of wood from forests and logging residues, sawdust from lumbermills, construction or organic municipal waste, energy crops (switchgrass), crop residue, and even chicken litter. Since the rapid expansion of biomass energy today relies largely on wood from forests, we’ll focus here on energy produced by the combustion of biomass from forest wood and woody residue.
According to the U.S. Forest Service, “Wood is an abundant, sustainable, homegrown cellulosic resource that can significantly contribute to meeting 30 percent of U.S. petroleum consumption from biomass sources by 2030 and help create a more stable energy future, improve environmental quality, and increase economic opportunities.”
Biomass advocates maintain that thinning out small-diameter or dead trees from overcrowded forests, and harvesting the byproducts of forest management such as limbs, treetops, needles, leaves, etc. improves the health of the trees that remain in the forest and helps reduce the incidence of wildfires. Biomass creates jobs and supports local economies by providing new markets for farmers and forest owners. It can also lessen our dependence on fossil fuels, and under certain conditions, can reduce greenhouse gas emissions.
Biomass is considered a renewable energy source because its inherent energy comes from the sun and because it can regrow in a relatively short time. Trees take in carbon dioxide from the atmosphere and convert it into biomass and when they die, it is released back into the atmosphere. Whether trees are burned or whether they decompose naturally, they release the same amount of carbon dioxide into the atmosphere. The idea is that if trees harvested as biomass are replanted as fast as the wood is burned, new trees take up the carbon produced by the combustion, the carbon cycle theoretically remains in balance, and no extra carbon is added to the atmospheric balance sheet—so biomass is arguably considered “carbon neutral.” Since nothing offsets the CO2 that fossil fuel burning produces, replacing fossil fuels with biomass theoretically results in reduced carbon emissions.
Nevertheless, biomass energy is currently considered renewable, and thus qualifies for tax credits, subsidies and incentives in the U.S. These include the Renewable Electricity Production Tax Credit which pays closed-loop (organic matter planted exclusively to produce electricity) biomass energy producers $.023 per kilowatt-hour and open-loop biomass (any other waste or residue) producers $.012 per kilowatt-hour; and Renewable Energy Certificates wherein every megawatt hour of electricity generated by biomass earns a credit that can be sold, traded or bartered, giving its owner the right to claim to have purchased renewable energy. The Investment Tax Credit will reimburse 30 percent of biomass plant development if construction is begun by the end of this year, and if operation begins by 2024. And biomass is eligible for subsidies from the U.S. Department of Agriculture.
In part due to these incentives and the pressure to reduce coal use, energy companies in the U.S. and Europe are turning to biomass. By 2030, biomass could account for 60 percent of total final global renewable energy use, according to the International Renewable Energy Agency.
Most of the new biomass electricity generating plants being proposed in the U.S. will burn wood. Plants in the Southeast U.S. are churning out wood pellets to meet Europe’s increasing need for wood. Last year, wood pellet exports from the Southeast increased 70 percent; the Southern U.S. is now the largest exporter of wood pellets in the world. Since there isn’t enough logging residue to meet the increased demand for biomass, many fear that more standing trees will be chopped and more forests clear-cut.
The new biomass plants produce 38 megawatts of electricity on average, but many are being built in the 50 to 110 megawatt range. According to the Partnership for Policy Integrity, a 50-megawatt plant burns 2,550 lb. of green wood each minute. As an example, the 50-megawatt McNeil plant in Burlington, VT burns 625,000 tons of green wood from trees and residue each year. Additional wood is needed for co-firing in coal plants where wood is burned with coal to meet state renewable energy mandates (resulting in additional carbon emissions), pellet production, and liquid biofuels. While admittedly most forests will not actually be clear-cut for biomass energy, the numbers make clear the amount of pressure that will be brought to bear on our forests.
Harvesting and removing limbs, leaves and plant parts from forests, which would normally recycle nutrients back into the soil as they decay, can diminish soil fertility and hasten erosion. Heavy machinery used for Iogging compacts soil and increases runoff, which may affect water quality. Removing vegetation from the ground also impacts wildlife habitats on the forest floor.
For five years, the EPA has been reassessing the climate impacts of biomass burning; it is still not clear how wood energy will eventually be regulated, but a decision is expected this year. The agency has been working with scientists to develop formulas so that states and power plant owners can calculate the climate impacts of wood fuel.
Members of the U.S. Senate recently proposed an amendment to the Energy Policy Modernization Act that would deem forest biomass “carbon neutral.” Under President Obama’s Clean Power Plan to reduce greenhouse gas emissions from power plants, this measure would make biomass equivalent to zero-emission wind and solar energy as a replacement for coal. In response, 65 scientists and stakeholders wrote a letter to the Senate protesting that “Granting carbon amnesty to forest biomass burning for energy could lead to significant depletion of U.S. forests. The potential implications of declaring carbon neutrality for forest biofuels are great because even small quantities of bioenergy require large quantities of wood. The U.S. Energy Information Agency estimates that for each 1 percent added to current U.S. electricity production from forest biomass an additional 18 percent increase in U.S. forest harvest is required. This policy would also encourage the destruction of forests in developing countries that would see the U.S. as an export market….We urge you and other members of the Senate to reconsider this well-intentioned legislation and eliminate the misrepresentation that forest bioenergy is carbon-neutral.”
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