Is Biomass Really Renewable?

by |August 18, 2011

Updated October 19, 2016

A woody biomass harvest site in MN. Photo credit: Eli Sagor

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. But just how renewable is biomass energy?

The Seattle Steam Company uses woody waste. Photo credit: Joe Mabel

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.

In fact, the reality is a lot more complicated. In 2014, the U.S. Environmental Protection Agency (EPA) found that “carbon neutrality cannot be assumed for all biomass energy a priori.” Whether or not biomass is truly carbon neutral depends on the time frame being studied, what type of biomass is used, the combustion technology, which fossil fuel is being replaced (since the combustion of both fossil fuels and biomass produces carbon dioxide), and what forest management techniques are employed in the areas where the biomass is harvested.

In 2010, a group of prominent scientists wrote to Congress explaining that the notion that all biomass results in a 100 percent reduction of carbon emissions is wrong. Biomass can reduce carbon dioxide if fast growing crops are grown on otherwise unproductive land; in this case, the regrowth of the plants offsets the carbon produced by the combustion of the crops. But cutting or clearing forests for energy, either to burn trees or to plant energy crops, releases carbon into the atmosphere that would have been sequestered had the trees remained untouched, and the regrowing and thus recapture of carbon can take decades or even a century. Moreover, carbon is emitted in the combustion process, resulting in a net increase of CO2.

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.

Photo credit: rebuildingdemocracy

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.

How is this increase in biomass burning impacting climate change, our health, and the environment? Today’s biomass-burning power plants actually produce more global warming CO2 than fossil fuel plants: 65 percent more CO2 per megawatt hour than modern coal plants and 285 percent more CO2 than natural gas combined cycle plants (which use both a gas and steam turbine together). In addition, burning wood biomass emits as much, if not more, air pollution than burning fossil fuels—particulate matter, nitrogen oxides, carbon monoxide, sulfur dioxide, lead, mercury, and other hazardous air pollutants—which can cause cancer or reproductive effects. The air pollution from biomass facilities, which the American Heart Association and the American Lung Association have called a danger to public health, produces respiratory illnesses, heart disease, cancer, and developmental delays in children.

Heavy machinery compacts soil. Photo credit: David Stanley

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.”

As the thinking about biomass continues to evolve, state, federal, and international regulations need to clearly distinguish between the types of biomass energy that are beneficial and those that are detrimental. Treating all biomass, regardless of its source, as carbon neutral, could lead to increased greenhouse gas emissions at home and around the world. As the scientists said in their 2010 letter to Congress, the “globally improper accounting of bioenergy could lead to large-scale clearing of the world’s forests… any legal measure to reduce greenhouse gas emissions must include a system to differentiate emissions from bioenergy based on the source of the biomass.”


8 thoughts on “Is Biomass Really Renewable?

  1. Keith says:

    Where was this data sourced from?

    “biomass-burning power plants actually produce more global warming CO2 than fossil fuel plants: 150% the CO2 of coal, and 300 to 400% the CO2 of natural gas, per unit of energy produced.”

  2. Renee Cho Renee says:

    Hi Keith,

    The data comes from the Partnership for Policy Integrity which has a vast amount of biomass information on its Web site:

    http://www.pfpi.net/biomass-basics-2

    Renee

  3. Annie Nelson says:

    Renee & Keith,

    Stationary energy is best coming from passive sources, such as wind, solar & geothermal. Biomass usually does require more energy to produce than it gives, with SUSTAINABLE biodiesel being the exception, as well as the only viable reality at this point. Recycled oils keep oil dumps from land fills, and does not effect food production. Sustainable also means that it is community based, produced & distributed!!!

  4. Krista Hiles says:

    The basic advantage of biomass energy is that organic garbage which is produced by human, plants and animal can be used for the production of biomass energy. It also provides help in cleaning our surroundings.

  5. Bengt Andersson says:

    You forget that each time you release CO2 into the atmosphere only a part goes back to land based photosynthesis.. The ocean takes a large part to make acid and biomass.
    Replacing fossils with biomass needs many earths.
    With 7 billion people transforming biomass, 1-5 kW/person, this must be compensated with fossil CO2, otherwise we loose to much CO2 into the ocean.
    This means that we are in an instable balance.
    From Sweden with big problems here.

  6. amar nath tandon says:

    bio mass is a form of Sun energy only it is a chemical deposition of sun energy only with certain combination of elements taken from mother earth . so this energy should be used in different way different than how it is being used.First of all we should try to return the elements back to mother mother earth as early and fast as possible this we can do by composting / digestion only. and using the energy in form of gas which is less polluting this will reduce the use of perishable carbon base fossil fuels.

  7. samuel katenda says:

    the advantage of biomass is that, 1 it is a renewable resource that is it is easier to replenish in a short period of time, 2 it helps us clean our environment by utilizing most of the waste materials we produce as humans. l still need to verify on the issue of biomass producing more C02 than fossil fuels, is it under anaerobic decomposition or…..

  8. Paul Elias says:

    The article focuss heavily on one major source of biomass,
    forestry. In CA biomass fuel comes from many sources: urban wood waste, orchard removal where fast growing trees are replanted, and forestry practices both from logging and forest fire fuel reduction including massive die offs due to beetle kill. Without nurning to generating of power from these sources the biomass is either burned in open fields, urban wood in buried in landfills to release CO2 over yrs and yrs or in the forest add to the danger of major forest fires that add tons and tons of Greenhouse gases yearly. The article addresses none of the benefits of managed burning of fuels for renewable power when the fuel source is from waste by-products that otherwise is openly burned as the case of agr and forestry or will emit CO2 while rotting in a landfills over time. Getting the benefits from biomass by offsetting fossil fuels power generation seems a great benefit to CA and the atmosphere overall then the alternative of open burning or rotting plus consuming landfill capacity.

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