Is Biopower Carbon Neutral?
Kelsi Bracmort
Specialist in Agricultural Conservation and Natural Resources Policy
January 2, 2013
Congressional Research Service
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Is Biopower Carbon Neutral?
Summary
Congress has expressed interest in biopower—electricity generated from biomass. Biopower, a
baseload power source, has the potential to strengthen rural economies, enhance energy security,
and improve the environment, proponents say. Biopower could be produced from a large range of
biomass feedstocks nationwide (e.g., urban, agricultural, and forestry wastes and residues). One
challenge to biopower production is a readily available feedstock supply. At present, biopower
requires tax incentives to be competitive with conventional fossil fuels. If Congress considers a
renewable electricity standard or other measures (e.g., farm bill energy programs) that include
biopower, there may be concerns about the carbon neutrality of biopower. Congressional support
for biopower has aimed to promote energy diversity and improve energy security, and has
generally assumed that biopower is carbon neutral. An energy production activity is typically
classified as carbon neutral if it produces no net increase in greenhouse gas (GHG) emissions on a
life-cycle basis. The premise that biopower is carbon neutral has come under scrutiny as its
potential to help meet U.S. energy demands and reduce U.S. greenhouse gas emissions is more
closely examined.
Whether biopower is carbon neutral depends on many factors, including the definition of carbon
neutrality, the feedstock type, the technology used, and the time frame examined. Carbon flux
(emission and sequestration) varies at each phase of the biopower pathway, given site- and
operation-specific factors. A life-cycle assessment (LCA) is a common technique to calculate the
environmental footprint, including the carbon flux, of a particular biopower pathway. However,
past legislation has not required a standardized LCA.
Interest in the carbon classification of biopower is in part due to sustainability and air quality
concerns. Where the feedstock supply for biopower originates, if it is managed in a sustainable
manner, and whether the associated air quality impacts from biopower generation are tolerable
are questions that are part of the biopower carbon-neutrality debate. Congress may decide
whether the current carbon-neutral designation for biopower is accurate, or whether additional
carbon accounting for biopower is warranted and what impact this accounting might have on
renewable energy, agricultural, and environmental legislative goals.
Rulings by the U.S. Environmental Protection Agency have raised questions about the carbon
neutrality of biopower. For instance, the 2010 Prevention of Significant Deterioration and Title V
Greenhouse Gas Tailoring Rule did not exempt emissions from biomass combustion. Some view
EPA’s decision as equating biomass emissions with fossil fuel emissions. EPA decided in 2011 to
defer for three years GHG permitting requirements for carbon dioxide emissions from bioenergy
and other biogenic stationary sources in order to conduct a detailed examination of the science
associated with these emissions. EPA’s Scientific Advisory Board conducted an independent
review of the agency’s biogenic accounting framework and released its findings in September
2012. The board acknowledged the “daunting task” of assessing the greenhouse gas implications
of bioenergy, and the “narrow regulatory boundaries” within EPA’s purview that limit the
consideration of greenhouse gas flux at various points along the bioenergy pathway.
State perspectives on the tailoring rule are divided. Some states contend that treating biomass
combustion the same as fossil fuel combustion will result in excessive permitting requirements
and fees that jeopardize renewable energy development. Other states argue that not treating it the
same will aggravate climate change over time.
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Is Biopower Carbon Neutral?
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Is Biopower Carbon Neutral?
Contents
Introduction ...................................................................................................................................... 1
Biomass Carbon Cycle..................................................................................................................... 2
Greenhouse Gas Accounting for Biopower Production ................................................................... 3
Recent Developments Affecting Biopower Assessment .................................................................. 6
Title V Greenhouse Gas Tailoring Rule ..................................................................................... 7
Manomet Biomass Study ......................................................................................................... 10
Is Biopower Carbon Neutral? It Depends ...................................................................................... 12
Legislative Implications ................................................................................................................. 13
Figures
Figure 1. Bioenergy CO2 Balance vs. Fossil Fuel CO2 Balance ...................................................... 4
Figure 2. Biopower and Biofuel Pathways ...................................................................................... 5
Figure 3. Cumulative GHG Flux for Biomass and Fossil Fuel ...................................................... 12
Tables
Table 1. Years to Achieve Equal Cumulative Flux with Fossil Fuels ............................................ 11
Contacts
Author Contact Information........................................................................................................... 14
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Is Biopower Carbon Neutral?
Introduction
Biomass energy, or bioenergy, is receiving increased attention as an alternative to fossil fuel
energy because of its potential to improve the environment, provide energy security, and promote
economic development. Biomass is organic matter—woody biomass, agricultural biomass,
animal wastes, aquatic biomass—that can be converted to energy (e.g., heat, electricity, or liquid
transportation fuels). A substantial supply of biomass feedstocks may be required to produce
bioenergy, depending on current and future renewable energy mandates. A large biomass
feedstock requirement could lead to water, land use, sustainability, and economic concerns.1
Federal support for bioenergy is available via tax incentives, loan guarantees, technical and
financial assistance, and mandated use requirements.
Legislative support for bioenergy, particularly for biopower (electricity generated from biomass),2
has thus far been granted under the premise that it is carbon neutral. As more public and private
resources are spent—or as greater spending is debated—on biopower, more attention is being
directed to the rationale for designating biopower as carbon neutral. The carbon-neutral
designation is typically assigned to an energy production activity that essentially produces no net
increase in greenhouse gas (GHG) emissions on a life-cycle basis (or one in which the amount of
carbon dioxide emitted during the power production cycle is absorbed).3 Where biopower stands
among the other renewable energy sources with respect to GHG emissions may affect the level of
future legislative support granted to it. Is biopower carbon neutral? If it is not, should it receive
the same type and amount of federal resources as carbon-neutral or less carbon-intensive energy
sources? How might the federal government account for carbon associated with biopower
ventures? How Congress addresses biopower’s carbon neutrality could shape how Congress treats
biopower in general.
Many views exist about whether biopower is carbon neutral. Some contend that biopower is
carbon neutral because the carbon released during bioenergy production comes from a carbon-
neutral feedstock—biomass. Some argue that biopower is not carbon neutral because the amount
of GHG emissions released per unit of energy during simple biopower combustion may be higher
for certain biomass fuels than for fossil fuels; or, if the GHG emissions from certain biomass fuels
are lower than fossil fuels, they are still not zero. These perspectives are often based on differing
assumptions, technologies, and time frames.
The debate concerning biopower’s designation as carbon neutral may intensify, given possible
congressional and Administration decisions. Congress may consider legislation involving
biopower (e.g., a renewable electricity standard, a clean energy standard, or the next farm bill).
The U.S. Environmental Protection Agency (EPA) has already promulgated regulations involving
biopower (e.g., the 2010 Prevention of Significant Deterioration and Title V Greenhouse Gas
Tailoring Rule) and may consider further regulatory actions. Although EPA deferred for three
years GHG permitting requirements for carbon dioxide emissions from biomass-fired and other
1 For more information, see CRS Report R41440, Biomass Feedstocks for Biopower: Background and Selected Issues,
by Kelsi Bracmort.
2 Biopower is a baseload power source offering “firm” power without the need for power storage. Combustion—the
burning of biomass in a power plant—is the dominant technology used to produce biopower.
3 The life cycle of a bioenergy pathway includes all stages of fuel and feedstock production and distribution, from
feedstock generation or extraction through distribution, delivery, and use of the finished fuel by the ultimate consumer.
The mass values for all greenhouse gases are adjusted to account for their relative global warming potential.
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Is Biopower Carbon Neutral?
biogenic sources,4 Congress may still decide to examine how the widely accepted premise of
biopower’s carbon neutrality contributes to energy, environmental, and economic development
goals.
This report discusses some of the most relevant factors to take into account when considering if
biopower is carbon neutral. It does not discuss carbon accounting for other bioenergy pathways.5
Biomass Carbon Cycle
The carbon cycle encompasses the many pathways through which carbon is exchanged between
the atmosphere and the land and water.6 Human activities (also called anthropogenic activities)
contribute to the carbon cycle by emitting carbon dioxide (CO2). The human contribution of CO2
to the carbon cycle is relatively small compared to other contributions, but CO2 released to the
atmosphere from human activities is taken up by soils, vegetation, and the ocean at a rate that is
relatively slower than the rate at which human activities are emitting CO2. If the excess carbon is
not stored in land and ocean sinks, the atmospheric concentration of CO2 increases, potentially
impacting the Earth’s climate.
One significant anthropogenic source of CO2 in the carbon cycle is energy production. The net
effect of an energy activity on the carbon cycle can be classified in one of three ways. A “carbon-
positive” activity releases CO2 into the atmosphere. A “carbon-negative” activity removes more
CO2 from the atmosphere than it emits. A “carbon-neutral” activity is one where the CO2 releases
and absorption are in balance. There is no commonly accepted definition for a “carbon-neutral”
activity in the biopower arena. Indeed, multiple assertions about carbon neutrality have been put
forth by those involved with biomass energy, including the following:7
• Biomass energy is carbon neutral because biomass is naturally carbon neutral.
• Biomass energy is neutral if the activity removes as much CO2 as was emitted
into the atmosphere.
• Biomass energy is neutral only if the net life-cycle emissions are zero.8
• Biomass energy is neutral if it achieves lower net increases in atmospheric GHGs
when compared to alternative energy activities.
4 U.S. Environmental Protection Agency, “Deferral for CO2 Emissions From Bioenergy and Other Biogenic Sources
Under the Prevention of Significant Deterioration (PSD) and Title V Programs: Final Rule,” July 1, 2011.
http://www.epa.gov/NSR/documents/Biogenic_Deferral_pre-pub.pdf.
5 Congress addressed carbon accounting for another major bioenergy pathway—liquid transportation biofuels—with a
life cycle emission analysis (a requirement within the Renewable Fuel Standard). For more information, see CRS
Report R40460, Calculation of Lifecycle Greenhouse Gas Emissions for the Renewable Fuel Standard (RFS), by Brent
D. Yacobucci and Kelsi Bracmort.
6 For more information, see CRS Report RL34059, The Carbon Cycle: Implications for Climate Change and Congress,
by Peter Folger. Carbon is an elemental building block of molecules that make up all organisms on Earth. Carbon
cycling is the process by which living things absorb carbon from the atmosphere, carbonate rocks and ocean deposits,
dead organic matter in the soil, or food and return it to the atmosphere or soil by respiration, combustion, or decay.
7 R. Miner, “Biomass ‘Neutrality’ in the Context of Forest-based Fuels and Products,” USDA Bioelectricty and GHG
Workshop, Washington, DC, November 15, 2010. Some of the definitions are not mutually exclusive.
8 GHGs from bioenergy production can be accounted for using a life-cycle assessment (LCA). The LCA is further
discussed in “Greenhouse Gas Accounting for Biopower Production,” below.
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There are pros and cons for each assertion. For instance, declaring that biomass energy is carbon
neutral because biomass is naturally carbon neutral does not account for GHG emissions released
due to management of crops grown for energy production (e.g., fertilizer). There may need to be
additional plantings of certain biomass feedstocks to remove the CO2 emitted from biomass
cultivated for energy production.
The carbon cycles for a bioenergy system and a fossil fuel system differ in at least two ways: the
carbon source (finite versus renewable) and the atmospheric carbon concentration (potentially
stable versus additional; see Figure 1). Three main factors contribute to the amount of carbon
emitted from biopower generation: feedstock production (cultivation and harvest), feedstock
transport, and the biopower technology type. However, as noted by many sources, feedstock
production also absorbs carbon during growth.
Greenhouse Gas Accounting for Biopower
Production
Whether and how to conduct GHG accounting for biopower is an issue at the forefront of the
bioenergy movement. GHG accounting can be used to compare the environmental footprint of a
biopower operation with that of conventional fossil fuel (e.g, electricity from coal). The
environmental footprint is often calculated using a life-cycle assessment (LCA), an analytic
method for identifying, evaluating, and comparing the environmental impacts of emissions and
the resource depletion associated with a specific process.9 An LCA generally uses observed data
and assumptions to model what GHGs are being released at each phase of the process. Ideally, an
LCA would encompass economic and social factors for a more comprehensive assessment.
Alternatively, an LCA can be one element used in assessing a preferred energy approach, along
with cost and performance data. In some cases, even if LCA results favor a particular approach,
an LCA alone might not be the deciding factor when choosing an energy process; financial
objectives, policy goals, and other factors may influence which approach is selected.
An LCA has four major stages: goal and scope definition, inventory analysis, impact assessment,
and interpretation.10 While an LCA can be performed to meet various goals, the goals most
applicable to the biopower arena are to support broad environmental assessments, support public
policy, and provide information and direction to decision-makers. The goal and scope definition
stage determines the amount of resources and time needed to conduct an LCA. The inventory
analysis stage of an LCA quantifies energy and raw material requirements, atmospheric
emissions, waterborne emissions, solid wastes, and other releases for the entire life cycle of a
product, process, or activity. The impact assessment stage evaluates the potential human health
and environmental impacts of the environmental resources and releases identified during the
inventory analysis stage. The interpretation stage identifies, quantifies, checks, and evaluates the
results of the inventory analysis and impact assessment stages, and communicates the results.
9 National Renewable Energy Laboratory, Energy Analysis, October 2010, http://www.nrel.gov/analysis/
tech_bio_analysis.html.
10 U.S. Environmental Projection Agency, Life Cycle Assessment: Principles and Practice, EPA/600/R-06/060,
Cincinnati, OH, May 2006, http://www.epa.gov/nrmrl/lcaccess/pdfs/600r06060.pdf.
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Is Biopower Carbon Neutral?
Figure 1. Bioenergy CO2 Balance vs. Fossil Fuel CO2 Balance
Source: International Energy Agency, IEA Bioenergy Task 38, Greenhouse Gas Balances of Bioenergy and
Bioenergy Systems, 2002. Adapted by CRS.
Notes: The magnitude of the carbon flows, as indicated by the width of the arrows, is a significant part of the
debate over the carbon neutrality of bioenergy.
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