Biomass Energy

How Biomass Energy Works | 
Union of Concerned Scientists ©2010 Union of Concerned Scientists

(Note by Alan Page: This paper is a vast improvement on the Manomet Study report 2010, but there is
more to say in relation to sustainability and how other technologies may fit in to the picture. So
even this paper should still be treated as a work in progress.)

To many people, the most familiar forms of renewable energy are the wind and the
sun. But biomass (plant material and animal waste) is the oldest source of
renewable energy, used since our ancestors learned the secret of fire.
Until recently, biomass supplied far more renewable electricity - or
"biopower" - than wind and solar power combined.[1]
If developed properly, biomass can and should supply increasing amounts of
biopower. In fact, in numerous analyses of how America can transition to a clean
energy future, sustainable biomass is a critical renewable resource.[2]

Contents
Types of Beneficial Biomass
Converting Biomass to Biopower
Potential for Biopower
Environmental Risks and Benefits
Carbon Emissions
Conclusions


Sustainable, low-carbon biomass can provide a significant fraction of the new
renewable energy we need to reduce our emissions of heat-trapping gases like
carbon dioxide to levels that scientists say will avoid the worst impacts of
global warming. Without sustainable, low-carbon biopower, it will likely be more
expensive and take longer to transform to a clean energy economy.
But like all our energy sources, biopower has environmental risks that need to
be mitigated. If not managed carefully, biomass for energy can be harvested at
unsustainable rates, damage ecosystems, produce harmful air pollution, consume
large amounts of water, and produce net greenhouse emissions.
However, most scientists believe there is a wide range of biomass resources that
can be produced sustainably and with minimal harm, while reducing the overall
impacts and risks of our current energy system. Implementing proper policy is
essential to securing the benefits of biomass and avoiding its risks.
Based on our bioenergy principles, UCS' work on biopower is dedicated to
distinguishing between beneficial biomass resources and those that are
questionable or harmful - in a practical and efficient manner - so that
beneficial resources can make a significant contribution to our clean energy future.

Note: This page addresses using biomass to generate biopower. For more
information on biofuels, go to the UCS Clean Vehicles Program's biofuels pages.

Biomass is a renewable energy source not only because the energy it comes from
the sun, but also because biomass can re-grow over a relatively short period of
time. Through the process of photosynthesis, chlorophyll in plants captures the
sun's energy by converting carbon dioxide from the air and water from the ground
into carbohydrates - complex compounds composed of carbon, hydrogen, and oxygen.
When these carbohydrates are burned, they turn back into carbon dioxide and
water and release the energy they captured from the sun. In this way, biomass
functions as a sort of natural battery for storing solar energy. As long as
biomass is produced sustainably - meeting current needs without diminishing
resources or the land's capacity to re-grow biomass and recapture carbon - the
battery will last indefinitely and provide sources of low-carbon energy.

Types of Beneficial Biomass
Most scientists believe that a wide range of biomass resources are "beneficial"
because their use will clearly reduce overall carbon emissions and provide other
benefits. Among other resources, beneficial biomass includes:
energy crops that don't compete with food crops for land
portions of crop residues such as wheat straw or corn stover
sustainably-harvested wood and forest residues, and
clean municipal and industrial wastes.[3]

BENEFICIAL BIOMASS:

Beneficial biomass use can be considered part of the terrestrial carbon
cycle - the balanced cycling of carbon from the atmosphere into plants and then
into soils and the atmosphere during plant decay. When biopower is developed
properly, emissions of biomass carbon are taken up or recycled by subsequent
plant growth within a relatively short time, resulting in low net carbon
emissions.
Beneficial biomass sources generally maintain or even increase the stocks of
carbon stored in soil or plants. Beneficial biomass also displaces carbon
emissions from fossil fuels, such as coal, oil or natural gas, the burning of
which adds new and additional carbon to the atmosphere and causes global
warming.
Among beneficial resources, the most effective and sustainable biomass resources
will vary from region to region and also depend on the efficiency of converting
biomass to its final application, be it for biopower, biofuels, bioproducts, or
heat.

Energy Crops
Energy crops can be grown on farms in potentially large quantities and in ways
that don't displace or otherwise reduce food production, such as by growing them
on marginal lands or pastures or as double crops that fit into rotations with
food crops. Trees and grasses that are native to a region often require fewer
synthetic inputs and pose less risk of disruption to agro-ecosystems.

Switchgrass

Grasses
Thin-stemmed perennial grasses used to blanket the prairies of the United States
before the settlers replaced them with annual food crops. Switchgrass, big
bluestem, and other native varieties grow quickly in many parts of the country,
and can be harvested for up to 10 years before replanting. Thick-stemmed
perennials like sugar cane and elephant grass can be grown in hot and wet
climates like those of Florida and Hawaii.
Switchgrass is a perennial grass that grows throughout the Great Plains, the
Midwest and the South. Switchgrass is a hardy species - resistant to floods,
droughts, nutrient poor soils, and pests - and does not require much fertilizer
to produce consistent high yields.[4] Today, switchgrass is primarily cultivated
either as feed for livestock or, due to its deep root structure, as ground cover
to prevent soil erosion. However, this prairie grass also has promise for
biopower and biofuel production (see profile of Show-Me Energy below). If
demand for switchgrass outstrips the capacity of marginal lands, it could,
however, compete with other crops for more productive land.[5]

Beneficial biomass: rice hulls in Arkansas
Riceland Foods and Riviana Foods built gasification facilities in
Stuttgart and Jonesboro, which together process 650 tons of rice hulls per
day to produce biogas for energy. Rice hulls, which make up about 20% of
the whole grain, are rubbed off the grain in processing. Due to their high
silica content, rice hulls should not be burned and cannot be fed to
cattle, so gasification is a cleaner way to produce energy from something
that would otherwise be a waste product. The gas produced at the Arkansas
facilities is used to replace natural gas and to generate biopower.[6]

Crop Residues
Depending on soils and slope, a certain fraction of crop residues should be left
in the field to maintain cover against erosion and to recycle nutrients, but in
most cases some fraction of crop residues can be collected for renewable energy
in a sustainable manner. Food processing also produces many usable residues.

Manure
Manure from livestock and poultry contains valuable nutrients and, with
appropriate management, should be an integral part of soil fertility management.
Where appropriate, some manure can be converted to renewable energy through
anaerobic digesters, combustion or gasification. The anaerobic digesters produce
biogas which can either directly displace natural gas or propane, or be burned
to generate biopower. For instance, dairy farms that convert cow manure with
methane digesters to produce biogas can use the biogas in three ways (or in some
combination of these end uses).
They can use the biogas on-site as a replacement for the farm's own natural gas
or propane use, clean up the biogas and pressurize and inject into nearby
natural gas pipelines, or burn it to produce steam that is run through a turbine
to generate renewable electricity for use on-site and/or fed into the local
energy grid. The best application of biogas from manure will be determined by
the type of manure, opportunity to displace natural gas or propane use, local
energy markets and state and federal incentives.

Beneficial biomass: food waste, forest residues and perennial grasses in
Minnesota
In Minnesota, food industry and other byproducts are feeding a new
combined heat and power (CHP) plant that generates renewable electricity
and efficiently uses waste heat from the boiler. Rahr Malting Company and
the Shakopee Mdewakanton Sioux partnered to form Koda Energy, which in
2009 began generating up to 22 megawatts of renewable electricity with oat
hulls, wood chips, prairie grasses, and barley malt dust from Rahr
Malting.
The Koda plant burns about 170,000 tons of these agricultural waste
products a year, and is able to operate at over 70 percent efficiency
because Rahr Malting also uses the waste heat from the boiler in their
operations, displacing the need for additional natural gas. About half of
the plant's renewable electricity is used to powering Rahr Malting, with
the remainder purchased by Xcel Energy to supply to their customers. In
the future, the Shakopee Mdewakanton Sioux Community hopes to use
switchgrass grown on restored prairies to provide some of the biomass for
Koda Energy.[7]

Poultry litter can be digested to produce biogas, or combusted to produce
renewable electricity, either directly or through gasification, which improves
efficiency and reduces emissions.

Woody biomass
Bark, sawdust and other byproducts of milling timber and making paper are
currently the largest source of biomass-based heat and renewable electricity;
commonly, lumber, pulp, and paper mills use them for both heat and power. In
addition, shavings produced during the manufacture of wood products and organic
sludge (or "liquor") from pulp and paper mills are biomass resources. Some of
these "mill residues" could be available for additional generation of renewable
electricity.
Beyond these conventional types of woody biomass, there are additional sources
of woody biomass that could be used for renewable energy. With the proper policy
(see below), these additional sources could be sustainably harvested and make a
significant contribution to renewable energy generation.

Forest residues
It is important to leave some tree tops and branches, and even dead standing
trees, on-site after forest harvests. Coarse woody debris left on the soil
surface cycles nutrients, especially from leaves, limbs and tops, reduces
erosion and provides habitat for invertebrates.
Dead standing trees provide bird habitat. Provided that appropriate amounts of
residues are left in the forest, the remaining amounts of limbs and tops, which
are normally left behind in the forest after timber-harvesting operations, can
be sustainably collected for energy use. Often, limbs and tops are already piled
at the "landing" - where loggers haul trees to load them unto trucks. Using these
residues for biomass can be cheaper than making additional trips into the woods -
and reduce impacts on forest stands, wildlife and soils.

Forest treatments
Many forest managers see new biomass markets providing opportunities to improve
forest stands.[9] Where traditional paper and timber markets require trees to
meet diameter and quality specifications, biomass markets will pay for otherwise
unmarketable materials, including dead, damaged and small-diameter trees. Income
from selling biomass can pay for or partially offset the cost of forest
management treatments needed to remove invasive species, release valuable
understory trees, or reduce the threat of fires, though the science behind fire
reduction is very complex and site specific.[10]
Removing undesired, early-succession or understory species can play an important
role in restoring native forest types and improving habitat for threatened or
endangered species, such as longleaf forests in the Southeast.[11]

Thinned trees
Thinning plantations of smaller-diameter trees before final harvest can also
provide a source of biomass. In addition, thinning naturally regenerating stands
of smaller-diameter trees can also improve the health and growth of the
remaining trees. With the decline in paper mills, some areas of the country no
longer have markets for smaller-diameter trees. Under the right conditions,
biomass markets could become a sustainable market for smaller-diameter trees
that could help improve forest health and reduce carbon emissions.

Beneficial biomass: bagasse in Florida
At its plant in South Bay, Florida Crystals burns 1 million tons of sugar
cane stalks per year to produce up to 140 MW of electricity - enough to
power the mill, refinery and 60,000 homes. Florida Crystals sells the
surplus energy to Florida Power & Light and other utilities.[8]

Short-rotation trees
Under the right circumstances, there may be a role for short-rotation tree
plantations dedicated to energy production. Such plantations could either be
re-planted or "coppiced." (Coppicing is the practice of cutting certain species
close to the ground and letting them re-grow.) Coppicing allows trees to be
harvested every three to eight years for 20 or 30 years before replanting.
Short-rotation management, either through coppicing or replanting, is best
suited to existing plantations - not longer-rotation naturally-regenerating
forests, which tend to have greater biodiversity and store more carbon than
plantations.
Policy is needed to ensure that the growing biomass industry will use these
beneficial resources, and use them on a sustainable basis. See below for more on
the policy needed to guide the biomass industry toward sustainable, beneficial
resources.


Urban wastes
People generate biomass wastes in many forms, including "urban wood waste" (such
as tree trimmings, shipping pallets and clean, untreated leftover construction
wood), the clean, biodegradable portion of garbage (paper that wouldn't be
recycled, food, yard waste, etc.). In addition, methane can be captured from
landfills or produced in the operation of sewage treatment plants and used for
heat and power, reducing air pollution and emissions of global warming gases.
Converting Biomass to Biopower
From the time of Prometheus to the present, the most common way to capture the
energy from biomass was to burn it to make heat. Since the industrial revolution
this biomass fired heat has produced steam power, and more recently this biomass
fired steam power has been used to generate electricity. Burning biomass in
conventional boilers can have numerous environmental and air-quality advantages
over burning fossil fuels.
Advances in recent years have shown that there are even more efficient and
cleaner ways to use biomass. It can be converted into liquid fuels, for example,
or "cooked" in a process called "gasification" to produce combustible gases,
which reduces various kinds of emissions from biomass combustion, especially
particulates.
In 1998, the first U.S. commercial scale biomass gasification
demonstration plant based on the SilvaGas process began at the McNeil
Power Station in Burlington, Vermont.
The SilvaGas process, a particular form of biomass gasification,
indirectly heats the biomass using heated sand in order to produce a
medium Btu gas.
The McNeil power station is capable of generating 50 MW of power from
local wood waste products.


Direct combustion
The oldest and most common way of converting biomass to electricity is to burn
it to produce steam, which turns a turbine that produces electricity. The
problems with direct combustion of biomass are that much of the energy is wasted
and that it can cause some pollution if it is not carefully controlled. Direct
combustion can be done in a plant using solely biomass (a "dedicated plant") or
in a plant made to burn another fuel, usually coal.
Co-firing
An approach that may increase the use of biomass energy in the short term is to
mix it with coal and burn it at a power plant designed for coal - a process known
as "co-firing." Through gasification, biomass can also be co-fired at natural gas-
powered plants. The benefits associated with biomass co-firing can include lower
operating costs, reductions of harmful emissions like sulfur and mercury, greater energy
security and, with the use of beneficial biomass, lower carbon emissions.
Co-firing is also one of the more economically viable ways to increase biomass
power generation today, since it can be done with modifications to existing
facilities.
Repowering Coal plants can also be converted to run entirely on biomass, known as
"re-powering." (Similarly, natural gas plants could also be converted to run on biogas
made from biomass; see below.)

Combined heat and power (CHP)
Direct combustion of biomass produces heat that can also be used to heat
buildings or for industrial processes (for example, see textbox on Koda Energy
above). Because they use heat energy that would otherwise be wasted, CHP
facilities can be significantly more efficient than direct combustion systems.
However, it is not always possible or economical to find customers in need of
heat in close proximity to power plants.

Biomass gasification
By heating biomass in the presence of a carefully controlled amount of oxygen
and under pressure, it can be converted into a mixture of hydrogen and carbon
monoxide called syngas. This syngas is often refined to remove contaminants.
Equipment can also be added to separate and remove the carbon dioxide in a
concentrated form. The syngas can then be run directly through a gas turbine or
burned and run through a steam turbine to produce electricity. Biomass
gasification is generally cleaner and more efficient that direct combustion of
biomass. Syngas can also be further processed to make liquid biofuels or other
useful chemicals.

Anaerobic digestion
Micro-organisms break down biomass to produce methane and carbon dioxide. This
can occur in a carefully controlled way in anaerobic digesters used to process
sewage or animal manure. Related processes happen in a less-controlled manner
in landfills, as biomass in the garbage breaks down. A portion of this methane
can be captured and burned for heat and power. In addition to generating
biogas, which displaces natural gas from fossil fuel sources, such collection
processes keep the methane from escaping to the atmosphere, reducing emissions
of a powerful global warming gas.

Beneficial biomass: crop residues, switchgrass, wood waste in Missouri
Among new biomass pelletizing facilities, Show Me Energy cooperative is
pioneering a unique way to combine the community benefits of
smaller-scale, locally owned biomass facilities with the efficiencies
needed to serve the export market. Founded with the investment of its
hundreds of farmer-members, Show Me is pelletizing crop residues,
switchgrass and urban wood residues. In addition to selling pellets
locally, Show Me is exporting pellets to Europe.
If successfully developed across the country, facilities like Show Me
could create markets for farmers and jobs in rural communities, make
biomass more economical to transport and easier for utilities to use and
reduce carbon emissions by displacing coal and other fossil fuels with a
variety of locally-available beneficial biomass resources.[13]

Energy density
Another important consideration with biomass energy systems is that unprocessed
biomass contains less energy per pound than fossil fuels - it has less "energy
density." Green woody biomass contains as much as 50% water by weight. This
means that unprocessed biomass typically can't be cost-effectively shipped more
than about 50-100 miles by truck before it is converted into fuel or energy.
It also means that biomass energy systems may be smaller scale and more
distributed than their fossil fuel counterparts, because it is hard to
sustainably gather and process more than a certain amount of in one place. This
has the advantage that local, rural communities will be able to design energy
systems that are self-sufficient, sustainable, and adapted to their own needs.
However, there are ways to increase the energy density of biomass and to
decrease its shipping costs. Drying, grinding and pressing biomass into
"pellets" increases its energy density. Compared to raw logs or wood chips,
biomass pellets can also be more efficiently handled with augers and conveyers
used in power plants. In addition, shipping biomass by water greatly reduces
transportation costs compared to hauling it by truck.
Thus, hauling pelletized biomass by water has made it economical to transport
biomass much greater distances - even thousands of miles, across the Atlantic and
Pacific, to markets in Japan and Europe. In the last few years, the
international trade in pelletized biomass has been growing rapidly, largely
serving European utilities that need to meet renewable energy requirements and
carbon-reduction mandates. Several large pellet manufacturers are locating in
the Southern US, with its prodigious forest plantation resource, to serve such
markets.[12]

Potential for Biopower
In the United States, we already get over 50 billion kilowatt-hours of
electricity from biomass, providing nearly 1.5 percent of our nation's total
electric sales. Biomass was the largest source of renewable electricity in the
U.S. until 2009, when it was overtaken by wind energy. Biopower accounted for
more than 35 percent of total net renewable generation in 2009, excluding
conventional hydroelectric generation.[14] The contribution for heat is also
substantial. But with better conversion technology and more attention paid to
energy crops, we could produce much more.

Technical resource potential for developing biopower from beneficial biomass:

Renewable Resource Electric Generation Capacity Potential (in gigawatts)
Electric Generation (billion kilowatt-hours) Renewable Electricity Generation
as % of 2007 Electricity Use:
Energy Crops 83 584 14%
Agricultural Residues 114 801 19%
Forest Residues 33 231 6%
Urban Residues 15 104 3%
Landfill Gas 2.6 19 0.4%
Total 248 1,739 42%

(Source: DOE, 2005 [15])
The growth of biopower will depend on the availability of resources, land-use
and harvesting practices, and the amount of biomass used to make fuel for
transportation and other uses. Analysts have produced widely varying estimates
of the potential for electricity from biomass. For example, a 2005 DOE study
found that the nation has the technical potential to produce more than a billion
tons of biomass for energy use (Perlack et al. 2005).
If all of that was used to produce electricity, it could have met more than 40
percent of our electricity needs in 2007 (see Table above). In a study of the
implementation of a 25 percent renewable electricity standard by 2025, the
Energy Information Administration (EIA) assumed that 598 million tons of biomass
would be available, and that it could meet 12 percent of the nation's
electricity needs by 2025 (EIA 2007). In another study, NREL estimated that more
than 423 million metric tons of biomass would be available each year (ASES
2007).
In UCS - Climate 2030 analysis, we assumed that only 367 million tons of biomass
would be available to produce both electricity and biofuels. That conservative
estimate accounts for potential land-use conflicts, and tries to ensure the
sustainable production and use of the biomass. To minimize the impact of growing
energy crops on land now used to grow food crops, we excluded 50 percent of the
switchgrass supply assumed by the EIA.
That allows for most switchgrass to grow on pasture and marginal agricultural
lands, and also provides much greater cuts in carbon emissions (for more details,
see Appendix G of Climate 2030:
http://www.ucsusa.org/assets/documents/global_warming/climate2030-app-g-biomass.pdf).

The potential contribution of biomass to electricity production in our analysis
is therefore just one-third of that identified in the DOE study, and 60 percent
of that in the EIA study.[16]

Distribution of biomass
Whether crop or forest residues, urban and mill wastes, or energy crops, biomass
of one kind or another is available in most areas of the country. For
information on the availability of various kinds of biomass resources in
particular parts of the country, see the National Renewable Energy Labs's
searchable biomass databases.

Environmental Risks and Benefits
Like all energy sources, biomass has environmental impacts and risks. The main
impacts and risks from biomass are sustainability of the resource use, air
quality and carbon emissions.

Sustainability
Biomass energy production involves annual harvests or periodic removals of
crops, residues, trees or other resources from the land. These harvests and
removals need to be at levels that are sustainable, i.e., ensure that current
use does not deplete the land's ability to meet future needs, and also be done
in ways that don't degrade other important indicators of sustainability. Because
biomass markets may involve new or additional removals of residues, crops, or
trees, we should be careful to minimize impacts from whatever additional demands
biomass growth or harvesting makes on the land.
Markets for corn stover, wheat straw and other crop residues are common and
considerable research has been done on residue management. In addition,
participation in some federal crop programs requires conservation plans. As a
result of established science and policy, farmers generally leave a certain
percentage of crop residues on fields, depending on soil and slope, to reduce
erosion and maintain fertility. Additional harvests of crop residues or the
growth of energy crops might require additional research and policy to minimize
impacts.
In forestry, where residue or biomass markets are less common, new guidelines
might need to be developed. Existing best management practices (BMPs) were
developed to address forest management issues, especially water quality, related
to traditional sawlog and pulpwood markets, with predictable harvest levels. But
the development of new biomass markets will entail larger biomass removals from
forests, especially forestry residues and small diameter trees. Current BMPs may
not be sufficient under higher harvesting levels and new harvests of previously
unmarketable materials.
However, because woody biomass is often a low-value product, sustainability
standards must be relatively inexpensive to implement and verify. Thankfully, we
can improve the sustainability of biomass harvests with little added cost to
forest owners through the use of existing forest management programs, including
1) biomass BMPs, 2) certification or 3) forest management plans.
Working with forest owner associations, foresters, forest ecologists, wildlife
conservation experts and biomass developers, UCS helped develop practical and
effective sustainability provisions that can provide a measure of assurance that
woody biomass harvests will be sustainable.
State-based biomass Best Management Practices (BMPs) or guidelines. Missouri,
Minnesota, Pennsylvania, Maine and Wisconsin developed biomass harvesting
guidelines to avoid negative impacts of biomass removals. Other states and
regions, including Southern states, are also developing biomass guidelines.
Developed through collaborative stakeholder processes, BMPs are practical enough
to be used by foresters and loggers.
Third-party forest certification. Certification can also be used to verify the
sustainability of biomass harvests. Between them, the Forest Stewardship
Council, the Sustainable Forestry Initiative, and Tree Farm have certified
nearly 275 millions of acres of industrial and private forestland in the U.S.
Certification programs already address, or are being updated to address, many of
the concerns related to biomass harvests.
Forest management plans written by professionally-accredited foresters.
Foresters can help anticipate and therefore minimize impacts of additional
biomass removals. Although a minority of smaller forest owners have management
plans, forest owner associations have long recommended that more forest owners
have them written to better achieve their financial and conservation objectives.
Forest owners who have management plans stand to make more money than if they
lacked such plans. To avoid out-of-pocket costs, proceeds from biomass sales
could cover the cost of writing management plans.
Whether implemented through BMPs, certification or management plans,
sustainability standards should minimize short-term impacts and avoid long-term
degradation of water quality, soil productivity, wildlife habitat, and
biodiversity - all key indicators of sustainability. Science and local conditions
need to be used in determining the standards. For example, fire-adapted forests
will likely require retention of less woody biomass than forests adapted to other
disturbances such as hurricanes.
Sustainability standards should ensure nutrients removed in a biomass harvest
are replenished and that removals do not damage long-term productivity,
especially on sensitive soils. Coarse woody material that could be removed for
biomass energy also provides crucial wildlife habitat; depending on a state's
wildlife, standards might protect snags, den trees, and large downed woody
material. Biodiversity can be fostered through sustainability standards that
encourage retention of existing native ecosystems and forest restoration.
Lastly, sustainability standards should provide for the regrowth of the
forest - surely a requirement for woody biomass to be truly renewable.

Air quality
Especially with the emissions from combustion systems, biomass can impact air
quality. Emissions vary depending on the biomass resource, the conversion
technology (type of power plant), and the pollution controls installed at the
plant. The table below from the National Renewable Energy Laboratory and Oak
Ridge National Laboratory compares air emissions from different biomass, coal
and natural gas power plants with pollution control equipment.
Because most biomass resources and natural gas contain far less sulfur and
mercury than coal, biomass and natural gas power plants typically emit far less
of these pollutants than do coal-fired power plants.[17] Sulfur emissions are a
key cause of smog and acid rain. Mercury is a known neurotoxin.

Direct Air Emissions from Biomass, Coal and Natural Gas Power Plants, by Boiler
Type -image missing- (Source: DOE, 2003 [18])

Similarly, biopower plants emit less nitrogen oxide (NOx) emissions than
conventional coal plants. NOx emissions create harmful particulate matter, smog
and acid rain that results in billions of dollars of public health costs each
year. Biopower systems that use either fluidized bed or gasification have NOx
emissions that are comparable to new natural gas plants.
Biopower facilities with stoker boilers do emit significant quantities of
particulates (PM 10) and carbon monoxide (CO), but these emissions can also be
significantly reduced with fluidized bed and gasification systems. Advanced
coal gasification power plants also produce significantly lower air emissions
than conventional coal plants.

CARBON EMISSIONS
Burning or gasifying biomass does emit carbon into the atmosphere. With
heightened interest in renewable energy and climate change, scientists have put
biomass' carbon emissions under additional scrutiny, and are making important
distinctions between biomass resources that are beneficial in reducing net
carbon emissions and biomass resources that would increase net emissions. While
our understanding of specific biomass resources and applications will continue
to evolve, we can group biomass resources into three general categories, based
on their net carbon impacts.

Beneficial biomass:
As mentioned previously, there is considerable consensus among leading
scientists that there are biomass resources that are clearly beneficial in their
potential to reduce net carbon emissions. These beneficial resources exist in
substantial supplies and can form the basis of increasing production of biopower
and biofuels.

Harmful biomass:
In contrast to these beneficial biomass resources, scientists generally agree
that harmful biomass resources and practices include clearing forests, savannas
or grasslands to grow energy crops, and displacing food production for bioenergy
production that ultimately leads to the clearing of carbon-rich ecosystems
elsewhere to grow food.[19] Harmful biomass adds net carbon to the atmosphere by
either directly or indirectly decreasing the overall amount of carbon stored in
plants and soils.

Marginal biomass:
Marginal biomass resources that could be beneficial - or harmful
Scientists think the carbon benefits and risks of some biomass resource
range widely, depending on how and where they are harvested, how
efficiently they are converted to energy, and what fossil fuels they
replace. In other words, these resources might be beneficial or harmful
depending on specific situations. The use of trees harvested especially
for energy use is a good example.
Using trees that will quickly and certainly re-grow to efficiently
displace more carbon-intensive fossil fuels may be beneficial. On the
other hand, using trees that will re-grow slowly or maybe not be fully
replaced in an inefficient facility or to displace less carbon-intensive
fuels may not be beneficial, or may be beneficial only over unacceptably
long time frames in comparison to other available resources.[20] Marginal
resources should only be used when their use can be demonstrated to reduce
net emissions.

NAVIGATING THE PATH FORWARD
We all should be concerned that biomass will be developed sustainably and
beneficially - in ways that are cleaner and safer than our current energy mix,
that are truly sustainable and that will reduce net carbon emissions. Beneficial
biomass resources will in most cases be cleaner, sustainable and beneficial.
Harmful biomass resources almost always will not. Marginal biomass resources may
be cleaner, sustainable and beneficial - or not - depending on specific
circumstances.
On the basis of the science, it would be unwarranted to support the use of all
biomass resources, with any conversion technology and for any application. It
would also be unwarranted to oppose all biomass on the basis that some biomass
resources, conversion technologies or applications are not sustainable or
beneficial.
Unfortunately, some biomass advocates and biomass opponents alike make just
these mistakes - failing to distinguish beneficial from harmful biomass resources.
Thus, all too often the debate about biomass is conducted in absolutist terms,
either arguing that all biomass is "carbon neutral" or that "biomass" writ large
will accelerate global warming, increase air pollution or lay waste to forests.
These absolutist approaches to biomass have led to two pitfalls in developing
biomass policy. Absolute advocates have supported policy that would let almost
any kind of biomass resource be eligible for renewable energy and climate
legislation. On the other extreme, absolutist opposition has led to proposals to
effectively remove most kinds of biomass from policy, especially at the state
level.
Both approaches pose challenges to the development of beneficial biopower
generation. The "anything goes" approach risks the development of harmful
biomass resources that will increase net carbon emissions and cause other harm.
Such a path also risks undermining the confidence the public and policymakers
can place in biomass as a legitimate climate solution - which could eventually
threaten the inclusion of beneficial biomass as a renewable energy resource in
policy.
In tarring biomass with too broad a brush, some biomass opposition lumps
beneficial resources with harmful ones and risks not developing beneficial
biomass at large enough scale to capture important benefits for the country and
the planet. As a group of biomass experts, comprising both advocates and
skeptics, noted in an article in Science, "society cannot afford to miss out on
the global greenhouse gas reductions and the local environmental and societal
benefits when biofuels are done right."[21]
To capture the benefits of beneficial biomass and avoid the risks of harmful
biomass, federal and state policies should distinguish between beneficial and
harmful biomass resources. Most policy related to biomass-based energy, be it
for fuels, electricity or thermal, includes a definition of eligible biomass
resources.
This definition should make beneficial biomass resources eligible, exclude
harmful biomass resources and practices, and include practical, reasonable
sustainability standards to ensure that harvests of biomass do not degrade
soils, wildlife habitat, biodiversity and water quality. UCS has developed
practical, effective sustainability standards for inclusion in biomass
definitions, especially at the federal level.

CONCLUSIONS:
When done well, biomass energy brings numerous environmental
benefits - particularly reducing many kinds of air pollution and net carbon
emissions. Biomass can be grown and harvested in ways that protect soil quality,
avoid erosion, and maintain wildlife habitat. However, the environmental
benefits of biomass depend on developing beneficial biomass resources and
avoiding harmful resources, which having policies that can distinguish between
them.
In addition to its many environmental benefits, beneficial biomass offers
economic and energy security benefits.[22] By growing our fuels at home, we
reduce the need to import fossil fuels from other states and nations, and reduce
our expenses and exposure to disruptions in that supply. Many states that import
coal from other states or countries could instead use local biomass
resources.[23]
With increasing biomass development, farmers and forest owners gain valuable new
markets for their crop residues, new energy crops and forest residues - and we
could substantially reduce our global warming emissions. For instance, a 2009
UCS analysis found that beneficial biomass resources could provide one-fourth of
the electricity needed to meet a 25 percent by 2025 RES, while generating $12
billion in new biomass income for farmers, ranchers, and forest owners and
reducing power plant carbon emissions as much as taking 45 million cars off the
road.[24]
Growing our use of beneficial biopower will require policy to guide industry to
the right kinds of resources, public confidence that biomass can be a sustainable
and beneficial climate solution, and the use of appropriate biomass
conversion technologies and applications.



Endnotes
1 Energy Information Administration (EIA). 2008. Renewable energy trends 2007.
Washington, DC. Online at
http://www.eia.doe.gov/cneaf/solar.renewables/page/trends/rentrends.html.
2 Union of Concerned Scientists. 2009a. UCS Climate 2030: A national blueprint
for a clean energy economy. Cambridge, MA.
3 Tilman, David., et al. 2009. Beneficial biofuels - the food, energy and
environment trilemma. Science, July 17, 270-271.
4 Natural Resources Conservation Service (NRCS). 2006. Switchgrass burned for
power. Washington, DC: U.S. Department of Agriculture. Online at
http://www.ia.nrcs.usda.gov/News/newsreleases/2006/switchgrass.html
5 Marshall, Liz., et al. 2010. Fields of Fuel World Resources Institute.
Washington, DC. Available online at: http://pdf.wri.org/fields_of_fuel.pdf
6 PRM Energy Systems. 1996. A case study of two biomass gasification systems
converting 650 tons/day of rice hulls to PRME NaturallyGas. Hot Springs, AR.
Online at:
http://gasifiers.bioenergylists.org/files/PRM%20ENERGY%20Gasification%20Systems.pdf
7 Schill, Susanne. 2008. Koda biomass energy facility to begin final testing.
Available only online at:
http://www.biomassmagazine.com/article.jsp?article_id=2237&q=koda
8 Burnham, Michael. 2009. Energy by the acre. E and E News. Available online at:
http://www.eenews.net/special_reports/everglades/energy_by_the_acre/
9 Forest Guild. 2008. Woody biomass removal case studies. Santa Fe, NM.
Available online at: http://biomass.forestguild.org/
10 Franklin, Jerry., et al. 2003. Forging a science-based national forest fire
policy. Forest Fires: Issues in science and technology. Available online at:
http://inr.oregonstate.edu/download/forging_a_science_based_national_forest_fire_policy.pdf
11 Brockaway, Dale., et al. 2005. Restoration of longleaf pine ecosystems. US
Forest Service, Southern Forest Research Station. Asheville, NC. Available
online at: http://www.srs.fs.usda.gov/pubs/gtr/gtr_srs083.pdf
12 Adrian Pirraglia, et al. 2010. Wood pellets: An expanding market opportunity.
Biomass Magazine. June. Online at
http://www.biomassmagazine.com/article.jsp?article_id=3853.
13 Johnson, R. 2010. It's show time. Biomass Magazine. 2010. Online at
http://www.biomassmagazine.com/article.jsp?article_id=3537
14 Energy Information Administration (EIA). 2010. Annual Energy Outlook 2010.
Online at http://www.eia.doe.gov/oiaf/aeo/index.html
15 Department of Energy (DOE) and Department of Agriculture (USDA). 2005.
Biomass as feedstock for a bioenergy and bioproducts industry: The technical
feasibility of a billion-ton annual supply. Oak Ridge, TN: Oak Ridge National
Laboratory. Online at
http://feedstockreview.ornl.gov/pdf/billion_ton_vision.pdf.
16 Union of Concerned Scientists. 2009a. UCS Climate 2030: A national blueprint
for a clean energy economy. Cambridge, MA. Online at
http://www.ucsusa.org/global_warming/solutions/big_picture_solutions/climate-2030-blueprint.html
17 Energy Information Agency (EIA). Biomass for electricity generation.
Washington, DC. Online at http://www.eia.doe.gov/oiaf/analysispaper/biomass/
18 Bain, Richard. 2003. Biopower Technical Assessment: State of the Industry and
the Technology. Department of Energy. Washington, DC.
Available online at:
http://www.fs.fed.us/ccrc/topics/urban-forests/docs/Biopower_Assessment.pdf
19 Tilman, Science.
20 Manomet Center for Conservation Sciences. 2010. Biomass Sustainability and
Carbon Policy Study. Brunswick, ME. Online at:
http://www.manomet.org/sites/manomet.org/files/Manomet_Biomass_Report_Full_LoRez.pdf
21 Tilman, Science.
22 U.S. Department of Energy (DOE). Biomass: Frequently asked questions.
Online at http://www1.eere.energy.gov/biomass/biomass_basics_faqs.html
23 Union of Concerned Scientists. 2010. Burning Coal, Burning Cash. Cambridge,
MA. Online at http://www.ucsusa.org/burningcoalburningcash
24 Union of Concerned Scientists. 2009b. Clean Energy, Green Jobs. Cambridge,
MA. Online at
http://www.ucsusa.org/clean_energy/solutions/renewable_energy_solutions/clean-energy-green-jobs.html
Last Revised: 10/29/10

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