How Biomass Energy Works

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= =20

How=20 they work
How = Biomass Energy=20 Works=20

To many people, the most = familiar=20 forms of renewable energy are the wind = and the=20 sun. But biomass (plant = material and animal=20 waste) supplies almost 15 times as much = energy=20 in the United States as wind and = solar=20 power combined=E2=80=94and has the = potential to supply=20 much more.[1]

There are a wide variety of biomass = energy=20 resources, including tree and grass = crops and=20 forestry, agricultural, and urban = wastes. It is=20 the oldest source of renewable energy = known to=20 humans, used since our ancestors learned = the=20 secret of fire.

Contents
1.=20 Types of Biomass
2.=20 Converting Biomass to Energy
3.=20 Potential for Biomass
4.=20 Environmental Benefits

Related = Links

in=20 Clean Energy

Renewable=20 Energy and Agriculture: A Natural = Fit

Growing=20 Energy on the Farm: Biomass Energy and=20 Agriculture

How=20 Biomass Energy = Works

Biomass is a renewable energy source = because=20 the energy it contains comes from the = sun.=20 Through the process of photosynthesis,=20 chlorophyll in plants captures the sun's = energy=20 by converting carbon dioxide from the = air and=20 water from the ground into = carbohydrates,=20 complex compounds composed of carbon, = hydrogen,=20 and oxygen. When these carbohydrates are = burned,=20 they turn back into carbon dioxide and = water and=20 release the sun's energy they contain. = In this=20 way, biomass functions as a sort of = natural=20 battery for storing solar energy. As = long as=20 biomass is produced = sustainably=E2=80=94with only as=20 much used as is grown=E2=80=94the = battery will last=20 indefinitely.

From the time of Prometheus to the = present,=20 the most common way to capture the = energy from=20 biomass was to burn it, to make heat, = steam, and=20 electricity. But advances in recent = years have=20 shown that there are more efficient and = cleaner=20 ways to use biomass. It can be converted = into=20 liquid fuels, for example, or cooked in = a=20 process called "gasification" to produce = combustible gases. And certain crops = such as=20 switchgrass and willow trees are = especially=20 suited as "energy crops," plants grown=20 specifically for energy = generation.

Types of=20 Biomass

There are many types of plants in the = world,=20 and many ways they can be used for = energy=20 production. In general there are two = approaches:=20 growing plants specifically for energy = use, and=20 using the residues from plants that are = used for=20 other things. The best approaches vary = from=20 region to region according to climate, = soils,=20 geography, population, and so=20 on.

Energy = Crops

Energy crops, also called "power = crops,"=20 could be grown on farms in potentially = very=20 large quantities, just like food crops. = Trees=20 and grasses, particularly those that are = native=20 to a region, are the best crops for = energy, but=20 other, less agriculturally sustainable = crops=20 such as corn tend to be used for energy = purposes=20 at present.

Trees. In=20 addition to growing very fast, some = trees will=20 grow back after being cut off close to = the=20 ground, a feature called "coppicing." = Coppicing=20 allows trees to be harvested every three = to=20 eight years for 20 or 30 years before=20 replanting. These trees, also called=20 "short-rotation woody crops," grow as = much as 40=20 feet high in the years between harvests. = In the=20 cooler, wetter regions of the northern = United=20 States, varieties of poplar, maple, = black=20 locust, and willow are the best choice. = In the=20 warmer Southeast, sycamore and sweetgum = are=20 best, while in the warmest parts of = Florida and=20 California, eucalyptus is likely to grow = well.

The Fuss About=20 Switchgrass

=20

In his 2006 State of = the Union=20 Address, President Bush remarked that = "We're=20 working on research=E2=80=94strong = research to figure=20 out cellulosic ethanol that can be made = from=20 wood chips or stalks or switchgrass." = What is=20 switchgrass, and why did it get = mentioned in a=20 major presidential address? Switchgrass = is a=20 summer perennial grass that grows = throughout the=20 Great Plains region of the United = States, as=20 well as various parts of the South. = Switchgrass=20 is a hardy species=E2=80=94resistant to = floods,=20 droughts, nutrient poor soils, and = pests=E2=80=94and=20 does not require much fertilizer to = produce=20 consistent high yields. Today, = switchgrass is=20 primarily cultivated and used by many = farmers as=20 either a feed for livestock or, due to = its deep=20 root structure, as ground cover to = prevent soil=20 erosion. However, this prairie grass was = recently put in the spotlight because of = its=20 promise for energy production. = Researchers=20 believe that switchgrass can be an = important=20 feedstock for the production of ethanol, = providing substantial advantages, = including=20 greater net energy savings and carbon = dioxide=20 reductions compared to corn-based = ethanol=20 production. It can also help reduce our = nations'=20 dependence on oil=E2=80=94a serious = problem that=20 President Bush has described as an=20 = addiction.

Grasses. Thin-stemmed=20 perennial grasses used to blanket the = prairies=20 of the United States before the settlers = replaced them with corn and beans. = Switchgrass,=20 big bluestem, and other native varieties = grow=20 quickly in many parts of the country, = and can be=20 harvested for up to 10 years before = replanting.=20 Thick-stemmed perennials like sugar cane = and=20 elephant grass can be grown in hot and = wet=20 climates like those of Florida and = Hawaii.

Other = crops. A=20 third type of grass includes annuals = commonly=20 grown for food, such as corn and = sorghum. Since=20 these must be replanted every year, they = require=20 much closer management and greater use = of=20 fertilizers, pesticides, and energy. = While corn=20 currently provides most of the liquid = fuel from=20 biomass in the United States, there are = more=20 sustainable ways to produce energy from=20 plants.

Oil=20 plants. Plants such = as=20 soybeans and sunflowers produce oil, = which can=20 be used to make fuels. Like corn, = though, these=20 crops require intensive management and = may not=20 be sustainable in the longer term. A = rather=20 different type of oil crop with great = promise=20 for the future is microalgae. These tiny = aquatic=20 plants have the potential to grow = extremely fast=20 in the hot, shallow, saline water found = in some=20 lakes in the desert Southwest. In = 2004,=20 Green Fuel Technologies, a = Massachusetts-based=20 company, harnessed the ability to = capture and=20 use carbon dioxide emissions from power = plants=20 as a means to stimulate algae growth.[2] The algae is = then=20 converted into a various range of = fuels. =20 This technology, known as = Emissions-to-Biofuels,=20 is demonstrating great promise and has = the=20 potential to transform the way utilities = produce=20 energy.

Biomass Residues

After plants have been used for other = purposes, the leftover wastes can be = used for=20 energy. The forestry, agricultural, and=20 manufacturing industries generate plant = and=20 animal wastes in large quantities. City = waste,=20 in the form of garbage and sewage, is = also a=20 source for biomass energy.

Forestry. Forestry=20 wastes are the largest source of heat = and=20 electricity now, since lumber, pulp, and = paper=20 mills use them to power their factories. = One=20 large source of wood waste is tree tops = and=20 branches normally left behind in the = forest=20 after timber-harvesting operations. Some = of=20 these must be left behind to recycle = necessary=20 nutrients to the forest and to provide = habitat=20 for birds and mammals, but some could be = collected for energy production. Other = sources=20 of wood waste are sawdust and bark from=20 sawmills, shavings produced during the=20 manufacture of furniture, and organic = sludge (or=20 "liquor") from pulp and paper mills.

Agriculture. As with=20 the forestry industry, most crop = residues=20 are left in the field. Some should be = left there=20 to maintain cover against erosion and to = recycle=20 nutrients, but some could be collected = for fuel.=20 Animal farms produce many "wet wastes" = in the=20 form of manure. These wastes are = commonly spread=20 on fields, not just for their nutrient = value,=20 but for disposal. Runoff from = overfertilization=20 threatens rural lakes and streams and = can=20 contaminate drinking water. Processing = crops=20 into food also produces many usable = wastes.

Cities. People=20 generate biomass wastes in many forms, = including=20 "urban wood waste" (such = as shipping=20 pallets and leftover construction wood), = the=20 biodegradable portion of garbage (paper, = food,=20 leather, yard waste, etc.) and the gas = given off=20 by landfills when waste decomposes. Even = our=20 sewage can be used as energy; = some sewage=20 treatment plants capture the methane = given off=20 by sewage and burn it for heat and = power,=20 reducing air pollution and = emissions of=20 global warming gases.

Related = Links

off-site

U.S.=20 DOE Biomass Program

National=20 Renewable Energy Laboratory

Institute=20 for Local Self Reliance Centre=20 for the Analysis and Dissemination of=20 Demonstrated Energy = Technologies U.S.=20 Farm Bill 2002

Converting=20 Biomass to Energy

The old way of converting biomass to = energy,=20 practiced for thousands of years, is = simply to=20 burn it to produce heat. This is still = how most=20 biomass is put to use, in the United = States and=20 elsewhere. The heat can be used = directly, for=20 heating, cooking, and industrial = processes, or=20 indirectly, to produce electricity. The = problems=20 with burning biomass are that much of = the energy=20 is wasted and that it can cause some = pollution=20 if it is not carefully controlled.

An approach that may increase the use = of=20 biomass energy in the short term is to = burn it=20 mixed with coal in power = plants=E2=80=94a process known=20 as "co-firing." Biomass feedstock can = substitute=20 up to 20 percent of the coal used in a = boiler.[3] The benefits = associated=20 with biomass co-firing include lower = operating=20 costs, reductions of harmful emissions, = and=20 greater energy security. Co-firing is = also one=20 of the more economically viable ways to = increase=20 biomass power generation today. In 2000, = the=20 Chariton Valley Biomass Project, a joint = effort=20 including Alliant Energy, the U.S. = Department of=20 Energy, and local biomass groups, began = testing=20 the co-firing of switchgrass with coal = at=20 Alliant's Ottumwa Generating Station in = Iowa.=20 The project has proved so successful = that in=20 2005, Alliant received permission to = build a=20 permanent biomass processing facility at = the=20 plant, capable of co-firing up = to five=20 percent of its energy with = switchgrass.[4]

A number of noncombustion methods are = available for converting biomass to = energy.=20 These processes convert raw biomass into = a=20 variety of gaseous, liquid, or solid = fuels that=20 can then be used directly in a power = plant for=20 energy generation. The carbohydrates in = biomass,=20 which are comprised of oxygen, = carbon, and=20 hydrogen, can be broken down into a = variety of=20 chemicals, some of which are useful = fuels. This=20 conversion can be done in three = ways:

Thermochemical. When plant = matter is=20 heated but not burned, it breaks down = into=20 various gases, liquids, and solids. = These=20 products can then be further processed = and=20 refined into useful fuels such=20 as methane and alcohol. Biomass = gasifiers=20 capture methane released from the plants = and=20 burn it in a gas turbine to produce = electricity.=20 Another approach is to take these fuels = and run=20 them through fuel cells, converting the=20 hydrogen-rich fuels into electricity and = water,=20 with few or no emissions.=20
Biochemical. Bacteria, yeasts, = and=20 enzymes also break down carbohydrates.=20 Fermentation, the process used to make = wine,=20 changes biomass liquids into alcohol, a=20 combustible fuel. A similar process is = used to=20 turn corn into grain alcohol or ethanol, = which=20 is mixed with gasoline to make gasohol. = Also,=20 when bacteria break down biomass, = methane and=20 carbon dioxide are produced. This = methane can be=20 captured, in sewage treatment plants and = landfills, for example, and burned for = heat and=20 power.=20
Chemical. Biomass oils, like = soybean=20 and canola oil, can be chemically = converted into=20 a liquid fuel similar to diesel fuel, = and into=20 gasoline additives. Cooking oil from=20 restaurants, for example, has been used = as a=20 source to make "biodiesel" for trucks. = (A better=20 way to produce biodiesel is to use algae = as a=20 source of oils.)

=20

In 1998, the first U.S. commercial = scale=20 biomass gasification demonstration plant = based=20 on the SilvaGas process began at the = McNeil=20 Power Station in Burlington, Vermont. = [5] The=20 SilvaGas process, a particular form of = biomass=20 gasification, indirectly heats the = biomass using=20 heated sand in order to produce a medium = Btu=20 gas. The McNeil power station is capable = of=20 generating 50 MW of power from local = wood waste=20 products.

One persistent myth about biomass is = that it=20 takes more energy to produce fuels from = biomass=20 than the fuels themselves contain. In = other=20 words, that it is a net energy loser. In = fact,=20 most of the studies done over the = past 10=20 years confirm that the production of = ethanol has=20 a positive energy balance. According to = a 2002=20 U.S. Department of Agriculture study,=20 technological advances in ethanol = conversion and=20 efficiency increases in farm production = have=20 caused the net energy value (NEV) of = corn=20 ethanol to increase gradually over = time.[6],[7] This study = states that=20 every British thermal unit (BTU) of = energy used=20 in the production of ethanol leads to a = 34=20 percent energy gain.[8]

Nonetheless, we could do much better. = Corn is=20 one of the most energy-intensive crops, = and=20 current corn-based ethanol production = uses just=20 the kernels from the corn plant, and not = even=20 the entire kernel. By making ethanol = from energy=20 crops, we could obtain between four and = five=20 times the energy that we put in, and by = making=20 electricity we could get perhaps 10 = times or=20 more. In the future, to make a truly = sustainable=20 biomass energy system, we would have to = replace=20 fossil fuels with biomass or other = renewable=20 fuels to plant and harvest the = crops.

Another important consideration with = biomass=20 energy systems is that biomass contains = less=20 energy per pound than fossil fuels. This = means=20 that raw biomass typically can't be=20 cost-effectively shipped more than about = 50=20 miles before it is converted into fuel = or=20 energy. It also means that biomass = energy=20 systems are likely to be smaller than = their=20 fossil fuel counterparts, because it is = hard to=20 gather and process more than this = quantity of=20 fuel in one place. This has the = advantage that=20 local, rural communities=E2=80=94and = perhaps even=20 individual farms=E2=80=94will be able to = design energy=20 systems that are self-sufficient, = sustainable,=20 and perfectly adapted to their own=20 needs.

Potential = for=20 Biomass

In the United States, we already get = 45=20 billion kilowatt-hours of electricity = from=20 biomass, about 1.2 percent of our = nation's total=20 electric sales.[9] We also get=20 nearly four billion gallons of = ethanol,=20 about two percent of the liquid = fuel used=20 in cars and trucks.[10] The = contribution for=20 heat is also substantial. But with = better=20 conversion technology and more attention = paid to=20 energy crops, we could produce much = more.

Estimates of the ultimate potential = for=20 biomass energy vary, and depend on = agricultural=20 forecasts, waste reduction by industry, = and=20 paper recycling. The Department of = Energy=20 believes that we could produce four = percent=20 of our transportation fuels from biomass = by=20 2010, and as much as 20 percent by = 2030.[11] For = electricity, the=20 U.S. Department of Energy (DOE) = estimates that=20 energy crops and crop residues alone = could=20 supply as much as much as 14 percent of = our=20 power needs.

Environmental=20 Benefits

Biomass energy brings numerous = environmental=20 benefits=E2=80=94reducing air and water = pollution,=20 increasing soil quality and reducing = erosion,=20 and improving wildlife habitat.

Biomass reduces air pollution by = being a part=20 of the carbon cycle (see the box below), = reducing carbon dioxide emissions by 90 = percent=20 compared with fossil fuels. Sulfur = dioxide=20 and other pollutants are also reduced=20 substantially.

Water pollution is reduced because = fewer=20 fertilizers and pesticides are used to = grow=20 energy crops, and erosion is reduced. = Moreover,=20 agricultural researchers in Iowa have = discovered=20 that by planting grasses or poplar trees = in=20 buffers along waterways, runoff from = corn fields=20 is captured, making streams cleaner.

In contrast to high-yield food crops = that=20 pull nutrients from the soil, energy = crops=20 actually improve soil quality. Prairie = grasses,=20 with their deep roots, build up topsoil, = putting=20 nitrogen and other nutrients into the = ground.=20 Since they are replanted only every 10 = years,=20 there is minimal plowing that causes = soil to=20 erode.

Finally, biomass crops can create = better=20 wildlife habitat than food crops. Since = they are=20 native plants, they attract a greater = variety of=20 birds and small mammals. They improve = the=20 habitat for fish by increasing water = quality in=20 nearby streams and ponds. And since they = have a=20 wider window of time to be harvested, = energy=20 crop harvests can be timed to avoid = critical=20 nesting or breeding seasons.

Riding the Carbon Cycle: The = carbon=20 cycle is nature's way of moving carbon = around to=20 support life on Earth. Carbon dioxide is = the=20 most common vehicle for carbon, = where one=20 carbon atom is bound to two oxygen = atoms.=20 Plant photosynthesis breaks the carbon = dioxide=20 in two, keeping the carbon to form the=20 carbohydrates that make up the plant, = and=20 putting the oxygen into the air. When = the plant=20 dies or is burned, it gives its carbon = back to=20 the air, which is then reabsorbed by = other=20 plants.

3D"Biomass

Fossil fuels, on the other hand, are = made of=20 plants that grew millions of years ago. = The=20 carbon they absorbed then is released = now when=20 the fossil fuels are burned. There are = no extra=20 plants to absorb that carbon, so the = cycle=20 becomes out of balance. There are two = different=20 carbon cycles in operation now: the = natural one=20 between plants and the air, which is in = balance,=20 and the human-made cycle where carbon is = pulled=20 from Earth and emitted into the=20 = atmosphere.

All of these benefits are described = in=20 comparison with food = crops such=20 as corn, wheat, and soybeans. = Compared to=20 undisturbed natural habitat, energy = crops are=20 not as good. But the strength of biomass = is that=20 it is much closer to the natural world = than our=20 modern industrial agriculture. The = harvest of=20 prairie grasses is not so different than = the=20 fires that periodically swept across the = plains.=20 Plantations of poplar and maple trees = may not be=20 the same as varied forests, but are = certainly=20 closer than pesticide-laden monocrops.=20 Nonetheless, the environmental benefits = of=20 biomass hinge on whether energy crops = are=20 managed with sustainable agricultural = practices.=20 Just like food crops, they can be = mishandled,=20 with productivity increased by greater = chemical=20 inputs. If biomass energy turns out to = have=20 unforeseen environmental effects, we = must be=20 willing to alter our methods to reduce = these=20 effects.

Conclusions

In addition to the many environmental = benefits, biomass offers many economic = and=20 energy security benefits. By growing our = fuels=20 at home, we reduce the need to import = oil and=20 reduce our exposure to disruptions in = that=20 supply. Farmers and rural areas gain a = valuable=20 new outlet for their products. Biomass = already=20 supports 66,000 jobs in the United = States; if=20 the DOE's goal is realized, the industry = would=20 support three times as many jobs.[12]

Photo: Warren Gretz, = NREL

Endnotes =20

[1] Energy Information = Administration (EIA).=20 2005. Renewable energy trends 2004. = Online at=20 http://www.eia.doe.gov/cneaf/solar.renewables/page/trends/rentre= nds04.html

[2] GreenFuel Technologies = Corporation.=20 Online at http://www.greenfuelonline.com

[3] Federal Energy Management = Program=20 (FEMP). 2004. Biomass Cofiring in = coal-fired=20 boilers, DOE/EE-0288. Washington, DC: = U.S.=20 Department of Energy. Online at = http://www1.eere.energy.gov/biomass/pdfs/33811.pdf

[4] Natural Resources Conservation = Service=20 (NRCS). 2006. Switchgrass burned For = power.=20 Washington, DC: U.S. Department of = Agriculture.=20 Online at http://www.ia.nrcs.usda.gov/News/newsreleases/2006/switchgrass.h= tml

[5] = National=20 Renewable Energy Laboratory (NREL). = 2000.=20 Project update: The Vermont gasifier,=20 DOE/GO-102000-1051. Washington, DC: U.S. = Department of Energy. Online at = http://www.nrel.gov/docs/fy00osti/27983.pdf

[6] United States Department of = Agriculture=20 (USDA). 2002. The Energy balance of corn = ethanol: An update, AER-813. Online at = http://www.transportation.anl.gov/pdfs/AF/265.pdf

[7] Lorenz, D. and D. Morris. = 1995. How much=20 energy does it take to make a gallon of = ethanol?=20 Washington, DC: Institute for Local Self = Reliance (ILSR). Online at http://www.carbohydrateeconomy.org/library/admin/uploadedfiles/<= BR>How_Much_Energy_Does_it_Take_to_Make_a_Gallon_.html

[8] United States Department of = Agriculture=20 (USDA). 2002. The energy balance of corn = ethanol: An update, AER-813. Online at = http://www.transportation.anl.gov/pdfs/AF/265.pdf

[9] Energy Information = Administration (EIA).=20 2005. Electric Power Annual. Online at = http://www.eia.doe.gov/cneaf/electricity/epa/epa_sum.html=

[10] U.S. Department of Energy = (DOE).=20 Biomass: Frequently asked questions. = Online at=20 http://www1.eere.energy.gov/biomass/biomass_basics_faqs.html

[11] Oak Ridge National Laboratory = (ORNL).=20 2005. Growth in biomass could put U.S. = on road=20 to energy independence. Online at = http://www.ornl.gov/info/press_releases/get_press_release.cfm?Re= leaseNumber=3Dmr20050421-01

[12] Renewable Energy Policy = Project (REPP).=20 Biomass: Frequently asked questions. = Online at=20 http://www.repp.org/articles/static/1/1004994679_6.html

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Contents

How=20 They Work

Energy=20 101: Take a tour

How=20 Wind Energy Works

How=20 Solar Energy Works

How=20 Biomass Energy Works

How=20 Geothermal Energy Works

How=20 Hydroelectric Energy Works

Coal=20 vs. Wind Power

more...

What=20 They Cost

Renewing=20 America's Economy

Increasing=20 Renewables: Costs and Benefits

Barriers=20 to Renewable Energy Technologies

Environmental=20 and Siting Issues

Wind=20 Power in New England Factsheet = Series

Environmental=20 Benefits of Renewable Energy

Public=20 Benefits of Renewable Energy Use

Environmental=20 Impacts of Renewable Energy = Technologies

Coal=20 vs. Wind Power: You be the Judge

Cape=20 Cod Offshore Wind Project

Agriculture=20 and Renewable Energy

Renewable=20 Energy and Agriculture: A Natural = Fit

Growing=20 Energy on the Farm: Biomass and=20 Agriculture

Farming=20 the Wind: Wind Power and = Agriculture

Up=20 with the Sun: Solar Energy and=20 Agriculture

Clean=20 Energy Blueprint Benefits Farmers and = Rural=20 Economies

Renewable=20 Energy Provisions in the Farm Bill =

What=20 You Can Do

How=20 You Can Be Involved

Buy=20 Green Power

Developing=20 a Statement of Support -- Web = Resources

Renewable=20 Energy Resources on the Web

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