Bioenergy 101

What is bioenergy?

Bioenergy? is a form of renewable energy? and comes from materials derived from recently living organisms including plants, animals and their byproducts. That is, bioenergy is a replenishable source of power, heat, and liquid and gas fuels that is sourced from biomass? rather than non-renewable fossil energy sources such coal, natural gas and petroleum. Fossil energy sources such as coal and petroleum are not sources of bioenergy since these materials are the result of geological processes that transformed plants living many thousands of years ago. Bioenergy is a form of renewable energy because the energy contained in biomass is energy from the sun captured through natural processes of photosynthesis, and so long as the quantity of biomass used is equal to or less than the amount that can be regrown, it is potentially renewable indefinitely. Bioenergy includes power and fuels derived from biomass. Biopower?, for example, is electricity generated from combustion of biomass. Heat and steam, or a combination of both, may also be produced through combustion of biomass, and may be produced in co-generation with electricity. Biofuel? is a term commonly referring to biomass-derived liquid fuels and gases most typically used in transportation.
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Where does bioenergy come from?

The majority of biomass for bioenergy comes from three sources: forests, agriculture, and waste (see figure 1). Algaculture is a fourth source currently in development. Forest-based biomass includes merchantable stem wood [wood in the stems of trees greater than 5” diameter at breast height (dbh)], tops and branches of harvested trees, and understory trees (less than 5” dbh). Agriculture-based biomass includes crops grown specifically for bioenergy production, or dedicated bioenergy crops?, and plant residues collected after harvest of crops grown for food or feed. Dedicated bioenergy crops include annual crops grown for their sugars or starches, such as sugarcane and grains, as well as perennial herbaceous and woody crops grown for their cellulose?. Cellulosic bioenergy crops? include grasses? like switchgrass? and woody plants like hybrid poplar? trees. Waste-based biomass includes organic materials leftover from industrial processes such as mill and pulp production, municipal solid wastes, construction wastes, and landfill gas. Biomass from algaculture involves production of microalgae - organisms less than 0.4 mm in diameter and capable of photosynthesis.
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How is biomass converted into energy?

To make use of the energy available in biomass it is necessary to utilize technology to either release the energy directly, as in burning of biomass materials for heat, or to transform it into other forms such as solid or liquid fuel. There are three types of conversion technologies currently available, each appropriate for specific biomass types and specific energy products: thermal, chemical and biochemical (see figure 2).

Fig1 dedicated biomass crops.jpg
Figure 1. Current major biomass materials and feedstocks.(CL Williams, after Baye, 2010)

As implied by its name, thermal conversion processes use predominantly heat to convert biomass into other forms. Thermal conversions processes include combustion, torrefaction, pyrolysis? and gasification?. Chemical conversion involves use of chemical agents to convert biomass into liquid fuels. Biochemical conversion involves use of enzymes of bacteria or other microorganisms to break down biomass through processes of anaerobic digestion, fermentation or composting. Although relevant technologies exist (and continue to be developed), some are not yet cost-effective, particularly for large-scale? conversion of cellulosic biomass. For additional information on conversion technologies see the reference resources appended at the end this module.
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Who produces and uses bioenergy?

Bioenergy production and use occurs along a continuum of scale from the household at one end to globalized industrial systems at the other. While residential use of biomass for heat and cooking has long been a part of human history, new technologies are enabling more efficient use of a wider variety of biomass types for these and other uses. At the other end of the bioenergy spectrum are large transnational energy companies who own the means of biomass production and conversion, as well as the means of distribution of bioenergy products. At this end of the spectrum utility companies take advantage of economies of scale to acquire vast quantities of biomass either from their own lands or lands they lease, or from large-scale suppliers, and then convert the biomass into bioenergy and make it available for thousands if not millions of consumers. In between these two extremes of scale are numerous production and distribution arrangements and organization types, including mixed-scale? operations, cooperatives, and community-based? or small-scale distributed? energy projects. There are economic and societal benefits and disadvantages associated with different scales of bioenergy production and use. There are advantages and disadvantages to each scale of bioenergy production and use. Decision-makers must often balance trade-offs? between the benefits and the costs associated with bioenergy production and use at any particular scale.

Figure 2. Bioenergy conversion technologies.(CL Williams, after Baye, 2010)

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Why is bioenergy being developed?

Interest in bioenergy is increasing in response to concerns about energy security?, energy independence?, and environmental and climate impacts associated with use of non-renewable energy resources. Proponents of agriculture and forestry see it as a tool to protect productive working landscapes and provide new markets for these volatile industries. Bioenergy is seen as a potential stimulus for economic development, particularly in rural areas. Much of current interest in bioenergy is a result of policy responses to challenges and perceived opportunities. As interest in bioenergy swells, there are many challenges related to knowledge, technology, economics, and society.

Interest in ethanol as a liquid transportation fuel, although used in the United States since at least 1908 with the Ford Model T, grew in the late 20th century as a result of oil supply disruptions in the Middle East and environmental concerns over the use of lead as a gasoline octane booster. Ethanol production in the U.S. soon grew with support from Federal and State ethanol tax subsidies and the mandated use of high-oxygen gasolines. Additional incentives in the 80s and 90s, and passage of the Clean Air Amendments of 1990, further incentivized expanded U.S. ethanol production. Today, nearly all ethanol production in the U.S. utilizes corn grain in fermentation processes. However, on-going bioenergy development is focused primarily on advanced biofuels? and biopower projects, and likewise these are being driven by policy at national and state levels.

In his 2006 President Bush rolled out the Advanced Energy Initiative which included increased research funding for cutting edge biofuel production processes. In early 2007, he announced the “Twenty-in-Ten” initiative, a plan to reduce gasoline consumption by 20% in 10 years. Congress responded in December 2007, by passing a Renewable Fuel Standard (RFS) as part of the Energy Independence and Security Act (EISA) of 2007. The RFS requires production of 36 billion gallons annually of biofuels by 2022, and includes specific provisions for advanced biofuels, paving the way for advanced technologies (figure 3). Many state governments have adopted similar policy initiatives and programs. In 2007, the Bush Administration proposed a Farm Bill that included funds for new renewable energy and energy efficiency-related spending at the US Department of Agriculture (USDA), including support for cellulosic ethanol? projects. In May 2008, Congress passed the 2008 Farm Bill, titled the Food, Conservation and Energy Act of 2008, with mandatory funding for bioenergy activities.

Additional major influences on bioenergy development are new or recently expanded federally-funded or sponsored research initiatives, programs and offices. Mostly notable are those within, administered by, or in partnership with the U.S. Department of Energy (DOE) and the USDA. Chief among the research centers are the National Renewable Energy Lab (NREL), and the DOE’s suite of three Bioenergy Research Centers: Oak Ridge National Laboratory (ORNL), the Great Lakes Bioenergy Research Center (GLBRC), and the Joint BioEnergy Institute (JBI). The DOE’s Office of Energy Efficiency and Renewable Energy (EERE) sponsors energy initiatives and leads ten programs supporting biomass research, and development and demonstration programs. Through its Farm Service Agency (FSA) the USDA administers important programs incentivizing bioenergy crop production, such as the Biomass Crop Assistance Program (BCAP).

Figure 3. Production Goals set by the Energy Independence and Security Act (2007).(University of Wisconsin.-Extension)

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What are the potential benefits of bioenergy?

The use of biomass in the production of electric power, steam, and liquid and gas fuels has the potential to substantially reduce greenhouse gas emissions – the release of gases that trap heat in the atmosphere and which are associated with global climate change. These gases include carbon dioxide (CO2), methane (CH4), and nitrous oxide (N20), and although these gases occur naturally and are emitted to the atmosphere, human activities also cause these gases to enter the atmosphere. Carbon dioxide, for example, enters the atmosphere through natural processes such as decomposition, but also through burning of materials that contain carbon. Carbon dioxide is removed from the atmosphere - or “sequestered” - when it is absorbed by plants in the process of photosynthesis. When biomass is used to produce bioenergy, the amount of carbon dioxide that is released in the process is potentially sequestered with the growing of new plants. In this cycle of growing and converting biomass to bioenergy, there is potentially no net increase in atmospheric CO2. Carbon neutrality? is the term used to describe this “closed circuit”. However, carbon neutrality can be thwarted if anywhere in the biomass-to-bioenergy cycle there is more carbon created than sequestered. For example, to meet growing demand for bioenergy, land areas currently covered by natural vegetation may be converted to biomass crops, and in the process soil tillage may accelerate natural processes that transform soil organic matter into CO2. Disturbance of forests can have the same effect. Carbon neutrality can also be thwarted if transport of biomass to conversion facilities requires use of fuels such that more CO2 is released to the atmosphere than is sequestered. Thus agriculture’s and forestry’s roles in the provisioning of biomass for bioenergy must be balanced with their roles in the overall global carbon balance.

Figure 4. Cellulosic biofuels and the carbon cycle.(US DOE)

The use of biomass can potentially reduce dependence on foreign oil. Energy independence is a stated goal of the US government and many state governments including Wisconsin, for improving national and state security, and improving domestic economics. When bioenergy produced from domestic biomass sources is used to replace imported oil there may be less risk of exposure to terrorism in foreign oil-producing countries, and reduced risk of oil price shocks induced by foreign oil-producing countries. Additionally, when domestic biomass is used to produced bioenergy, new jobs may be created and profits may be more likely to remain in domestic markets rather than being sent overseas. The potential economic benefits of agriculturally-produced biomass are especially attractive to rural communities in the U.S. Midwest where rural depopulation, agricultural job losses, and subsequent socio-economic decay are troublesome.
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Are there any disadvantages of bioenergy?

While there are many potential benefits of bioenergy, there are also potential negative consequences. Disadvantages include air quality issues related to, and production of greenhouse gases by combustion; unsustainable impacts on soil and water resources, such as those induced by agricultural intensification on marginal or degraded lands, as well as conversion of natural areas to energy cropping - agricultural extensification; and competition for land use – what has come to be known as the food versus fuel debate. Additional challenges include the low bulk-density of biomass, or relatively small energy content per unit volume, which requires that it be densified or aggregated prior to transport which adds costs and reduces overall energy system performance; water use demands in biological conversion technologies; and the seasonal nature of biomass crops.
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Is bioenergy sustainable?

There are many definitions of sustainability each supporting various principals and concepts. Essentially, however, sustainability can be described as 1) a set of goals, and 2) practices and behavior that support such goals. As a set of goals sustainability variably describes desired conditions of the environment, and the ability of humans to receive benefits directly and indirectly from the environment in the present as well as the future. As practices and behaviors, sustainability describes human actions that support and enhance human well-being derived through interaction with the environment and its components, and which support the ability of the environment and human society to interact in ways that discourage reduced benefits. Sustainability of bioenergy, therefore, will depend on the goals defined (and when and where and by whom those goals are defined), what actions and behaviors people are willing and able to adopt to support those goals, and the ability of science to assist human knowledge of connections between the many aspects of bioenergy and sustainability goals.

Bioenergy is frequently evoked as an important tool in improving environmental sustainability, as well as the sustainability of energy, agriculture, forestry and other sectors of human activity. However, much remains to be understood about the impacts of bioenergy on the environment and human society. Whether and to what degree bioenergy is sustainable, and whether and to what degree it contributes to increased environmental sustainability as well as that of other sectors requires further analysis. Regardless, bioenergy currently provides a focus for improving our understanding and communications about sustainability, therefore increasing the likelihood of achieving desired outcomes.
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Baye, T. 2010. Managing the biomass value proposition: business planning, contracting, pricing and execution (presentation). University of Wisconsin Extension, Madison. Used with permission.

Bioeconomy Institute, Iowa State University (

Biomass Conversion Research Laboratory (BCRL;

Bioenergy Feedstock Information Network (BFIN;

Biomass Energy Resource Center (BERC;

Purdue University – Extension, Renewable Energy: Bioenergy (

Renewable Energy Policy Project, Bioenergy (

United States Energy Information Agency, “Energy in Brief”. (

United States Environmental Protection Agency, “Biomass Conversion: emerging technologies, feedstocks, and products”:

University of Wisconsin – Extension, Biomass Feedstocks and Energy Independence (

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Anerobic Digestion and Biogas

UW Extension have created seven modules focused on the use of anaerobic digestion technologies. Details of the process are introduced, as well as factors that influence start-up, operation and control of anaerobic digesters at different scales.

Contact Us:


Carol Williams
(608) 890-3858 (office)
(515) 520-7494 (mobile)
Department of Agronomy
1575 Linden Dr.
University of Wisconsin, Madison, WI 53706

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Wisconsin Sustainable Planting and Harvest Guidelines for Non-forest Biomass? on Public and Private Lands (2011)


These Guidelines are an effort to encourage decision-making and land use practices that benefit farmers financially while protecting the state’s natural resources.

Perennial Herbaceous Biomass Production and Harvest in the Prairie Pothole Region of the Northern Great Plains: Best Management Guidelines to Achieve Sustainability of Wildlife Resources (2013)


These Guidelines are provided by the National Wildlife Federation. These Best Management Guidelines were developed through a process involving an advisory group of natural resource professionals with expertise in agronomy, production aspects of energy crops, wildlife ecology and management, and native ecosystems. Although the guidelines are targeted for the Northern Great Plains, many of the general principles apply to Wisconsin.

Crop Fact Sheets

Get the information you need for informed decisions:
- switchgrass.pdf
- Miscanthus.pdf