What is bioenergy?
Bioenergy is energy contained in ãbiomassä such as plant matter and animal waste. These sources can provide energy in the form of electricity, heat, steam, and fuels.
Why is bioenergy considered renewable?
Biomass is a replenishable resource÷it can be replaced fairly quickly without permanently depleting the Earthâs natural resources. By comparison, fossil fuels such as natural gas and coal require millions of years of natural processes to be produced. Therefore, mining coal and natural gas depletes the Earthâs resources for thousands of generations.
How is biomass used to create energy?
Plant and animal matter can go through many types of energy conversion processes in order to yield power, heat, steam and fuel.
- Co-firing. Woody and herbaceous biomass such as poplar, willow and switchgrass can fuel a small portion of an existing coal power plant. This process, known as co-firing, entails biomass that represents between 1% and 15% of the energy of the coal plant, with the remainder consisting of coal.
- Conventional steam boiler. Burning biomass in a conventional power plant (that is, one with a conventional boiler to produce steam that runs through a turbine) built solely for the biomass is another option.
- Biomass gasification. Solid biomass can be converted into a gaseous form. The gas can then can run through ãcombined-cycleä gas turbine or another power conversion technology such as a coal power plant. Many experts hope that gasification can yield more efficient biomass power plants. At this stage, gasification is still in the ãdemonstrationä phase as projects slowly come online.
- Anaerobic digestion. Bacteria can decompose animal matter and landfill garbage in an airless environment to yield usable methane. The methane can then run through a number of power generation technologies such as gas turbines or even fuel cells.
Heat and Steam
The same power plants that produce power also yield useful steam and heat in a process called combined heat-and-power (CHP). Taking advantage of these products can improve the efficiency of the operation by over 35%. Pulp and paper mills in the Southeast, Northeast and Great Lakes region of the U.S. already generate power, steam and heat from biomass. Finland hosts CHP operations that heat homes and businesses.
Of course, biomass such as wood in fireplaces and kilns also heat homes and provide energy for cooking.
Solid biomass can be converted into liquid fuels that power cars, engines including those in diesel generators, and even industrial operations. Ethanol (which comes from cellulosic biomass such as corn) is produced through fermentation. Biodiesel is the result of combining alcohol (including ethanol) with oil extracted from soybeans, rapeseed, animal fats, or other biomass.
What are the main forms of biomass?
The are many types of biomass, including:
- Pulp and paper operation residues. The byproducts of logging and processing operations.
- Forest residues. Wood from forest thinning operations that reduce forest fire risk.
- Agricultural residues. Crop residues such as corn stover (stalks) and processing residues such as nut hulls.
- Urban wood waste. Lawn and tree trimmings, wood pallets, construction and demolition wastes.
- Animal waste. Cattle, chicken and pig waste converted to gas or burned directly for heat and power.
- Landfill gas. The natural byproduct of bacterial digestion of organic garbage.
- Energy crops. Trees or herbaceous biomass grown specifically for energy.
In the U.S., residues from mill operations are the biggest source of biomass for power plants and combined-heat-and-power projects. Agricultural residues such as orchard prunings and nut hulls as well as forest residues are also important contributors to power plants in CHP operations, particularly in California. Landfill gas projects are growing steadily, while animal waste digestion projects and energy crop plantations are still at an early stage of commercialization.
In Europe, urban wood waste is an important source of bioenergy. In developing nations, a major source of biomass is timber cut by the rural poor specifically for heating and cooking.
What percentage of the world and U.S. energy mix does bioenergy represent?
According to the International Energy Agency, the world derives 11% of its energy from biomass. That percentage rises to 35% for developing nations, and to 90% for the poorest nations.
In the U.S., biomass contributes the most to the nationâs non-hydro renewable energy supply. According to the U.S. Energy Information Administration, biomass supplied over 3.3% of the nationâs energy in 1999. (This includes tires and portions of municipal solid waste that many do not consider to be renewable.)
The United States is currently the largest biopower (that, biomass for electricity) generator, with over half of the world's installed capacity. Biomass also represents 1.5% of the total electricity supply. This compares to 0.1% for wind and solar combined. There are about 7,800 MW of biomass power capacity installed at more than 350 locations in the U.S., representing 1% of total U.S. electricity generation capacity. The U.S. biomass power industry is primarily located in the Northeast, Southeast, and West Coast regions, representing a $15 billion investment and 66,000 jobs.
Biofuels such as ethanol and biodiesel represent 0.4% of the transportation fuels market in the United States.
How much does bioenergy cost?
The answer is as varied as the technologies and forms of biomass under consideration. In short, since there are different combinations of biomass feedstocks and biomass conversion technologies, the number of different estimates will equal the number of different feedstock-technology combinations.
For self-use in the forest products industry, which is the leading owner of biomass generation in Michigan and Maine, biomass is essentially free.
Purchasing forestry-produced biomass will cost between $0.50 and $3 per million Btu (mmBtu), with economically successful projects paying less than $1.50/mmBtu.
Burnable municipal solid waste (MSW) is usually landfilled for a fee. Thus, it has a negative fuel price. However, plant operators must process MSW to eliminate toxics. They also need to install emissions control equipment.
Dedicated feedstocks, such as woody and herbaceous crops, cost almost 3 times more than residues ($2.50 per Gigajoule [GJ] compared to $0.95/GJ).
By comparison, the cheapest coal costs between $1.50 to $2 per mmBtu. Natural gas costs $3 to $4 per mmBtu. So overall, biomass is the cheapest combustion fuel available.
Overall, biomass plants have higher capital costs and O&M costs than fossil fuel plants. And traditionally, their power output efficiencies are poor (an average of 20% nationwide), so fuel costs are higher than those for more efficient fossil fuel plants. Observers expect more efficient technologies such as gasifiers to have electrical output efficiencies of 25% to 35%.
- The cost of power from conventional biomass combustion can range from 6 cents to 12 cents per kilowatt-hour.
- Co-firing biomass with coal is much cheaper, since the power plant is already built and costs are limited to the biomass fuel and its preparation at the plant site. Costs can hover from almost nothing to 4 cents per kilowatt-hour for a project where biomass is 10% to 15% of the total fuel input of the power plant.
- The cost of power from of landfill gas can range from 3.5 ö 7.9 cents per kilowatt-hour, depending on the size of landfill, financing available, distance from the grid or local application, and other factors.
Combined Heat and Power
CHP represents an improvement in the energy efficiency of power plants. Instead of releasing steam and heat that are byproducts of power generation, CHP systems capture this energy. Thus, CHPâs cost is primarily capital costs for installing equipment for energy capture. An estimate for the Powering the South effort, which estimates clean energy potential in the South, finds that CHP projects will yield power that costs 3.3 cents per kWh in 2010.
- Biodiesel based on soybeans can cost approximately $2 per gallon, which is higher than petroleum-based diesel though wild oil price fluctuations have sharply reduced the price gap during periods within 2000 and 2001.
- Ethanol costs in the range of $1.10 to $1.30 per gallon, which compares very favorably to petroleum-based gasoline.
What are the environmental impacts of bioenergy?
Environmental impacts can be roughly divided into those of cultivating and collecting biomass feedstocks, and converting biomass to energy. When considering the impacts of biomass, one must also think about two different comparisons:
(1) What would have happened to the biomass otherwise, and what would the environmental impacts of that be?
(2) What would have been the energy source used in place of the bioenergy?
Different biomass feedstocks have different ãalternative fatesä. For example:
- If landfill gas is not collected for bioenergy, it would be leaked to the atmosphere as methane, a potent greenhouse gas. Thus, landfill gas projects help to cut greenhouse gas emissions. However, some landfill gas may contain toxics that must be cleaned before the gas is sent to the power plant.
- Agricultural residues such as rice straw and nut hulls could be burned in the open if they were not collected for burning in controlled power plants. However, agricultural residues left on the soil can regenerate soil nutrients and reduce the need for fertilizers.
- Similarly, by collecting forest thinnings for fire prevention, one can avoid a forest fire that is essentially open burning of the biomass, leading to much more air pollution than combustion in a controlled power plant. However, on an institutional level, some environmentalists fear that opening forests to thinning merely opens the way to logging, since thinning, like logging, requires roads and other infrastructure helpful for logging.
- If animal waste is not collected and concentrated in an animal waste digester, it will be stored in an open-air lagoon that can overflow during heavy rains, taint groundwater and release strong odors.
- If energy crops are not grown on agricultural land, that land may either be used to grow other crops or left fallow. Typically energy crops require less fertilizer, herbicides and pesticides than most food crops.
Biomass energy conversion
Bioenergy conversion requires a comparison with other energy sources that are displaced by the bioenergy. Thus, biomass for power must be compared to coal, natural gas, nuclear, and other power sources including other renewables. While comprehensive data is not available, one study by REPP shows that emissions from biomass plants burning waste wood would release far less sulfur dioxide (SO2), nitrogen oxide (NOx) and carbon dioxide (CO2) than coal plants built after 1975. The comparison with combined cycle natural gas power plants is more ambiguous, since biomass releases far more sulfur dioxide, similar levels or greater levels of nitrogen oxide, but far less carbon dioxide than combined cycle natural gas plants.
Several studies by the National Renewable Energy Laboratory examined the ãlife-cycleä impact of bioenergy for power. That is, the studies examined the air, land and water impacts of every step of the bioenergy process, from cultivating, collecting, and transporting biomass to converting it to energy. One study found that a bioenergy operation featuring biomass gasification with combined-cycle power plant technology would release far less SO2, NOx, CO2, particulate matter, methane and carbon monoxide than coal power plants meeting new federal air pollution standards.
What are some barriers to bioenergy?
There are at least three barriers to expanded bioenergy markets:
Supply infrastructure. If bioenergy is to play a larger role in the U.S. energy mix, energy generators will require a steady supply of biomass. However, this is not a small task÷essentially, a new industry must be formed to harvest, transport and prepare biomass into a useable form. If biomass power plant operators must supply steady power year-round, there must be enough biomass available throughout the year to fulfill their obligations.
However, suppliers of biomass do not sell just to the energy market. For example, wood chips can go into mulch or animal bedding. Other wood waste can be recycled into new products. Thus bioenergy operators must compete with other industries for biomass. This means that they must pay enough money consistently to secure the supplies they need.
Lack of familiarity. Professionals in the energy sector are usually not familiar with biomass, biomass energy conversion technologies, and biomass markets. As a result, project initiators often rely on local professionals with limited knowledge. Such professionals often ãreinvent the wheelä when designing projects, thereby driving up costs or creating a less than optimal project. And farmers have no experience with growing, processing, storing, and transporting crops suitable for combustion. With biomass competing against fossil fuels for different applications, inconveniences based on inexperience are enough to discourage early adoption.
Technology challenges. There are still a number of challenges to mass commercialization of bioenergy. For example, co-firing can be difficult if the coal power plant has selective catalytic reduction (SCR) to comply with new, more stringent limits of nitrogen oxide emissions. The alkali content of biomass fuels may contaminate SCR technologies. Up to 70% of coal-fired power plants potentially capable of biomass co-firing are likely candidates of SCR retrofits.
What are some policies that might promote bioenergy in the U.S.?
Research, development and demonstration
There is a continued need for technology development to address issues such as SCR contamination among others, as well as improving efficiencies and reducing costs. There is also a need for more research on growing energy crops cheaply and with minimum environmental impact. U.S. Department of Agriculture extension offices, for example, can work with farmers to better understand efficient production of energy crops.
Power. Section 45 of the Energy Policy Act of 1992 offers a 1.5 cent per kWh tax credit to wind power and ãclosed-loop biomassä, which means only energy crops. The credit would allow bioenergy operators to pay enough for biomass they need. Such a tax credit can be extended to include many more forms of biomass, which are cheaper than energy crops. The credit does not have to be restricted to biomass for power plants÷it can include biomass for small industrial boilers and district energy operations. The tax credit allows bioenergy operators to compete with other industries that use biomass, so that a consistent, high quality supply of biomass is possible.
Combined heat and power (CHP). Accelerated depreciation and investment tax credits can help catalyze new biomass CHP projects by making near-term economics more attractive to financiers.
Renewable fuels standard
The renewable fuels standard requires an increasing percentage of transportation fuel sold in the United States be biofuels. The policy features a credit trading system to allow refiners, blenders, and retailers to buy and sell credits from each other to meet their goals.
Renewable portfolio standard
Biomass power plants can be included in renewable portfolio standards, which require a certain percentage of power within a state or the entire U.S. to come from renewables. The RPS also features a credit trading system similar to the renewable fuels standard.
Where can I get more information on bioenergy?
Biomass on CREST
CREST Bioenergy Discussion Lists
CREST's Renewables Kiosk
DOE Renewable Energy Technology Characterizations
Bioenergy Information Network (Oak Ridge National Laboratory)
American Bioenergy Association
The BioEnergy Home Page
ERENâs Bioenergy Page
Southeastern Regional Biomass Energy Program
Renewable Energy Policy Project, 2001