Biomass is a scientific term for living matter, but the word biomass is also used to denote products derived from living organisms - wood from trees, harvested grasses, plant parts and residues such as twigs, stems and leaves, as well as aquatic plants and animal wastes. All the Earth's biomass exists in a thin surface layer called the biosphere. This represents only a tiny fraction of the total mass of the Earth, but in human terms it is an enormous store of energy - as fuel and as food. More importantly, it is a store which is being replenished continually. The source which supplies the energy is of course the Sun, and although only a tiny fraction of the solar energy reaching the Earth each year is converted into biomass, it is nevertheless equivalent to over five times total world energy consumption.
Biomass energy or "bioenergy" includes any solid, liquid or gaseous fuel, or any electric power or useful chemical product derived from organic matter, whether directly from plants or indirectly from plant-derived industrial, commercial, or urban wastes, or agricultural and forestry residues. Thus bioenergy can be derived from a wide range of raw materials and produced in a variety of ways. Because of the wide range of potential feedstocks and the variety of technologies to produce them and process them, bioenergy is usually considered as a series of many different feedstock / technology combinations.
In practice, we tend to use different terms for different end uses - e.g. electric power or transportation. The term "biopower" describes biomass power systems that use biomass feedstocks instead of the usual fossil fuels (natural gas or coal) to produce electricity, and the term "biofuel" is used mostly for liquid transportation fuels which substitute for petroleum products such as gasoline or diesel. "Biofuel" is short for "biomass fuel."
Since 1978, the ORNL Bioenergy Feedstock Develoment Program (BFDP) has been developing and demonstrating environmentally acceptable crops and cropping systems for producing large quantities of low-cost, high-quality biomass which may be used to "feed" energy-intensive processes such as electricity production or transportation. BFDP also develops the technology and information needed to use agricultural, forestry and urban residues for energy production.
Energy crops, also called "bioenergy crops", are fast-growing crops that are grown for the specific purpose of producing energy (electricity or liquid fuels) from all or part of the resulting plant. The plants that have been selected by the U.S. Department of Energy for further development as energy crops are mostly perennials such as switchgrass, willow and poplar. They were selected for their advantageous environmental qualities such as erosion control, soil organic matter build-up and reduced fertilizer and pesticide requirements. There are many other perennial plant species which could be used for energy crops. In addition, some parts of traditional agricultural crops such as the stems or stalks of alfalfa, corn or sorghum may be used for energy production.
Renewable energy is any energy source that can be either replenished continuously or within a moderate timeframe, as a result of natural energy flows. The so-called "renewables" include solar energy (heat and electricity), bioenergy, wind power, hydropower, and geothermal power.
During photosynthesis, plants combine carbon dioxide from the air and water from the ground to form carbohydrates, which form the biochemical "building blocks" of biomass. The solar energy that drives photosynthesis is stored in the chemical bonds of the carbohydrates and other molecules contained in the biomass.
Yes. If biomass is cultivated and harvested in a way that allows regrowth without depleting nutrient and water resources, it is a renewable resource that can be used to generate energy on demand, with little net additional contributions to global "greenhouse gas" emissions.
8. Does bioenergy contribute to
greenhouse gas emissions?
Worldwide, total "standing crop" biomass (99% on land, and 80% in trees) is a huge resource, equivalent to about 60 years of world energy use in the year 2000 (1250 billion metric tonnes of dry plant matter, containing 560 billion tonnes of carbon). For the U.S. alone, standing vegetation has been variously estimated at between 65 and 90 billion tonnes of dry matter (30-40 billion tonnes of carbon), equivalent to 14-19 years of current U.S. primary energy use. However, the Earth actually grows every year about 130 billion tonnes of biomass on land (60 billion tonnes of carbon) and a further 100 billion tonnes in the rivers, lakes and oceans (46 billion tonnes carbon). The energy content of this annual biomass production is estimated to be more than 6 times world energy use or 2,640 exajoules (2500 Quads) on land, with an additional 2024 exajoules (1920 Quads) in the waters.
Estimates of how much of the Earth's land-based production is used by the human population worldwide range from a low figure of about 5% to a high of over 30% (this includes food, animal fodder, timber and other products, as well as bioenergy). The higher estimates include a lot of wasted material and inefficient activities such as forest clearance, as well as losses of productivity due to human activity. Biomass energy use worldwide has been independently estimated at about 55 exajoules per year, or about 2% of annual biomass production on land.
Worldwide, biomass is the fourth largest energy resource after coal, oil, and natural gas - estimated at about 14% of global primary energy (and much higher in many developing countries). In the U.S., biomass today provides about 3-4% of primary energy (depending on the method of calculation). Biomass is used for heating (such as wood stoves in homes and for process heat in bioprocessing industries), cooking (especially in many parts of the developing world), transportation (fuels such as ethanol) and, increasingly, for electric power production. Installed capacity of biomass power generation worldwide is about 35,000 MW, with about 7,000 MW in the United States derived from forest-product-industry and agricultural residues (plus an additional 2,500 MW of municipal solid waste-fired capacity, which is often not counted as part of biomass power, and 500 MW of landfill gas-fired and other capacity). Much of this 7,000 MW capacity is presently found in the pulp and paper industry, in combined heat and power (cogeneration) systems.
Nearly every part of the world has a biomass resource that can be tapped to make biofuels and generate electric power. From coconut or rice husks to fast-growing trees, from perennial grasses to scrap wood, there is a (probably under-utilized) form of biomass almost anywhere you go on Earth.
Not in the U.S., although MSW is burned here, in Europe, and elsewhere to generate electric power and heat. Most of the mass of municipal solid waste is derived from plant matter and could be used to fire special MSW power systems, but MSW also contains a variety of potentially toxic materials such as creosote-treated wood, batteries that contain mercury, and other hazardous products. As a result, MSW power systems must either remove these materials from their feedstocks before burning them, or treat the exhaust very carefully to avoid toxic emissions. "Biopower" plants in the U.S. use only uncontaminated feedstocks. Ordinary biomass contains no toxic chemicals and, when used in modern power systems, produces fewer emissions than conventional fossil-fuel fired power plants.
When biomass is burned, it produces heat (as in any simple fireplace or furnace). In most power plants (steam-cycle or steam-turbine systems), this heat is captured by boiling water to generate steam, which turns turbines and drives generators that convert the energy into electricity. New technologies now being evaluated include several types of biomass gasifiers in which biomass is heated to convert it into a gas. This gas is used directly in a gas turbine, which drives a generator (a simple gas turbine system). In some cases, the waste heat from the gas turbine may be used to drive a secondary steam turbine, thus converting more of the fuel energy into electricity (a combined-cycle system).
"Co-firing" refers to the blending of biomass with coal in the furnace of a conventional coal-fired steam-cycle electric power plant. This is currently one of the simplest ways of utilizing biomass to displace fossil fuels, requiring no new investment or specialized technology. Between 5% and 15% biomass (by heat content) may be used in such facilities at an additional cost estimated at less than 0.5 cents/kWh (compared with coal-firing alone). Co-firing is known to reduce carbon dioxide emissions, sulphur dioxide (SOx) emissions, and potentially some emissions of nitrogen oxides (NOx) as well. Many electric utilities around the United States have experimented successfully with co-firing, using wood chips, urban waste wood and forestry residues.
The main needs for further development of biomass-electric technology are to improve the efficiency of energy conversion, to lower emissions, and to reduce costs. Gasification offers greater flexibility, both in the range of possible biomass feedstocks and in the end-use of the energy. For example, as well as driving a gas turbine, the gas from a gasifier can power a fuel cell to generate electricity, or it can be used to generate steam in a gas boiler, sometimes in combination with natural gas. Large steam-turbine systems in power plants 200 MW or larger (such as most coal-fired power plants) are relatively efficient at energy conversion, whereas smaller biomass-fired steam-turbine systems (20-100 MW) require further research to improve their cost-competitiveness with fossil fuels. Biomass gasification systems may be able to combine high efficiency with cost-competitiveness in this size range (20-100 MW). Other research is continuing to develop small modular biomass conversion systems (100 kW - 5 MW) to provide electricity cost-effectively to communities and industries.
Today, wood and wood-processing residues and by-products are the most widely used biomass fuels in the USA (where more than 500 electric power plants operate on biomass). These conventional steam-cycle power systems have the longest operating experience, and are well understood. A wider range of biomass fuels may be used by gasifiers (for example, rice hulls from the food processing industry), but although this more recent technology has great future potential, there is less operating experience with it.
The most common liquid fuel from biomass in the USA is ethanol, produced by fermentation. Typically, sugars are extracted from the biomass feedstock by crushing and washing (or in the case of starchy feedstocks like corn [maize], by breakdown of starch to sugars). The sugar syrup is then mixed with yeast and kept warm, so that the yeast breaks down the sugars into ethanol. However, the fermented product is only about 10% ethanol, so a further stage of distillation is required to concentrate the ethanol to 95%. If the ethanol is intended for blending with gasoline, a "dehydration" phase may be required to make 100% pure ethanol. In the near future, ethanol may be made from cellulose, again by breakdown into sugars for fermentation. Cellulose is widely and cheaply available from many other biomass feedstocks, energy crops, agricultural and forestry residues.
Another form of liquid fuel from biomass is "biodiesel", which is derived from the vegetable oils extracted by crushing oil-seeds, although waste cooking oil or animal fats (tallow) can also be used. The oil is strained and usually "esterified", by combining the fatty acid molecules in the oil with methanol or ethanol. Vegetable oil esters have been shown to make good-quality clean-burning diesel fuel; in 1998 there were 85 biodiesel processing plants worldwide, mostly in Europe.
The projected cost depends on where you are located, because of a variety of factors such as differences in yields, different input prices, and differences in the profitability of alternative uses for the land occupied by the switchgrass. In some areas, small quantities could be available at "farmgate" prices as low as $25/ U.S. ton (multiply by approximately 1.1 for metric tonnes or imperial tons). However, most parts of the U.S. would require farmgate prices of $30-40/t to encourage significant amounts of switchgrass production. Transport costs of $5-15/t should be added to farmgate prices for delivery to conversion facilities at distances from 5 to 50 miles. [Source: Ugarte, Walsh, Shapouri and Slinsky (1999) The Economic Impacts of Bioenergy Crop Production in U.S. Agriculture.]
2. How many acres of trees would need to be planted in order to have a steady supply of bioenergy feedstock for a power plant?
A rough "rule of thumb" based on recent experience is that it takes a little under 1000 acres (400 hectares) of poplar (grown as a short-rotation crop at a usable yield of 5 dry U.S. tons/acre, or 11 metric tonnes/hectare) to supply an electric power plant with a capacity of one megawatt (1 MW). A typical small biomass-fired power plant (25 MW) with 80% availability (i.e. actually operating 80% of the time) would produce about 175 million kWh per year, or approximately the electricity needs of 25,000 people. The required 25,000 acres of land (about 10,000 hectares) would occupy about 2% of the total land area within a radius of 25 miles (40 km).
These calculations are based on a 30% conversion efficiency from heat to electricity, and an energy content for dry poplar wood of 17 Btu/U.S. ton (19.7 GJ/metric tonne). [Source: Walsh, M. (1999) personal communication.]
The cost of electricity from two contrasting technologies (one present-day, one future), for a biomass-fired power plant from 10 to 50 MW in size, breaks down as follows:
The capital cost of building a biomass-fired steam-turbine plant is about $2000-2500 per kW of installed capacity, including a return on the investment, although capital costs are expected to decrease in the future. The currently high capital cost is a function of small plant size, which also increases operating costs in terms of capacity per employee (these figures are based on actual costs in California, using wastes as feedstock rather than dedicated energy crops). The capital cost of the advanced gasifier power plant is based on equipment costs alone, estimated at $1037 per kW (costs are projected to fall into this range by 2010-2020). Projected total costs for the year 2020 for electricity from biomass gasifier/gas-turbine combined-cycle systems range from 4.0-5.0 cents/kWh in the U.S. southeast to 5.0-7.0 cents/kWh in the U.S. north-central region. [Sources: Morris, G. (1999?) The Environmental Costs and Benefits of Biomass Energy Use in California; Larson, E. and C.I. Marrison (1997?) Economic scales for first-generation biomass-gasifier/gas turbine combined cycles fueled from energy plantations; Paisley, M.A. and D. Anson (1997) Biomass gasification for gas turbine based power generation].
Based on a capital cost of $2.50-3.00 per U.S. gallon of annual capacity (for production plants of around 50 million gallons/year), the fixed costs are about 60 cents/gallon. Operating costs are expected to be about 35 cents/gallon and feedstock costs in the range 30-50 cents/gallon. Assuming an electricity co-product credit equivalent to 10-15 cents/gallon, total costs could range from about $1.10 to 1.35/gallon. These are estimates based on research at the National Renewable Energy Laboratory in Golden, Colorado, since no large production plant for converting cellulosic biomass to ethanol has yet been built. Currently, ethanol is produced from corn, and sells for around $1.20-1.50/gallon. Other options for producing ethanol, such as with thermal gasification instead of biological breakdown of cellulose, might reduce the cost further. Costs are also expected to decline over time with improvements in technology and operating experience.
5. If I plant a bioenergy crop today, when can I expect to see a financial return from selling the crop?
It is essential to identify a market for your bioenergy crop first. Compared with annually-harvested arable crops (which provide an income within 12 months of planting), the returns from selling a perennial bioenergy crop are delayed until the crop is ready for harvest (after two or more years). Tree crops are usually harvested every 3-5 years, although harvests on different plots may be staggered so as to provide a regular annual income. A field of switchgrass would not usually be harvested in the first year, to promote good establishment; thereafter it can be harvested annually, and should last for a 10-year rotation. Willow may be harvested from year 4, with subsequent harvests every 3 years, and replanting after 22 years (7 harvests). Poplar takes 6-10 years to reach harvest size for energy or fiber use. In short, like many investments, you should expect to wait a few years before the profits come rolling in.
If you are interested in experimenting with one or more of the most likely candidate bioenergy species in your area, you can start by gaining some working knowledge of growth characteristics and management responses under local conditions - this will be useful if a later opportunity for commercial production and sale of biomass occurs in your area. The primary bioenergy crops at this time are native perennial grasses, such as switchgrass, and trees, such as hybrid poplar and willow (the optimum varieties depend on region). You should not expect an economic return from such efforts at this stage unless a market for your biomass has been identified in advance.
The two main bioenergy markets are (1) electric power/ heat plants that convert plant biomass into heat and (2) chemical processing plants that convert biomass to ethanol, a transportation fuel. In general, it is expected that such facilities should be within 50 miles (80 km) of the biomass production site to keep transportation costs at a reasonable level.
A number of nurseries stock both grass seed and tree seedlings suitable for bioenergy. Your regional USDA Natural Resource Conservation Service or agricultural extension agent should be the best source for information on planting practices and best cultivars for your growing region.
For switchgrass, the best performing cultivars have been "Alamo" for the deep South and mid-Atlantic regions of the U.S., "Kanlow" for the mid-Atlantic region, and "Cave-in-Rock" for more northerly locations where the growing season is shorter and greater cold tolerance is required. Among the tree crops, willows grow best in the North-East and North Central regions, and hybrid poplar in the Great Lakes states and Pacific North-West. Poplar, cottonwood, and sycamore are all candidates currently being evaluated in the U.S. South-East. However, growers are strongly advised to consult with local agricultural extension agents before deciding on a cultivar.
These markets are just beginning to develop as the benefits of renewable energy are being increasingly documented and recognized, and issues of production rates, costs, handling, and energy conversion efficiencies are being documented and improved through research. Current economic research indicates that biomass fuel would be very inexpensive if the benefits of improved air, soil, and water quality and economic returns to agriculture were factored into the cost/benefit equation for figuring biomass energy costs. Currently renewable energy constitutes about 4% of U.S. national energy consumption.
Ethanol derived from corn contributes about 1% of U.S. national gasoline consumption. The 7,000 MW of "conventional" U.S. biopower capacity also represents about 1% of total electricity generating capacity - there is clearly plenty of room for growth.
Anyone who can look after a woodlot for "firewood" could establish and manage short-rotation tree crops for home heating. Like native tree species, the energy content of different short-rotation tree crops varies according to their wood density, although the energy content of wood on a dry weight basis is fairly consistent. However, growth rates of individual tree crops, for example, sycamore, sweetgum, hybrid poplar, cottonwood, and willow, will differ according to region and climate. If grown as stands of a single species, tree crops would also require management, e.g., thinning, to maintain a constant source of wood fuel.
Depending upon where you live, there may be interest in your local area for some of the different energy crops for co-firing or fiber production. You would have to check with local electricity utility companies or fiber processors (paper and board manufacturers) to see if there is market for these intensively managed crops before establishing them. Remember that tree crops may take from 4 to 10 years before they are large enough to harvest, although perennial grass crops like switchgrass may be harvested from the second year onwards. Establishing the crop also requires commitment and effort to control weeds until the plants can shade-out weeds on their own. You cannot just plant-and-walk-away, expecting to come back years later to harvest the crop! In the U.S., many electricity utilities considering co-firing with bioenergy crops have established guidelines to help growers meet their needs.
Perennial bioenergy crops can increase overall biodiversity in the landscape by adding one or more new crops (switchgrass, hybrid poplar, and/or willow) on existing agricultural lands. These new perennial crops can replace less profitable agricultural crops so that there will be more different kinds of plants growing on individual farms; thereby increasing the landscape complexity in different areas of the country. Biomass crops require less pesticides and herbicides for establishment and production, which decreases the adverse effects on soil organisms and contributes to improving soil health and biodiversity.
Yes, in so far as they usually comprise a single planted species; but the bioenergy crops being developed today are mostly perennial and do not need to be disturbed as frequently as agricultural crops (for pest control, harvesting, etc.). Bioenergy crops can be managed and harvested over multiple years to provide varied structure, land cover, and habitat for wildlife. Studies by BFDP have shown that tree crop plantings are used more extensively as habitat by breeding birds than are agricultural crops. Limited studies of switchgrass plantings show that they were used by grassland birds, although we do not know yet how very large areas of switchgrass would be used.
While woody crops (tree crops) are used more extensively as habitat, they are used less extensively by breeding birds than natural forests. Species using young tree crop plantings are those that are found in shrubland and young early successional forests. As the tree crops become older and close their canopies to look more like natural forests, the wildlife species using them change to become more similar to those using natural forests. This is the same change that occurs with changes in the physical structure of natural forests. BFDP is investigating whether shrubs that provide food sources can be established adjacent to tree crop plantings to increase the value of the tree crops for wildlife.
There are extensive lands in pasture, annual row crops, and idle lands that have been identified as available for production of biomass crops. These lands would be much less expensive to convert to biomass crop production than natural forests, so there should be no increased pressure on national forests. BFDP is encouraging sustainable production of biomass crops for energy. Preliminary economic analysis suggests that the production of short-rotation woody crops (SRWC) can actually reduce the pressure on natural forests. With 3-10 times the productivity of natural forests or traditional plantations, SRWC can readily substitute for many forest species in fiber uses, at competitive prices.
Potentially these lands could be used for bioenergy crop production. This might be a good use of such lands because the crops would take up carbon dioxide, sequester carbon in their above and below-ground growth, remove other pollutants from the air, and minimize maintenance needs and fossil energy use for grass-cutting, etc. However, harvesting and removing the crops safely might present problems, and there may be no markets nearby for the biomass, making transport rather expensive.
Switchgrass can range from 3 to 8 feet (1-2.5 m) in height. Tree crops are more typically 10-20 feet (3-6 m) in height, depending on the frequency of harvest. Some interstate medians and roadsides already feature trees of this size or taller, so visibility is unlikely to be a problem.
Many watersheds in the USA experience extensive degradation from run-off from agricultural operations. Biomass crops can contribute to improving water quality by providing a continuous soil cover that helps stabilize the soil, decreases transport of nutrients, and protects the soil from erosion. The perennial cover provided by bioenergy crops reduces rainfall impact on the soil and sediment transport compared with annual row crops. Bioenergy crops do not require extensive fertilization like agricultural crops, so that there are lower levels of nutrients to be transported by run-off from production sites. Run-off is generally negligible once bioenergy crops are established.
Perennial biomass crops are not fertilized repeatedly like agricultural crops, although specific fertilizer requirements will vary with location and production system. Soil cover provided by biomass crops can increase soil stability and reduce runoff; this in turn can reduce nutrient transport. Studies of poplar and switchgrass show that the extensive rooting systems of biomass crops reduce leaching transport of nutrients through the soil column and, thus, can contribute to reducing groundwater contamination from agricultural practices.
Data from sites in the Southeastern U.S. show that after the initial year of establishment, nitrate losses under switchgrass and sweetgum decreased to less than 1 kg/ha compared with approximately 2-4 kg/ha from no-till corn. The highest N run-off was associated with rainfall occurring within a short period of time following fertilizer application in the spring - before the fertilizer had a chance to dissolve and move into the soil to be taken up by the plants. Timing and rates of application can minimize N run-off from biomass crops. This makes economic sense for the producers as well as being good environmental stewardship.
Bioenergy crops will not be planted in wetlands in the U.S. However, they do have the potential to be planted as buffer strips along waterways and streams to intercept nutrient runoff from agricultural crops, thus helping to protect water quality. They would also contribute to decreasing sediment transport from agricultural lands. Studies are looking at planting bioenergy crops in flood-prone areas, because as perennial crops they do not have to be re-established annually and can withstand periods of flooding. Harvesting of these crops on wet areas would have to be timed carefully to occur during dry periods to minimize rutting and compaction of the land.
Probably not. While there may be benefits to soil and water quality from establishing buffer strips 20' (6 m) wide, 50 to 100' strips (15-30 m) could provide greater benefits for water quality and stream temperature protection, because of the increased cover and area for filtering of nutrients and sediment before run-off water reaches the stream. It should also be recognized that harvesting the crop would remove the buffer until some regrowth took place, so the strip should really be wide enough to allow partial harvest.
Yes. Most bioenergy crops are perennial, which means that they grow over multiple years rather than being harvested each year. Because they are grown for 5-15 years on one site, they create extensive rooting systems that are sources of below-ground carbon storage. This below-ground carbon and associated organic matter also contributes to improving soil quality and nutrient reserves. The tree crops also store carbon in their aboveground stems and branches, that continues to be stored until the trees are harvested for energy production. Of course, using the trees for energy also helps off-set carbon dioxide emissions to the atmosphere, by substituting for the burning of fossil fuels.
Bioenergy crops need only one-tenth the amounts of herbicides and pesticides required on average by agricultural crops, but it may be hard to reduce this further without accepting uneconomically low yields. Both tree crops and switchgrass require herbicide application prior to establishment and during the first year to minimize competition from weeds until the crops are well established. Sustainable management of biomass crops requires that soil and water quality be protected. This can be done by applying herbicides and pesticides only as required to minimize competition and economic damage. Timing application to outbreaks of pests or weeds can minimize chemical requirements and off-site impacts. Studies are showing that herbicide migration into groundwater does not occur with application to biomass crops.
Probably not. There are other powerful economic factors behind large animal operations, and they already have a nutrient disposal problem. Use of animal wastes as nutrient sources for production of biomass crops would not solve the waste disposal problems of these operations, although it could contribute to alternative, economic and ecologically viable use of these nutrient resources.