Biomass EnergyUpdated June 2, 2022 Energy Science
The term "biomass" refers to organic matter that has stored energy through the process of photosynthesis. It exists in one form as plants and may be transferred through the food chain to animals' bodies and their wastes, all of which can be converted for everyday human use through processes such as combustion, which releases the carbon dioxide stored in the plant material.
What Is Bioenergy?
Bioenergy uses biomass -- plant matter or animal waste -- to produce electricity, fuels, and heat. Examples include ethanol motor fuel, landfill gas and wood burned in fireplaces and stoves. EMS's biomass web pages deal mainly with ethanol motor fuel and the use of plant matter to generate electricity in power plants.
Biomass Energy Potential
Current ethanol production uses the kernels from the corn plant. Farming corn is a relatively energy-intensive process, but ethanol from corn still yields 34 percent more energy than the total amount required to farm the corn and make the ethanol.
Other crops have a much higher energy yield: Ethanol made from "energy crops" -- grasses and trees -- yields 4-5 times as much energy as needed to farm the crops and make the ethanol.
The Department of Energy (DOE) believes that we could produce 10 percent of our transportation fuels from biomass by 2010, and as much as 50 percent by 2030. For electricity, DOE estimates that biomass could supply 5 percent by 2010, while the Electric Power Research Institute puts the portion at 8 percent.
"Repowering the Midwest," a report by environmental groups, estimates that energy crops and waste biomass from the Midwest alone could provide about 16 percent of the country's electricity, without irrigation and without competing with food crops.
The extensive subsidy programs for both food crops and fossil fuels have created a substantial barrier to energy crops, according to the Union of Concerned Scientists.
Many of the biomass fuels used today come in the form of wood products, dried vegetation, crop residues, and aquatic plants. Biomass has become one of the most commonly used renewable sources of energy in the last two decades, second only to hydropower in the generation of electricity. It is such a widely utilized source of energy, probably due to its low cost and indigenous nature, that it accounts for almost 15% of the world's total energy supply and as much as 35% in developing countries, mostly for cooking and heating.
Biomass Is Organic Energy
Biomass is one of the most plentiful and well-utilized sources of renewable energy in the world. Broadly speaking, it is organic material produced by the photosynthesis of light. The chemical material (organic compounds of carbons) are stored and can then be used to generate energy. The most common biomass used for energy is wood from trees. Wood has been used by humans for producing energy for heating and cooking for a very long time.
Biomass has been converted by partial pyrolysis to charcoal for thousands of years. Charcoal, in turn, has been used for forging metals for millennia. Both wood and charcoal formed part of the backbone of the early Industrial Revolution (much of Northern England, Scotland, and Ireland were deforested to produce charcoal) prior to the discovery of coal for energy.
Wood is still used extensively for energy in both household situations and industry, particularly in timber, paper and pulp, and other forestry-related industries. Woody biomass accounts for over 10% of the primary energy consumed in Austria, and it accounts for much more of the primary energy consumed in most of the developing world, primarily for cooking and space heating.
It is used to raise steam, which, in turn, is used as a by-product to generate electricity. Considerable research and development work is currently underway to develop smaller gasifiers that would produce electricity on a small scale. For the moment, however, biomass is used for off-grid electricity generation, but almost exclusively on a large industrial scale.
There are two issues that affect the evaluation of biomass as a viable solution to our energy problem: the effects of the farming and production of biomass and the effects of the factory conversion of biomass into usable energy or electricity. There are as many environmental and economic benefits as there are detriments to each issue, which presents a difficult challenge in evaluating the potential success of biomass as an alternative fuel.
For instance, the replacement of coal with biomass could result in "a considerable reduction in net carbon dioxide emissions that contribute to the greenhouse effect." On the other hand, the use of wood and other plant material for fuel may mean deforestation. We are all aware of the problems associated with denuding forests, and widespread clear cutting can lead to groundwater contamination and irreversible erosion patterns that could literally change the structure of the world's ecology.
Biomass has to be considered in the search for an alternative source of energy that is abundant in a wide-scale yet non-disruptive manner since it is capable of being implemented at all levels of society. Although tree plantations have "considerable promise" in supplying an energy source, "actual commercial use of plantation-grown fuels for power generation is limited to a few isolated experiences."
Supplying the United States ' current energy needs would require an area of one million square miles. That's roughly one-third of the area of the 48 contiguous states. There is no way that plantations could be implemented at this scale, not to mention that soil exhaustion would eventually occur. Biomass cannot replace our current dependence on coal, oil, and natural gas, but it can complement other renewables such as solar and wind energy.
According to Flavin and Lenssen of the Worldwatch Institute, "If the contribution of biomass to the world energy economy is to grow, technological innovations will be needed, so that biomass can be converted to usable energy in ways that are more efficient, less polluting, and at least as economical as today's practices."
Environmental Concerns of Biomass Energy
The use of biomass as a fuel offers some environmental advantages over fossil fuels like coal and oil but can also have significant negative impacts on the environment.
Some environmental groups support development of biomass energy depending on factors such as:
- Choice of biomass "feedstock" used to make the fuel (e.g. crop wastes, trees and grasses, corn, etc.)
- The manner in which crops are farmed (whether there is heavy use of pesticides and fertilizers, use of irrigation, etc.)
- The effectiveness of pollution controls used when energy is generated.
Most environmental groups do not promote ethanol as a strategy for reducing smog. In particular, the Sierra Club and Clean Air Trust have voiced concerns that ethanol may actually lead to an increase in smog-forming pollutants. Indeed, studies show that adding a small amount of ethanol to gasoline can lead to a slight increase in the formation of smog. On the other hand, motor fuels composed primarily of ethanol (mixtures containing upwards of 80 percent ethanol) are thought to reduce smog, compared with conventional gasoline.
Some environmental groups support the use of biomass energy as a way to reduce America's fossil fuel dependence and to help combat global warming. Energy crops can play a significant role in addressing global warming and fossil fuel dependence; ethanol made from corn provides, at best, only a small benefit because of the amount of petroleum required to farm corn.
Power plants or automobile engines that generate energy from biomass can emit no more carbon than the biomass crops have absorbed from the atmosphere, so there are no net carbon emissions from the fuel itself. However, a significant amount of energy is needed to farm the crops -- particularly in the case of food crops, such as corn, that require annual plowing and replanting and typically are grown with fertilizers and pesticides.
To the extent that the energy used to farm biomass crops is generated by burning fossil fuels, biomass energy has a global warming impact. Farming of biomass crops can also have the effect of releasing soil carbon into the atmosphere.
American Lands Alliance has expressed concerns that native forests will be replaced with "tree farms" to grow fuel for bioenergy generation.
Ethanol and Smog
While formation of smog (ground-level ozone) is a complex process involving many factors, studies indicate that motor fuel comprised of at least 80 percent ethanol can reduce smog, while a gasoline/ethanol mixture containing less than 80 percent ethanol appears to lead to a small increase in smog.
But the debate over the use of ethanol as a more environmentally friendly alternative fuel will no doubt continue. Blending small amounts of ethanol with gasoline has little impact, or a small net positive impact, on smog formation.
According to a May 1999 report by a committee of the National Academies of Sciences (NAS), the addition of oxygenates such as MTBE and ethanol to gasoline "has little impact on improving ozone air quality." The NAS press release says "the overall impact of either oxygen additive [ethanol or MTBE] on reducing ozone -- a major component of smog -- is very small."
In July 2001, the Northeast States for Coordinated Air Use Management issued a report, "Health, Environmental, and Economic Impacts of Adding Ethanol to Gasoline in the Northeast States."
According to the report, "ethanol-blends provide ... lower rates of carbon monoxide and particulate emissions, as well as greenhouse gas benefits."
The report suggests that blending ethanol with gasoline increases some of the chemical emissions that contribute to smog, such as NOx and VOCs, while reducing emissions of carbon monoxide, another factor in the formation of smog: "With ethanol, the carbon monoxide benefits will partially offset the adverse ozone impacts associated with increased NOx and VOC emissions."
An ethanol/gasoline mix containing upwards of 80 percent ethanol appears to reduce formation of smog. According to the website of the American Lung Association, "ethanol produces lower emissions of ozone-forming compounds and toxic air pollutants" than gasoline when 85 percent ethanol is blended with 15 percent gasoline.
A study by Jennifer L. Brand, a researcher at the University of Nebraska-Lincoln, found that a gasoline mixture with 10 percent ethanol leads to increased evaporative, smog-forming emissions, compared with standard gasoline. Brand concluded that smog-forming emissions are reduced only when the ethanol portion of the fuel mixture approaches 80 percent, according to a June 2001 article in the Grand Island Independent (Nebraska).
The Renewable Fuels Association, a trade group, says on its website that ethanol reduces smog: "Some ethanol opponents seize upon the fact that when ethanol is blended with gasoline, it slightly raises the volatility of the fuel. Increased volatility can lead to increased evaporation of smog-forming emissions. But as is often the case, this is only half the story.
Blending ethanol in gasoline dramatically reduces carbon monoxide tailpipe emissions. According to the National Research Council, carbon monoxide emissions are responsible for as much as 20 percent of smog formation.
Additionally, ethanol-blended fuels reduce tailpipe emissions of volatile organic compounds, which readily form ozone in the atmosphere. Thus, the use of ethanol plays an important role in smog reduction."
A report done in 2009 concluded, "Recent improvements in crop production, biorefinery operation, and coproduct utilization in U.S. corn-ethanol systems result in greater GHG emissions reduction, energy efficiency, and ethanol-to-petroleum output/input ratios compared to previous studies.”
Direct-effect GHG emissions reductions were found to be 48% to 59% compared to gasoline, which is two to three times greater than estimated in previous reports (Farrell et al. 2006). The NER has improved from 1.2 in previous studies to 1.5 to 1.8 on the basis of updated data.
Ethanol-to-petroleum ratios were 10:1 to 13:1 for today’s typical corn-ethanol systems but could increase to 19:1 with progressive crop management that increases both yield and input use efficiency. A closed-loop biorefinery with an AD system reduces GHG emissions by 67% and increases the net energy ratio to 2.2. Such improved performance moves corn-ethanol much closer to the hypothetical estimates for cellulosic biofuels.
The critics of this study say that it does not take into consideration the effects of the changes to land use by concentrating more acreage on growing corn at the expense of other vital crops such as soybeans. This will increase the pressure on the remaining land to be cleared for even more crop growing and thus affect the environment negatively in that way.
Biomass Feedstocks: Energy Crops
Food Crops & Agricultural Wastes
"Feedstock" is a general term for the plant matter used to make fuel. Agricultural wastes, trees, grasses, corn, wood wastes and residues, aquatic plants, animal wastes, and municipal wastes are examples of biomass feedstocks.
Agricultural wastes include corn stalks, sugar cane wastes and rice hulls. Natural Resources Defense Council (NRDC) advocates increased government investment in the use of these wastes for making ethanol motor fuel. "Tapping agricultural wastes and other renewable feedstocks to produce fuel has tremendous potential to reduce U.S. oil dependence," according to an NRDC report.
Net environmental benefits are generally thought to be greater when crop wastes are used as a feedstock for fuel, compared to corn and other crops. Since crop wastes are the by-product of existing agricultural activity, use of these wastes does not contribute to pesticide and fertilizer pollution, soil erosion, or water use.
Though use of crop wastes to generate energy causes air pollution, these wastes might otherwise be landfilled or subject to open burning. Open burning, in particular, results in worse pollution than when energy is generated in a process using effective pollution controls.
In its biomass guidance document, the Sierra Club favors returning crop wastes to the soil ("for soil health, tilth, fertility, and nurturing the organisms populating the below ground ecosystem") rather than using the wastes as fuel. Meanwhile, the document acknowledges that in many cases farmers burn off these wastes, "posing a health threat to nearby residents."
Energy Crops vs. Food Crops
The term "energy crops" is often used to refer to trees and grasses that offer greater environmental and energy benefits compared with food crops like corn. Corn is the crop most often used as a feedstock for ethanol at present.
Some trees -- such as poplar, maple, black locust, willow, sycamore, sweetgum, and eucalyptus -- will grow back after being cut off close to the ground, allowing them to be harvested every three to eight years for 20 or 30 years before replanting. Certain native grasses can be harvested for up to 10 years before replanting.
Food crops, like corn, must be replanted every year and require much closer management and greater use of fertilizers, pesticides, and energy, compared with trees and grasses.
Ethanol can be made from either cellulose or carbohydrates. Trees and grasses are a source of cellulose while corn is used as a source of carbohydrates. According to a paper by the Oak Ridge National Laboratory, "more cellulose can be produced per unit land area than carbohydrates. Therefore, cellulose-based ethanol production is a more efficient use of land."
The energy yield from biomass is highest when energy crops are used to generate electricity in a power plant, with energy yields perhaps 10 times greater than total energy inputs.
In contrast to food crops that pull nutrients from the soil, energy crops actually improve soil quality. Prairie grasses, with their deep roots, build up topsoil, putting nitrogen and other nutrients into the ground. Since they are replanted only every 10 years, there is minimal plowing that causes soil to erode.
Energy crops can create better wildlife habitat than food crops. Since they are native plants, they attract a greater variety of birds and small mammals than modern industrial food-producing farms. They improve the habitat for fish by increasing water quality in nearby streams and ponds. And since they have a wider window of time to be harvested, energy crop harvests can be timed to avoid critical nesting or breeding seasons.
Compared to undisturbed natural habitats, energy crops are not as good for supporting biodiversity. But energy crop farms can be managed to be much closer to the natural world than industrial food-producing farms. Nonetheless, the environmental benefits of biomass hinge on whether energy crops are managed with sustainable agricultural practices. Just like food crops, they can be mishandled, with productivity increased by greater chemical inputs.
From the Natural Resources Defense Council website: "Prospects for lowering costs on and expanding ethanol production are limited due to the high level of inputs required to produce agricultural crops (e.g., fertilizer, pesticides, tractor fuel) and the resulting high cost and substantial environmental impact.
Biomass energy crops, if grown in bulk, however, could be a profitable alternative for farmers, complementing, not competing with, existing crops and thus providing an additional source of income for the agricultural industry.
A substantial amount of agricultural land exists which is marginal for conventional crop production but which can be brought into productive use to grow energy crops (since perennial herbaceous and woody energy crops can be selected which provide advantages such as erosion protection or drought tolerance)."
When we have enough government support and have allotted enough land for the continuous growth of energy crops for biomass-based energy, we may have a successful form of alternative energy.
But "as long as worldwide prices of coal, oil, and gas are relatively low, the establishment of plantations dedicated to supplying electric power or other higher forms of energy will occur only where financial subsidies or incentives exist or where other sources of energy are not available." Although it is currently utilized across the globe, biomass energy is clearly not capable of sustaining the world's energy needs on its own.