Bioenergy (Biofuels and Biomass)
Biomass can be used to produce renewable electricity, thermal energy, or transportation fuels (biofuels). Biomass is defined as living or recently dead organisms and any byproducts of those organisms, plant or animal. The term is generally understood to exclude coal, oil, and other fossilized remnants of organisms, as well as soils. In this strict sense, biomass encompasses all living things. In the context of biomass energy, however, the term refers to those crops, residues, and other biological materials that can be used as a substitute for fossil fuels in the production of energy and other products. Living biomass takes in carbon as it grows and releases this carbon when used for energy, resulting in a carbon-neutral cycle that does not increase the atmospheric concentration of greenhouse gases.
The energy stored in biomass can be released to produce renewable electricity or heat. Biopower can be generated through combustion or gasification of dry biomass or biogas (methane) captured through controlled anaerobic digestion. Cofiring of biomass and fossil fuels (usually coal) is a low-cost means of reducing greenhouse gas emissions, improving cost-effectiveness, and reducing air pollutants in existing power plants. Thermal energy (heating and cooling) is often produced at the scale of the individual building, through direct combustion of wood pellets, wood chips, and other sources of dry biomass.
Combined heat and power (CHP) operations often represent the most efficient use of biomass (utilizing around 90 percent of potential energy). These facilities capture the waste heat and/or steam from biopower production and pipe it to nearby buildings to provide heat or to chillers for cooling.
A number of transportation fuels can be produced from biomass, helping to alleviate demand for petroleum products and improve the greenhouse gas emissions profile of the transportation sector. Ethanol from corn and sugarcane, and biodiesel from soy, rapeseed, and oil palm dominate the current market for biofuels, but a number of companies are moving forward aggressively to develop and market a number of advanced second-generation biofuels made from non-food feedstocks, such as municipal waste, algae, perennial grasses, and wood chips. These fuels include cellulosic ethanol, bio-butanol, methanol and a number of synthetic gasoline/diesel equivalents. Until we are able to produce a significant amount of electric vehicles that run on renewably-produced electricity, biofuels remain the only widely available source of clean, renewable transportation energy.
Just as biomass can substitute for fossil fuels in the production of energy, it can also provide a renewable substitute for the many industrial products and materials made from petroleum or natural gas – biobased foams, plastics, fertilizers, lubricants, and industrial chemicals are a few of the possibilities.
Every region has its own locally generated biomass feedstocks from agriculture, forest, and urban sources.
A wide variety of biomass feedstocks are available and biomass can be produced anywhere that plants or animals can live. Furthermore, most feedstocks can be made into liquid fuels, heat, electric power, and/or biobased products. This makes biomass a flexible and widespread resource that can be adapted locally to meet local needs and objectives.
Some of the most common (and/or most promising) biomass feedstocks are:
- Grains and starch crops – sugar cane, corn, wheat, sugar beets, industrial sweet potatoes, etc.
- Agricultural residues – Corn stover, wheat straw, rice straw, orchard prunings, etc.
- Food waste – waste produce, food processing waste, etc.
- Forestry materials – Logging residues, forest thinnings, etc.
- Animal byproducts – Tallow, fish oil, manure, etc.
- Energy crops – Switchgrass, miscanthus, hybrid poplar, willow, algae, etc.
- Urban and suburban wastes – municipal solid wastes (MSW), lawn wastes, wastewater treatment sludge, urban wood wastes, disaster debris, trap grease, yellow grease, waste cooking oil, etc.
Like wind, solar, and other renewable energy sources, biomass can make a positive impact on our atmosphere by lessening our dependence on climate change-inducing fossil fuels. Biomass energy differs from other renewables, however, in the extent to which its use is directly tied to the farms, forests, and other ecosystems from which biomass feedstocks are obtained. Because of this close association, the use of biomass has the potential to result in a wide range of environmental and social impacts, both positive and negative, above and beyond its use as a substitute for fossil fuels. Impacts on soils, water resources, biodiversity, ecosystem function, and local communities will differ depending on what choices are made regarding what types of biomass are used, as well as where and how they are produced. This is why biomass needs to be produced and harvested as sustainably as possible. In this sense, sustainability refers to choosing management practices that minimize adverse impacts and complement local land-management objectives, such as farm preservation, forest stewardship, food production, and wildlife management.
One land use issue that often arises is the perceived conflict between food production and bioenergy (the so-called ‘food-vs.-fuel’ debate). Many traditional food crops, such as corn, sugar and vegetable oils, are also some of the most commonly used energy feedstocks. Furthermore, agricultural land may be shifted from producing food to the production of dedicated energy crops. The use of agricultural crops and lands has undoubtedly contributed in part to increased prices for many of these commodities. Many other factors, however, have contributed much more substantially to this increase, including inflation of the dollar and especially the rapid rise in price of fossil fuels. Oil and natural gas, in the form of fuel and synthetic fertilizers, are two of the biggest economic inputs in food production and distribution. There are many opportunities to further reduce the conflict between food and fuel production, including an increased use of agricultural wastes, logging residues, food scraps, municipal solid waste, and marginal lands.
Another issue heavily associated with biomass production is greenhouse gas emissions from land management and land use change. These refer to emissions of greenhouse gases (especially CO2, CH4, and N2O) resulting from agricultural inputs, management practices, and land use changes associated with production of biomass. These emissions can be divided into direct and indirect sources. Direct emissions refer to those resulting from land clearing, agricultural inputs (such as fertilizers), or management practices undertaken in the process of growing or harvesting a biomass crop. Indirect emissions are associated with market-driven land use change. These are the emissions that occur when forests, grasslands, or other ecosystems are cleared to produce crops or other commodities to compensate for land that has been diverted to energy production. The effects are difficult to quantify or attribute, making indirect emissions from land use change (ILUC) a very controversial subject.
Finally, it is important to remember that biomass markets will add value to biomass products, residues, and productive lands. This value will help improve the economic viability of working lands and act as a positive incentive to help preserve farms and forests from the accelerating threat of urban and suburban sprawl – the greatest land use impact.