Biomass is often classified along a simple division of either woody or non-woody material. These bio-materials are also often referred to as “feedstocks” but should not be confused with animal feed used for domestic livestock. Researchers have offered a more nuanced view of sources for biomass, using eight specific categories: natural forests/woodlands, forest plantations, agro-industrial plantations, trees outside forests and woodlands, agricultural crops, crop residues, processed residues, and animal wastes.
In its raw forms, biomass is highly variable in terms of chemical and physical properties, dependent on plant physiology, environmental growing conditions, and how it is harvested, stored, and processed prior to conversion into useable energy forms. Availability and cost-efficiency of renewable energy feedstocks differs by region in the United States with regional boundaries often divided into the American North, South, and West. Harvesting efficiencies associated with various feedstocks, and production of energy from those raw materials, also varies by region (see: Department of the Interior, 2011).
According to the U.S. Energy Information Administration, renewable energy consumption in the United States grew by 6 percent, from 7.60 quadrillion Btu to 8.09 quadrillion Btu, between 2009 and 2010. The relative share of renewable energy to total energy consumption grew to 8 percent in 2010.
In 2011, renewable energy production accounted for about 13 percent of all energy in the United States and, according to the EIA “Annual Energy Outlook 2013 Early Release Overview,” is projected to top 16 percent by 2040. Concerns about peak oil, climate change, domestic economic development, and dependence on petroleum fuels from politically volatile regions have, in part, driven expansion in the bioenergy sector.
Of the dominant renewable energy categories, which also include wind, solar, hydroelectric, and geothermal; biomass made up over half (53%) of total American renewable energy consumption in 2010, followed by hydroelectric power accounting for nearly one-third (31%). Growth in biomass consumption has been spurred by increased ethanol production as a result of government policies such as the Renewable Fuel Standard for biofuels production and the Renewable Portfolio Standard for bio-power production (see: US Department of Energy, 2010 - pdf), contributing to a two-fold increase in renewable energy consumption in the American transportation sector between 2006 and 2010.