challenge was a primary objective of this study—the common thread throughout the committee’s deliberations.
Different coals have different heating values (energy per unit mass). Therefore, the amount of coal in the overall U.S. energy economy should be considered in terms of both its mass (commonly expressed in tons) and its energy content (commonly expressed in British thermal units, abbreviated as Btu1). Annual U.S. coal production has roughly doubled over the past 50 years, and now exceeds 1 billion tons per year (Figure 1.2) (EIA, 2006a). Since the mid-1980s, the proportion of coal in the total U.S. energy mix has remained broadly constant and supplied approximately 23 percent of the 101 quadrillion (1015) Btu of total energy consumed in 2005 (Figures 1.3 and 1.4).
On a tonnage basis, production from large surface mines that are located mostly in the western states (Figures 1.5 and 1.6) has grown rapidly since 1970, while production from underground coal mines, located largely in the interior eastern part of the country, has remained approximately constant (Figure 1.6). Just four states—Wyoming, West Virginia, Kentucky, and Pennsylvania—produce 65 percent of the coal mined in the United States on a tonnage basis. Wyoming supplies almost two and a half times as much coal on a tonnage basis (or about 1.6 times as much on an energy basis) as West Virginia, the next largest coal producer.
Historically, most coal produced in the United States has been consumed in the United States (EIA, 2006c). In 2005, 1.128 billion tons of coal were consumed and 1.133 billons tons were produced. That year, the United States imported 30.5 million tons of coal, mostly from Colombia, and exported 49.9 million tons, with about a third going to Europe and a third going to Canada (EIA, 2006c). Metallurgical coal made up more than half of coal exports (28.7 million tons), primarily to Europe but with lesser amounts going to Canada, Brazil, and Asia (Freme, 2006).
Coal use for electric power generation has risen dramatically in the last half century (Figure 1.7) with most U.S. coal that is produced at present consumed by the electric power sector. That sector alone consumed 1 billion tons of coal in 2005, or 92 percent of all coal produced in the United States that year (EIA, 2006a). Today, coal supplies the energy to produce more than half of the electricity generated in this country, making it a vital part of the U.S. energy economy.
Although the standard measure of energy content used by the coal industry in the United States is the Btu, other countries use the International System of Units (metric) measurement system. Unit conversion factors and energy ratings are listed in Appendix G.