Types of coal
Lignite is the lowest rank of coal and has the lowest energy content. Lignite is crumbly and has high moisture content. Lignite accounted for about 9% of U.S. coal production in 2017.
Subbituminous coal has a higher heating value than lignite. Subbituminous coal typically contains 35%–45% carbon, compared to 25%–35% for lignite. About 45% of the coal produced in the United States in 2017 was subbituminous.
Bituminous coal contains 45%–86% carbon and has two to three times the heating value of lignite. Bituminous coal was formed under high heat and pressure. Bituminous is the most abundant rank of coal found in the United States. Bituminous coal accounted for about 45% of U.S. coal production in 2017.
Anthracite contains 86%–97% carbon and has a heating value that is slightly higher on average than bituminous coal. Anthracite is the least abundant rank of coal in the United States, and it accounts for less than 1% of annual U.S. coal production.
Coal is classified into four main ranks—lignite, subbituminous, bituminous, and anthracite—depending on the amounts and types of carbon it contains and the amount of heat energy it can produce. Prices are generally higher for coal with high heat content.
The average annual sale prices of coal at mines by main rank of coal in 2017, in dollars per short ton (2,000 pounds)
Coal prices at surface mines are generally lower than prices at underground mines. In locations where coal beds are thick and near the surface, such as in Wyoming, mining costs and coal prices tend to be lower than in locations where the beds are thinner and deeper, such as in Appalachia. The higher cost of coal from underground mines reflects the more difficult mining conditions and the need for more miners.
When coal is burned, it releases impurities that can combine with oxygen to form sulfur dioxide (SO2). When SO2 combines with moisture in the atmosphere, it produces acid rain that can harm forests and lakes. Because of environmental regulations limiting sulfur emissions, low-sulfur coals can command a higher price than high-sulfur coals.
Coal transportation costs can be significant
Once coal is mined, it must be transported to consumers. Transportation costs add to the delivered price of coal. In some cases, such as in long-distance shipments of Wyoming coal to power plants in the East, transportation costs are more than the price of coal at the mine.
Most coal is transported by train, barge, truck, or a combination of these modes. All of these transportation modes use diesel fuel. Increases in oil and diesel fuel prices can significantly affect the cost of transportation, which affects the final delivered price of coal.
In 2017, the national average sales price of coal at coal mines was $33.72 per short ton, and the average delivered coal price to the electric power sector was $39.09 per short ton, resulting in an average transportation cost of $5.37 per short ton, or about 14% of the delivered price.
Most coal is purchased for power plants
About 93% of the coal consumed in the United States is used to generate electricity. In 2017, about 30% of total U.S. electricity generation was from coal. When based only on the cost per million British thermal units (Btu), coal has been the least expensive fossil fuel used to generate electricity since 1976.
The price of coal can depend on the type of transaction
Most of the coal sold for electric power generation is sold through long-term contracts. Supplies are supplemented with spot purchases of coal. Spot purchases are shipments of fuel purchased for delivery within one year. Spot prices can fluctuate based on short-term market conditions, but contract prices tend to be more stable. In 2017, the average delivered price of coal to the electric power sector was $39.09 per short ton, which includes both spot and contract purchases.
A more expensive coal is used to make iron and steel
In addition to producing electricity, coal is also used to produce coal coke, or coke, which is used in smelting iron ore to make steel.
Coke is made by baking certain types of coal in special high-temperature ovens to remove non-carbon elements and compounds as gases. The resulting coke is mostly carbon. Coking coal must be low in sulfur and requires more thorough cleaning than coal used in power plants, which makes the coal more expensive.
In 2017, the average delivered price of coal used to make coke was about $122.14 per short ton—about three times higher than the price of coal delivered to the electric power sector.
The outlook for coal prices in the United States
In the Annual Energy Outlook 2018, the U.S. Energy Information Administration (EIA) projects that U.S. coal prices will generally increase through the year 2050. The amount that coal prices increase depends on projections for coal demand and coal mining productivity.