hours (kWh), megawatt hours (MWh), gigawatt hours (GWh), or terawatt hours (TWh) (109 kWh). One kWh is equal to a power of 1,000 watts (the typical electricity that is consumed by a hand-held hair dryer) supplied or consumed over the period of an hour. Annual total delivered electricity in the United States is about 4,000 TWh and the average annual electricity consumption per U.S. household is about 11,000 kWh.

  • 1 kWh of electricity is equivalent to 3,410 Btu of thermal energy if the conversion has no inefficiencies.

  • In a 33% efficient power plant, 10,230 Btu of input primary energy are required to produce 1 kWh of electricity.

Fossil Fuels and Other Liquid Fuels

  • Coal supply and consumption in the United States is usually expressed in units of metric tons (sometimes written as tonnes and equal to 1,000 kg or 2,200 pounds [lb]) or short tons (2,000 lb); most of the rest of the world uses metric tons. This report uses short tons when discussing coal use in the United States.

    • A ton of typical coal contains about 22 MJ of energy.

    • A tonne of typical coal contains about 24 MJ of energy.

  • Petroleum and gasoline supply and consumption quantities are expressed in the United States in gallons or barrels (1 barrel = 42 gallons) and internationally in liters (3.88 liters = 1 gallon). In the United States, the energy content of liquid fuel is expressed in British thermal units (Btu), million Btu (MMBtu or 106 Btu), and quadrillion Btu (quad = 1015 Btu). The rest of world uses joules (J) to express the energy content of liquid fuels (1 Btu = 1,055 J). A Btu is defined as the amount of energy (in the form of heat) needed to raise the temperature of 1 lb of water by 1 degree Fahrenheit.1 The energy content of different fuels can be converted to Btu using the following approximate factors:

    • 1 barrel crude oil = 5,800,000 Btu = 5.8 MMBtu

    • 1 barrel gasoline = 5.2 MMBtu

    • 1 barrel fuel ethanol = 3.5 MMBtu

  • When different liquid fuels and blends are compared, this is often done on the basis of what volume would give the same energy as a gallon of gasoline. Therefore, about 1.5 gallons of ethanol would provide the energy equivalent of 1 gallon of gasoline.

  • Natural gas supply and consumption usage is expressed in units of a thousand cubic feet (MCF or mcf). This is the equivalent volume of gas at atmospheric pressure and temperature. Here the prefix M stands for

1

A joule is the amount of energy needed to heat a kilogram of water by 1 degree centigrade. 1,055 joules = 1 Btu.



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement