Overview - Electricity Generation
The production of electricity is generally referred to as generation and is measured in kilowatthours. Various sources of energy are used to generate electricity, including fossil fuels, uranium, water, solar, geothermal, and biomass. The different energy sources used to produce electricity are discussed in this section.
| Gross generation is the amount of power produced by an electric power plant (station), measured at the terminals of the plant (that is, prior to the point at which the power leaves the station and is available to the system). Some of the electric power generated at a power plant is used to operate equipment at the plant; plant use (or "in-house use") generally ranges between 1 percent (for hydroelectric units) and 7 percent (for steam-electric units). Net generation is the power available to the system (gross generation less use at the plant); however, it is greater than that available to consumers due to losses during transmission and distribution (approximately 8 to 9 percent). Note that the measure used for electric utilities is net and for nonutility facilities is gross generation.1 |
Fossil fuels supply about 70 percent of the Nation's requirements for electricity generation. Currently the dominant fossil fuels used by the industry are coal, petroleum, and gas. Other fossil fuels include petroleum coke, refinery gas, coke oven gas, blast furnace gas, and liquefied petroleum gas.
Coal. Historically, most generation of electricity in the United States has been from coal. Coal-fired generation became even more important following the OPEC oil embargo of 1973 due to concerns over the availability of petroleum imports, increasing petroleum costs, and curtailments of natural gas. In 1978, the passage of the Powerplant and Industrial Fuel Use Act and the Natural Gas Policy Act encouraged further use of coal by electric utilities. Although both Federal and State environmental laws and regulations existed during the 1970's, renewed interest in environmental issues raised concerns about electric power plant emissions, particularly from those plants burning coal. The Clean Air Act Amendments of 1990 established a goal of a 10-million-ton reduction in sulfur dioxide emissions and a 2-million-ton reduction in nitrogen oxide emissions from 1980 levels by 2000. Coal-fired generation continued to provide more than 56 percent of the total net generation by electric utilities and approximately 17 percent of gross generation at nonutility facilities in 1998.
Petroleum. During the early 1970's, electric
utilities used petroleum extensively to generate electricity. However, after the 1973 embargo by
the Organization of Petroleum Exporting Countries (OPEC) on petroleum exports to the United States,
petroleum prices rose sharply. Further price increases occurred in 1979 and 1980 following the
Iranian revolution and subsequent reductions in Iranian petroleum exports. Consequently during the
past decade, utilities have not built large, petroleum-fired steam units. In addition, many
utilities have either converted steam units to coal or switched fuels where dual-fired capability
exists. Most of the utilities that still rely heavily on petroleum to generate electricity are
located along the eastern seaboard. In 1998, petroleum was used for approximately 3 percent of the
utility generation and 4 percent of generation by nonutility power producers.
Gas. The demand for gas (primarily natural gas) to
heat homes and serve business and industry has historically taken priority over demand from
electric utilities under both Federal and State regulations. In the 1970's, many utilities were on
occasion denied gas when available pipelines reached capacity in serving heating demand during the
months from November to March (the peak heating season). By the middle 1970's, curtailments to
electric utilities also occasionally occurred during the nonheating season as producers conserved
supply in preparation for heating season demand. In the face of an attractive interstate price
structure, but deprived of supplies during many months of the year, utilities in the 1970's used
relatively less expensive gas when it was available, then switched to other more expensive fuels
when gas supplies were curtailed. Gas became more available to utilities with the passage of the
Natural Gas Policy Act of 1978 and more frequent exemptions from the gas-use restrictions of the
Powerplant and Industrial Fuel Use Act (Fuel Use Act) of 1978. Amendments to the Fuel Use Act in
1987 created potential for additional use of gas. These amendments eased restrictions on the use
of gas by removing a legal requirement to obtain an exemption for the construction of new gas-fired
generating capability. Gas was used
for approximately 10 percent of the total net generation at utilities, but 59 percent of the
requirements for gross generation at nonutilities in 1998.
 | Figure 11. Share of Total Nonutility Generation by Energy Source, 1998 |
Generation from nuclear power has generally increased since the 1950's, and this trend continues. Since 1984, nuclear plants have provided the second largest share of total U.S. electric utility generation of electricity, after coal-fired plants. Nuclear generation accounted for 14 percent of total utility net generation.
Hydroelectric. Water is currently the leading renewable energy source used by electric utilities to generate electric power. Hydroelectric plants operate where suitable waterways are available; many of the best of these sites have already been developed. Generating electricity using water has several advantages. The major advantage is that water, a renewable resource, is a source of cheap power. In addition, because there is no fuel combustion, there is little air pollution in comparison with fossil fuel plants and limited thermal pollution compared with nuclear plants. Like other energy sources, the use of water for generation has limitations, including environmental impacts caused by damming rivers and streams, which affects the habitats of the local plant, fish, and animal life. Seventy percent of the hydroelectric power in the United States is generated in the Pacific and Rocky Mountain States. In 1998, electric utilities used hydroelectric facilities for 10 percent of their total net generation while 4 percent of the total gross generation at nonutilities came from hydroelectric facilities. Other Sources. Other renewable resources--geothermal (heat energy beneath the surface of the earth), wood, waste, wind, and the sun (solar)--are energy sources that are constantly replenished.
Currently, renewable resources (other than water) supply less than 1 percent of the electricity generated by electric utilities. Most of the electricity produced from this category is from geothermal power. Electric utilities currently operate geothermal plants in two States (California and Utah). The Geysers, operated by the Pacific Gas and Electric Company, is the largest geothermal plant in the Nation. Only a few utilities operate units that produce electricity from wind and solar energy. Wood and waste resources can be used to replace fossil fuels in utility boilers. To date, just a few electric utility generating units have been built that use wood or waste products as a primary fuel.
Nonutility power producers, however, used renewable energy sources to produce approximately 17 percent of that segment's total gross generation in 1998. Those renewable energy sources include other gas, geothermal, solar, and biomass. Biomass may include:
- black liquor, pitch, peat, railraod ties, sludge wood, wood/wood waste, spent sulfite liquor, red liquor
- agricultural byproducts, fish oil, liquid acetonitrile waste, landfill gas, municipal solid waste, sludge waste, straw, tires, waste alcohol, solid byproducts, tall oil.
1More detailed information regarding generation of electricity is accessible on the Internet at the following web site addresses:
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