Electricity Generation

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“Consumers expect electricity to be available whenever they plug in an appliance, turn a switch, or open a refrigerator.  Satisfying these instantaneous demands requires an uninterrupted flow of electricity. In order to meet this requirement, utilities and non-utility electricity power producers operate several types of electric generating units, powered by a wide range of fuel sources” [1].

There are many different types of generating plants both in use and possible for future development.  Electric generating units are typically grouped by the type of device that drives the electric generator: steam turbine, combustion turbine, or reciprocating engine.  Generating facilities are typically described using characteristics such as size, energy source, efficiency, type of use, and availability [2].

Statistics for electric generation and capacity are readily available from a number of sources.  The Energy Information Administration (EIA) provides a tidy summary of basic electricity statistics and updates the data yearly.  According to the EIA’s most recent Electricity Power Annual: “Total net summer generating capacity as of January 1, 2006 was 978,020 MW, an increase of 1.6% from January 1, 2005. New generating capacity added during 2005 totaled 17,622 MW while retirements totaled 3,172 MW. Natural gas-fired generating units accounted for 14,753 MW or 84% of capacity additions. Of that amount, 11,908 MW were highly efficient combined-cycle units. Since the late 1990’s, natural gas has been the fuel of choice for the majority of new generating units, resulting in a nearly 81% increase in gas-fired capacity since 1999. The construction of natural gas plants began increasing in 1999, peaked during 2002 and 2003, and since then declined considerably.”  There has been a notable decrease in annual additions of new generating capacity: the approximate 18,000 MW of net new capacity in 2005 was slightly less than the amount added in 2004, and less than half the amount added in 2003 [3].

Fossil fuels supply about 70% of the energy sources for the generation requirements of the US [4].  However, the electricity generation mix has evolved over the years.  Because certain fuels in the electricity generation mix are better suited than others for particular applications, electric companies now use a diverse mix of fuels to generate electricity [5, 6]. Furthermore, different regions of the country use different fuel mixes to generate electricity [7].

As oil’s percent contribution has steadily decreased, renewables have emerged as a notable addition to the generation mix in the past couple decades.  Increasingly used alternatives to fossil fuels now include wind, geothermal, solar thermal, photovoltaic, wave, tidal, and biomass (“biomass” is a diverse classification including wood, wood waste, peat, wood liquors, railroad ties, pitch, wood sludge, municipal solid waste, agricultural waste, straw, tires, landfill gasses, fish oils, and other waste materials) [4].  Fuel diversity in the electric sector is key to providing affordable and reliable electricity and protects electric companies and consumers from disruptions in fuel supply, price fluctuations, or changes in regulations [6].

Figure 1 (view figure) provides net generation by energy source for 2000 through 2005 [8].  In 2005, generation from coal accounted for approximately 50%, petroleum 3%, natural gas 19%, nuclear 19%, hydroelectric 7%, renewables (solar, biomass, wind, and geothermal) 2%, and other (including hydrogen and batteries) 0.1%.  Figure 2 (view figure) provides net generation by energy source, by type of producer for 2005 [8].  Electricity generation from electric utilities accounted for approximately 63% of total generation, while independent power producers accounted for approximately 29%, electric power CH&P 4%, commercial CH&P 0.2%, and industrial CH&P 4%.  Noteworthy is the fact that over 20% of electricity generated from commercial and industrial CH&P is from renewable sources.

The EIA estimates that by 2030, a total of 65,000 MW of capacity is expected to be retired, virtually all fossil fired [3].  To meet fill the gap created by the retired plants and to meet future demand, the EIA predicts that 245 GW of new generating capacity will be needed by 2030.  At 300 MW per plant, 817 new power plants will need to be built to meet the demand [9].

For more information on energy sources, see Coal; Natural Gas; Oil; Nuclear Power; or Renewable Energy.

References:

1. EIA. Electricity Generation.  2006  [cited 2007 27 March].

2. Casazza, J. and F. Delea, Understanding Electric Power Systems. 2003, Hoboken, NJ: The Institute of Electrical and Electronics Engineers.

3. EIA. Electricity Capacity.  2006  [cited 2007 26 March].

4. EIA. Electric Power Industry Overview.  2000  [cited 2007 27 March].

5. EEI, Electric Companies Use a Diverse Mix of Fuels to Generate Electricity 2007, Edison Electric Institute: Washington, DC.

6. EEI. Fuel Diversity.  2007  [cited 2007 27 March].

7. EEI, Different Regions of the Country Use Different Fuel Mixed to Generate Electricity. 2006, Edison Electric Institute: Washington, DC.

8. EIA. Electric Power Annual.  2006  [cited 2007 27 March].

9. EEI. Generation.  2007  [cited 2007 27 March].