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Energy in the United States
The United States is the largest energy consumer in terms of total use, using 100 quadrillion BTU (105 exajoules, or 29000 TWh) in 2005, equivalent to an (average) consumption rate of 3.3 TW. The U.S. ranks seventh in energy consumption per-capita after Canada and a number of small countries.[1][2] The majority of this energy is derived from fossil fuels: in 2005, it was estimated that 40% of the nation's energy came from petroleum, 23% from coal, and 23% from natural gas. The remaining 14% was supplied by nuclear power, hydroelectric dams, and miscellaneous renewable energy sources.[3]
History
US energy consumption, by source, 1850-2000. Vertical axis is in quadrillion BTU From its founding until the late 1800s, the United States was a largely agrarian country with abundant forests. During this period, energy consumption overwhelmingly focused on readily available firewood. Rapid industrialization of the economy, urbanization, and the growth of railroads led to increased use of coal, and by 1885 it had eclipsed wood as the nation's primary energy source. Coal remained dominant for the next 7 decades, but by 1950, it was surpassed in turn by both petroleum and natural gas. While coal consumption today is the highest it has ever been, it is now mostly used to generate electricity. Natural gas, which is cleaner-burning and more easily transportable, has replaced coal as the preferred source of heating in homes, businesses and industrial furnaces. At the beginning of the 20th century, petroleum was a minor resource used to manufacture lubricants and fuel for kerosene and oil lamps. One hundred years later it had become the preeminent energy source for the U.S. and the rest of the world. This rise closely paralleled the emergence of the automobile as a major force in American culture and the economy. While petroleum is also used as a source for plastics and other chemicals, and powers various industrial processes, today two-thirds of oil consumption in the U.S. is in the form of its derived transportation fuels.[4] Current consumption
U.S. Energy Flow - 2002. Note that the breakdown of useful and waste energy in each sector (yellow vs. Grey) is estimated arbitrarily and is not based on data. 
The U.S. Department of Energy tracks national energy consumption in four broad sectors: industrial, transportation, residential, and commercial. The industrial sector has long been the country's largest energy user, currently representing about 33% of the total. Next in importance is the transportation sector, followed by the residential and commercial sectors.
The breakdown of energy consumption by source is given here:
Regional variation
Average annual residential electricity usage by city, 2000-2005. Measured in Kilowatt hours per customer.[10] Household energy use varies significantly across the United States. An average home in the Pacific region (consisting of California, Oregon, and Washington) consumes 35% less energy than a home in the South Central region. Most of the regional differences can be explained by climate. The heavily populated coastal areas of the Pacific states experience generally mild winters and summers, reducing the need for both home heating and air conditioning. The warm, humid climates of the South Central and South Atlantic regions lead to higher electricity usage, while the cold winters experienced in the Northeast and North Central regions result in much higher consumption of natural gas and heating oil. Another reason for regional differences is the variety of building codes and environmental regulations found at the local and state level. California has some of the strictest environmental laws and building codes in the country, which may contribute to the fact that its per-household energy consumption is lower than all other states except Hawaii. Major U.S. cities also show significant variation in per capita energy consumption. In addition to differences in regional climates and variations in building code standards, factors affecting energy use in cities include population density and building design. Townhouses are more energy efficient than single-family homes because less heat, for example, is wasted per person. Oil consumptionThere have been economic and political problems associated with the country's past dependence on foreign supply. America's past consumption of petroleum has resulted in environmental problems as well. U.S. oil consumption is approximately 21 million barrels/day, yet domestic production is only . Cost to import oil is approximately $630 billion dollars a year (at $115/barrel). While it costs the Arabian Peninsula just one U.S. dollar to extract a barrel of oil, the cost on the world market has varied up to $100/barrel in 2007 dollars. While U.S. oil usage increases by 2% per year, the economy has been growing at 3.3% per year. The Strategic Petroleum Reserve currently holds about of oil and is being filled to a level of . Should, for example, oil production be stopped entirely, or becomes depleted, the U.S. would have only 32 to 35 days of resources to fall back upon. From a national security standpoint, such a situation is untenable. During the Carter administration, in response to an energy crisis and hostile Iranian and Soviet Union relations, President Jimmy Carter announced the Carter Doctrine which declared that any interference with U. S. interests in the Persian Gulf would be considered an attack on U.S. vital interests.[11] This doctrine was expanded by Ronald Reagan.[12] Today, many scholars and politicians call for the immediate incubation of long term energy solutions prior to a 'peak oil' scenario which would force the economy to grinding halt. Although additional drilling in areas such as continental shelf, the Gulf of Mexico, off the U.S. West Coast, Alaska, and the Great Lakes may stave off the inevitability of the problem, it would be only a temporary solution, and carries the risk of further polluting our environment. Electricity Production
Electricity production by source.
From 1992 to 2005 some 270,000 MWe (Megawatt electric) of new gas-fired plant were built, but only 14,000 MWe of new nuclear and coal-fired capacity came on line, mostly coal, with 2,315 MWe of that being nuclear.[13] Nuclear and coal are considerably capital intensive when compared to gas, and the great shift to gas plant construction is often attributed to deregulation and other political and economic factors. U.S. wind power capacity now exceeds 18,302 MW which is enough to serve 4.5 million average households.[14] Several solar thermal power stations, including the new 64 MW Nevada Solar One, have also been built. The largest of these solar thermal power stations is the SEGS group of plants in the Mojave Desert with a total generating capacity of 354 MW, making the system the largest solar plant of any kind in the world.[15]
Energy consumption of computers in the USAVisible or embedded (i. e. hidden) computers are found everywhere: in all sectors listed in the above chapter, as well as in all subsectors listed in the column entitled Major uses in the above tables. In 1999, a study by Mark. P. Mills [17] of the Green Earth Society reported that computers consumed 13% of the entire US supply. Numerous researchers questioned Mills' methodology and it was later demonstrated that he was off by an order of magnitude; for example, Lawrence Berkeley Labs concluded that the figure was nearer three percent of US electricity use. Although The Mills' study was inaccurate[18][19][20], it helped drive the debate to the national level, and in 2006 the US Senate started a study of the energy consumption of Server farms. ReferencesSee also
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