Fossil fuels — petroleum, coal, and natural gas — represent mainstream energy sources: alternative fuels include everything else — from biomass to nuclear. Most of the energy consumed in the US, about 84 percent, comes from fossil fuels according to the Energy Information Administration (EIA) (www.eia.doe.gov). Of this, crude oil-based petroleum products are the dominant source.
Renewable energy resources, like biomass, wind, and solar, supply a relatively small but steady portion, about seven percent of US total consumption. Unlike fossil fuels, which are exhaustible, renewable energy sources regenerate and can be sustained indefinitely. In the late 1950s, nuclear fuel began to be used to generate electricity, and now is responsible for about nine percent of our energy, surpassing renewable energy sources.
In addition to these three mainstream, or primary sources, the EIA classifies electricity and hydrogen as secondary energy sources; they result from the conversion of other primary sources of energy, such as coal, nuclear, or solar energy. While hydrogen is not currently widely used, it has potential as an energy carrier in the future.
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