Chart by Dan Schroeder; data from Suits, Matteson, and Moyer and EIA
This chart shows energy use in the United States, broken down into nine major energy sources, for each year since 1800. Hover over the plotted data to see numerical values, and use the interactive controls to customize the chart’s appearance.
This chart shows what’s called primary energy, which is often greater than the energy delivered to end users. For fossil fuels, biomass, and nuclear energy, the primary energy is the heat released during combustion (or nuclear reaction). When this heat is used in an engine to produce mechanical or electrical energy, the conversion to these other forms of energy is only partial. As of 2021, average conversion efficiencies are about 44% at gas-fired electric power plants and 33% at coal-fired and nuclear power plants. Efficiencies were much lower in the past.
When water, wind, geothermal, or solar energy is used to generate electricity, the U.S. Energy Information Administration (EIA) defines the “primary” energy to be the amount of fossil fuel that would be needed, at the then-current average fossil power plant efficiency, to produce the same amount of electrical energy. This definition provides for a fair comparison between different energy sources in any given year. However, because average fossil plant efficiencies have improved over time (from about 10% in 1920 to 39% in 2021), this definition can lead to misleading comparisons between years. This inconsistency is especially problematic for water and wind, which have been in use since the days of water wheels and sailing ships. So the user controls below the chart provide you with two options:
For simplicity I have not offered a “constant” option for geothermal or solar electricity. These data series include a mix of electricity generation and direct thermal use, and they don’t extend back to times when fossil efficiencies were below 30%.
We most commonly measure the rate of energy use (“power”) in watts (W). A typical LED light bulb, for instance, uses electrical energy at a rate of about 10 watts. A kilowatt (kW) is 1000 watts (about 1.3 horsepower); a megawatt (MW) is 1,000,000 watts; a gigawatt (GW) is 1,000,000,000 watts; and a terawatt (TW) is 1,000,000,000,000 watts, or 1012 W.
A watt-hour (Wh) is the amount of energy we use in one hour, when using it at a rate of one watt. A kilowatt-hour (kWh) is 1000 Wh, enough energy to run a refrigerator for about a day, or to drive a gasoline-powered car about a mile (and costing around 15 cents in either gasoline or electrical form, at average US retail prices in 2022). The other metric prefixes also work with watt-hours, so a terawatt-hour (TWh) is 1012 Wh or 109 kWh.
A joule (J) is the amount of energy we use in just one second, when using it at a rate of one watt. This is the official scientific unit of energy, but it is awkwardly small (just 1/3600 of a Wh) when we’re talking about the energy used by a person—much less an entire nation—in a year. Fortunately, metric prefixes come to the rescue! One gigajoule (GJ) equals 109 J, while one exajoule (EJ) equals 1018 J, or 109 GJ.
Here in the U.S., many people (including our friends at the EIA) still measure energy in British thermal units (Btu), where 1 Btu equals the amount of thermal energy needed to raise the temperature of a pound of water by one degree Fahrenheit. Conveniently, this amount turns out to be just over 1 kJ (more precisely, 1055 J). Inconveniently, someone decided that “MBtu” means not a million Btu but only a thousand, so the usual abbreviation for a million Btu is MMBtu. For national energy totals we need a bigger multiplier: a quadrillion Btu, often shortened to “quad”, equals 1015 British thermal units or 1.055 EJ.
None of these data are exact. Earlier numbers tend to be less accurate.
Copyright ©2022 by Daniel V. Schroeder. This work is licensed under a Creative Commons Attribution 4.0 International License.
Feel free to copy and share images of the chart with your chosen settings, but please include either the credit line above it, or an equivalent citation, or a link to this page. The URL in your browser window should update as you change settings, so you can copy, save, and share the customized URL for your settings.
If you would like to further customize the chart, just download this page and edit the source code, which I’ve tried to make human-readable. This page loads the Chart.js library from a CDN, but is otherwise self-contained.