We use many different energy sources to do work. Energy sources are either renewable or nonrenewable energy. Renewable and nonrenewable energy can be used as primary energy sources to produce useful energy such as heat, or they can be used to produce secondary energy sources such as electricity and hydrogen.

Nonrenewable energy sources

In the United States, nonrenewable energy sources supply most of the energy we use. Nonrenewable energy sources include coal, natural gas, petroleum made from crude oil and natural gas liquids, and uranium. These energy sources are called nonrenewable because their supplies are limited and take a very long time to form. Coal, petroleum, and natural gas took thousands of years to form from the buried remains of ancient sea plants and animals that lived millions of years ago, which is why we also call those energy sources fossil fuels.

Renewable energy sources

Renewable energy sources include biomass, geothermal energy, hydropower, solar energy, and wind energy. They are called renewable because they are naturally replenished in a shorter period of time. Day after day, the sun shines, the wind blows, and rivers flow.

Difference between primary sources of energy and secondary sources of energy

Primary sources of energy, such as coal and natural gas, must be used to make secondary sources of energy such as electricity and hydrogen. For example, coal can be converted to electricity; in this example, coal is primary energy, and the electricity produced is secondary energy. Essentially, primary energy is an energy source in its original form, and secondary energy is the converted primary energy source in its usable and transformed form.

The chart below shows U.S. energy sources, their major uses, and their percentage shares of total U.S. energy consumption in 2023.