We use many different energy sources to do work. Energy sources are classified as renewable or nonrenewable. Renewable and nonrenewable energy can be converted into secondary energy sources such as electricity and hydrogen.

Chart of Energy Consumption by Source, 2016 with biomass=4.9%, hydropower=2.5%, geothermal=0.2%, wind=2.2%, solar =0.6%, petroleum=36.9%, natural gas=29.2%, coal=14.6%, uranium=8.6%

Most of our energy is nonrenewable

In the United States, most of our energy comes from nonrenewable energy sources. Coal, petroleum, natural gas, and uranium are examples of nonrenewable energy sources. Nonrenewable energy sources are used to make electricity, to heat our homes, to move our cars, and to manufacture products.

These energy sources are called nonrenewable because their supplies are limited. Petroleum, for example, was formed millions of years ago from the remains of ancient sea plants and animals.

Use of renewable energy is growing

Renewable energy sources include biomass, geothermal energy, hydropower, solar energy, and wind energy. They are called renewable energy sources because they are naturally replenished regularly. Day after day, the sun shines, the wind blows, and rivers flow. Renewable energy sources are used for electricity generation, for heat generation, and for transportation fuels.

How are secondary sources of energy different than primary energy sources?

Electricity and hydrogen are different than other energy sources because they are secondary sources of energy. Secondary sources of energy—energy carriers—are used to store, move, and deliver energy in an easily useable form. A primary energy source must be used to make secondary sources of energy such as electricity and hydrogen.