Energy sources
Energy comes in many forms, but all sources are either renewable or nonrenewable. Both types of energy can be used as primary energy sources (an energy source in its original form) to produce useful energy such as heat, or they can be used to produce secondary energy sources such as electricity and hydrogen.
Nonrenewable energy
In the United States, nonrenewable energy is the primary source of the energy we use, which includes:
These energy sources are called nonrenewable because their supplies are limited to what we can mine or extract from the earth, and they take a very long time to form. Coal, natural gas, and petroleum 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.
Most of the petroleum products consumed in the United States are made from crude oil, but petroleum liquids can also be made from natural gas and coal.
Nuclear energy is produced by splitting uranium atoms—a common metal found in rocks all over the world—through nuclear fission to create heat and, eventually, electricity. Uranium is found throughout the earth’s crust, but most of it is too difficult or too expensive to mine and process into fuel for nuclear power plants.
Renewable energy
Renewable energy sources are constantly replenished by nature, which means they will always be there when we need them. Day after day, the sun shines, the wind blows, and rivers flow, offering a continuous supply of energy. These sources are virtually inexhaustible, but they are limited by availability. For example, solar energy is only available during the day when the sun is shining.
The five major renewable energy sources include:
- Solar energy from the sun
- Geothermal energy from heat inside the earth
- Wind energy from uneven heating from the sun
- Biomass from plants
- Hydropower from flowing water
Throughout most of human history, biomass from plants was the primary source of energy. Biomass, such as wood from trees, was burned to provide heat and light, to cook food, and to feed the animals people used for transportation and plowing.
Nonrenewable energy, particularly fossil fuels, began replacing renewable energy in the United States in the early 1800s and became the primary fuel source by the early 1900s. In rural areas, biomass continues to be used to heat homes, and to a lesser extent, in urban areas to provide supplemental heat. In the mid-1980s, biomass and other forms of renewable energy began increasing, largely because of incentives to use them, especially for electricity generation.
