There are many different sources of energy, which can be classified as renewable or nonrenewable. Renewable energy sources are naturally replenished and include:
- Solar energy: energy from the sun
- Wind energy: energy from the wind
- Geothermal energy: energy from heat inside the earth
- Hydropower: energy from flowing water
- Biomass: energy from plants
Nonrenewable energy sources are limited and include:
- Fossil fuels: coal, natural gas, and petroleum formed over thousands of years from the buried remains of ancient sea plants and animals that lived millions of years ago
- Nuclear energy: energy stored inside tiny atoms that are invisible, but make up the elements of the entire universe
Energy sources 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. Primary energy sources are converted to electricity, a secondary energy source, which flows through power lines and other transmission infrastructure to homes and businesses. Some examples of different types of energy include:
- Chemical energy: stored within bonds between molecules. Sources include natural gas, gasoline, coal, and batteries. Even the food we eat is considered chemical energy.
- Electrical energy: comes from tiny charged particles called electrons. The electricity in our homes is made by humans.
- Nuclear energy: stored inside tiny atoms that are invisible, but make up the elements of the entire universe. Nuclear energy is released when atoms join together (fusion) or split (fission) .
- Solar (radiant) energy: energy that comes from the movement of light.
- Sound energy: produced when an object is made to vibrate producing a sound. Our voice is an example of sound energy.
It is important to note that the use of nonrenewable energy sources accounts for most energy consumption in the United States and many other countries.
