The main sources of electricity are fossil fuels, nuclear power and renewable energy. Electricity is a secondary source of energy derived from primary sources.
Electricity is a secondary source of energy because it cannot be extracted from the ground, like fossil fuels, or captured from moving phenomena, such as water or wind. Most electricity consumed in the United States has a fossil fuel as its source, according to the United States Environmental Protection Agency. Renewable resources, such as wind and solar, represent a small but growing percentage of electricity sources.
Fossil fuels occur naturally in the earth and are the remains of living organisms from the geological past. They include coal, oil and natural gas, which generate electricity when they burn in large electric power plants.
Nuclear power is a nonrenewable energy source that uses radioactive materials as part of the process of heating water to generate electricity. The process generates zero atmospheric emissions, as stated by the National Academy of Sciences.
Renewable energy sources are naturally replenished and include biomass, hydro, geothermal, solar and wind. Some of these renewable sources are intermittent, such as wind, which can create complications when using them to generate electricity on a large scale.