Primary energy (PE) is an energy resource found in nature that has not been subjected to any conversion or transformation process. It is the energy contained in raw fuels and other forms of energy received as input to a system. Primary energy sources take many forms, including nuclear energy, fossil energy — like oil, coal, and natural gas — and renewable sources like wind, solar, geothermal, and hydropower. These primary sources can be converted to a secondary energy sources, so-called energy carriers. Primary energy sources can be divided into:
- Non-renewable sources
- Fossil fuels
- Oil
- Coal
- Natural gas
- Mineral fuels
- Natural Uranium
- Natural Thorium
- Fossil fuels
- Renewable sources
- Solar energy
- Wind energy
- Hydro and tidal energy
- Geothermal energy
- Biomass energy (if sustainably exploited)