Primary fuels or primary energy sources are dense sources of primary energy found as natural resources. Primary fuels are fuels that are found in nature and can be extracted, captured, cleaned, or graded without any sort of energy conversion or transformation process. This means that all processing and collecting of the fuel is done before the fuel is converted into heat or mechanical work. These primary fuels tend to be non-renewable, and some of the most commonly known primary fuels are fossil fuels. Energy harvested from primary fuels tends to make up most of a country's total primary energy supply or TPES.
Primary fuels such as coal should be distinguished from primary energy flows like wind and solar power. Although they are all sources of primary energy, primary fuels are "consumed". In contrast, a flow such as wind doesn't get "consumed"—rather, it makes more sense to think of flows as being "utilized". It is also important to distinguish primary fuels from secondary fuels like gasoline. Secondary fuels are derived from primary fuels through some sort of distillation process. Gasoline, for example, is created after distilling a primary fuel, oil.
The distinction between primary fuels and energy currencies like electricity is also important. Primary fuels are sources of primary energy, and this energy—once obtained from the fuel itself—is transformed into forms that are easier to use, transport, or store. Essentially, energy currencies are ways of transporting the energy obtained from primary fuels.
Primary fuels such as these can be obtained from the ground using several different mining techniques. While coal is mined more "traditionally" using strip mines or deep mines, certain sources of natural gas such as shale gas or tight gas are obtained by fracturing large stones with poor permeability. Overall, there are many different ways to obtain these vital resources.
The data simulation below shows the energy production of countries worldwide based on their energy source. Note that some of the energy sources are from flows, such as hydro, wind, and solar. Other energy sources are known as primary fuels which include oil, coal, peat, natural gas, and nuclear (uranium and thorium).