Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Primary energy is energy found in nature that has not been subjected to any conversion or transformation process. It is energy contained in raw fuels as well as other forms of energy received as input to a system. The concept of primary energy is used especially in energy statistics in the compilation of energy balances. It includes non-renewable energy and renewable energy. Primary energies are transformed in energy conversion processes to more convenient forms of energy, such as electrical energy, refined fuels, or synthetic fuels such as hydrogen fuel. In energy statistics these forms are called secondary energy. Secondary energy is an energy form which has been transformed from another one. Electricity is the most common example, being transformed from such primary sources as coal, oil, natural gas, and wind.

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