3. Renewable and non-renewable grey energy

In grey energy, a distinction is often made between the non-renewable part derived from energy sources that are not renewable on a human scale, such as fossil fuels (coal, oil or natural gas), and the renewable part derived from energy sources that are renewable, such as hydro, solar or wind power. A distinction is also made between material energy and process energy, each of which has a renewable and non-renewable component. Energy is evaluated in its primary form, i.e. before transformation, to take account of the losses that occur during its conversion into usable energy.

It is also possible to adopt a different classification of the total energy consumed by a system. CLIP