Primary energy is calculated based on the 'substitution method' which takes account of the inefficiencies in fossil fuel production by converting non-fossil energy into the energy inputs required if they had the same conversion losses as fossil fuels. Measured in TWh. (A terawatt-hour is a unit of energy equal to outputting one trillion watts for one hour. It is equal to 3.6x1015 Joules.) | The Infographics Show