Energy consumption refers to the heat value of a fuel. This is the amount of heat released during the combustion of a fuel source type. This is also referred to as energy or calorific value. Heat value is a measure of a fuel's energy density and is expressed in energy (joules) per specified amount (e.g. kilograms). The kilowatt-hour generated per unit of fuel used is calculated by dividing the fuel heat content (in Btu per physical unit) by the heat rate (in Btu per kWh).