Energy content of biofuel

The energy content of biofuel is the chemical energy contained in a given biofuel, measured per unit mass of that fuel, as specific energy, or per unit of volume of the fuel, as energy density. A biofuel is a fuel produced from recently living organisms. Biofuels include bioethanol, an alcohol made by fermentation—often used as a gasoline additive, and biodiesel, which is usually used as a diesel additive. Specific energy is energy per unit mass, which is used to describe the chemical energy content of a fuel, expressed in SI units as joule per kilogram (J/kg) or equivalent units. Energy density is the amount of chemical energy per unit volume of the fuel, expressed in SI units as joule per litre (J/L) or equivalent units.

Different substances contain different amounts of potential energy, that is, the ability to do work.

To extract energy from a substance, a process must convert the substance into another state, releasing the potential energy as kinetic energy in the process, usually in the form of heat. Most man-made machines for harnessing this energy then convert the heat released into mechanical energy (such as a spinning turbine), then finally into electrical energy if needed, using a generator.

These machines vary in their effectiveness at capturing and harnessing the energy released. The proportion of energy usefully captured and converted into mechanical or electrical form is called its efficiency. No machines are 100% efficient. Thus the amount of useful work actually performed by these substances upon processing will never equal their potential energy content.

Furthermore, the mass and volume of a substance contributes to overhead energy costs for producing, processing, shipping, and storing of the substance required to utilize it as a fuel. When calculating economic or environmental impact of a particular fuel, all of these factors must be considered holistically.{{cite web |access-date=2008-05-18