Quick guide: Biofuels
What are biofuels?
Biofuels are any kind of fuel made from living things, or from the waste they produce.
This is a very long and diverse list, including:
- wood, wood chippings and straw
- pellets or liquids made from wood
- biogas (methane) from animals' excrement
- ethanol, diesel or other liquid fuels made from processing plant material or waste oil
In recent years, the term "biofuel" has come to mean the last category - ethanol and diesel, made from crops including corn, sugarcane and rapeseed.
Bio-ethanol, an alcohol, is usually mixed with petrol, while biodiesel is either used on its own or in a mixture.
Pioneers such as Henry Ford and Rudolph Diesel designed cars and engines to run on biofuels. Before World War II, the UK and Germany both sold biofuels mixed with petrol or diesel made from crude oil; the availability of cheap oil later ensured market dominance.
Ethanol for fuel is made through fermentation, the same process which produces it in wine and beer. Biodiesel is made through a variety of chemical processes.
There is interest in trying biobutanol, another alcohol, in aviation fuel.
Are biofuels climate-friendly?
In principle, biofuels are a way of reducing greenhouse gas emissions compared to conventional transport fuels.
Burning the fuels releases carbon dioxide; but growing the plants absorbs a comparable amount of the gas from the atmosphere.
However, energy is used in farming and processing the crops, and this can make biofuels as polluting as petroleum-based fuels, depending on what is grown and how it is treated.
A recent UK government publication declared that biofuels reduced emissions "by 50-60% compared to fossil fuels".
