biofuel

Biofuel is any fuel that derives from biomass - recently living organisms or their metabolic byproducts, such as manure from cows. It is a renewable energy, unlike natural resources such as petroleum, coal and nuclear fuels. Typically biofuel is burned to release its stored chemical energy. Research into more efficient methods of converting biofuels and other fuels into electricity utilizing fuel cells is an area of very active work. The carbon in biofuels was recently extracted from atmospheric carbon dioxide by growing plants, so burning it does not contribute carbon dioxide to the Earth's atmosphere.

Classes of Biofuels

Solid

There are many forms of solid biomass that are combustible as a fuel¹ such as:

Wood — see wood fuel
Dried compressed peat
straw and other dried plants
animal waste such as poultry droppings or cattle dung.
husks or shells from crops such as rice, groundnut and cotton.
bagasse

Liquid

There are also a number of liquid forms of biomass that can be used as a fuel:

Bioalcohols — see alcohol as a fuel.

Ethanol produced from sugar cane is being used as automotive fuel in Brazil. Ethanol produced from corn is being used as a gasoline additive (oxygenator) in the United States.
Methanol, which is currently produced from natural gas, can also be produced from biomass — although this is not economically viable at present.

Biologically produced oils can be used in diesel engines:

Straight vegetable oil (SVO).
Waste vegetable oil (WVO).
Biodiesel obtained from transesterification of animal fats and vegetable oil.

Oils and gases can be produced from various wastes:

Thermal depolymerization can extract methane and oil similar to petroleum from waste.
Methane and oils are being extracted from landfill wells and leachate in test sites.

Gaseous

Methane produced by the nature decay of garbage or agricultural manure can be collected for use as fuel.

Biogas

Hydrogen can be produced by cracking any hydrocarbon fuel in a reformer or by the electrolysis of water.
Gasification

Small scale use of biofuels

A widespread use of biofuels is in home cooking and heating. Typical fuels for this are wood, charcoal or dried dung. The biofuel may be burned on an open fireplace or in a special stove. The efficiency of this process may vary widely from 10% for a well made fire up (even less if the fire is not made carefully) to 40% for a custom designed charcoal stove¹. Inefficient use of fuel may be a minor cause of deforestation (though this is negligible compared to deliberate destruction to clear land for agricultural use) but more importantly it means that more work has to be put into gathering fuel, thus the quality of cooking stoves has a direct influence on the viability of biofuels. Unfortunately, much cooking with biofuels is done indoors, without efficient ventilation and using those fuels such as dung which cause most airborne polution. This can be a serious health hazard; 1.5 million deaths were attributed to this cause by the World Health Organisation in 2000². There are various responses to this, such as improved stoves, including those with inbuilt flues and switching to alternative fuel sources. Most of these responses have difficulties, for example flues are expensive and easily damage; alternative fuels tend to be more expensive which is difficult to implement since the people who rely on biofuels often do so precisely because they cannot afford alternatives.³ Organisations such as Intermediate Technology Development Group work to make improved facilities for biofuel use and better alternatives accessible to those who cannot currently get them. This work be done through designing improved ventilation, a switch to different usage of biomass such as through the creation of biogas from solid biomatter or a switch to other alternatives such as micro-hydro power.