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.
Bioenergy covers about 15% of the world's energy consumption. Sweden and Finland supply 17% and 19% respectively, of their energy needs with bioenergy. Biomass can be used both for centralized production of electricity and district heat, and for local heating.
Oxidisation of biomass does not release more CO2 than that which was absorbed by production of that same biomass. Both agricultural products specifically grown for this use and waste from industry, agriculture, forestry, and households -including straw, lumber, manure, and food leftovers-can be used for the production of bioenergy.
Classes of Biofuels
There are many forms of solid biomass that are combustible as a fuel1 such as:
There are also a number of liquid forms of biomass that can be used as a fuel:
Energy content of Biofuel
Biofuels have a low specific energy density compared to fossil fuels. This means that biomass energy schemes must work at a local level as their success depends on well-structured and sustainable fuel supply networks from local producers.
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.
Biomass Technical Brief, Simon Ekless, Intermediate Technology Development Group, retrieved 2005/01/01 from http://www.itdg.org/docs/technical_information_service/biomass.pdf.
Smoke – the killer in the kitchen, Intermediate Technology Development Group, 2004/03/19, retrieved 2005/01/01 from http://www.itdg.org/?id=smoke_report_1
Reducing exposure to indoor air pollution, Intermediate Technology Development Group, 2004/03/19, retrieved 2005/01/01 from http://www.itdg.org/?id=smoke_report_3