Biofuel is any fuel that is derived from biomass — recently living organisms or their metabolic byproducts, such as manure from cows. It is a renewable energy source, unlike other natural resources such as petroleum, coal, and nuclear fuels.

One definition of biofuel is any fuel with an 80% minimum content by volume of materials derived from living organisms harvested within the ten years preceding its manufacture^{[citation needed]}.

Like coal and petroleum, biomass is a form of stored solar energy. The energy of the sun is "captured" through the process of photosynthesis in growing plants. (See also: Systems ecology) One advantage of biofuel in comparison to most other fuel types is it is biodegradable, and thus relatively harmless to the environment if spilled.

Agricultural products specifically grown for use as biofuels include corn and soybeans, primarily in the United States; as well as flaxseed and rapeseed, primarily in Europe; sugar cane in Brazil and palm oil in South-East Asia. Biodegradable outputs from industry, agriculture, forestry, and households can also be used to produce bioenergy; examples include straw, timber, manure, rice husks, sewage, biodegradable waste, and food leftovers. These feedstocks are converted into biogas through anaerobic digestion. Biomass used as fuel often consists of underutilized types, like chaff and animal waste.

Much research is currently in progress into the utilization of microalgae as an energy source, with applications being developed for biodiesel, ethanol, methanol, methane, and even hydrogen. On the rise is use of hemp, although politics currently restrains this technology.

Paradoxically, in some industrialized countries like Germany, food is cheaper than fuel compared by price per joule ^{[citation needed]}. Central heating units supplied by food grade wheat or maize are available.

Biofuel can be used both for central- and decentralized production of electricity and heat. As of 2005, bioenergy covers approximately 15% of the world's energy consumption ^{[citation needed]}. Most bioenergy is consumed in developing countries and is used for direct heating, as opposed to electricity production.

The production of biofuels to replace oil and natural gas is in active development, focusing on the use of cheap organic matter (usually cellulose, agricultural and sewage waste) in the efficient production of liquid and gas biofuels which yield high net energy gain. The carbon in biofuels was recently extracted from atmospheric carbon dioxide by growing plants, so burning it does not result in a net increase of carbon dioxide in the Earth's atmosphere. As a result, biofuels are seen by many as a way to reduce the amount of carbon dioxide released into the atmosphere by using them to replace non-renewable sources of energy.

Noticeable is the fact that the quality of timber or grassy biomass does not have a direct impact on its value as an energy-source.

Dried compressed peat is also sometimes considered a biofuel. However, it does not meet the criteria of being a renewable form of energy, or of the carbon being recently absorbed from atmospheric carbon dioxide by growing plants. Though more recent than petroleum or coal, on the time scale of human industrialisation, peat is a fossil fuel and burning it does contribute to atmospheric CO₂.

Biofuel was used since the early days of the car industry. Nikolaus August Otto, the German inventor of the combustion engine, conceived his invention to run on ethanol. While Rudolf Diesel, the German inventor of the Diesel engine, conceived it to run on peanut oil. Henry Ford originally had designed the Ford Model T, a car produced between 1903 and 1926, to run completely on ethanol, after surreptitious efforts were successful at thwarting Ford's desires to mass produce electric cars. However, when crude oil began being cheaply extracted from deeper in the soil (thanks to oil reserves discovered in Pennsylvania and Texas), cars began using fuels from oil.

Nevertheless, before World War II, biofuels were seen as providing an alternative to imported oil in countries such as Germany, which sold a blend of gasoline with alcohol fermented from potatoes under the name Reichskraftsprit. In Britain, grain alcohol was blended with petrol by the Distillers Company Ltd under the name Discol and marketed through Esso's affiliate Cleveland.

After the War cheap Middle Eastern Oil lessened interest in biofuels. Then with the oil shocks of 1973 and 1979, there was an increase in interests from governments and academics in biofuels. However, interest decreased with the counter-shock of 1986 that made oil prices cheaper again. But since about 2000 with rising oil prices, concerns over the potential oil peak, greenhouse gas emissions (Global Warming), and instability in the Middle East are pushing renewed interest in biofuels. Government officials have made statements and given aid in favour of biofuels. For example, U.S. president George Bush said in his 2006 State of Union speech, that he wants for the United States, by 2025, to replace 75% of the oil coming from the Middle East.

Biologically produced alcohols, most commonly ethanol and methanol, and less commonly propanol and butanol are produced by the action of microbes and enzymes through fermentation — see alcohol fuel.

• Methanol, which is currently produced from natural gas, can also be produced from biomass — although this is not economically viable at present. The methanol economy is an interesting alternative to the hydrogen economy.
• Biomass to liquid, synthetic fuels produced from syngas. Syngas in turn, is produced from biomass by gasification. [1]
• Ethanol fuel produced from sugar cane is being used as automotive fuel in Brazil. Ethanol produced from corn is being used mostly as a gasoline additive (oxygenator) in the United States, but direct use as fuel is growing. Cellulosic ethanol is being manufactured from straw (an agricultural waste product) by Iogen Corporation of Ontario, Canada; and other companies are attempting to do the same. ETBE containing 47% Ethanol is currently the biggest biofuel contributor in Europe.
• Butanol is formed by A.B.E. fermentation (Acetone, Butanol, Ethanol) and experimental modifications of the ABE process show potentially high net energy gains with butanol being the only liquid product. Butanol can be burned "straight" in existing gasoline engines (without modification to the engine or car), produces more energy and is less corrosive and less water soluble than ethanol, and can be distributed via existing infrastructures.
• Mixed Alcohols (e.g., mixture of ethanol, propanol, butanol, pentanol, hexanol, and heptanol, such as Ecalene^TM), obtained either by biomass-to-liquid technology (namely gasification to produce syngas followed by catalytic synthesis) or by bioconversion of biomass to mixed alcohol fuels.
• GTL or BTL both produce synthetic fuels out of biomass in the so called Fischer Tropsch process. The synthetic biofuel containing oxygen is used as additive in high quality diesel and petrol.

Biogas is produced by the process of anaerobic digestion of organic material by anaerobes. Biogas can be produced either from biodegradable waste materials or by the use of energy crops fed into anaerobic digesters to supplement gas yields. The solid output, digestate, can also be used as a biofuel.

Biogas contains methane and can be recovered in industrial anaerobic digesters and mechanical biological treatment systems. Landfill gas is a less clean form of biogas which is produced in landfills through naturally occurring anaerobic digestion. Paradoxically if this gas is allowed to escape into the atmosphere it is a potent greenhouse gas.

Biologically produced oils and gases can be produced from various wastes:

• Thermal depolymerization of waste can extract methane and other oils similar to petroleum.
• GreenFuel Technologies Corporation has developed a patented bioreactor system that utilizes nontoxic photosynthetic algae to take in smokestacks flue gases and produce biofuels such as biodiesel, biogas and a dry fuel comparable to coal.^[1]

Biologically produced oils can be used in diesel engines. Biologically produced crude oil can be refined into kerosene, pertroleum, diesel and other fractions.

• Straight vegetable oil (SVO).
• Waste vegetable oil (WVO) — waste cooking oils and greases produced in quantity mostly by commercial kitchens
• Biodiesel obtained from transesterification of animal fats and vegetable oil, directly usable in petroleum diesel engines.
• Biologically derived Crude oil is produced together with biogas and carbon solids via the thermal depolymerization of complex organic materials including non oil based materials (for example waste products such as old tyres, offal, wood and plastic).
• Pyrolysis oil may be produced out of biomass, wood waste etc. using heat only in the flash pyrolysis process. The oil has to be treated before using in conventional fuel systems or internal combustion engines (water + pH).

Examples include wood, charcoal, and dried dung

One 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 (even less if the fire is not made carefully) up to 40% for a custom designed charcoal stove¹. Inefficient use of fuel is a 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.

"American homeowners are turning to burning corn in special stoves to reduce their energy bills. Sales of corn-burning stoves have tripled this year [...] Corn-generated heat costs less than a fifth of the current rate for propane and about a third of electrical heat"^[2]

Biodiesel and bioethanol are widely used in automobiles and freight vehicles. For example, in Germany most diesel on sale at gas stations contains a few percent biodiesel, and many gas stations also sell 100% biodiesel[2] -- this is typically cheaper than conventional petroleum diesel because of German tax breaks. Some supermarket chains in the UK such as Tesco have switched to running their freight fleets on 50% biodiesel, and often include biofuels in the vehicle fuels they sell to consumers[3], and many gas stations also sell 100% biodiesel. Biodiesel can be used in the majority of diesel vehicles without requiring any modification to the vehicle.

The methane in biogas is often pure enough to pass directly through gas engines to generate green energy. Anaerobic digesters or biogas powerplants convert this renewable energy source into electricity. This can either be used commercially or on a local scale.

Different combustion-engines are being produced for very low prices lately ^{[citation needed]}. They allow the private house-owner to utilize low amounts of "weak" compression of methane to generate electrical and thermal power (almost) sufficient for a well insulated residential home.

Unfortunately, much cooking with biofuels is done indoors, without efficient ventilation, and using fuels such as dung causes airborne pollution. This can be a serious health hazard; 1.5 million deaths were attributed to this cause by the World Health Organisation as of 2000 ². 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. One is that fuels are expensive and easily damaged. Another is that alternative fuels tend to be more expensive, but the people who rely on biofuels often do so precisely because they cannot afford alternatives. ³ Organizations 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 is done through improving ventilation, switching to different uses of biomass such as the creation of biogas from solid biomatter, or switching to other alternatives such as micro-hydro power. Many environmentalists are concerned that first growth forest may be felled in countries such as Indonesia to make way for palm oil plantations, driven by rising demand for diesel in SE Asia and Europe.

Direct biofuels are biofuels that can be used in existing unmodified petroleum engines. Because engine technology changes all the time, exactly what a direct biofuel is can be hard to define; a fuel that works without problem in one unmodified engine may not work in another engine. In general, newer engines are more sensitive to fuel than older engines, but new engines are also likely to be designed with some amount of biofuel in mind.

Straight vegetable oil can be used in some (older) diesel engines. Only in the warmest climates can it be used without engine modifications, so it is of limited use in colder climates. Most commonly it is turned into biodiesel. No engine manufacturer explicitly allows any use of vegetable oil in their engines.

Biodiesel can be a direct biofuel. In some countries manufacturers cover many of their diesel engines under warranty for 100% biodiesel use, although Volkswagen Germany, for example, ask drivers to make a telephone check with the VW environmental services department before switching to 100% biodiesel (see biodiesel use). Many people have run thousands of miles on biodiesel without problem, and many studies have been made on 100% biodiesel. In many European countries, 100% biodiesel is widely used and is available at thousands of gas stations[4][5].

Butanol is often claimed as a direct replacement for gasoline. It is not in wide spread production at this time, and engine manufacturers have not made statements about its use^{[verification needed]}. While on paper (and a few lab tests) it appears that butanol has sufficiently similar characteristics with gasoline such that it should work without problem in any gasoline engine, no widespread experience exists.

Ethanol is the most common biofuel, and over the years many engines have been designed to run on it. Many of these could not run on regular gasoline. It is open to debate if ethanol is a direct replacement in these engines though - they cannot run on anything else. In the late 1990's engines started appearing that by design can use either fuel. Ethanol is a direct replacement in these engines, but it is debatable if these engines are unmodified, or factory modified for ethanol^{[verification needed]}.

Small amounts of biofuel are often blended with traditional fuels. The biofuel portion of these fuels is a direct replacement for the fuel they offset, but the total offset is small. For biodiesel, 5% or 20% are commonly approved by various engine manufacturers^{[citation needed]}. See Common ethanol fuel mixtures for information on ethanol.

On the other hand, recognizing the importance of bioenergy and its implementation, there are international organizations such as IEA Bioenergy,^[3] established in 1978 by the International Energy Agency (IEA), with the aim of improving cooperation and information exchange between countries that have national programs in bioenergy research, development and deployment.

European Union has set a goal for 2008 that each member state should achieve at least 5.75% biofuel usage of all used traffic fuel. By 2006 it looks like most of the members states will not meet this goal.

For a comprehensive chart of energy contents from different biofuels please see Energy content of Biofuel

The energy content of biodiesel is about 90 percent that of petroleum diesel.
The energy content of ethanol is about 67 percent that of gasoline.
- Note: Chinese Tallow (Sapium sebiferum, or Triadica Sebifera) is also known as the "Popcorn Tree".
Source: Used with permission from the Global Petroleum Club

Typical oil extraction from 100 kg. of oil seeds

Source: Petroleum Club (with permission)

Source: Petroleum Club (with permission)
The energy content of ethanol is about 67 percent that of gasoline.
The energy content of biodiesel is about 90 percent that of petroleum diesel.

• Proposed oil phase-out in Sweden

1. Biomass Technical Brief, Simon Ekless, Intermediate Technology Development Group, retrieved 1 January 2005 from http://www.itdg.org/docs/technical_information_service/biomass.pdf.
2. Cellulosic Ethanol vs. Biomass Gasification, 22 October 2006, retrieved 19 November 2006 from http://i-r-squared.blogspot.com/2006/10/cellulosic-ethanol-vs-biomass.html
3. Smoke — the killer in the kitchen, Intermediate Technology Development Group, 19 March 2004, retrieved 1 January 2005 from http://www.itdg.org/?id=smoke_report_1
4. Reducing exposure to indoor air pollution, Intermediate Technology Development Group, 19 March 2004, retrieved 1 January 2005 from http://www.itdg.org/?id=smoke_report_3
5. Biofuels Crop Index

• Alternative Fuels Portal
• Anaerobic Digestion from Municipal Waste
• Biofuels for Transportation: Global Potential and Implications for Sustainable Agriculture and Energy in the 21st Century
• Biofuelwatch
• Circle Biodiesel & Ethanol
• Biomass
• "Biomass as Feedstock for a Bioenergy and Bioproducts Industry", a 2005 joint study sponsored by the United States Department of Energy and Department of Agriculture
• Educational Web Site for Biomass and Bioenergy the oldest source of energy used by humans
• Domesticfuel.com
• Ghent Bio Energy Valley
• IEA Bioenergy
• IEA Bioenergy - Task 29
• National Non Food Crops Centre
• PEFI Alcohol Process Development & Demonstration (Ecalene^TM)
• Russian National Biofuels Association
• What is Biodiesel
• Wood Energy Organisation Informations about energy out of wood
• Biofuel Crops: Power to the Poor

Template:Sustainability and energy development group

• The Potential of Bagasse-Based Cogeneration in the US, Kevin Ho, Columbia University, 2006.