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Bioenergy is energy derived from biofuels. Biofuels are fuels produced directly or indirectly from organic material – biomass – including plant materials and animal waste.
Overall, bioenergy covers approximately 10% of the total world energy demand. Traditional unprocessed biomass such as fuelwood, charcoal and animal dung accounts for most of this and represents the main source of energy for a large number of people in developing countries who use it mainly for cooking and heating.
More advanced and efficient conversion technologies now allow the extraction of biofuels from materials such as wood, crops and waste material. Biofuels can be solid, gaseous or liquid, even though the term is often used in the literature in a narrow sense to refer only to liquid biofuels for transport.
Biofuels may be derived from agricultural crops, including conventional food plants or from special energy crops. Biofuels may also be derived from forestry, agricultural or fishery products or municipal wastes, as well as from agro-industry, food industry and food service by-products and wastes.
A distinction is made between primary and secondary biofuels. In the case of primary biofuels, such as fuelwood, wood chips and pellets, organic materials are used in an unprocessed form, primarily for heating, cooking or electricity production. Secondary biofuels result from processing of biomass and include liquid biofuels such as ethanol and biodiesel that can be used in vehicles and industrial processes.
Bioenergy is mainly used in homes (80%), to a lesser extent in industry (18%), while liquid biofuels for transport still play a limited role (2%).
Even though the production of liquid biofuels for transport has grown rapidly in recent years it currently represents only 1% of total transport fuel consumption and only 0.2 to 0.3% of total energy consumption worldwide. More...
The most widely used liquid biofuels for transport are ethanol and biodiesel.
Ethanol is a type of alcohol that can be produced using any feedstock containing significant amounts of sugar, such as sugar cane or sugar beet, or starch, such as maize and wheat. Sugar can be directly fermented to alcohol, while starch first needs to be converted to sugar. The fermentation process is similar to that used to make wine or beer, and pure ethanol is obtained by distillation. The main producers are Brazil and the USA.
Ethanol can be blended with petrol or burned in nearly pure form in slightly modified spark-ignition engines. A litre of ethanol contains approximately two thirds of the energy provided by a litre of petrol. However, when mixed with petrol, it improves the combustion performance and lowers the emissions of carbon monoxide and sulphur oxide.
Biodiesel is produced, mainly in the European Union, by combining vegetable oil or animal fat with an alcohol. Biodiesel can be blended with traditional diesel fuel or burned in its pure form in compression ignition engines. Its energy content is somewhat less than that of diesel (88 to 95%). Biodiesel can be derived from a wide range of oils, including rapeseed, soybean, palm, coconut or jatropha oils and therefore the resulting fuels can display a greater variety of physical properties than ethanol.
Diesel engines can also run on vegetable oils and animal fats, for instance used cooking oils from restaurants and fat from meat processing industries.
The production processes for both bioethanol and biodiesel yield additional by-products such as animal feed. More...
Currently used liquid biofuels, which include ethanol produced from crops containing sugar and starch and biodiesel from oilseeds, are referred to as first-generation biofuels. These fuels only use a portion of the energy potentially available in the biomass.
Most plant matter is composed of cellulose, hemicellulose and lignin, and “second-generation biofuel” technologies refer to processes able to convert these components to liquid fuels. Once commercially viable, these could significantly expand the volume and variety of sources that could be used for biofuel production.
Potential cellulosic sources include municipal waste and waste products from agriculture, forestry, processing industry as well as new energy crops such as fast growing trees and grasses. As a result second generation biofuel production could present major advantages in terms of environmental sustainability and reduced competition for land with food and feed production. It could also offer advantages in terms of greenhouse gas emissions.
Various techniques are currently being developed to produce second generation biofuels. However, it is uncertain when such technologies will enter production on a significant commercial scale.
The conversion of cellulose to ethanol involves two steps. The cellulosic and hemicellulosic components of the plant material are first broken down into sugars, which are then fermented to obtain ethanol. The first step is technically difficult, although research continues on developing efficient and cost-effective ways of carrying out the process. Lignin cannot be converted to ethanol, but it can provide the necessary energy for the conversion process.
Gasification is a technique that converts solid biomass such as wood into a fuel gas. Gasifiers operate by heating biomass to high temperatures in a low-oxygen environment releasing an energy-rich gas. This gas can be burned in a boiler, used in a gas turbine to generate electricity. More...
Current world oil demand amounts to about 4000 Million tonnes of oil equivalent (Mtoe) while the production of liquid biofuels amounts to 36 Mtoe representing less than 1% of this world demand.
Around 85% of the liquid biofuels are currently produced in the form of bioethanol with the main producers being Brazil and the USA. Biodiesel production is essentially concentrated in the European Union.
Table 1: Biofuel production by country, 2007
Large-scale production of biofuels from crops requires large land areas to grow them, which generates increasing competition for natural resources, notably land and water.Crop yields per hectare vary widely depending on the type of crop, the country and the production system. Currently, ethanol production from sugar cane and sugar beet produces the highest yields per hectare.
Table 2: Biofuel yields for different feedstocks and countries
In its World Energy Outlook 2006, the IEA projected an increase in the share of the world’s fertile land used to grow plants for liquid biofuel production from 1% in 2004 to around 4% in 2030, assuming favourable government policies and reasonable technical development.
Using conventional biofuel technologies, this land use would allow 5% of transport fuel demand to be met. If second-generation biofuel technologies were available, this could rise to 10%.
This illustrates that biofuels can only be expected to displace fossil fuels for transport to a very limited extent. Nevertheless, they have a significant effect on global agriculture and agricultural markets because of the large volumes of feedstocks and land areas needed for their production. More...
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