Bioenergy denotes the use of organic material (biomass) as a source of energy for power (or electricity) generation and direct source heat applications in all energy sectors including domestic, commercial and industrial purposes as well as the production of liquid fuels for transport.
Bioenergy is a form of renewable energy. Biomass releases carbon dioxide (CO2) and small amounts of other greenhouse gases when it is converted into another form of energy. However CO2 is absorbed during the regrowth of the restored vegetation (biomass) through photosynthesis process.
Biomass is vegetable and animal derived organic materials, which are grown, collected or harvested for energy. Examples include wood waste, bagasse (sugar cane residues) and animal fats.
A conventional combustion process converts solid biomass through direct burning to release energy in the form of heat which can be used to generate electricity and heat. Chemical conversion processes breaks down the biomass into fuels, in the form of biogas or liquid biofuels, which are then used for electricity generation and transport.
Biogas is composed principally of methane and CO2 produced by anaerobic digestion of biomass. It is currently captured from landfill sites, sewage treatment plants, livestock feedlots and agricultural wastes.
Biofuels are liquid fuels, produced by chemical conversion processes that result in the production of ethanol and biodiesel. Biofuels can be broadly grouped according to the conversion processes:
- First generation biofuels are based on fermentation and distillation of ethanol from sugar and starch crops or chemical conversion of vegetable oils and animal fats to produce biodiesel. First generation technologies are proven and are currently used at a commercial scale.
- Second generation biofuels use biochemical or thermochemical processes to convert lignocellulosic material (non-edible fibrous or woody portions of plants) and algae to biofuels. Second generation technologies and biomass feedstocks are in the research, development and demonstration (RD&D) stage.
- Third generation biofuels are in research and development (R&D) and comprise integrated biorefineries for producing biofuels, electricity generation and bioproducts (such as petrochemical replacements).
World bioenergy resources
Around 10 per cent of the world’s primary energy consumption comes from bioenergy. The share of bioenergy in primary energy consumption is higher in non-OECD countries than in OECD countries. In Australia, the bioenergy share is comparable to the OECD average, at around 4 per cent. The majority of the world’s bioenergy is used directly for heat production through the burning of solid biomass; only 4 per cent is used for electricity generation and another 2.5 per cent is in the form of biofuels used in the transport sector.
Global bioenergy resources are difficult to quantify due to the resources being committed to food, animal feed and material for construction. The availability of biomass for energy is also influenced by population growth, diet, agricultural intensity, environmental impacts, climate change, water and land availability (IEA Bioenergy 2008).
Current bioenergy resources consist of residues from forestry and agriculture, various organic waste streams and dedicated biomass production from pasture land, wood plantations and sugar cane. Unused residues and waste are a significant underexploited resource.
At present, the main biomass feedstocks for electricity and heat generation are forestry and agricultural residues and municipal waste in cogeneration and co-firing power plants. In 2007, fuel wood dominates (67 per cent) the share of biomass sources in the bioenergy mix. Fuel wood is used in residential applications in inefficient stoves for domestic heating and cooking, which is also considered a major health issue in developing countries (IEA Bioenergy 2009). This traditional use is expected to grow with increasing population, however there is scope to improve efficiency and environmental performance.
The main growth markets for power generation from bioenergy are the European Union, North America, Central and Eastern Europe and Southeast Asia (IEA Bioenergy 2007). China continues to increase power generation from industry-scale biogas (mainly livestock farms) and straw from agricultural residues. The sugar industry in many developing countries continues to build bagasse-fuelled power plants (REN21 2009).
A small share of sugar, grain and vegetable oil crops is used for the production of biofuels. There is increasing interest in transport biofuels in Europe, Brazil, North America, Japan, China and India (IEA Bioenergy 2007). There is potential to expand the use of conventional crops for energy; however careful consideration of land availability and food demand is required.
There is a mature commercial market for first generation biofuels. Biofuels from commercially available technology are more prospective in regions where energy crop production is feasible: for example, sugar cane in subtropical areas of South America and sub-Saharan Africa, and sugar beet in more temperate regions such as the United States, Argentina and Europe. In the longer term, lignocellulosic crops could provide bioenergy resources for second generation biofuels which are considered more sustainable, provide land use opportunities and will reduce the competition with food crops.
Australia’s bioenergy resources
There is a range of bioenergy resources (feedstocks) available for multiple conversion technologies to generate electricity and heat and produce biofuels. Bioenergy resources are difficult to estimate due to their multiple and competing uses. There are production statistics for current commodities such as grain, sugar, pulp wood and saw logs; however these commodities are currently largely committed to food, animal feed and materials markets. They could be switched to the bioenergy market in certain conditions, but this may not be the highest order use for them.
Australia’s potential bioenergy resources are large. There are under-utilised resources in crop residues, plantation and forest residues and waste streams. There is a significant expansion into a new range of non-edible biomass feedstocks with the development of second generation technologies. Potential feedstocks of the future include modifying existing crops, growing of new tree crops and algae.
There are many factors to be taken into account for each bioenergy resource, such as moisture content, resource location and distribution, and type of conversion process. Different sources of biomass have very different production systems and therefore can involve a variety of sustainability issues. These range from very positive benefits (e.g. use of waste material, or growing woody biomass on degraded agricultural land) through to large scale diversion of high input agricultural food crops for biofuels (O’Connell et al. 2009). There is also a range of potential impacts on the resources including drought, flood, fire, climate change and energy prices. Future biomass feedstocks from agricultural production are dependent on whether production areas expand or reduce or yields increase.
The proportion of biomass potentially available will depend on the value of biomass relative to competing uses, impact of their removal (retention of biomass in situ returns nutrients to soil, improves soil structure and moisture retention), and global oil prices. The right economic conditions may result in some of the biomass potentially being used for bioenergy production. Depending on the price point, biomass may be diverted to biofuels or electricity generation – sawmill residues otherwise sold for garden products, for example, or pulpwood chipped and exported or used for paper production may be diverted to bioenergy if it is a higher value product.