Encyclopedia of Renewable Energy. James G. Speight
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Bioenergy
Bioenergy is renewable energy produced from organic matter – the conversion of the complex carbohydrates in organic matter to energy; organic matter may either be used directly as a fuel, processed into liquids and gasses, or be a residual of processing and conversion. Bioenergy (although not quite correct) is often used interchangeably with, biofuel and biomass. More typically, the term bioenergy refers to electricity and gas that is generated from biomass, which can be any form of plants and timber to agricultural and food waste – and even sewage. The term bioenergy also covers transport fuel (biofuel) produced from organic matter.
Biofuel is fuel derived from biological sources and biomass is the biological material used as a biofuel, as well as the social, economic, scientific, and technical fields associated with using biological sources for energy. In reality, bioenergy is the energy extracted from the biomass, as the biomass is the fuel and the bioenergy is the energy contained in the fuel.
The terms bioenergy and renewable energy are often (incorrectly used) interchangeably. However, bioenergy is specific and refers to energy produced from biological course (i.e., biomass). On the other hand, renewable energy is a more collective term that includes not only bioenergy but also nuclear energy, solar energy, tidal energy, and wind energy.
Bioenergy can offer renewable, low-carbon energy systems, sequestering atmospheric carbon as well as offer numerous environmental and socioeconomic benefits and therefore supporting global climate change targets and wider environmental, social, economic, and sustainable targets.
In addition, it is important to consider various sustainable aspects of bioenergy systems beyond carbon. Ensuring that bioenergy offers the required holistic emission reduction, context, specific and long-term approaches are necessary to understand synergies and the tradeoff of the bioenergy and related agricultural and forestry systems.
See also: Biofuel, Biomass, Nuclear Energy, Solar Energy, Tidal Energy, Wind Energy.
Bioenergy Crops
Bioenergy crops are low-cost and low-maintenance crops grown solely for energy production by (for example) combustion. The crops are processed into solid, liquid, or gaseous fuels, such as pellets, bioethanol, or biogas. The fuels are burned to generate electrical power or heat. The plants are generally categorized as woody or herbaceous. The former – woody plants include willow and poplar while the latter – herbaceous plants – include miscanthus and these crops, while physically smaller than trees, store (approximately) twice the amount of carbon dioxide (in the form of carbon) below ground, compared to woody crops.
Thus, bioenergy crops include fast-growing trees such as hybrid poplar, black locust, willow, and silver maple in addition to annual crops such as corn, sweet sorghum, and perennial grasses such as switch grass. The first-generation bioenergy crops include corn, sorghum, rapeseed, and sugarcane, whereas the second-generation bioenergy crops are comprised of switchgrass, miscanthus, alfalfa, reed canary grass, Napier grass, and other plants.
Briefly, switch grass is a thin-stemmed, warm season, perennial grass that has shown high potential as a high yielding crop that can be readily grown in areas that are also suitable for crop production. In fact, there are many perennial crops (grass and tree species) that show high potential for production of cost-competitive cellulosic biomass. Switch grass can be viewed as a surrogate for many perennial energy crops when estimating biomass supply and availability.
Bioenergy crops increase soil carbon and fix atmospheric carbon. In addition, bioenergy crops (miscanthus, sorghum, and poplar) could also be used for the phytoremediation of heavy metal-contaminated soils. The bioenergy crops include specific plants that are grown and maintained at lower costs for biofuel production. Many other crops are possible, and the optimal crop will vary with growing season and other environmental factors. Most fast-growing woody and annual crops are high in hemicellulose sugars such as xylose.
See also: Bioenergy, Biofuel, Biomass.
Bioenergy System
A bioenergy system is an energy system which is comprised of a source which generates energy and modulates it in some manner such that it conveys energy. There is also a mechanism connecting the bioenergy source to a transfer medium and a transfer medium through which the bioenergy flows. There is a coupling mechanism connecting the transfer medium bioenergy sink and a terminal sink which includes a mechanism for the storage and use of the energy. The input and output coupling depend on properties of the source and the transfer medium, likewise for the sink.
To evaluate the performance of a bioenergy system, the entire chain from biomass production up to the end-use should be considered. A major criterion for comparing total bioenergy systems is the net energy yield per hectare. If this net yield is low, the amount of land needed for the net production of a certain amount of energy is high and vice versa. Since land is a scarce commodity, high net energy yields per hectare are favored. Also, the environmental impacts of a specific energy crop are a criterion for selection. Logically, another major criterion is the cost of the biomass per GJ produced (or per GJ of fossil energy replaced).
Biomass for energy conversion is usually considered as a local resource. With appropriate logistic systems, access to biomass can be improved over a large geographical area. In this study, life cycle inventory has been used as a method to investigate the environmental load of selected bioenergy transport chains. As a case study, chains starting in Sweden and ending in Holland have been investigated. Biomass originates from tree sections or forest residues, the latter upgraded to bales or pellets. The study is concentrated on production of electricity; hot cooling water is considered as a loss.
See also: Bioenergy, Bioenergy Crops, Biomass.
Bioethanol
Bioethanol is ethanol produced from biomass feedstocks, which includes ethanol produced from the fermentation of crops, such as corn, as well as cellulosic ethanol produced from woody plants or grasses. The resource base is gradually widening to cellulosic crops, and even wood. Such low-cost feedstock would result in a global increased production potential for low-cost ethanol.
Unlike crude oil, bioethanol is a form of renewable energy that can be produced from agricultural feedstocks. It can be made from various crops such as sugar cane, potato, and maize.
The long-term prospects of bioethanol, or any other biofuels such as methanol and biodiesel, depend on biomass availability. Concerns related to its production and use relate to the large amount of arable land required for crops, as well as the energy and pollution balance of the whole cycle of ethanol production. The availability of bioethanol depends on future food demand and food patterns, other types of land use, and agricultural productivity.
See also: Alcohols, Bioethanol Production, Ethanol.
Bioethanol Production
Bioethanol can be produced from a variety of crops, although the traditional feedstocks for the production of ethanol are still starch crops like corn, wheat and cassava and from sugar crops like sugar cane and sugar beet.
The development of lignocellulosic technology has meant that not only high energy content starch and sugar crops can be used but also woody biomass or waste residues from forestry. This process requires an additional pretreatment process of pulping and enzymes to break down the organic compounds.
Additional steps that may be taken in a biorefinery include the drying and pelletization of bagasse (the waste component of sugar cane after juice extraction) to produce a secondary product along with ethanol, which makes the plant more economically feasible. In addition to the production of fuel pellets, one can also produce feed for animals, which could be