Although large hydroelectric installations generate most of the world's hydroelectricity, small hydro schemes are particularly popular in China, which has over 50% of world small hydro capacity. Some jurisdictions do not consider large hydro projects to be a sustainable energy source due to human and environmental impacts, though this judgment depends on the definition of sustainability used.
2008. augusztus 12., kedd
Hydroelectricity
Although large hydroelectric installations generate most of the world's hydroelectricity, small hydro schemes are particularly popular in China, which has over 50% of world small hydro capacity. Some jurisdictions do not consider large hydro projects to be a sustainable energy source due to human and environmental impacts, though this judgment depends on the definition of sustainability used.
Fuel economy
Sources
About 5% of the ethanol produced in the world in 2003 was actually a petroleum product. It is made by the catalytic hydration of ethylene with sulfuric acid as the catalyst. It can also be obtained via ethylene or acetylene, from calcium carbide, coal, oil gas, and other sources. Two million tons of petroleum-derived ethanol are produced annually. The principal suppliers are plants in the United States, Europe, and South Africa. Petroleum derived ethanol (synthetic ethanol) is chemically identical to bio-ethanol and can be differentiated only by radiocarbon dating.
Bio-ethanol is obtained from the conversion of carbon based feedstock. Agricultural feedstocks are considered renewable because they get energy from the sun using photosynthesis, provided that all minerals required for growth (such as nitrogen and phosphorus) are returned to the land. Ethanol can be produced from a variety of feedstocks such as sugar cane, bagasse, miscanthus, sugar beet, sorghum, grain sorghum, switchgrass, barley, hemp, kenaf, potatoes, sweet potatoes, cassava, sunflower, fruit, molasses, corn, stover, grain, wheat, straw, cotton, other biomass, as well as many types of cellulose waste and harvestings, whichever has the best well-to-wheel assessment.
Current, first generation processes for the production of ethanol from corn use only a small part of the corn plant: the corn kernels are taken from the corn plant and only the starch, which represents about 50% of the dry kernel mass, is transformed into ethanol. Two types of second generation processes are under development. The first type uses enzymes and yeast to convert the plant cellulose into ethanol while the second type uses pyrolysis to convert the whole plant to either a liquid bio-oil or a syngas. Second generation processes can also be used with plants such as grasses, wood or agricultural waste material such as straw.
Anhydrous ethanol
Ethanol can be mass-produced by fermentation of sugar or by hydration of ethylene (ethene CH2=CH2) from petroleum and other sources. Current interest in ethanol mainly lies in bio-ethanol, produced from the starch or sugar in a wide variety of crops, but there has been considerable debate about how useful bio-ethanol will be in replacing fossil fuels in vehicles. Concerns 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. Recent developments with cellulosic ethanol production and commercialization may allay some of these concerns.
According to the International Energy Agency, cellulosic ethanol could allow ethanol fuels to play a much bigger role in the future than previously thought. Cellulosic ethanol offers promise as resistant cellulose fibers, a major component in plant cells walls, can be used to generate ethanol. Dedicated energy crops, such as switchgrass, are also promising cellulose sources that can be produced in many regions of the United States.
Ethanol fuel
2008. július 7., hétfő
Non-conventional oil
2008. május 4., vasárnap
About alternative fuel source
(from Wikipedia) The definition of alternative fuel varies according to the context of its usage. In the context of petroleum substitutes, the term 'alternative fuel' can simply any available fuel or energy source, and does not necessarily refer to a source of renewable energy. In the context of environmental sustainability, alternative fuel often implies an ecologically benign renewable fuel. Often, they produce less pollution than gasoline or diesel. Alternative fuels, also known as non-conventional fuels, are any materials or substances that can be used as a fuel, other than conventional fuels. Conventional fuels include: fossil fuels (petroleum (oil), coal, propane, and natural gas), and also in some instances nuclear materials such as uranium. Some well known alternative fuels include biodiesel, bioalcohol (ethanol, butanol), chemically stored electricity (batteries and fuel cells), hydrogen, non-fossil methane, non-fossil natural gas, vegetable oil and other biomass sources.