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Renewable fuels, such as biofuels (eg. Vegetable oil used as fuel, ethanol, or biodiesel) and hydrogen (when produced with renewable processes) are fuels produced from renewable resources. This is in contrast to non-renewable fuels such as natural gas, LPG (propane), petroleum and other fossil fuels and nuclear energy.

Renewable fuels have gained in popularity due to their sustainability, low contributions to the carbon cycle, and in some cases lower amounts of greenhouse gases. The and geo-political ramifications of these fuels are also of interest, particularly to industrialized economies which desire independence from Middle Eastern oil.

Each fuel is still in development and no fuel is yet seen as a ready-made replacement for petroleum. For example, ethanol has both advantages and disadvantages. Many caution that ethanol is only one part of a solution to a complex problem which must include an enormous ramp-up in alternative energy sources that include wind and solar power, hydroelectric power, bio-diesel, hydrogen fuel-cells, improved batteries, nuclear energy, and energy conservation.

Contents

Motivations for renewable fuel development

Hubbert's peak oil theory suggests that petroleum is a finite resource that is rapidly depleting. Of the worldwide total remaining petroleum reserves of approximately 1,277,702,000,000 barrels (about one half of the original virgin reserves) and a worldwide usage rate of 25,000,000,000 per year, only about 50 years worth of petroleum is predicted to remain at the current depletion rate. Petroleum is imperative for the following industries: fuel (home heating, jet fuel, gasoline, diesel, etc.) transportation, agriculture, pharmaceutical, plastics/resins, man-made fibers, synthetic rubber, and explosives. If the modern world remains reliant on petroleum as a source of energy, the price of crude oil could increase markedly, destabilizing economies worldwide. Consequently, renewable fuel drivers include: high oil prices, imbalance of trade, instability in oil exporting regions of the world, the Energy Policy Act of 2005, the potential for windfall profits for American farmers and industries, avoidance of economic depression, avoidance of scarcity of products due to a volatile ‘peak oil’ scenario expected to begin as early as 2021,[1] (though peak oil is not a new idea) and a slowing of global warming that may usher in unprecedented climate change.

Furthermore, the global debate on climate change, along with regional geopolitical instabilities have challenged nations to act to develop both alternative and carbon-neutral sources of energy. Renewable fuels are therefore becoming attractive to many governments, who are beginning to see sustainable energy independence as a valuable asset.

Biofuel

Global fossil carbon emissions, an indicator of consumption, for 1800-2004. Total is black. Oil is in blue.

Hydrocarbons, molecules of hydrogen and carbon, are combustible compounds resulting from eons of compression of vegetation, or fossil fuels. This means that when, for example, gasoline is fed into an internal combustion engine, a large amount of energy per pound (high energy density) is captured by the engine. Hydrocarbons are all substances with low entropy (meaning they hold a lot of energy potential), which can be released and harnessed by burning them. The downside is that they emit pollution such as carbon monoxide and soot.

Carbohydrates, like hydrocarbons contain hydrogen and carbon atoms, as well as one additional atom: oxygen. They are a chief source of food energy. The simplest model is in which the sun’s energy is stored in plants as sugar, and used as a source of food to grow. When animals eat those plants – our metabolism releases that energy to us, enabling us to live. For example, the sugar in sugar cane and corn can be converted into 'moonshine', which is ethyl alcohol or ethanol, and is usable as fuel. It is also possible to convert the sugar in the corn husks, which are inedible and ordinarily thrown away, into ethanol. Refined ethanol is similarly inflammable and combustible. Also, because it possesses an oxygen atom, it is dubbed an 'oxygenate,' which endows it with the additional advantage over gasoline of combusting with reduced engine knocking; it also helps gasoline burn cleaner by reducing smog.[citation needed] Although many different renewable fuels can be derived from carbohydrate biomass, (e.g. methanol, dimethyl ether, methane, hydrogen, etc.), ethanol has generally received the most attention in the United States.

Hydrogen fuel

Hydrogen fuel requires the development of a specific infrastructure for processing, transport and storage.

Hydrogen fuel refers to the use of hydrogen gas (H2) for use as an energy source. Broadly speaking, the production of renewable hydrogen fuel can be divided into two general categories: biologically derived production, and chemical production.[2] This is an area of current research, and new developments and technologies are causing this field to evolve rapidly.

The biological production of hydrogen fuel has been a topic of research since at least the 1970s. Hydrogen gas can be produced from biomass sources like agricultural and forest residues, consumer waste and other specific agricultural crops.[2] Specifically, hydrogen fuel is produced by a process called gasification, where biomass is processed into a combustible gas and then burned, or by pyrolysis, a related process which can lead to hydrogen gas suitable for fuel-cell applications. One continuing subject of research regards the production of unwanted co-products in both of these processes. The presence of other contaminant gases often depend on specific composition of the biomass source, which can be difficult to control.[2] Another source for biological production of hydrogen fuel is algae. In the late 1990s it was discovered that if algae are deprived of sulfur they will switch from the production of oxygen, as in normal photosynthesis, to the production of hydrogen.[3] Experimental algae farms are attempting to make algae an economically feasible energy source.[4]

There are also several physico-chemical methods for producing hydrogen; most of these methods require electrolysis of water. When this process draws its power from renewable energy sources like wind turbines or photovoltaic cells, the production requires little consumption of non-renewable resources. Hydrogen fuel, when produced by renewable sources of energy like wind or solar power, is a renewable fuel.[2]

See also

References

  1. ^ Biomass for biofuel isn't worth it
  2. ^ a b c d National Renewable Energy Laboratory 2003 Research Review: "New Horizons for Hydrogen."
  3. ^ Wired, It Came from the Swamp: Reengineering Algae To Fuel The Hydrogen Economy, accessed September 17, 2007.
  4. ^ The Register, Pond life: the future of energy, accessed September 17, 2007.
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