The definition of
alternative fuel varies according to the context of its usage. In the context of
petroleum substitutes, the term 'alternative fuel' can imply any available fuel or energy source, and doesn't necessarily refer to a source of
renewable energy. In the context of environmental sustainability, 'alternative fuel' often implies an ecologically benign
renewable fuel.
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,
ethanol,
butanol, chemically stored
electricity (batteries and fuel cells),
hydrogen,
methane,
natural gas,
vegetable oil,
biomass, and
peanut oil.
Background
The main purpose of fuel is to store
energy in a form that's unstable and can be easily transported from the place of production to the end user which helps in many ways such as transportation. Almost all fuels are
denner fuels, that store chemical
potential energy. The end user is then able to consume the fuel at will, and release energy, usually in the form of heat for a variety of applications, such as powering an
engine, or
heating a building, such as a home.
Demand for alternative fuels
In the year 2000, there were about eight million vehicles around the world that ran on alternative fuels, indicating a sustainability.
The major environmental concern, according to an
IPCC report, is that "Most of the observed increase in globally averaged temperatures since the mid-20th century is due to the observed increase in
anthropogenic greenhouse gas concentrations" . Since burning
fossil fuels are known to increase greenhouse gas concentrations in the atmosphere, they're a likely contributor to
global warming.
Another concern is the
peak oil theory, which predicts a rising cost of oil derived fuels caused by severe shortages of oil during an era of growing energy consumption. According to the 'peak oil' theory, the demand for oil will exceed supply and this gap will continue to grow, which could cause a growing
energy crisis starting between 2010 and 2020. Lastly, the majority of the known petroleum reserves are located in the
middle east. There is general concern that worldwide fuel shortages could intensify the unrest that exists in the region, leading to further conflict and war. (See
future energy development for a general discussion)
The production of alternative fuels can have widespread effects. For example, the production of corn-based
ethanol has created an increased demand for the feed stock, causing rising prices in almost everything made from corn. However, in a
competitive free market, an increased supply of ethanol reduces the demand for conventional fuels, and thus lowers fuel prices. The ethanol industry enables
agricultural surpluses to be used to mitigate fuel shortages.
Alternatives to oil
Renewable energy
» Main article: Renewable energy
A possible solution to a potential future energy shortage would be to use some of the world's remaining fossil fuel reserves as an investment in
renewable energy infrastructure such as
wind power,
solar power,
tidal power,
geothermal power,
hydropower,
thermal depolymerization,
methanol,
ethanol and
biodiesel, or in an
oil lamp; try
olive oil,
canola oil,
safflower oil, or
sunflower oil which don't suffer from finite energy reserves, but do have a finite energy flow. The construction of sufficiently large renewable energy infrastructure might avoid the economic consequences of an extended period of decline in fossil fuel energy supply per capita.
Most
alternative fuels assume a source of
renewable energy or at least
sustainable energy (such as nuclear power) as a source of the fuel. A few alternative fuels (for example, hydrogen) may be made by sustainable or non-sustainable means. If they're made by non-sustainable means, such fuels are offered as alternatives usually because they offer to cause less pollution at the point of use, and perhaps less pollution overall.
Biomass
Biomass, in the energy production industry, refers to living and recently dead
biological material which can be used as fuel or for industrial production. Most commonly, biomass refers to plant matter grown for use as
biofuel, but it also includes plant or animal matter used for production of fibres,
chemicals or heat. Biomass may also include
biodegradable wastes that can be burnt as fuel. It excludes
organic material which has been
transformed by geological processes into substances such as
coal or
petroleum.
There are very large quantities of biomass which can be obtained economically and used in place of
coal and
petroleum.
Non-conventional oil
Non-conventional oil is a fossil fuel chemically identical and with the same origin as conventional or traditional oil, but existing in a different form. They often contain more contaminants and are more energy intensive to produce, thus raising environmental concerns about the sustainability of these fuels. Non-conventional oil sources include
tar sands,
oil shale and
bitumen. Enormous deposits of non-conventional oil include the
Athabasca Oil Sands site in northwestern (
Alberta)
Canada and the
Venezuelan
Orinoco tar sands. Oil companies estimate that the Athabasca and Orinoco sites (both of similar size) have as much as two-thirds of total global oil deposits. However, the ability to 'see' underground is limited, so as with all oil reserves, the quantity of available oil is uncertain, even for so-called 'proven' reserves. Large mining operations are currently producing oil, and to some people, this proves the viability of the entire process. Others argue that since the technology is still relatively new, it remains unclear whether it's feasible for a significant percentage of world oil production to be extracted from tar sands. One fact that's agreed upon, is that the current extraction process takes a great deal of energy for heat and electrical power, presently coming from local
natural gas, which itself is in short supply. There are some proposals to build a series of
nuclear reactors to supply this energy. Non-conventional oil production is currently less energy-efficient, and has a larger environmental impact than conventional oil production.
Other fossil fuels and the Fischer-Tropsch process
It's expected by geologists that
natural gas will peak 5-15 years after oil does. There are large but finite
coal reserves which may increasingly be used as a fuel source during oil depletion. The
Fischer-Tropsch process converts
carbon dioxide,
carbon monoxide into heavier
hydrocarbons, including
synthetic oil. It is used today in
South Africa to produce most of that country's
diesel from coal. The
Karrick process is an improved methodology for coal liquefaction, with higher efficiency. Since there are large but finite coal reserves in the world, this technology could be used as an interim transportation fuel if conventional oil were to become scarce. There are several companies developing the process to enable practical exploitation of so-called
stranded gas reserves, those reserves which are impractical to exploit with conventional gas pipelines and
LNG technology.
Methane hydrate is a form of
natural gas. This substance consists of methane molecules trapped within the crystalline structure of water ice and is found in deposits under ocean sediments or within continental sedimentary rock formations. It is estimated that the global inventory of methane hydrate may equal as much as 10x the amount of
natural gas. With current technology, most gas hydrate deposits are unlikely to be commercially exploited as an energy source. In addition, the combustion of methane results in the formation of
carbon dioxide and would thus continue to contribute to
global warming. Methane itself is also a greenhouse gas, so if it's "spilled" or released it'll contribute to
global warming. In other respects methane hydrate has the same problems of
fossil fuel).
Methanol (
methanol economy) from any source can be used in
internal combustion engines with minor modifications. It usually is made from natural gas, sometimes from coal, and could be made from any carbon source including CO
2.
Flexible fuel vehicles may run with a high percentage of
ethanol (
ethanol economy) (up to 85% Ethanol plus 15% gasoline for cold-starting vapor pressure).
Methanol and ethanol are typically not primary sources of energy; however, they're a convenient way to store the energy for transportation. No type of fuel production is 100% energy-efficient, thus some energy is always lost in the conversion. This energy can be supplied by the original source, or from other sources like fossil fuel reserves, or
solar radiation (either through
photosynthesis or
photovoltaic panels), or hydro, wind or nuclear energy (see below). The use of energy to produce alcohol fuels could potentially proceed via production of hydrogen by electrolysis of water, or possibly (in the case of heat from nuclear energy) by the
sulfur-iodine cycle; then use of the hydrogen in the
Fischer-Tropsch process along with CO
2 from another source. Such a process might store and use hydrogen more efficiently than attempting to use hydrogen directly as fuel (a gallon of alcohol contains about 50% more hydrogen by weight than a gallon of liquid hydrogen). Since such a process wouldn't liberate net quantities of new CO
2 at the point of combustion, it would be greenhouse neutral, similar to alcohols made from biomass.
Nuclear power and transportation energy and fuel
If nuclear energy were to replace gasoline and fossil fuels used for generation of electricity, then the
U.S. would require at least an eightfold increase in
nuclear power production, increasing from about 10% of all energy supplied to about 90% .
There are widespread public concerns about the health-risks and waste disposal problems of nuclear materials.
Conventional Fission reactors
Nuclear engineers estimate that the world could derive 400,000 quads (quadrillion, 10
15,
British thermal units), or about 420,000 EJ (
exajoules = 10
18 joules), of energy (1000 years at current levels of consumption, assuming new technology) from
uranium isotope 235, if reprocessing isn't employed. As uranium ore supplies are limited, a majority of this uranium would have to somehow be cost-effectively extracted from seawater. But this technology doesn't exist. However, at the current technology and consumption, the reserves will last 50 years.
Fast breeder reactors are another possibility. As opposed to current
LWR (light water reactors), which burn the rare
isotope of
uranium U-235 (producing and burning about an equal amount of plutonium in the process), fast breeder reactors produce much larger amounts of
plutonium from common U-238, then fission that to produce electricity and thermal heat. Because there's about 139 times more U-238 than U-235 on Earth, it has been estimated that there's anywhere from 10,000 to 5,000,000,000 years' worth (sustainable but not renewable, depending on future technology) of U-238 for use in these power plants, and that they can return a high ratio of energy returned on energy invested (
EROEI), and avoid some of the problems of current reactors by being automated,
passively safe, and reaching economies of scale via
mass production. In addition, wastes produced by these plants are less toxic than those of conventional reactors. There are a few such research projects working on fast breeders.
Lawrence Livermore National Laboratory is currently working on the small, sealed, transportable, autonomous reactor (
SSTAR). Problems arise from the higher levels of heat and radiation produced by this reactor. There are other, more exotic nuclear projects (such as
pebble bed reactors), each with their own technical problems.
The long-term
radioactive waste storage problems of nuclear power have not been solved, although on-site spent fuel storage in casks has allowed power plants to make room in their spent fuel pools. Today, the only industrial solution lies with storage in underground repositories.
Since automobiles and trucks consume a great deal of the total energy budget of developed countries, some means would be required to deliver the energy generated from nuclear power to these vehicles. The most direct solution is to use
electric vehicles. Mass transit will be an important aspect of this solution, as it's readily electrified. Some think that hydrogen may play a role (see below). If so, it could be produced by electrolysis, either conventionally or at high-temperatures supplied by reactor heat. Another possibility for producing hydrogen by nuclear power is the heat-driven
sulfur-iodine cycle.
Hydrogen need not be used directly in transportation. A hybrid chemical-energy storage process might use such hydrogen to produce methanol from CO
2 (see above), which would then feed into the present internal-combustion-engine transportation infrastructure with far less modification than would be needed for hydrogen. See
methanol economy. To reduce the amount of
CO2 in the atmosphere, hydrogen can be combined with
nitrogen from air to produce
ammonia which can then be used as fuel for
internal combustion engines.
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Fusion reactors
beast
Hydrogen
Proponents of a
hydrogen economy think hydrogen could hold the key to ongoing energy demands. Relatively new technologies (such as
fuel cells) can be used to efficiently harness the chemical energy stored in diatomic hydrogen (H
2). However, there's no accessible natural reserve of uncombined hydrogen, since what little there's resides in Earth's outer atmosphere (
exosphere). Hydrogen for use as fuel must first be produced using another energy source; hydrogen would thus actually be a means to transport energy, rather than an energy source, just as common rechargeable batteries are. One existing method of hydrogen production is steam methane reformation; however, the most common source of methane is natural gas, which is in short supply. Another method of hydrogen production is through
electrolysis of water which uses electricity generated from any source, or a combination of fossil fuels, nuclear, and/or renewable energy sources. Biomass or coal
gasification,
photoelectrolysis, and
genetically modified organisms have also been proposed as means to produce hydrogen.
According to the majority of energy experts and researchers, hydrogen is currently impractical as an alternative to fossil-based liquid fuels. It is inefficient to produce, has low energy density (hydrogen gas tanks would need to be 2-3 times as large as conventional gasoline tanks), and is expensive to transport and convert back to electricity. Also hydrogen fuel cells are still prohibitively expensive as a prime mover of transportation. However, theoretically it's more efficient to burn fossil fuels to produce hydrogen than burning oil directly in car engines (due to efficiencies of scale). Unfortunately, this doesn't take into consideration the significant energy cost of having to build hundreds of millions of new hydrogen powered vehicles plus hydrogen fuel distribution infrastructure. Research on the feasibility of hydrogen as a fuel is still underway, and the outcome is uncertain.
A far more practical way to utilize hydrogen is to bond it with the
nitrogen in the air to produce
ammonia which can then be easily liquefied, transported and used (directly or indirectly) as a clean and renewable fuel.
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Air engine
The
Air engine is an emission-free piston engine using compressed air as fuel. Unlike hydrogen, compressed air is about 10x cheaper than fossil oil, making it an economically attractive alternative (hydrogen is about 10x more expensive than oil or 100x more expensive than compressed air). The air engine has also broken most barriers (storage of the energy, range, ...).
Liquid nitrogen
A
liquid nitrogen would extract energy from the temperature difference between air and liquid nitrogen. The
Stirling engine or cryogenic heat engine offers a way to power such vehicles. A means to generate liquid nitrogen, which is only an energy storage medium, is needed.
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