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Biofuel refers to many different types of alternative energy sources that could supplement or even replacefossil fuels. Although they only account for a few percent of the world's transport fuel to date, they are increasingly

popular due to higher oil prices and an increasing concern with global warming and investments into them are

therefore growing each year. Biofuels are normally divided into three categories: solid biomass, liquid fuel and

biogases. Each group does not only effectively describe the form of the fuel, but also hints at the uses for which the

fuel is intended.

Solid biofuels are biomasses that may be burnt directly for energy, as has been done for thousands of years. ood,

charcoal, dried manure, non!food energy crops and domestic refuse are e"amples of these, as are things li#e

sawdust and grass cuttings. $sing especially the latter three is an e"cellent way of handling the disposal of these

products, never mind the significant amount air pollution that they produce when burnt. %owever even if any of these

were conveniently portable or burnt cleanly enough to be suited to engines, none of them pac# enough of a punch to

be viable as vehicle fuel& it would ta#e unreasonable quantities thereof to provide enough motive power to travel a

mere #ilometre.

he most common liquid biofuel is ethanol, which is made from fermentation of any sugar or starch from whichalcohol may be made. (t can also be produced from cellulosic combustion of bagasse and similarly inedible waste

products or non!food energy crops. )reen diesel and biodiesel are some of many other forms of liquid biofuels that

may be produced from vegetable or animal fats. All are mainly used for vehicle locomotion as they burn cleanly, are

easily portable and contain high amounts of energy , thus ma#ing

them compatible with combustion engines.

)aseous biofuels tends to be used either for electricity generation or, in the case of those that can be stored in liquid

form, for vehicle propulsion. An e"ample of the former type is biogas, which is essentially methane gas produced from

biodegradable waste or energy crops. Syngas, which is mi"ture of carbon mono"ide and hydrogen derived from

partial combustion of biomass, is better representative of the latter group. *ot only can it be used directly in

combustion engines or turbines, but it can also be used to produce methanol and hydrogen or even be converted into

diesel substitutes or gasoline.

Biofuels are very much under development, for which the above types are only a sample of what might be available

in only a few years' time. )enerally the oil! and alcohol!based products listed above are referred to as the first

generation of biofuels, as are other biofuels based on products that are normally considered part of the food chain.

he second generation of biofuels is thus those that have ta#en a step away from consumable items, instead

generating energy from human waste or non!edible plants. +ellulose!based ethanol fermentation is the best e"ample

of this in how it ma#es use of waste products li#e gabasse, which is made possible by refined techniques and new

scientific discoveries. +urrently third! and fourth generation biofuels are also researched by various companies all

over the world. hese promise not only to locate yet more potential energy sources, some possibly far more potent

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than e"isting ones in terms of energy content, but also to e"pand the uses of and improve upon e"isting techniques

for producing the ones that are already in the mar#et. (n other words we are li#ely to hear a lot more about biofuels in

the future.

%ydrogen is one of many potential replacements for gasoline as fuel for ground vehicles. (t is not apower source in itself, but an energy carrier that is produced rather than found naturally. (t tends to be made from

methane or other fossil fuels, but it can also be obtained from sources li#e wind, solar or nuclear power. hese are

readily available non!fossil energy sources that themselves are unsuited to propelling vehicles, but if used to ma#e

hydrogen would allow for a vehicle economy entirely void of carbon dio"ide emissions. As farfetched as it might

seem, it is very much a possibility if one ta#es into account that vehicles such as airplanes, submarines and space

shuttles already run by hydrogen at least partially.

%ydrogen motor vehicles can either be electric cars or of the combustion engine variety. he former type would be

powered by a fuel cell that lets hydrogen react with o"ygen to run an electric motor. %owever today's hydrogen fuel

cells tend to be highly fragile and would currently not endure the bumps and vibrations that motor vehicles inevitably

are subect to. As they moreover require rare and e"pensive substances li#e platinum as catalysts they would also be

costly. -ess e"pensive alternatives are currently under development, but if cheaper models would brea# ust as easilyit might be a while before hydrogen fuel cell cars become commonplace. he structure of the fuel cell would also

cause problems, being that it contains an internal vaporous water supply that could solidify in temperatures below

freeing. As the fuel cell process generates heat as a by!product it would not be an issue in a running engine, but if

left turned off until froen solid it would not be able to start and could, given the aforementioned fragility, perhaps

even be permanently damaged.

 A cold weather option could instead be vehicles with combustion engines converted to burn hydrogen instead of

gasoline. Such engines have already been built, and they are cheaper by far because of how they are based on

e"isting combustion engine technology. %owever they would not currently be good for much in commercial vehicles

given the general lac# of a hydrogen infrastructure for refuelling. here are currently a number of e"perimental

%ydrogen refuelling stations operational in the $S, but they are few and only e"ist in certain parts of the country. A

nationwide e"pansion would be necessary for hydrogen to ever become a large!scale gasoline replacement, and forsuch a proect to become reality investments of millions of dollars would be required.

(f these factors alone did not spea# against hydrogen as vehicle fuel in the near future, the currently inefficient

methods of producing and storing hydrogen would be problematic as well. )ranted, many companies are wor#ing on

technologies that could enable electrolysis of water on a large enough scale and for a cheap enough price for

hydrogen to become a feasible fuel source for vehicles, but as with the problems with the fuel cell, the completion

thereof probably cannot be e"pected to occur in the near future.

hat does not mean that we will have to wait to see hydrogen vehicles in use. %ydrogen buses are currently on trial in

many locations of the world, a fleet of hydrogen!run -ondon ta"is is planned to be ready for trial for the -ondon /01/

2lympic )ames and many car producers have already produced functional hydrogen demonstration models of

personal vehicles. %ydrogen is, in other words, indeed a potent alternative to gasoline, but in all li#elihood thetechnology required to put it to use as such needs years to mature before it is ready to be launched for the public

he fuel cell is a so!called electrochemical cell that generates electricity through chemical reactions between a fuel

source and an o"idant. he fuel source is generally hydrogen and the o"idant o"ygen, but versions that wor# on

hydrocarbons and alcohols or chlorine and chlorine dio"ides also e"ist. hese substances are simply inserted into the

fuel cell and are there consumed, being converted into water or carbon dio"ide and electricity. Although often

compared to batteries, fuel cells differ from these in how they rely on e"ternal fuel and o"idant supplies& which

essentially means that a fuel cell can operate indefinitely as long as the flow of the fuel and the o"idant is maintained.

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)ranted, the long!term efficiency of the cell depends in part on the amount of power that is drawn from it. 3ore power 

effectively translates to a greater electrical current, which increases the energy loss of the process and results in

lower efficiency in terms of lower cell voltage. hus fuel cells could technically be worn down over time. his

threatens to compromise the amount of power that may be generated from a cell. %owever this problem is wor#ed

around by the fact that fuel cells are often installed in series or parallel circuits, the former permitting higher voltage

and the latter a stronger electrical current. -arger cells with greater surface areas also produce this effect. a#ing this

into account the fuel cell is not only a powerful energy source, but its lac# of maor moving parts also means that it

requires minimal maintenance and minimal downtime in comparison to alternative power generators.

he fuel cell's comparable simplicity moreover ma#es it conveniently compact and lightweight. +onsequentially fuel

cells are ideal as portable power sources or as stationary ones in remote or inaccessible locations. Spacecrafts,

weather stations, rural locations and military submarines are a few e"amples of where fuel cells are currently

employed for electricity generation. (t is less ideal for vehicles in how it does not store energy, for which sieable

storage systems are needed to maintain the fuel supply. his is one of the foremost reasons for why fuel cell

technology has not yet been e"tensively implemented in vehicle propulsion. Suffice it to say that while a space craft

or submarine can carry the e"tra weight, it is not as easy to add it to a normal!sied automobile. 4et solutions are

underway in this department as well, with several fuel cell!driven vehicles currently e"isting in either limited editions

or as demonstration models of future methods of propulsion. hey still suffer from the fuel cell's incompatibility with

cold weather, but this too is being addressed by more recent models thereof by a proton e"change membrane that

prevents the fuel cell's liquid stores from freeing.

his potential to supplement or even supplant gasoline has ensured that hydrogen power cell technology has been

subect to considerable investments worldwide as a preventative measure against greenhouse gas omissions and

global warming. (t was particularly favoured as an alternative by the Bush administration of the $S, but it has since

been de!prioritied as other alternatives are thought li#ely to become fully developed ! and thus more li#ely to ma#e

an impact ! much sooner than hydrogen fuel cell cars. his might have set bac# the arrival of hydrogen!run vehicles

by years or even decades, but it has far from stopped it dead in its trac#s. (n the meantime fuel cells will continue to

serve as primary or emergency power generators for hospitals, universities and office buildings and etcetera, as well

as potential power sources for portable electric devices that are unli#ely to see many opportunities for recharging.