The entire world, with its dependence upon, and sharp competition to secure, fossil fuel energy sources, is coming to a crisis that may be unmatched in its history. Serious questions are raised about whether the world can maintain a population that it is already straining to provide for unless it has the availability of cheap petroleum fuel to drive nations' economies. Complicating this is the unquestionable negative impact that fossil fuel use has on the environment, which threatens the well being of the population that it is needed to support.
It is clear to even the most casual observers that a change away from fossil fuels to clean, non-polluting renewable fuels is required, and several forms are available. There is no single source of these fuels that can be provided in adequate amounts to satisfy a huge and growing demand, but a mix of these technologies can fill the bill.
Let's begin with an inventory of the technologies that are most frequently touted in the popular media.Biomass Fuels
Fuels from plant materials, like ethanol and methanol, are an easy option to replace some petroleum used in powering internal combustion engines. The attraction of this option rests exclusively in its being a renewable option, since more biomass can be grown to provide refinery feed stocks. It also enjoys strong political support in states with large agricultural industries. However, it does have its disadvantages.
One disadvantage is the arable acreage that is required to grow enough biomass to provide enough energy to satisfy demand. In Brazil, significant strides have been made to use this type of fuel to replace gasoline, but they have the luxury of much land, a long growing season and a smaller population to provide with this transportation fuel. The United States does not have that much additional farmland to provide for its significant demand, which means that acreage that is devoted to providing food crops would have to be diverted to energy production.
Another disadvantage is that burning the fuel still releases carbon, so the pollution problems presented by fossil fuels are not fully addressed with the use of biomass.
Hydrogen is cited as a relatively safe, clean replacement for organic (carbon based) motor fuels. It may be burned as in internal combustion or turbine engines, or it may be used in fuel cell stacks to generate electricity for small-scale applications. In either case, the byproduct of the process, or its "exhaust" product, is plain water.
It is also an abundant fuel, being the major component of water. There is no free hydrogen in the atmosphere for very long, since it is so light that it floats off into outer space rather than staying gravitationally bound in the atmosphere. The problem is in separating it from its abundant matrix (water) since the method of separation, electrolysis, requires more energy input in the form of electricity than the equivalent energy value of the hydrogen it releases. This means that the electricity used to produce hydrogen must come from sources that are less than dirt cheap to operate.
Storing the fuel becomes another problem, as it must be contained in pressure tanks that represent a risk of explosion, although not that much greater a risk than that which exists with a gasoline tank.