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Hydrogen

Fuel Source

Hydrogen does not occur free in nature; it can be made by "re-forming" natural gas or another fossil fuel, or by using electricity to split ("electrolyze") water into its components of oxygen and hydrogen. In this sense, hydrogen is like electricity: the energy to generate it can be obtained from sources ranging from the burning of high-sulfur coal to pollution-free photovoltaic cells (solar cells).

Wholesale Availability

There is not currently a bulk hydrogen distribution infrastructure on anything like the scale of that for fossil fuels, though studies have been undertaken of the possibility of sending it through the existing natural-gas pipeline network (with some substantial modifications). Because hydrogen can be made from natural gas by re-forming or from water by electrolysis, and natural gas, electricity, and water are readily available, it might be simpler to make the hydrogen at the point of sale, rather than ship it there.

Retail Availability

See above; hydrogen is currently available only as an industrial or scientific chemical product, not as a bulk fuel.

Advantages

Hydrogen has been called the "most alternative" of the alternative fuels: if it is made by electrolysis of water using electricity from a nonpolluting source like wind or solar power, then no pollutants of any kind are generated by burning it in an internal combustion engine except for trace amounts of nitrogen oxides, and if it is used in a fuel cell then even these disappear. Furthermore, no greenhouse gases are generated because there's no carbon in the fuel. All that comes out the vehicle's exhaust is drinkable water! Using hydrogen as the "battery" to store energy from a nonpolluting, renewable source would result in a truly unlimited supply of clean fuel. The advantage of using hydrogen to store energy rather than a battery pack is that a hydrogen tank can be refilled in minutes rather than recharged in hours, and it takes less space and weight to store enough hydrogen to drive a given distance on a single refueling than it does to carry enough battery capacity to go the same distance on a single recharging. The battery-electric drivetrain uses energy more efficiently, and can handle the vast majority of daily commute-and-errands driving that people do, but for long trips hydrogen could prove to be a lot more convenient.

Disadvantages

Hydrogen is currently very expensive, not because it is rare (it's the most common element in the universe!) but because it's difficult to generate, handle, and store, requiring bulky and heavy tanks like those for compressed natural gas (CNG) or complex insulating bottles if stored as a cryogenic (super-cold) liquid like liquefied natural gas (LNG). It can also be stored at moderate temperatures and pressures in a tank containing a metal-hydride absorber or carbon adsorber, though these are currently very expensive. It is possible to store a hydrogen-bearing fuel like natural gas, methanol, or even gasoline aboard the vehicle and re-form it to get hydrogen as needed; this simplifies storage and refueling, but adds cost and complexity to the drivetrain (and reduces efficiency). It is not a very good fuel for an internal combustion engine, being prone to preignition, though BMW, Mazda, and Ford have done some tests; the most efficient way to use it is in fuel cell vehicles, but these are still in the demonstration stage.

Under "Advantages" above, I discussed the benefits of using hydrogen generated from renewable, nonpolluting power like solar electricity. However, as hydrogen fuel has gained political momentum, concern is growing that the inefficiencies of generating, transporting, and storing hydrogen may make it a poor choice if the energy used to generate the hydrogen comes from fossil fuels (whether via re-forming those fuels directly, or by burning them to generate electricity for electrolysis of water). It is definitely more efficient to generate electricity from a fossil fuel, transport it via wires, and use it to charge up a battery-electric vehicle than it is to burn the same fossil fuel in an internal-combustion engine aboard a conventional vehicle; however, it is uncertain whether it is more or less efficient to use that fossil fuel to generate hydrogen for use in a vehicle. If the hydrogen is produced at a central plant, there are inefficiencies associated with generating it, transporting it via truck or pipeline, and storing it aboard the vehicle as a compressed gas or cryogenic liquid; if it is generated at the point of sale by electrolysis, you can replace the inefficiency of trucking or piping the hydrogen with the efficient utility-line transportation of electricity, but you still have the other losses, and you add the fact that a smaller-scale hydrogen generator will be less efficient than a large-scale one. The jury is still out on whether it is more energy-efficient to use fossil fuels to make hydrogen than it is to burn them in a hybrid-electric vehicle, though on balance it looks likely that use of hydrogen will cut down on ordinary combustion-engine pollutants like carbon monoxide, soot, and oxides of nitrogen. Stay tuned...

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