Hydrogen as the Hope?
Never let facts get in the way of a good theory!
Many people advocate hydrogen as a transport fuel but they have not done their homework. The basic science of hydrogen as a fuel do not add up. Hydrogen has more energy per unit mass than other fuels. The problem with hydrogen is that it is much less dense than other fuels. For a given volume of liquid hydrogen, it has only 27.6% of the energy in the same volume of gasoline. The Space Shuttle used hydrogen as a fuel, because its mass is low, and the fuel was carried in an external fuel tank that was jettisoned during lift-off. Automobiles can not have external fuel tanks that are discarded. Compressed gaseous hydrogen is even less dense than liquid hydrogen. At 5,000 psi of pressure gaseous hydrogen only has a density of 0.25 pounds per gallon or one twenty fourth the density of gasoline. Gasoline and diesel are far superior fuels to hydrogen in this regard.
Finally hydrogen is not the clean green fuel that it is promoted as. Being the smallest molecule there is, it leaks very easily and the free hydrogen reacts with ozone producing water.
3H2 + O3 ® 3H2O
Widespread hydrogen use has been enthusiastically embraced by major corporations and environmentalists alike as a panacea for global warming and the depletion of fossil fuels. But skeptics, and even some hydrogen advocates, say that use of hydrogen could instead make the air dirtier and the globe warmer.
The 2004 BP report shows that at current rates of production,
the world's proved reserves of oil are sufficient to last for 40 years, although
nearly 77 percent of those reserves are located in OPEC countries. The
reserves of natural gas are sufficient to last for 67 years at current rates of
production, with the largest reserves in the countries of the former Soviet
Union. Proven reserves of coal are sufficient to last 192 years at current
production rates, with most reserves in North America, the Asia Pacific region,
and Europe and Eurasia. So with these dwindling supplies people are
looking for alternatives.
Use of hydrogen fuel cells could certainly help eliminate tailpipe pollution and dependence on foreign oil. But hydrogen is only a way to store energy. Where the energy comes from in the first place is where one of the problems start.
The most ambitious use of hydrogen is in a car powered by a fuel cell, a device like a battery that turns hydrogen into electricity while emitting only heat and water vapor. Hydrogen can also be burned directly in engines much like those that run on gasoline, but the US Energy Department's goal is fuel cells because they get twice as much work out of a pound of hydrogen.
Intense research is now going on at major companies and universities in North America on the development of a practical fuel cell. Success could have a profound effect on the 200 million motor vehicles in use in the United States, making the streets cleaner and quieter, with hydrogen-powered electric motors. The transition to hydrogen could also wean the country away from gasoline and diesel fuel.
The main source for hydrogen today is natural gas, which is in short supply, is cumbersome to convert, and may have better uses. Waiting in the wings is coal, burned in old power plants around the US that are already the focus of a national dispute over their emissions. Coal is cheap and abundant, and produced by major companies that are eager to continue mining and using it. But it is a leading source of carbon dioxide, an important global warming gas, and pollutants that cause more immediate problems, like smog and acid rain.
The long-term hope is to make hydrogen from emission-free "renewable" technologies, like windmills or solar cells. In fact, hydrogen may be an essential step to translate the energy of wind or sunlight into power to turn a car's wheels, experts say. But electricity from renewable technologies is so costly that even companies based on these technologies see problems.
"Hydrogen," the US Department of Energy said in November, 2002, "is the 'man on the moon' equivalent for this generation." In fact, the latter analogy might prove apt, with hydrogen fuel cells resembling the Apollo rockets, as an impressive technology that was made workable and repeatedly demonstrated, but not capable of making major inroads into general use. For now, fuel cells are about 100 times as expensive, per unit of power, as internal combustion engines.
If you look at the image on the left of the space scuttle you
will notice that the hydrogen tank is a huge disposable item. This
is one of the niches that hydrogen is used for. When you consider the
total mass of hydrogen as an energy source it is the best option as a fuel, that
is if you have to lift it, but cars can't carry disposable tanks.
A likely source of hydrogen is from a machine called an electrolyzer, which is like a fuel cell in reverse. The difference is that a fuel cell combines oxygen from the air with hydrogen to produce an electric current, and water as a byproduct; an electrolyzer runs an electric current through water, to split the water molecule into its constituent hydrogen and oxygen atoms. The problem is that if the electricity came off the power grid to run an electrolyzer for the production of hydrogen, about half of it, on people are stunned when told that the weekly cost of charging an electric car would be equivalent to their monthly electricity bill.
Another problem is carbon dioxide, a greenhouse gas. According to the Energy Department, an ordinary gasoline-powered car emits 374 grams of carbon dioxide per mile it is driven, counting the energy used to make the gasoline and deliver it to the service station, and the emissions of the vehicle itself. The same car powered by a fuel cell would emit nothing, but if the energy required to make the hydrogen came from the electric grid, the emissions would be 436 grams per mile, 17 percent worse than the figure for gasoline.
Hydrogen is commonly manufactured today at refineries and chemical plants, by mixing natural gas and steam. Natural gas is made of hydrogen and carbon atoms; steam is made of hydrogen and oxygen atoms. The reaction, called steam reforming, produces hydrogen and carbon dioxide. This reaction is similar to the old method of making coal gas:
heated coal + water ® hydrogen + carbon monoxide
According to the energy department, if fuel cells in cars
used hydrogen from steam reforming of natural gas, cars
would emit 145 grams of global warming gases per mile. That
is a drastic improvement over the 436 grams emitted by the
production of hydrogen using grid electricity, and a major
improvement over gasoline's 374 grams, but experts say it
may not be a particularly good use of natural gas.
One reason is that if the engineers had simply replaced the
gasoline with the natural gas, skipping the hydrogen fuel
cell step in between, the total carbon dioxide emissions
per mile would fall to 310 grams, according to the Energy
Department. No new technology is required for that step;
buses burning natural gas in internal combustion engines
are common today.
There is a second option that involves hardly any new technology, hybridization. In a hybrid, a fossil-fueled internal combustion engine can turn the wheels or a generator that is used to charge batteries, and the batteries run an electric motor to drive the wheels. The Toyota Prius and the Honda Insight use that system. Hybridization improves the fuel economy of the Honda Civic by 43 percent, according to the company. So replacing a gasoline car with a hybrid electric fueled by natural gas would cut the grams of global warming gases to about 177 a mile.
That still leaves the fuel cell that runs on hydrogen from natural gas with an advantage over the typical hybrid of about a fifth, or a further reduction of about 32 grams of global warming gases per mile. But the fuel cell bus is many times more expensive than an ordinary or hybrid bus, and the fuel costs several times as much as diesel. And the natural gas hybrid solution is available almost immediately; it would be many years before fuel cell buses made a substantial debut.
Supporters of fuel cell cars say that hydrogen can be made from almost anything, including hydropower, new nuclear reactors, and technologies barely dreamed of, like microbes that will produce hydrogen from waste materials, and that this justifies the research even if early batches of hydrogen come from coal. But is this still reaching for the Moon?
Adopted from an article in the New York Times November 12, 2003
An objective look at hydrogen as a fuel can be found on this web page.
Justice Oliver Wendell Holmes said, "we need education in the obvious more than investigation of the obscure."
Lindsay Leveen has written an excellent book on Hydrogen usage that he has published.
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