A Pollution-Free Hydrogen Economy? Not So Soon
Electric cars powered by hydrogen fuel cells don’t produce greenhouse-enhancing carbon dioxide.
But producing hydrogen does—and if we want to reduce our petroleum dependence,
we’re going to have to reconcile ourselves to that fact.
Richard A. Muller
Technology Review Online
Technology for Presidents
July 11, 2003
Think hydrogen—the clean fuel of the future. It burns with oxygen to make water vapor, and only water vapor—no soot, no nitrous oxides, no carbon dioxide with its potential greenhouse warming. In his State of the Union message in January, President Bush announced a major new initiative. He proposed $1.2 billion in research funding that he said would enable the United States to “lead the world in developing clean, hydrogen-powered automobiles.” Spurred by this new federal support, Bush said, “our scientists and engineers will overcome obstacles to taking these cars from laboratory to showroom, so that the first car driven by a child born today could be powered by hydrogen, and pollution-free.” His surprise announcement met with enthusiastic applause.
Now here is a more pessimistic view of the hydrogen economy: huge open pit
mines scarring much of Pennsylvania, Illinois, Utah, and Colorado. Billions
of carbon dioxide are dumped into the atmosphere every year from facilities
that produce hydrogen—by burning the fossil fuels coal, oil, and natural
Where is the truth? Undoubtedly somewhere in between—but it probably involves heavy burning of fossil fuels.
The key fact is this: hydrogen is not a source of energy. It is only a way
of storing and transporting it. Although hydrogen is the most abundant element
the Universe (and in the more immediate neighborhood, it makes up 90 percent
of the atoms in the Sun and Jupiter), there is virtually no hydrogen gas on
Earth. Our gravity is so weak that essentially all our primordial hydrogen—except
that which bound itself into heavier compounds—escaped into space billions
of years ago. So hydrogen fuel must be “manufactured” by extracting
it from water and methane. You get out from hydrogen fuel only the energy you
put into extraction, or from burning carbon in the process.
Water can be split into hydrogen and oxygen by electric current, the process known as electrolysis. Plain heat will do the trick too. Above 2,700 C water spontaneously decomposes. On a sufficiently hot fire (e.g., the oil well fires of Kuwait), water decomposes and then recombines when it cools above the well.
But splitting water is expensive, and we don’t need the oxygen. There’s
a much cheaper way to produce hydrogen: spray steam on white-hot coals and out
comes mostly hydrogen gas (40 percent) and carbon monoxide (50 percent), a mixture
known appropriately as “water gas.” It’s the least expensive
way to make hydrogen. Unfortunately, the carbon monoxide produced along with
it is highly poisonous. To extract the last bit of energy, the carbon monoxide
can be burned, and that turns it into the greenhouse gas carbon dioxide.
The production of water gas began in earnest in the 1870s. The other common “manufactured” gas back then was coal gas, extracted from bituminous coal by heating it in an oxygen-free environment. Coal gas went to streetlamps and homes, and the more dangerous water gas was used by industry. Water gas is still extensively in steel manufacture and in the so-called Fisher-Tropsch process, which is used to make synthetic gasoline and alcohols.
In the 1920s, the discovery of large underground reserves of methane provided a cheaper alternative to coal gas. Since it wasn’t manufactured, it was called “natural gas,” the name still used today. Methane also replaced coal for water gas production. As with coal, producing hydrogen from methane yields abundant carbon monoxide that upon combustion becomes carbon dioxide. But the news isn’t all bad. For the same energy delivered, producing hydrogen from methane dumps about half as much carbon dioxide into the atmosphere as burning fossil fuels does. That’s largely because hydrogen-based fuel cells are more efficient than internal combustion engines. In addition, serious research programs are underway to find a way to sequester carbon dioxide, whether it comes from hydrogen production or any other process that burns fossil fuels. One cheap solution could be to bury it in depleted gas and oil wells. My pessimistic bet, though, is that sequestering will be expensive. Politicians will choose to dump carbon dioxide into the atmosphere, and pay the hidden price of pollution, rather than ask the public to pay an up-front price at the pump.
Still, hydrogen is far from an ideal automobile fuel. Even in its densest form (liquid), hydrogen has only one-third as much energy per liter as gasoline. If stored as compressed gas at 300 atmospheres (a more practical option), it delivers less than one-fifth the energy per volume as gasoline. Such low energy density means that fuel storage would take up lots of room in a hydrogen-powered car—or, alternatively, a modest-sized fuel tank would severely restrict the vehicle's range between fill-ups. Technology being developed to allow higher pressures would make hydrogen cars more attractive.
The known U.S. reserves of natural gas will be gone in a few decades, or sooner if we start using it for automobiles. The key assumption behind the push for a hydrogen economy appears to be the belief that there exist vast, undiscovered reserves of natural gas in the United States and around the world. But even if that belief proves wrong, we can always go back to making hydrogen from coal; we have enough of that for a century, if we don’t mind open pit mines.
I believe that the hydrogen economy is inevitable. Apparently so do big investors, who are setting up port facilities for future importation of large quantities of liquefied natural gas.
I also believe that the hydrogen will be made by whatever method is cheapest.
In the short run, we could revert to electrolysis, powered by electricity from
nuclear plants. Right now nuclear energy is expensive, largely, I believe, because
of regulations driven by the perceived risk of radioactivity. Yet I think that
carbon dioxide in the atmosphere offers a much greater long-term threat to the
environment and to health than do nuclear power plants. We experienced the dangers
of nuclear power in Chernobyl. For the carbon-based economy, the equivalent of
Chernobyl is not just global warming; it is war. We saw that in Iraq. So on balance,
I prefer nuclear-produced to methane-produced hydrogen.
When solar-generated electricity becomes cheaper than natural gas or coal, we can leave the fossil fuels in the ground, and have the best of all worlds. Cheap solar is inevitable, and we will not have to plaster the state of California with solar cells to enjoy its benefits. In a square kilometer of sunlight there is are 1,000 megawatts of solar power—the equivalent of a large nuclear power plant. Even if only 10 or 20 percent of the sunlight’s energy is extracted as electricity, the area of the solar cells will not be much larger than what we currently devote to nuclear, gas, or coal plants. Energy can be stored at night (and during cloudy days) in hydrogen. The solar future is coming.
Creating a hydrogen economy is good goal. But in the near term, barring a
nuclear-power revival, the transition to hydrogen will probably mean a growing
on imported natural gas, and the continued pollution of the atmosphere with
dioxide. Despite President Bush’s optimism, the first cars of today’s
children are highly unlikely to be powered by hydrogen that was cleanly produced.
But maybe the cars of their children will be. And in the long term, our switch
to hydrogen could ease the transition to a solar-powered economy.
Richard A. Muller, a 1982 MacArthur Fellow, is a physics professor at the University of California, Berkeley, where he teaches a course called “Physics for Future Presidents.” Since 1972, he has been a Jason consultant on U.S. national security.