July 1, 2005 |
"Switching from a fossil-fuel economy to a hydrogen economy would be
subject to technological hurdles, the difficulty of creating a new energy
infrastructure, and considerable conversion costs but could provide health,
environmental, climate and economic benefits and reduce the reliance on
diminishing oil supplies."
- Stanford authors
Stanford, California [RenewableEnergyAccess.com] What if all the vehicles now on the road in the United States were suddenly powered by hydrogen fuel cells? Stanford researchers say in a June 24 article in the journal Science that such a conversion would improve air quality, health and climate -- especially if wind were used to generate the electricity needed to split water and make hydrogen in a non-polluting process.
Associate Professor Mark Z. Jacobson and postdoctoral fellow Whitney
Goldsborough Colella (both in the Civil and Environmental Engineering
Department) and Consulting Professor David M. Golden (Mechanical Engineering
Department) report that annually such a conversion could prevent millions of
cases of respiratory illness and tens of thousands of hospitalizations and save
more lives than were lost in the World Trade Center attacks.
"Converting all the current vehicles to fuel cell vehicles powered by wind
would save 3,000 to 6,000 lives in the United States annually, and it could be
done at a fuel cost that's comparable to the cost of gasoline, and less than the
cost of gasoline when you consider the health effects of gasoline," said
Jacobson, who has no financial interest in any wind or hydrogen endeavor but
whose commitment to clean air is manifest in his choice of car (a Toyota Prius),
house (it's solar-powered) and career (atmospheric scientist).
Sponsored by the Global Climate and Energy Project at Stanford and by NASA, the
Science study compared emissions that would be produced in five cases-if all
vehicles on the road were powered by 1) conventional internal-combustion
engines, 2) a combination of electricity and internal combustion of gasoline, as
in hybrid vehicles, 3) hydrogen generated from wind electrolysis, 4) hydrogen
generated from natural gas and 5) hydrogen generated from coal gasification.
Wind is the most promising means of generating hydrogen, said Jacobson, who with
former postdoctoral fellow Cristina Archer recently published a study that
mapped global winds and showed the world, especially the United States, has more
than enough wind to meet all its energy needs. Jacobson envisions wind turbines
generating electricity on wind farms that are linked in a network to ensure
energy production even when parts of the grid have windless days. The
electricity would travel through transmission lines to a filling station-similar
to today's gas stations. There, it would enter an electrolyzer, passing through
water and splitting it into oxygen, which would be released into the air, and
hydrogen, which would get compressed and stored.
A lot of hydrogen is currently produced by another method Jacobson's group
analyzed: steam reforming of natural gas. If you take methane, the main
component of natural gas, and expose it to steam, the final products are
primarily carbon dioxide and hydrogen. While the production of carbon dioxide, a
greenhouse gas, is undesirable, the process produces about 55 percent less
carbon dioxide than does internal combustion, Jacobson said. Other pollutants
result as well, such as oxides of nitrogen and carbon monoxide, but these are
still far lower than emissions from gasoline combustion. Steam reformers could
be placed at individual filling stations, and methane could be piped in through
existing natural gas lines. But natural gas supplies are limited and subject to
price fluctuations that hurt the long-term feasibility of this option.
The third hydrogen production method the researchers analyzed is coal
gasification, in which hydrogen could be produced at centralized plants,
compressed and most likely transported in trucks. Coal is mostly carbon, but
also contains hydrogen and sulfur. Exposed to water at high temperature and high
pressure, it chemically reacts to yield carbon monoxide and hydrogen. Oxygen
from additional water vapor turns carbon monoxide into carbon dioxide. So the
end products are primarily carbon dioxide and hydrogen gas. Since coal contains
more carbon per unit energy than does natural gas, making a given amount of
hydrogen from coal produces a lot more carbon dioxide than does making it from
natural gas.
Hybrid vehicles were better at reducing carbon dioxide than vehicles using
hydrogen from coal gasification, Jacobson said. But health costs were lower with
coal gasification compared with hybrids, which produce more pollutants since
they employ a combustion process.
A hydrogen economy
"Switching from a fossil-fuel economy to a hydrogen economy would be
subject to technological hurdles, the difficulty of creating a new energy
infrastructure, and considerable conversion costs but could provide health,
environmental, climate and economic benefits and reduce the reliance on
diminishing oil supplies," the Stanford authors wrote.
While envisioning such a switch may seem like a purely academic exercise, it's
not. Such exercises inform policy -- albeit sometimes too late. Currently
congress is debating an energy bill that contains a $4,000 tax credit for diesel
vehicles-the same break hybrid vehicles get-because of their perceived higher
mileage compared to gasoline vehicles. But a study led by Jacobson and published
in 2004 by Geophysical Review Letters showed that converting the U.S. vehicle
fleet from gasoline to diesel vehicles-even with advanced emissions and particle
control technologies-would actually increase photochemical smog, particularly in
the Southeastern United States. The reason is that even advanced diesel vehicles
may emit more oxides of nitrogen than do gasoline-powered vehicles, and these
oxides spur ozone production. Jacobson believes such a tax break may provide an
unintentional incentive to damage people's health.
Computer simulations that model the effects of future vehicle fleets may help
society assess its best energy options. "Going down the hydrogen pathway is
a good thing overall and it's a practical thing, and it's going to be beneficial
in terms of air pollution and climate and health," Jacobson said.
The hydrogen economy is on the horizon. California already has several hydrogen
filling stations, and Gov. Arnold Schwarzenegger has proposed an ambitious
network of hydrogen filling stations by 2010. Most car manufacturers have
prototype hydrogen fuel cell vehicles. California even has a test fleet of
hydrogen buses.
While some are concerned about hydrogen's explosiveness, Jacobson said another
property of hydrogen-its lightness-may lessen this danger. He cited an example
of two cars-one conventional, one hydrogen-powered-that were hit from behind.
The car powered by an internal combustion engine became engulfed in flames when
its gas tank was punctured. But when the hydrogen car's fuel cell was punctured,
since hydrogen is 14 times lighter than air, the flames just shot straight up.
The car was saved.
Hydrogen's volatility, however, underscores the need to develop tight seals to
prevent leakage from storage tanks, filling stations and the fuel cells
themselves.
Because wind generation of hydrogen provided the best health and climate
benefits, the researchers did a cost analysis to compare the cost of a gallon of
gasoline with that of a gallon of hydrogen generated by wind electrolysis. The
cost of making hydrogen from wind is $1.12 to $3.20 per gallon of gasoline or
diesel equivalent ($3 to $7.40 per kilogram of molecular hydrogen)-on par with
the current price of gas. But gasoline has a hidden cost of 29 cents to $ 1.80
per gallon in societal costs such as reduced health, lost productivity,
hospitalization and death, as well as cleanup of polluted sites. So gasoline's
true cost in March 2005, for example, was $2.35 to $3.99 per gallon, which
exceeds the estimated mean cost of hydrogen from wind ($2.16 equivalent per
gallon of gasoline).
The Stanford study, unprecedented in its detail, used an inventory of more than
600,000 pollution sources reported by the U.S. Environmental Protection Agency
from August 1999. Colella altered the EPA emission inventory in response to each
of the different scenarios. Her work led to a separate paper as well, now in
press at the Journal of Power Sources. Golden contributed expertise in
atmospheric chemistry, and Jacobson plugged Colella's new emission scenarios
into his own computer model to run simulations and analyze the resulting costs
and effects.
"We believe the results are conservative since health costs associated
mostly with particles are now thought to be greater than those used in our
study," Jacobson said. "In addition, in the future we will have more
fossil [fuel] vehicles than we currently have. So the future health benefit of
switching will be greater than in our current study, which assumes an
instantaneous switch."
But no matter how many vehicles are on the road, fuel-cell vehicles using
hydrogen from wind are not going to produce any real pollution, he emphasized.
"Hybrids are a stepping stone, but they can't be the final destination
because even though they result in an improved efficiency over the current
vehicle fleet, their numbers will increase," Jacobson said. "Carbon
dioxide and other pollutant emissions associated with hybrids will increase as
well. So this is not a viable, long-term solution in the presence of a growing
population and the desire of many developing countries to industrialize."
Next the group plans to look at the effects of converting all power plants to
hydrogen fuel cell power plants. They also plan to explore the long-term effects
of switching to a hydrogen economy on global climate change and the ozone layer.
'Apollo Program'
Jacobson advocates an 'Apollo Program' for generating electricity from wind and
producing hydrogen using wind-generated electricity. Such a program would
involve fossil sources paying their true health and climate costs. For example,
some old coal-fired plants are exempt from modern performance standards required
by Clean Air Act amendments and therefore run inexpensively while saddling
society with huge hidden costs. An Apollo Program would provide additional
subsidies for wind and other renewable energy sources. While wind subsidies are
on the order of $100 million per year, Jacobson said, other energy sources hog
subsidies of $15 to $20 billion. He advocates supporting the infrastructure
needed for wind production of hydrogen to a level similar to the $20 billion
recently proposed for a new natural gas pipeline from the continental United
States to Alaska.
"If you want to encourage hydrogen and [wind-produced] hydrogen, then you
do need to undertake an Apollo Program because even though the cost of a new
wind turbine averaged over a long time is similar to a new coal or natural gas
power plant, there's no incentive to replace these other sources with
wind."
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