A hydrogen vehicle is a vehicle that uses hydrogen as its on-board fuel for motive power. The term may refer to a personal transportation vehicle, such as an automobile, or any other vehicle that uses hydrogen in a similar fashion, such as an aircraft. The power plants of such vehicles convert the chemical energy of hydrogen to mechanical energy (torque) in one of two methods: combustion, or electrochemical conversion in a fuel-cell:
- In combustion, the hydrogen is burned in engines in fundamentally the same method as traditional gasoline cars.
- In fuel-cell conversion, the hydrogen is reacted with oxygen to produce water and electricity, the latter of which is used to power an electric traction motor.
The molecular hydrogen needed as an on-board fuel for hydrogen vehicles can be obtained through many thermochemical methods utilizing natural gas, coal (by a process known as coal gasification), liquefied petroleum gas, biomass (biomass gasification), by a process called thermolysis, or as a microbial waste product called biohydrogen or Biological hydrogen production. Hydrogen can also be produced from water by electrolysis. If the electricity used for the electrolysis is produced using renewable energy, the production of the hydrogen would (in principle) result in no net carbon dioxide emissions. On-board decomposition to produce hydrogen can occur when a catalyst is used.
Hydrogen is an energy carrier, not an energy source, so the energy the car uses would ultimately need to be provided by a conventional power plant. A suggested benefit of large-scale deployment of hydrogen vehicles is that it could lead to decreased emissions of greenhouse gases and ozone precursors.[1] Further, the conversion of fossil fuels would be moved from the vehicle, as in today's automobiles, to centralized power plants in which the byproducts of combustion or gasification can be better controlled than at the tailpipe. However, there are both technical and economic challenges to implementing wide-scale use of hydrogen vehicles, as well as better and less expensive alternatives. The timeframe in which challenges may be overcome is likely to be at least several decades, and hydrogen vehicles may never become broadly availableAdvantages of the hydrogen economy
In the previous section we saw the significant, worldwide problems created by fossil fuels. The hydrogen economy promises to eliminate all of the problems that the fossil fuel economy creates. Therefore, the advantages of the hydrogen economy include:- The elimination of pollution caused by fossil fuels - When hydrogen is used in a fuel cell to create power, it is a completely clean technology. The only byproduct is water. There are also no environmental dangers like oil spills to worry about with hydrogen.
- The elimination of greenhouse gases - If the hydrogen comes from the electrolysis of water, then hydrogen adds no greenhouse gases to the environment. There is a perfect cycle -- electrolysis produces hydrogen from water, and the hydrogen recombines with oxygen to create water and power in a fuel cell.
- The elimination of economic dependence - The elimination of oil means no dependence on the Middle East and its oil reserves.
- Distributed production - Hydrogen can be produced anywhere that you have electricity and water. People can even produce it in their homes with relatively simple technology.
As politicians and the public leap aboard the hydrogen fuel bandwagon, a University of California, Berkeley, energy expert suggests we all step back and take a critical look at the technology and consider simpler, cheaper options.
In a paper appearing in the July 18 issue of Science magazine, Alex Farrell, assistant professor of energy and resources at UC Berkeley, and David Keith, associate professor of engineering and public policy at Carnegie Mellon University, present various short- and long-term strategies that they say would achieve the same results as switching from gasoline-powered vehicles to hydrogen cars.
"Hydrogen cars are a poor short-term strategy, and it's not even clear that they are a good idea in the long term," said Farrell. "Because the prospects for hydrogen cars are so uncertain, we need to think carefully before we invest all this money and all this public effort in one area."
Farrell and Keith compared the costs of developing fuel cell vehicles to the costs of other strategies for achieving the same environmental and economic goals.
"There are three reasons you might think hydrogen would be a good thing to use as a transportation fuel - it can reduce air pollution, slow global climate change and reduce dependence on oil imports - but for each one there is something else you could do that would probably work better, work faster and be cheaper," Farrell said.
President George W. Bush has proposed a federally funded, five-year, $1.7 billion FreedomCAR and Fuel Initiative to develop hydrogen-powered fuel cells, a hydrogen infrastructure and advanced automotive technologies. Several announced candidates for president have also proposed major research efforts to develop hydrogen-fueled vehicles and technologies to produce, transport and store the hydrogen, while many scientists have praised the initiative.
For many people, the attraction of hydrogen is that it produces no pollution or greenhouse gases at the tailpipe. For others, the attraction is that hydrogen is a research program, not a regulation, and that some hydrogen-related research will also help develop better gasoline-powered cars.
One problem, said Farrell, an expert on energy and environment issues, is that this glosses over the issue of where the hydrogen comes from. Current methods of producing hydrogen from oil and coal produce substantial carbon dioxide. Unless and until this carbon can be captured and stored, renewable (wind or solar) and nuclear power, with their attendant problems of supply and waste, are the only means of producing hydrogen without also producing greenhouse gases.
In addition, Farrell points out that setting up a completely new infrastructure to distribute hydrogen would cost at least $5,000 per vehicle. Transporting, storing and distributing a gaseous fuel as opposed to a liquid raises many new problems.
More billions of dollars will be needed to develop hydrogen fuel cells that can match the performance of today's gasoline engines, he said.
The benefits might be worth the costs of fuel-cell development and creating a new infrastructure, however, if air pollution, greenhouse gases and imported petroleum could not be reduced in other ways. But they can, said Farrell.
Improvements to current cars and current environmental rules are more than 100 times cheaper than hydrogen cars at reducing air pollution. And for several decades, the most cost-effective method to reduce oil imports and CO2 emissions from cars will be to increase fuel efficiency, the two scientists found.
"You could get a significant reduction in petroleum consumption pretty inexpensively by raising the fuel economy standard or raising fuel prices, or both, which is probably the cheapest strategy," Farrell said. "This would actually have no net cost or possibly even a negative cost - buying less fuel would save more money than the price of the high-efficiency cars. The vehicles would still be large enough for Americans and they would still be safe."
Technologies are now on the shelf to achieve better fuel efficiency, he said. All that's lacking are economic incentives to encourage auto makers to make and drivers to buy fuel-efficient cars.
"Automobile manufacturers don't need to invest in anything fancy - a wide number of technologies are already on the shelf," he said, quoting, among other studies, a 2002 report by the National Academy of Sciences. "The cost would be trivial compared to the changes needed to go to a hydrogen car."
Petroleum substitutes like ethanol that can be used in today's vehicles also are a possible way to reduce oil imports, the researchers say, but more research is needed to reduce the environmental impact and cost of these options.
If one goal is to reduce greenhouse gases, it would be cheaper, Farrell and Keith argue, to focus on reducing carbon dioxide emissions from electric power plants than to focus solely on hydrogen-powered vehicles. But if passenger cars are targeted, fuel economy is still the key.
If it becomes necessary to introduce hydrogen into the transportation sector, the scientists say, a better alternative is to develop hydrogen-powered fuel cells for vehicles such as ships, trains and large trucks instead of cars. Because these heavy freight vehicles have higher emissions, this strategy could provide greater air quality benefits. On-board hydrogen storage would be less of a problem also, and it would require a smaller fuel distribution network.
Farrell and Keith provide figures that support their arguments and conclude that more research needs to be done before committing ourselves to a hydrogen economy, which might begin to make sense 25 years down the road.
"Hydrogen cars are an attractive vision that demands serious investigation, but it's not a sure thing," they wrote.
Farrell speculates that hydrogen has become attractive to people across the political spectrum in part because it doesn't challenge drivers to change their habits. It also doesn't challenge the auto industry to change its behavior, providing, instead, a subsidy for research that will lead to better cars whether they are hydrogen-powered or gasoline-powered.
Adapted from materials provided by University Of California - Berkeley.
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