You don’t hear so much about the ‘hydrogen economy’ anymore. But hydrogen fuel cells remain the closest we are likely to get to zero-emissions transportation.
 | Zero Emissions Motoring?A General Motors fuel-cell vehicle is refueled with hydrogen in California (Photo: Reuters) |
Hydrogen fuel cells have long promised to be the ultimate in environmentally friendly propulsion, potentially offering zero-emissions motoring. The fuel cells work by combining stored hydrogen with oxygen in the air to generate electricity that can drive a vehicle engine. A hydrogen car’s only emission is water vapour. Hydrogen is readily available everywhere, in natural gas or in water, and fuel cells are highly energy-efficient.
Whether the car is totally emissions-free, however, depends on the source of the energy used to produce the hydrogen in the first place. One way to produce hydrogen is to make it from natural gas through a process called “steam reforming,” either at hydrogen filling stations or large biomass or coal plants from which the hydrogen would be distributed by truck or pipeline.
According to the U.S. National Renewable Energy Laboratory, producing a kilogram of hydrogen by steam reformation generates emissions equivalent to 11.9 kilograms of carbon dioxide. Two existing hydrogen fuel cell prototypes, General Motors’ Chevy Equinox and Honda’s FCX Clarity, can travel 63 kilometers and 109 kilometers on a kilogram of hydrogen, respectively. Powering these cars using hydrogen produced by steam reformation would actually create more CO2 emissions per kilometer than the gasoline-electric powered Toyota Prius hybrid and many small conventional cars.
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However, this does not take into account the emissions generated by the production and distribution of the gasoline used by conventional cars. The UN Intergovernmental Panel on Climate Change (IPCC) calculates that if hydrogen is produced from natural gas at 60 percent efficiency, total “well-to-wheel” CO2 emissions could be reduced by 50 to 60 percent compared to current gasoline vehicles. And if the CO2 produced by steam reformation were to be sequestered, the numbers would be even more promising.
An even greener alternative is using renewable electricity to extract hydrogen from water via electrolysis. Using solar, wind, or nuclear energy to produce hydrogen, the IPCC says, has the potential to be truly zero emissions.
Hydrogen faces similar distribution and storage problems as electricity for vehicles. Storing hydrogen is a challenge as compressed hydrogen tanks are not yet suitable for mass-produced vehicles. Meanwhile, despite billions of dollars in subsidies from governments worldwide, only a few dozen hydrogen filling stations exist in Europe and America.
Hydrogen-powered public buses have been tested in ten cities in Europe, China and Australia under the European Commission-backed HyFLEET:CUTE project, and London for one has promised to introduce some hydrogen buses by 2010. However, mass production of hydrogen buses is not expected until at least 2012.
This year, GM and Honda are road-testing Equinox and Clarity cars with a few selected drivers. Honda hopes to get around the distribution problem with its Home Energy Station, which drivers can use to make hydrogen at home by tapping into the domestic natural-gas supply. However, fuel cells remain too expensive for mass production, and some companies, like energy giant BP, have switched their focus from hydrogen to electricity and biofuels.
editor: James Tulloch
publication date: September 29, 2008
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