April 4, 2007 4:00 AM PDT
Studying the hydrogen energy chain
Researchers look at the entire energy chain (the energy equivalent of a food chain) when evaluating a potential alternative fuel. While cars powered by hydrogen are more efficient than those powered by gasoline, the leading production method for hydrogen fuel requires a lot of electricity. And if hydrogen fuel isn't produced efficiently by this method, it becomes less viable as a fuel source overall, according to Ken Kurani, an associate researcher at the Institute of Transportation Studies at the University of California at Davis.
To create a hydrogen-based transportation system that has a low overall carbon footprint, primary methods of producing hydrogen can't be based around coal-fired power plants, Kurani said. Such a process would require a system for capturing and safely storing carbon dioxide emitted by the burning coal--a process called carbon capture sequestration. "If you burn all this coal (to generate electricity to make the hydrogen) and have all this CO2, what are you going to do with it?" said Kurani.
In areas where such resources are abundant, solar and wind energy can efficiently produce the electricity needed for electrolysis, a step in hydrogen-fuel production that liberates hydrogen from water.
Chemical processes that produce hydrogen in a closed, looped system--where chemicals are not completely consumed or denatured--are being researched by the Department of Energy and many groups in the private and public sectors.
The DOE is also looking at tapping into nuclear facilities because they already produce waste heat that could be used to reduce the amount of electricity needed for electrolysis, according to Patrick Davis, acting program manager for hydrogen fuel cells and infrastructure technologies at the DOE.
Companies such as Ecotality are thinking of ways to generate hydrogen in a fuel-cell car as the vehicle's fuel cell needs it.
Ecotality's implementation of hydrogen-fuel technology features an apparatus called the Hydratus, which was developed by NASA's Jet Propulsion Laboratory. The Hydratus is built in to a vehicle and makes hydrogen for a fuel cell using a chemical reaction between magnesium and water to liberate the hydrogen. Drivers use a three-prong pump to fill up on magnesium pellets and water, and pump out spent magnesium oxide in powder form. The spent powder is 99.8 percent renewable and can be recycled (using electricity) right at the filling station.
While the Hydratus can be adapted for use in other settings--as a support system for fuel cells powering cell phone towers and computers, for example--its first integration will be with hydrogen buses for cities and towns, which could install their own magnesium filling stations to service their fleet. Ecotality is already in touch with several interested municipalities and expects to produce the first prototype bus by the end of 2007.
Making hydrogen available to consumers is another issue. While there are about 700 miles of hydrogen pipeline for a range of applications, mostly in the Gulf states and Southern California, there is currently no hydrogen infrastructure to support hydrogen filling stations, according to ITS' Davis.
In order to make hydrogen economically viable to transport, the gas can be stored in highly compressed form. It can also be stored in liquefied form. But compressed hydrogen or liquid hydrogen can be difficult to transport. Because hydrogen dissipates rapidly on contact with air, a tank leak, while it wouldn't lead to a flammable pool of liquid on the ground, would result in loss of product.
In addition to high-pressure cryogenic tanks, one solution being researched by DOE programs and private companies is hydrogen in a solid state, in the form of solid-state metal hydride or carbon-based materials.
Another factor affecting hydrogen's economic viability is the relatively short range of hydrogen-fueled cars. As it stands now, a hydrogen car can go no more than 200 miles between fuelings, using a tank whose fuel is stored at 5,000 pounds per square inch. Under 10,000 psi, according to Davis, enough hydrogen fuel could be stored on board a vehicle to go about 300 miles, but the technology for that type of storage capacity is still being researched.
And the technology is not cheap. The DOE estimates that hydrogen fuel cells cost about $107 per kilowatt, if the supplier produced the cells at a rate of 500,000 units per year. For the fuel to become economically viable for consumers, the cost per kilowatt would have to be $30, Davis said.
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