Hydrogen storage and refueling is less of an issue for transit buses than for light-duty vehicles, as buses are primarily refueled centrally at the transit depots.

While fuel cell buses to date have used a varying hydrogen storage methods and fuel sources -- including compressed hydrogen, liquid hydrogen, and onboard methanol reformation -- there seems to be a trend towards off-board reformation. While on-board reformation has been demonstrated to work, off-board reformation reduces the complexity of the vehicle systems and has lower temperatures, which are important for vehicle crash safety testing.

Some questions still remain, however. One key question is whether a transit agency would want to generate the hydrogen on site at the refueling facility, or have the hydrogen shipped to the site. If the hydrogen is generated on site, there is also a question of the fuel source. The following is an overview of the two possible methods of supplying the hydrogen to the refueling site.

Hydrogen reformation at centralized locations

One option for the fuel cell bus market is to reform hydrogen at centralized reformation facilities and ship the hydrogen to the refueling site. The hydrogen would be shipped to the local refueling site either in gaseous form via pipelines or as liquid hydrogen in tanker trucks.

Pipeline distribution: As of 1995, there were approximately 450 miles of hydrogen pipelines, mostly located in industrialized areas of Texas, Louisiana and New Jersey. It may be possible to utilize natural gas pipelines during the initial stages of hydrogen infrastructure development; however hydrogenÕs lower energy density would require higher pressure pumps and compressors. Hydrogen also causes metal embrittlement in conventional pipes, which would need to be addressed before converting a natural gas infrastructure.

Tanker truck distribution: Long distance transport of hydrogen is conducted via tanker truck, typically in liquid form, since LH2 tanks carry more energy per volume than compressed hydrogen gas. This option requires an inner and outer tank with an empty space in between them as an added safety protection for the hydrogen stored in the inner tank. This approach of distributing has high maintenance costs. The U.S. has an annual LH2 production capacity of 90,000 tons, which is transported by approximately 20,000 LH2 tanker truck loads each year. The liquefaction process requires large economies-of-scale to be cost-effective, however.

Centralized reformation can offer the advantage of improved economies-of-scale, which could potentially reduce the cost of the hydrogen reformation. In addition, a large reforming plant would be better able to have advanced environmental controls which would ensure that the hydrogen generation process is as low-emission as possible.

The Chicago Transit fuel cell program used liquid hydrogen delivered via truck from a large industrial plant 300 miles away to a LH2 storage tank at the station. During refueling, the hydrogen was pumped out and pressurized into compressed hydrogen gas stored on the fuel cell bus' roof. As part of their fuel cell bus demonstration program, the Sunline Transit Agency is trying several hydrogen supply options, including having liquid hydrogen shipped to their refueling site in Thousand Palms, California. They intend to review the benefits of this option compared to generating hydrogen on site (see below).