Challenges - Research and Innovative Technology Administration ...

Storage technologies under development include high-pressure tanks with gaseous hydrogen compressed
at up to 10,000 pounds per square inch, cryogenic liquid hydrogen cooled to -423°F (-253°C) in
insulated tanks, and chemical bonding of hydrogen with another material (such as metal hydrides).
DOE and DOT are funding research to explore fuel cell bus operations in 14 cities and some of these
conveyances will be fueled with hydrogen. They also are studying how innovative composites can permit
higher rates of hydrogen storage. The goal is to identify materials that increase the amount of hydrogen a
tank holds and facilitate its flow during refueling.
The infrastructure requirements for different vehicle onboard storage designs differ. If the preferred vehicle
design is for liquefied hydrogen, this presents a significant challenge for the design of the infrastructure.
Gaseous hydrogen has to be cooled, compressed, and stored before delivery to the vehicle at yet to
be defined locations conditions and locations. An all-liquefied hydrogen supply chain would be difficult and
is probably infeasible. Safety and cost considerations will probably argue for liquefaction relatively close
to the point of sale, but probably not at the service station (though this is possible). However, a liquefied
hydrogen service station is a much more elaborate facility than a gaseous hydrogen station, and may
present somewhat different safety and siting considerations.
Raising storage pressures to 10,000 psi would likely increase the attractiveness of hydrogen vehicles.
However, 10,000 psi storage raises design questions for service stations and local distribution. The
fundamental question is whether service stations locally compress hydrogen to 10,000 psi for delivery to
vehicles, or whether some portion of the supply chain (delivery trucks, for example) ought to operate at
higher pressures as well.
As in other cases, the challenge for infrastructure planners is to design an infrastructure when key parameters
remain uncertain.
Figure 2.6: Relative Volume Needed for Hydrogen Storage to Achieve a Range of More
Than 300 Miles
Source: U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Hydrogen Learning Demonstration.
According to DOE, its Hydrogen Learning Demonstration has collected data on refueling rates, which has
shown that, on the average, at 350 bar pressure, the refueling rate is 0.81 kg/min (with over 25% at a rate
of more than 1 kg/min). At 700 bar pressure, the average refueling rate is 0.59 kg/min (with only 3% over
1 kg/min).
18 Challenges of Building a Hydrogen Infrastructure