Hydrogen - Energy Policy Analysis: A Conceptual Framework - page 194

that can achieve similar performance, at a similar cost, to gasoline fuel storage systems (USDOE
2011b). Although automakers have recently demonstrated progress with some prototype vehicles
traveling more than 300 miles on a single fill, this driving range must be achievable across different
vehicle models and without compromising space, performance, or cost.
Compressed Gas and Liquid Hydrogen Tanks
Traditional compressed hydrogen gas tanks are much larger and heavier than what is needed for
light-duty vehicles. Light-weight, safe, composite materials are needed that can reduce the weight
and volume of compressed gas storage systems. Liquefied hydrogen is denser than gaseous hy-
drogen and thus contains more energy in a given volume. Similar sized liquid hydrogen tanks can
store more hydrogen than compressed gas tanks, but it requires about 30 to 40 percent of the energy
content of the hydrogen to liquefy it (Armaroli and Balzani 2011, 288). Tank insulation required to
prevent hydrogen loss adds to the weight, volume, and costs of liquid hydrogen tanks. A hybrid tank
concept is being evaluated that can store high-pressure hydrogen gas under cryogenic conditions
(cooled to -120 to -196°C); these “cryo-compressed” tanks may allow relatively lighter weight
and more compact storage (USDOE 2011b). Gasoline tanks used in cars and trucks today may be
shaped to take maximum advantage of available vehicle space. Compressed hydrogen tanks have
to be cylindrical to ensure their integrity under high pressure (Armaroli and Balzani 2011, 288).
High-pressure hydrogen tanks that may be shaped to available space are being evaluated as an
alternative to cylindrical tanks, which do not package well in a vehicle (USDOE 2011b).
Materials-Based Storage
Hydrogen atoms or molecules bound tightly with other elements in a compound, or potential storage
material, may make it possible to store larger quantities of hydrogen in smaller volumes. Several
different kinds of materials are under investigation, including metal hydrides, adsorbent materi-
als, and chemical hydrides, in addition to identifying new materials with potential for favorable
hydrogen storage attributes. Hydrogen storage in materials offers great promise, but additional
research is required to better understand the mechanism of hydrogen storage in materials under
practical operating conditions and to overcome critical challenges related to capacity, the uptake
and release of hydrogen, management of heat during refueling, cost, and life cycle impacts (US-
DOE 2011b). In 2004 the U.S. Department of Energy stopped funding research and development
for onboard reforming of conventional fuels into hydrogen, shifting attention toward improved
onboard storage of hydrogen as a compressed gas, a liquid, or in other materials (Wald 2009;
Ekins, Hawkins, and Hughes 2010, 29-30).
Transportation
Most of the hydrogen used in the United States today is produced at or near where it is used—
typically at large industrial sites. As a result, an efficient means of transporting large quantities
of hydrogen fuel over long distances and at low cost does not yet exist. Before hydrogen can be-
come a mainstream energy source, the infrastructure (i.e., miles of transmission and distribution
pipelines, bulk storage vessels, and refueling stations) must be built.
Suppliers currently transport hydrogen by pipeline or over roadways using tube trailers or
cryogenic liquid hydrogen tankers. In some cases, liquefied hydrogen is transported by barge.
Hydrogen can also be moved by barge or truck using chemical carriers, which are substances