Page 285 - Alternative Energy Systems in Building Design

FUEL CELLS AS ALTERNATIVES TO INTERNAL COMBUSTION FUELS 259

Owing to their small size and perpetual agitation, hydrogen molecules tend to dif-
fuse through any liner material used in the construction of compartments, which may
lead to hydrogen embitterment and weakening of the container.

CHEMICAL HYDRIDE STORAGE
Instead of using it in a liquefied form, hydrogen can be stored as a chemical hydride
compound. In this type of process, hydrogen gas reacts with some other materials to
produce the hydrogen storage or energy-carrier material, which can be transported
relatively easily. At the point of use, the hydrogen storage material, under controlled
conditions, decomposes, yielding hydrogen gas. In addition to the mass and volume
density problems associated with molecular hydrogen storage, hydride storage schemes
also require high-pressure and high-temperature conditions, also known as external
energy. Another issue associated with the dehydration process is heat disposal and
management, which has not yet been mitigated.
At present, the common method of onboard-type hydrogen storage used in vehicles
is a compressed hydrogen gas maintained at a pressure of about 700 bars.
Present-day hydrogen fuel cells cost more by several orders of magnitude compared
with the per-kilowatt output of conventional internal combustion engines. In view of
the high cost associated with vehicular fuel cell technology, car manufacturers have
been experimenting with Li-ion and Li-polymer batteries for onboard energy storage,
which have proven to be more efficient and less expensive than hydrogen-fueled cars.

HYDROGEN FUEL EFFICIENCY FOR AUTOMOBILE USE
The economics of liquid hydrogen are definable in terms of energy that must be used
to produce 1 kg of fuel and losses associated with transport and delivery to filling sta-
tions. As discussed earlier, well-to-tank energy loss is about 40 percent, whereas by
comparison, regular gasoline requires less energy input per gallon at the refinery, and
comparatively little energy is required for transport and storage. Therefore, well-to-
tank gasoline supply-chain efficiency loss is about 20 percent. It is also noteworthy
that the most efficient distribution is in electrical power, which has an efficiency loss
of less than 5 percent. As a result, electric vehicles are three to four times as efficient
as hydrogen-powered vehicles.

Fuel Cells as Alternatives to Internal

Combustion Fuels

One of the most significant aspects of a hydrogen economy is that hydrogen fuel cells
can replace internal combustion engines and turbines as the primary method of con-
verting chemical energy into kinetic or electrical energy. The principal reason for such
conversions is that fuel cells theoretically are assumed to be more efficient than inter-
nal combustion engines. At present, fuel cell technology is in a developmental stage