Environmental Engineering Reference
In-Depth Information
4.6
Hydrogen Energy Society and Fuel Cells
The major application of fuel cells, especially of the PEFC, is anticipated to be
in fuel cell vehicles. However, demand for fuel cell cars will be dependent on the
availability of a hydrogen station near to the fuel cell car owner. From the reverse
perspective, who would be willing to build a hydrogen station without a sufficient
number of fuel cell vehicles coming to the station? Solving this dilemma requires
political action and in Japan, related companies made an agreement under the sup-
port of the government to promote the development of hydrogen vehicles and hy-
drogen stations simultaneously, and much effort is going into bringing the technol-
ogy to commercialization. However, a vision of a future energy system necessary
for achieving reductions in energy use and CO
2
emissions, is still unclear and awaits
new technologies or concepts to emerge.
With present technology, the hydrogen for hydrogen filling stations is mainly
produced from natural gas or petroleum resources. The efficiency of fuel cell ve-
hicles thus should be discussed on a complete system ('well-to-wheel') basis, and
any energy losses in production and reformation of the fuel included with those in
conversion of the chemical energy to electrical energy and propulsion systems in
the car. Although different groups use different calculations on well to wheel effi-
ciencies, a common conclusion is that the hydrogen fuel cell vehicle does not have
a big advantage over a popular technology such as a gasoline hybrid vehicle when
the hydrogen is supplied from fossil fuel resources.
Efforts on building hydrogen stations and on commercializing fuel cell vehicles
are not however meaningless if the hydrogen-supply infrastructure is built up and
becomes an integral part of society. This would support the introduction of any
renewable energy technology since hydrogen can be produced through other renew-
able routes such as solar or wind electricity. Thus, development of fuel cells should
be discussed not only from the fuel cell technology and economy but also from the
viewpoint of future energy strategy.
4.7
Fuel Cells in Cogeneration Systems
In a power plant of efficiency
η
, 1-
η
of the energy in the fuel is released into the
environment as heat. This waste heat is difficult to re-use in large-scale central-
ized power generation facilities, but in localized relatively small power generation
equipment using gas engines or stationary fuel cells, the heat discharged may be
used to meet local demand through providing a hot water supply or steam. We
called these Cogeneration of Heat and Power (CHP) systems—a cogeneration sys-
tem of electricity and heat. This is considered as effective means for the efficient
use of chemical energy.
The efficiency of a CHP system is often discussed in terms of overall efficiency;
simply summing up the amount of electricity generation and heat recovered. For
