|
Applications — The fuel cell is being
considered as an eventual replacement for the internal combustion
engine for cars, trucks and buses. Major car manufacturers
have teamed up with fuel cell research centers or are doing
their own development. There are plans for mass-producing
cars running on fuel cells. However, because of the low operating
cost of the combustion engine, and some unresolved technical
challenges of the fuel cell, experts predict that a large
scale implementation of the fuel cell to power cars will not
occur before 2015, or even 2020.
Large power plants running in the 40,000kW range
will likely out-pace the automotive industry. Such systems
could provide electricity to remote locations within 10 years.
Many of these regions have an abundance of fossil fuel that
could be utilized. The stack on these large power plants would
last longer than in mobile applications because of steady
use, even operating temperatures and absence of shock and
vibration.
Residential power supplies are also being tested.
Such a unit would sit in the basement or outside the house,
similar to an air-conditioning unit of a typical middle class
North American home. The fuel would be natural gas or propane,
a commodity that is available in many urban settings.
Fuel cells may soon compete with batteries for
portable applications, such as laptop computers and mobile
phones. However, today’s technologies have limitations in
meeting the cost and size criteria for small portable devices.
In addition, the cost per watt-hour is less favorable for
small systems than large installations.
Let’s examine once more the cost to produce 1kW
of power. In Figure 17-5 we learned that the investment
to provide 1kW of power using rechargeable batteries is around
$7,000. This calculation is based on 7.2V; 1000mAh NiCd packs
costing $50 each. High energy-dense batteries that deliver
fewer cycles and are more expensive than the NiCd will double
the cost.
The high cost of portable power opens vast opportunities
for the portable fuel cell. At an investment of $3,000 to
$7,500 to produce one kilowatt of power, however, the energy
generated by the fuel cell is only marginally less expensive
than that produced by conventional batteries.
The DMFC, the fuel cell designed for portable
applications would not necessarily replace the battery in
the equipment but serve as a charger that is carried separately.
The feasibility to build a mass-produced fuel cell that fits
into the form factor of a battery is still a few years away.
 The
advantages of the portable fuel cell are: relatively high
energy density (up to five times that of a Li-ion battery),
liquefied fuel as energy supply, environmentally clean, fast
recharge and long runtimes. In fact, continuous operation
is feasible. Miniature fuel cells have been demonstrated that
operate at an efficiency of 20 percent and run for 3000 hours
before a stack replacement is necessary. There is, however,
some degradation during the service life of the fuel cell.
Portable fuels cells are still in experimental stages.
Advantages and limitations of the fuel cell
— A less known limitation of the fuel cell is the marginal
loading characteristic. On a high current load, mass transport
limitations come into effect. Supplying air instead of pure
oxygen aggregates this phenomenon.
The issue of mass transport limitation is why
the fuel cell operates best at a 30 percent load factor.
Higher loads reduce the efficiency considerably. In terms
of loading characteristics, the fuel cell does not match the
performance of a NiCd battery or a diesel engine, which perform
well at a 100 percent load factor.
Ironically, the fuel cell does not eliminate
the chemical battery — it promotes it. Similar to the argument
that the computer would make paper redundant, the fuel cell
needs batteries as a buffer. For many applications, a battery
bank will provide momentary high current loads and the fuel
cell will serve to keep the battery fully charged. For portable
applications, a supercapacitor will improve the loading characteristics
and enable high current pulses.
 Most
fuel cells are still handmade and are used for experimental
purposes. Fuel cell promoters remind the public that the cost
will come down once the cells are mass-produced. While an
internal combustion engine requires an investment of $35 to
$50 to produce one kilowatt of power, the equivalent cost
in a fuel cells is still a whopping $3,000 to $7,500. The
goal is a fuel cell that would cost the same or less than
diesel engines.
The fuel cell will find applications that lie
beyond the reach of the internal combustion engine. Once low
cost manufacturing is feasible, this power source will transform
the world and bring great wealth potential to those who invest
in this technology.
It is said that the fuel cell is as revolutionary
in transforming our technology as the microprocessor has been.
Once fuel cell technology has matured and is in common use,
our quality of life will improve and the environmental degradation
caused by burning fossil fuels will be reversed. However,
the maturing process of the fuel cell may not be as rapid
as that of microelectronics.
|
