Environmental Engineering Reference
In-Depth Information
Table 4.17 Comparison of metal-air thermodynamic couples to hydrocarbon fuel
Type
Cell potential
(V)
Theoretical
(Wh/kg)
Practical
(Wh/kg)
Specific
power (W/kg)
Cycling
(#)
Zinc-air
1.65
1,370
470
100
<
450
Aluminium-air
1.2
~6,000
1,300
<
300
<
500
Lithium-air
2.91
11,140
>
1,800
?
?
Gasoline
N/A
12,400
Work on lithium-air batteries stopped in 1990 after Moli Energy experienced a
fire with their battery product and about this same time Sony introduced the lithium
ion chemistry. Recently, IBM's Almaden Research Center along with PolyPlus
Technology has started work on lithium-air batteries. Metal-air batteries are
of high interest because conventional battery chemistries are unlikely to exceed
250 Wh/kg and still remain stable.
4.4.5 Fuel cell
The market for fuel cells is split amongst high volume transportation, particularly
personal transportation, stationary applications and specialty applications. Each of
these niches is driven by very different volume and cost pressures. Specialty
applications have volumes in 100s of units per year and consist of spacecraft power
supply as well as prototype applications to city buses. Costs are currently at or
above $3,000/kW, with most development funding provided by industrial devel-
opers. Fuel cell markets are now beginning to open up with applications as standby
power generation units. During this growth phase, the volumes must exceed 1,000s
of units per year and cost is expected to drop into the $300/kW range to be
acceptable. Mass market acceptance as a fuel cell hybrid requires that volumes
enter into the 100,000s of units per year with cost reaching a target of $30/kW to be
competitive with today's internal combustion engine costs ranging from $35 to
$50/kW. What remains unclear is the timescale over which the costs will decrease
by two orders of magnitude. Fuel cells are nominally rated for 4,000 starts, about
the same as the deep cycling capability of lithium-iron-phosphate.
It is clear that twenty-first century transportation systems will be dominated by
internal combustion engine technology for at least the next 30-50 years. This is the
time frame over which liquid fossil fuels will remain available, perhaps at higher
costs as the rate of new oil field exploration declines, but still able to meet demand.
According to some predictions, the oil gap will occur when demand outpaces pro-
duction and new field exploration will virtually vanish. At this point in time, perhaps
in the period from 2025 to 2040 there will be very pressing need for alternatives to
liquid fossil fuel and the fuel cell will become the dominant power source for per-
sonal and mass transportation. This describes the entry into a hydrogen economy.
Some industry estimates suggest that there will not be any significant volume man-
ufacture of hydrogen fuel cell vehicles before 2020-2025. During the interim, clean
diesel and hydrogen fuelled ICEs will become more prevalent.
