Civil Engineering Reference
In-Depth Information
Table 4.2
Operating parameters of various batteries
Specific energy
(Wh/kg)
Specific power
(W/kg)
Cycle life to 80 %
(cycles)
Lead-acid
40
90
400
Nickel/iron
50
100
>
1,000
Nickel/zinc
60
100
250
Zinc/bromine
50
90
200
Nickel/cadmium
50
400
>
1,000
Lithium aluminum/iron
sulfide
80
70
200
Sodium/sulfur
100
120
250
Iron/air
70
90
150
These values, although higher than those of flywheel storage, are still far from
the energy storage capacity of combustibles, thus limiting this kind of storage to
particular applications for short periods of demand.
In addition to industrial applications, electric storage affects electric vehicle
diffusion. With typical consumption per kilometer and per metric ton of
490 kJ/t
km) if measured at the utility delivering node, a
wide use of these vehicles is strictly dependent on the availability of high-
performance electric storage systems. With an equal division of the gross weight
among payload, vehicle body and traction equipment, and batteries, the urban
range is about 70-80 km; this range could be improved by using higher energy-
density batteries and by reducing vehicle weight through a proper design of the
body and of the traction equipment.
km (0.15 kWh/t
4.9.4 Fuel Cells
Fuel cells are electrochemical devices in which electric energy is produced by
combining hydrogen and oxygen and by releasing water vapor into the atmosphere.
Basically, the main components of a fuel cell are the anode, the cathode, and the
electrolyte (liquid, solid, membrane) between them. To obtain the required voltage
a stack of many fuel cells in series is required.
Fuel cells can be classified according to the working temperature (see Table
4.3
where the main operating parameters are reported) as (1) low-temperature cells
(AFC, PEM, PEFC, PAFC) and (2) high-temperature cells (MCFC, SOFC).
Hydrogen can be produced by different techniques: natural gas steam reforming,
electrolysis by using electric energy, coal gasification, and waste or biomass
gasification. Table
4.4
reports the main operating parameters of hydrogen produc-
tion and of electricity production by using hydrogen-fed fuel cells.
