Lightweight Electric/Hybrid Vehicle Design

Waste heat
and water
Hydrogen
fuel
Water when
refuelling
Air
Fig. 1.4 Fuel-cell electric vehicle.
Hydride
storage tank
Desulphurization
100-200 V
battery
»
Non-return valve
Pump
3 bar
Buck/boost
chopper
Control
valves
300 V DC
Current EV design approaches 7
Fuel-cell
stack
60 V 250 A
Boost chopper
Power
converter
220 V 3ø 1000 Hz
kW average power would produce about 60–70 V DC at 250 amps. In size it would be about 200
mm square and about 600 mm long. The cell operates at a temperature of 80 ° C. When cold, it can
give 50% power instantly and full power after about 3 minutes. The units exhibit very long life.
The problem until recently has been seal life when operated on air as opposed to oxygen. New
materials have solved this problem. Output doubles when pure oxygen is used. Fuel cells do not
like pollutants such as carbon monoxide in the source gases. Gas is normally injected at 0.66
atmospheres into the stack. The main challenge now is to refine the design so as to optimize the
cost relative to performance. This will take time because the effort deployed at this time is small in
relation to the effort put into batteries or other fuel-cell types. There is a very real case for a major
multinational effort to train scientists and engineers in this technology in the short term, and to
reduce the time to introduction on a large scale.
1.2.6 THE ROLE OF BATTERIES
Batteries have been with us for at least 150 years and have two main problems: they are heavy and
they do not like repeated deep discharge. Batteries which are deep cycled, irrespective of the
technology, deteriorate in performance with age. So the question must be asked ‘what can batteries
do well?’. The answer is to provide limited performance in deep discharge, or alternatively, much
better performance as a provider of peak power for hybrid and fuel-cell vehicles.
Much work is under way on high temperature cells. These are unlikely to meet cost or weight
constraints of primary transport applications. The best high temperature batteries can offer 100
Wh/kg. Overall, fuel cells already give 300 Wh/kg and this can be improved with development.
What is needed is a battery with different capabilities to normal car starter batteries, namely
very low internal resistance, long life, excellent gas recombination, room temperature operation,
totally sealed, compact construction, reasonable deep discharge life as well as being physically
robust.
The battery which satisfies the above criteria is the lead–acid foil battery, as manufactured by
Hawker Siddeley. This type of construction has replaced nickel–cadmium pocket batteries on
many aircraft. In particular the lead–acid foil battery retains far more charge from regeneration
Motor
Diff
Vehicle
heating Waste