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2.2 COMPONENTS OF ELECTRIC VEHICLES AND CURRENT AREAS
OF DEVELOPMENT FOCUS
2.2.1 ENERGY STORAGE DEVICES
Electric propulsion must always obtain the required energy from a
suitable energy source - which it then converts into propulsion po-
wer with efficiency greater than 90 percent. Thus the energy sto-
rage device is the core component of electromobility, as it plays a
significant role in determining both the performance and range of
the vehicle.
2.2.1.1 ENERGY STORAGE DEVICES IN GENERAL
Based on the current state of the technology, various alternatives
are available: In particular, it is necessary to consider the various
types of rechargeable secondary batteries (lead-acid, NiMH, Li-
Ion), hydrogen as an energy source together with the energy con-
verter fuel cell, as well as capacitors. Gravimetric energy density
[Wh/kg] as well as power density [W/kg] is an essential selection
criteria. These are usually presented in a so-called Ragone plot
(see Fig. 4).
If you compare the energy density of batteries with that of gasoli-
ne or hydrogen, then a serious disadvantage of the secondary cell
becomes apparent (see Fig. 5). This relatively low energy density
results in the requirement to install heavy battery packs in the ve-
hicle in order to obtain acceptable ranges. On the other hand, the
advantages relative to the combustion engine include the outstan-
ding efficiency of the electric propulsion (max. combustion engine
efficiency of 30 percent vs. electric motor efficiency of 90 percent),
as well as local emission-free mobility.
Fig. 4: Ragone plot
4
4 Sauer (2009)