Environmental Engineering Reference
In-Depth Information
''well'') the following energy losses have to be considered to evaluate the final
energy usable for traction: (i) losses due to fuel production and distribution, in order
to attain the actual energy entering the vehicle, (ii) losses due to vehicle on road
management (conditioning, lighting) to draw the net energy entering the power-
train, (iii) losses due to road load and heat lost by the engine, to obtain the
remaining energy actually available for the ''wheels''. These evaluations are very
complex as involve several assumptions on the long-term development of tech-
nologies which can present very different progress trends; however, quite a few
results regarding this type of comparison based on different primary resources are
present in scientific literature [
52
-
54
], and the results up today available seem to
converge towards some general conclusions. Tables
1.5
and
1.6
report the results of
such evaluations effected for the different types of vehicles above mentioned, with
reference to fossil and renewable energy resources, respectively. These data are
based on the comprehensive analysis reported in [
52
] and other references therein.
Table
1.5
evidences that well-to-wheels efficiencies of fossil resources are
approximately comprised between 20 and 30%, with a maximum value of 31%
estimated for BEVs using electricity derived by natural gas. The minimum well-to-
wheels efficiency is obtained for Diesel vehicles, in spite of the very high effi-
ciency of carrier production (95%), this is due to the lower efficiency of the
internal combustion powertrain with respect to electric or hybrid thermal-electric
ones (internal combustion engines could work at their maximum efficiency
comprised between 35 and 40% only in conditions close to their maximum power,
while all vehicles efficiencies in Table
1.5
are estimated on US Federal Test
Procedure driving cycle, characterized by a mean power very lower than the
maximum power of the vehicle). HTEVs present a very interesting well-to-wheels
efficiency, thanks to the higher vehicle efficiency if compared to ICVs. The pri-
mary energy efficiency evaluated for HFCEVs is also quite elevated (25%), but
hydrogen is considered deriving from natural gas by catalytic reforming processes
(see
Sect. 2.1
), then its production is accompanied by carbon dioxide emissions.
Table 1.5 Well to wheels percentage efficiencies for different types of vehicles starting from
fossil primary energy resources
Primary
energy
Energy
carrier
Type of
vehicle
Primary energy to energy
carrier % eff.
a
Vehicle %
eff.
b
Well-to-wheels
% eff.
Coal
Electricity
BEV
37
61
22
Natural
gas
Electricity
BEV
51
61
31
Natural
gas
Hydrogen
HFCEV
73 (350 bar)
34
25
Crude oil
Diesel oil
ICV
95
20
19
Crude oil
Diesel oil
HTEV
95
29
27
Adapted from Ref. [
52
]
a
Includes carrier distribution efficiency (93% for electricity, 86% for compressed hydrogen,
99.8% for oil)
b
Evaluated on US FTP driving cycle, NiMH batteries for electric drivetrains
