Environmental Engineering Reference
In-Depth Information
Table 1.6 Well to wheels percentage efficiencies for different types of vehicles starting from
non-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.
28
c
Nuclear
Electricity
BEV
61
17
28 to electricity
c
Nuclear
Hydrogen
HFCEV
34
4.5
47 for electrolysis
c
11
c
Photovoltaic
Electricity
BEV
61
6.7
11 to electricity
c
Photovoltaic
Hydrogen
HFCEV
34
1.8
47 for electrolysis
c
1 for photosynthesis
d
Biomass
Electricity
BEV
61
0.26
42 for biomass to
electricity
c
1 for photosynthesis
d
Biomass
Hydrogen
HFCEV
34
0.20
59 for biomass to H
2
c
a
Include carrier distribution efficiency (93% for electricity, 86% for compressed hydrogen [
52
])
b
Taken from Ref. [
52
], evaluated on US FTP driving cycle, NiMH batteries for electric drive-
trains
c
Taken from Ref. [
54
] and corrected for footnote a
d
Generally considered as comprised between 0.1 and 1% [
55
]
Table
1.6
refers only to non-fossil primary energy resources, and presents a
comparison between BEVs and HFCEVs, i.e., between electricity and hydrogen as
energy carriers for transportation sector, since both these two energy carriers can
be produced starting from several carbon-free resources, such as nuclear and
renewable. The well-to-wheels efficiencies show that only starting from nuclear
and producing electricity for direct use on BEVs, it is possible to obtain a primary
energy utilization comparable to that of fossil resources (17%), while very low
values can be estimated for solar biomass (0.26% for BEVs), mainly because of
low efficiency of the photosynthesis process (the efficiency of the natural process
which converts the energy of light—photons, electromagnetic waves—into
chemical potential energy stored in organic structures such as plants is generally
considered comprised between 0.1 and 1% [
55
]).
The overall well-to-wheels efficiencies for BEVs and HFCEVs starting from
solar biomass evidence that this path cannot be considered as a massive solution
for application of biofuels to electric vehicles, unless biomass is not obtained from
already existing organic wastes (forestry residues, straw, food waste, manure, etc.).
The comparison between electricity and hydrogen is more significant when
nuclear and solar photovoltaic are considered as primary resources. It is possible to
notice from Table
1.6
that for both these primary resources the well-to-wheels
efficiency of BEVs results about four times higher than of HFCEVs.
This is not only due to the higher efficiency of battery powered vehicles, but
also to the lower efficiency of the overall process necessary to assure hydrogen
feeding to fuel cells, i.e., production of electricity starting from the primary
resource plus hydrogen production by electrolysis (13% from nuclear and 5% from
photovoltaic, to be compared with values corresponding to electricity production
