Environmental Engineering Reference
In-Depth Information
The motor output power efficiency, also known as vehicle-to-road (V2R), can be
detailed as:
M
phev
G
V
2
R
η
V
2
R
=
(4.39)
where
V
2
R
is the net electric power flow output to the electric motor (W
el
)
M
phe
G
is the electric power injected to the transmission system (W
el
)
The penetration level of PHEV units within a node is defined as the percentage
of dwellings with plug-in facilities connected to the grid, and detailed as:
N
phev
N
clients
%
phev
=
(4.40)
A key concern in PHEV technology focuses on the type of battery the vehicle
employs. This is because the energy storage capacity of the PHEV battery, measured
in kilowatt hour (kWh), needs to have a greater capacity than for HEV models. By
achieving larger battery sizes, it creates the possibility for displacing large amounts
of petrol with electricity from the grid. Thus, PHEV batteries need to store sufficient
energy to satisfy the driving range requirements of users. However, similar to PHEV
architectures, battery models have trade-offs, primarily between energy and power
density performance [204]. For instance, lead-acid batteries have a low energy den-
sity for PHEV applications, usually around 30 Wh/kg, while the nickel-metal hydride
(Ni-MH) battery has an energy density around 80 Wh/kg. Although the nickel-metal
hydride type has an improved energy density when compared to lead acid batteries,
they suffer from lower energy efficiency. On the other hand, lithium-cobalt (Li-Co)
batteries are characterised by both high energy efficiency and high energy density,
as good as 90% and 160 Wh/kg respectively [203]. Furthermore, lithium is lighter
in weight and smaller in volume than most technologies, therefore further increas-
ing its competitive advantage. Based on these conditions, lithium-based batteries
are presently at the forefront of PHEV and BEV applications [205]. As a summary,
Table 4.3 compares the performance characteristics of the most common batteries
used for electric transportation [206].
Table 4.3
Comparison of electro-chemical batteries
Variable
Lead-acid
Ni-MH
Li-CO
Energy density (Wh/kg)
30
80
160
Power density (W/kg)
300
800
320
Energy efficiency (%)
60
70
90
No electric car is zero carbon operational. This is because the electricity used to
charge its battery is generated in power plants that produce CO
2
emissions. To begin
addressing this concern, Table 4.4 allows us to compare the efficiency of different
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