Environmental Engineering Reference
In-Depth Information
Contrary to diverse peak charging times of G2V injections, peak V2G injections
only vary in a subtle way; this is because the scarce back-up capacity PHEV
represents is reserved specifically for moments when the network is most stressed.
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Although much of the charging is done during the night-time, Figure 6.25 high-
lights the drastic differences in the optimal manner PHEV units can be charged.
Case 2 has a continuous and stochastic profile, having a pronounced peak just
before 7 a.m. in order to have all PHEV units fully charged. Case 3 is similar to
case 2 but with most of the charging occurring in the early morning hours. Since
case 4 reduces operating costs, the G2V profile is very subtle and spread out except
in the evening when it ceases. In case 5 the fleet of vehicles are charged according to
the moments of lowest demand, thus providing valley-filling load. Meanwhile, case 6
commands and allocates the charging of PHEVs based on when the spot market makes
it more economically viable, while in case 7 the carbon cost only influences slightly
the charging of PHEVs, when compared to case 6.
Overall, results show PHEV technologies have great charging flexibility, thus
creating opportunities for load control and demand response schemes. Likewise,
V2G possibilities are addressed in Figure 6.26 by showing the various ways in which
back-up capacity from the vehicles would be dispatched if required by the aggre-
gator (
e.g.
TCOPF coordinator). Although V2G flows are far away from becoming
commercial applications yet, their ancillary service value is worth illustrating.
Although the daily V2G capacity is equivalent for all cases and they all occur
in the evening, the intensity and time intervals in which the resources are employed
have slightly distinctive patterns. Cases 2-4 distribute their resources in a similar
fashion, having a broader operating range but less intense than that in cases 5-7.
Meanwhile, cases 5-7 operate within a narrower time range than the other cases
and they have a much more intense presence during the electrical peak demand.
Particularly in cases 6 and 7 the economic incentive makes the dispatch of V2G
injections stand out when the electricity is most expensive; however, this dispatch
could easily change if the price of electricity was higher during other moments of the
day or if the carbon intensity of the fuel mix radically changed in the future.
Analogous to Figure 6.14, Figure 6.27 describes the aggregated PHEV storage
profiles obtained from the optimal formulations evaluated. Notice all state of charge
levels are at a maximum by 7 a.m., and although the amount of electrical power
charged and discharged is the same for all cases, each solution presents unique fea-
tures. However, in this figure due to the large aggregated capacity and travelling
profiles given (
i.e.
40% of battery) the variations do not appear to distinct from each
other.
The following conclusions can be gathered from the PHEV storage profile results:
Since the capacity of the PHEV fleet is abundant and the travel log is the same
for all cases, the state of charge oscillates between 10 and 20 MWh
el
;
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All the state of charge profiles follow a similar curve, storing energy in the
early morning and then using it to fulfil travel requirements until recharging
takes place, cases 2-4 begin charging earlier than in cases 5-7. Notice how the
charging inflection point at night occurs earlier for cases 2, 3 and 4 (in this order);
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