NHP Technical News
AVAILABLE METHODS FOR LOAD
MANAGEMENT
No Load Management
In cases where a small number of AC chargers are being installed
in a commercial premise, load management will typically not be
required, unless the switchboard is already routinely overloaded.
A review of historical interval data should enable determination
on this point. summer afternoons. In the future, apartment complexes will
either need some form of load management for EV charging,
or they will need to drastically increase the size of their
main switchboard and the infrastructure that supports that
switchboard (typically the transformer in the street).
Installations of AC EV chargers in commercial premises today
are typically handled in an unmanaged fashion, because most
installations today are ‘ones and twos’ of units in the 7kW peak
range. An important point to make here is on the subject of diversity,
which in the electrical context means the degree to which
electrical loads in a building consume energy at the same
time. The wiring rules have recently been updated to include
informative guidance around electric vehicles (AS/NZS 3000:2018
Appendix P) assuming that all EV charging equipment installed
runs at full capacity all the time. So, for example, an installation of
100 x 7kW chargers in an apartment complex basement should
be assumed for the purposes of electrical design to present a
continuous 700kW load to the upstream supply.
However, as the transition to electric vehicles ramps up, this will
not be a viable approach. Using NHP’s head office as an example,
we have a 1200A main incomer, and up to 150 vehicles on site
each day in the car park. If we assume a future where 100 of
these vehicles are plug-in electric, and that employees turn up
between 7:30 and 8:30, plug in, and draw on the average about
5kW for an hour or two, we would have a new load of ~500kW
presented to the main switchboard. On hot summer days
when the night time temperature has stayed above 25C, the
air conditioning is already operating at 8am, there is not always
500kW of headroom available to be used.
The practical effect of following this guidance is that the site
connection, transformer, switchboard, and distribution boards
will all end up sized and designed significantly larger, at a
substantial additional cost to either the developer (in the case
of new builds) or the body corporate (in the case of upgrades to
existing apartment complex stock).
The first observation to this point is that this would be a
reasonable design philosophy in the absence of smart load
management in an apartment complex, since most EV charging
loads could reasonably be expected to coincide with peak air-
conditioning loads on hot summer weekday afternoons when
everyone gets home from work.
The second observation is that it if smart load management is
implemented, substantial additional cost can be avoided. If we
assume that:
• The EV charging load is spread across 12 hours
• The 100 drivers in the example above do an average of 50km
of driving per day
• They do not charge at their workplaces,
Apartment complexes will present an even more significant
problem. People will typically plug in when they arrive home.
Without any load management in place to defer charging until
later in the evening and spread the load throughout the night,
the vehicles will start charging immediately, for a typical period
of an hour or two. This timing will coincide with peak demand,
both on the grid and within the local infrastructure, on hot
then the actual average load is more like 80kW, not 700kW. If
we compress the charging time into the period from 11pm to
7am, when air-conditioning load is minimised, the average load
presented is around 125kW. Loading at this level at this time of
day is unlikely to require a network connection, switchboard, or
transformer any larger than the apartment complex would have
installed already to service the existing peak demand.
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