Page 45 - Energize May 2021

TECHNICAL

Technology The EMS uses this information, together
Hybrid inverter/battery chargers with the state-of-charge of the storage
The availability of high-power off-the-shelf, multifunction, hybrid inverter/battery chargers system and historical data on energy
such as the Victron quatro 15 has made the residential microgrid a relatively easily achievable consumption, to decide what energy source
and effective economic possibility. There are numerous models available on the market. is to be used, whether to discharge or
Characterised by multiple inputs and multiple outputs, typical construction or connection is charge the ESS, either from solar or the grid
shown in Figure 4. The maximum power-point tracking (MPPT) solar charge controller may be and when to load shed or load control.
internal to the hybrid inverter/battery charger or a completely separate external unit.
The hybrid inverter/battery charger can accept AC or DC inputs from several sources and Load management/load shedding
provides several AC outputs. The AC outputs can be controlled to perform load shedding. The The application of load shedding could be
hybrid inverter/battery charger can also be set up to operate in different modes and could be applied specific to residential complexes
controlled by an energy management system (EMS). where all residences have similar high
load devices such as water heaters, which
Microgrid management functions are inherent energy storage devices and
Energy management it is possible to selectively deactivate the
A smart controller can perform advanced functions such as estimating energy demand and same device in each unit. Individual unit
PV production based on weather forecasts and previous performance. It could adjust the controllers could switch off any high load
amount of energy stored accordingly, as well as balance between PV, grid power and stored device. Residents would be advised to
energy. It could also be used to control common devices such as pool cleaners, water pumps reduce load via a data communications or
etc., based on demand and available energy. Advanced microgrid features over a common mobile phone system.
property allow such functions as load management to be installed at every consumer Aggregate demand would be made
connected to the grid. up of demand from individual units,
The energy management system controls the generation, storage and flow of energy in the and common units such as outdoor
system. Various data, such as weather forecasts, load shedding schedules, electricity tariffs and passage lighting, security systems,
(when ToU tariffs are applied) and other information which may affect the availability of grid swimming pool equipment and water
power and production of solar energy, could be gathered by the system from online sources. reservoir pumps. As opposed to
commercial and industrial loads, the
demand during daylight hours is fairly
constant. A typical domestic load profile is
shown in Figure 5.
The fact that all units on the microgrid
will have a similar profile means that
the microgrid load will have the same
profile, which allows the PVH system to
exploit the relatively low demand at the
solar peak, to offset the high demand
at the evening peak using the storage.
Lockdown and working from home could
affect the shape of this curve.

Solar PV smoothing
Figure 4: Hybrid inverter/charger.
Residential microgrids would be located
in urban areas which are subject to cloud
cover and moving clouds. This would affect
the output of the solar PV system. Storage
could be used to stabilise the system under
conditions of rapidly changing PV output.

Metering, billing, and control
Smart meters make it possible to meter
energy flow at multiple points in the system
and collect and analyse this information on
site. Figure 6 shows a possible metering
arrangement. Collection of meter data at
several points allows accurate calculation
Figure 5: Typical residential demand curve. of billing data.

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