25
- when the battery voltage or SOC is lower than the generator ‘Charge start Volt/SOC’ setting
Generator Stop Conditions
When battery voltage or SOC is higher than the Charge end Volt/SOC settings.
4.7
Off-Grid
The 18kPV can fully function in Off-Grid only mode. It does not need the utility or generator to function.
Purely off-grid systems that do not have access to the utility should strongly consider having a 2-wire
start backup generator for extended cloudy periods (8-12 kW diesel recommended per 18kPV inverter -
21kWs max per inverter). Off-Grid systems should have robust battery banks sized to ensure multiple
days of power and to reduce generator run time.
The 18kPV can also utilize AC Coupled solar input through the GEN port in purely Off-Grid Systems. The
Generator can then be connected to the Grid Port.
4.7.1 Off-Grid Wiring
The 18kPV can accept up to 90 Amps (21.kWs) of generator power and will pass through all available
power to the loads. Therefore, the Loads subpanel can be sized up to the size of the backup generator
with a 60 Amp minimum per inverter.
Refer to Off-Grid Wiring Diagram 4.8 for an example.
4.8
AC Coupling Installation Connection
The inverter can accept PV solar inputs to both MPPT channels and AC coupled solar input at the same
time. The AC coupled solar input can be up to 90A of AC power or 21.6kW of solar. The MPPT channels
can handle up to 18kW of solar, with 12kW available for back feeding the utility grid. Therefore, up to
33.6kW of AC power could be sent back to the grid. For this amount of back feed, users will need either
a feeder tap or supply side tap as the point of utility interconnection. (See Diagrams 4.3 and 4.4 for more
information) The existing solar system is connected to the inverter's GEN terminal. For AC Coupling
wiring configuration, see Diagram 4.9.
After the AC couple function is enabled:
When the grid is on, the GEN terminal is connected to the GRID terminal inside the inverter. In this case,
the hybrid inverter will bypass the interactive inverter AC to the GRID and LOAD. Any remaining energy
will be exported to the grid.
When the grid is off, the GEN terminal is connected to the LOAD terminal inside the inverter. In this
case, the hybrid inverter will work as a power source for the grid-interactive inverter to synchronize and
feed power to the micro-grid. The loads will be supplied by solar power first. If solar panels are generat-
ing more power than load consumption, the excess solar power will be stored in the batteries. When
solar power exceeds the sum of load power and max battery charging power (e.g., when the batteries
are nearly full), the inverter will signal the grid interactive inverter to reduce power via the frequency-
shifting, power-reduction mechanism, thus maintaining the balance of generation and consumption of
the micro-grid system.
What is frequency-shifting power reduction?
All UL1741SA compliant grid-interactive inverters have the Frequency-Watt feature, which requires the
grid-interactive inverter to reduce power with increasing grid frequency. The power will drop to zero
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