3
1.5.2 Backup Solar plus Storage
During a grid outage, the DURACELL HUB isolates the battery
system and backup electrical panel from the grid. In this mode, the
EMC is in a monitoring state, with most control handed over to the
ESS. The ESS curtails PV when the battery is either full or exceeds
the charge limit of the battery. On low SOC, the battery system
goes into a standby state until either the solar resource or the grid
returns.
IMPORTANT! Shutting off the DURACELL HUB circuit breaker at the
main electrical panel will place the ESS into backup mode and
continue to energize the backup panel.
1.5.3 Backup Solar PV curtailment method:
Frequency Shift Power Control (FSPC)
During backup power operation of the ESS, PV curtailment is achieved by shifting the frequency up or down to trip
the PV inverter. This curtailment method, defined as frequency shift power control (FSPC), is required to prevent
solar from over-charging the battery. By default, the ESS will ramp up frequency to a PV trip range of 62.1 Hz, but
this is adjustable depending on the regulatory frequency trip limits within the jurisdiction.
IMPORTANT! PV inverters connected to the backup panel must have frequency trip settings programmed within the
following ranges: PV low frequency trip range: 57.0 to 59.3 Hz, PV high frequency trip range: 60.5 to 62.0 Hz.
If the PV inverter cannot be adjusted within the range specified, the PV inverter must not be connected to the backup
panel.
NOTE: The DURACELL HUB is not suitable for use in applications where the electric utility prohibits PV power export
to the grid. For non-export applications, consult your DURACELL POWER CENTER 5KW dealer for alternate EMS
panel solutions.
1.5.4 Circuit and system sizing for 100 / 125 / 150 Amp electrical panels
Line side tapping the main electrical panel is required for ESS installations where the electrical service rating is under
200 Amp. Refer to section 2.3, figure 11.
1.5.5 Circuit and system sizing for 200+ Amp electrical panels
The DURACELL HUB may be connected to a 200+ Amp electrical panel using a single 40A breaker. For this
configuration, the total solar PV output connected to the backup electrical panel will depend on the curtailment
features of the solar PV inverter. If the PV inverter is equipped with its own curtailment controls that can limit PV
output to 5kW or less in backup mode, the maximum rating of the PV inverter connected to the DURACELL HUB is 7.6
kW AC. For PV inverters without internal curtailment methods, the 5 kW PV restriction applies. Regardless of PV
size, this configuration permits the DURACELL HUB EMS to limit continuous combined solar plus storage output to 7.6
kW AC (32 Amp).
1.5.6 Over-sized PV systems
For installations with PV systems that are
larger than the DURACELL HUB and ESS can
accommodate, the PV inverters must be split
up such that the balance of PV is wired directly
to the main electrical panel.
NOTE: An additional CT must be added to the
main panel connected PV inverter.
PV
I
nverter
Backup
P
anel
PV
I
nverter
PV panels
Main
P
anel
Backup
P
anel
loads
PV
I
nverter
PV panels
Figure 4: Backup solar plus storage.
Figure 5: Over-sized PV systems connected to main panel.
PV panels
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