Operation
42
900-0167-01-00 Rev A
Offset
Offset is an automatic operation which occurs in certain conditions. It is not a programmable function.
This operation uses excess battery energy to power the loads when an AC source is present. The
system can take advantage of renewable energy sources, “offsetting” dependence on the AC source.
The battery voltage increases as a renewable energy source charges the batteries. When the voltage
exceeds a designated reference voltage, the FXR inverter begins inverting. It draws power from the
batteries (discharging them) and uses that power to offset the use of the AC source.
The FXR inverter uses excess DC energy for offset under the following rules:
If the load demand is higher than the inverted power, the inverter’s use of the AC source is reduced. The
amount of inverted power has “offset” the same amount of demand on the AC source. (This is sometimes
known as “selling to the loads”.)
If the excess DC energy (and inverted power) is equal or greater than the load demand, and the inverter is in
the
Grid Tied
input mode, the inverter will sell the additional power to the utility grid. This is the key priority
of the
Grid Tied
mode.
The FXR inverter uses several set points as reference voltages for the Offset operation, particularly the
FXR battery charger settings.
The charger settings
Absorb Voltage
,
Float Voltage
, and
Equalize Voltage
(as shown in the system display)
are all used as reference voltages. Normally the charger regulates to these set points by adding power to
the batteries. Offsetting does the opposite; it uses the same set points but regulates the voltage by
removing
power from the batteries.
If none of the battery charger’s timers are active, the reference voltage is
Sell Voltage
in the
Grid-Tie Sell
menu. This is true in any input mode where Offset is used, not just the
Grid Tied
input mode.
The
GridZero
mode only uses a single reference voltage for Offset, the
DoD Volts
setting.
NOTES
:
The
Offset Enable
menu item must be set to
Y
(yes) for Offset to work.
Offset operation is available in the
Support, Grid Tied
, and
GridZero
modes.
Offset operation is available in the
Mini
Grid
mode. However, it may not be used often since the
Mini
Grid
priority is to avoid grid use.
Offset operation is not available in the
Generator, UPS,
and
Backup
input modes.
Table 4
Offset Interaction with AC Source
Mode
Excess DC ≥ loads
Excess DC < loads
Generator
Does not function
Support
Offsets load use, but also uses DC to support the AC source based on
Support
mode settings
Grid Tied
Sells excess to AC source (grid); remains connected
Offsets loads with whatever power is available
UPS
Does not function
Backup
Does not function
Mini Grid
Offsets loads with whatever power is available; inapplicable if disconnected from utility grid
GridZero
Offsets load use, but only according to the
DoD Volts
setting
