Outback Power GS4048A and GS8048A Operator's Manual

Operation
900-0161-01-00 Rev A 35
Offset
This operation is designed to use excess battery energy to power the loads when an AC source is
present. This allows the system to take advantage of renewable energy sources, in effect “offsetting”
dependence on the AC source.
A renewable energy source will raise the battery voltage as it charges the batteries. When the voltage
exceeds a designated reference voltage, the Radian inverter begins drawing power from the batteries
(discharging them) and using that power to offset usage of the AC source. The batteries are kept at
equilibrium and are maintained at the reference voltage.
The Radian inverter uses excess DC energy for offset under the following rules:

If the load demand is higher than the exported power, the inverter’s use of the AC source is reduced. The
exported amount of 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 exported power) is equal or greater than the load demand, and the Radian 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 Radian inverter uses several set points as reference voltages for the Offset operation, particularly
the 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 Offset 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
Grid Zero
mode only uses a single reference voltage for Offset, the
DoD Volts
setting.
NOTES
:

Offset operation is not available in the
Generator, UPS,
and
Backup
input modes.

Offset operation is available in the
Support, Grid Tied
, and
Grid Zero
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.

The
Grid-Tie Enable
menu item must be set to
Y
(yes) for Offset to work. This is true even if the inverter is
not used in a grid-tied mode or application.
Table 3 Offset Interaction with AC Source
Mode
Excess DC ≥ loads
Excess DC < loads
Generator
N/A; Offset operation does not function
Support
Offsets load use, but also uses DC and batteries 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
N/A; Offset operation does not function
Backup
N/A; Offset operation does not function
Mini Grid
Offsets loads with whatever power is available; inapplicable if disconnected from utility grid
Grid Zero
Offsets load use, but only according to the
DoD Volts
setting