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GRID-TIE !!!
System Overview
OutBack Power Systems GFX’s (Grid-tie FX) come in two styles. The GTFX (Grid-tie Turbo FX) is a sealed FX
with an external fan to provide cooling and an extra power boost. The GVFX (Grid-tie Vented FX) is a vented FX
that intakes air and directs it over the transformer. These GFX’s are capable of selling power back to your local
utility while giving you the piece of mind of a back-up power system in case the utility fails.
The components necessary to a system involving a GFX are (in order of power flow) the sun, solar panels (or other
renewable energy sources), solar charge controller(s) (OutBack’s MX-60 is recommended), battery bank of the
proper voltage and capacity (minimum of 100 amp-hours recommended), the GFX(s), and the utility grid. The
utility grid attaches to the GFX at its AC Input terminals.
The GFX comes pre-programmed to operate, even without the Mate. The Mate is necessary to program the GFX
(stacking, auto generator start, etc.) and must be connected for functions that involved the clock (advanced generator
start) or to view voltage and current meters and “Error” messages. The Mate is highly recommended for Grid-Tie
systems.
Setup
The GFX has a set of default settings pertaining to its Grid-Tie capabilities. The default setting for selling power
back to the utility grid is called the “Sell RE Volts” and is set at 25.6 volts (for a 24 volt battery bank) or 51.2 volts
(for a 48 volt battery bank). This is the optimal setting for most systems. When the GFX is working with an MX-60
charge controller (serial numbers 2000 and above) through the HUB there is some programming of the MX-60
necessary for proper communication. Go to the MX-60’s “Optimization” menu, then to the “MPPT mode”.
Change the parameter from “nonGT” to “FX-GT” by pressing the button underneath it. This will enable correct
communications between the MX-60 and the GFX. Specifically, this will tell the MX-60 to raise its Float voltage to
its Bulk voltage, effectively allowing it to sell more power back by keeping the battery voltage higher. The “Absorb”
voltage on the MX-60 must be raised above the “Absorb” voltage on the GFX. This is necessary in all cases,
whether the HUB is in the system or not. It is a good idea to raise the “Absorb” voltage of the MX-60 up a few
tenths of a volt and lower the “Absorb” voltage of the GFX down a few tenths of a volt so the MX-60’s “Absorb”
voltage is at least 0.3 volts (for a 24 volt system) or 0.6 volts (for a 48 volt system) higher than the GFX’s “Absorb”
voltage. If there is another Renewable Energy source (wind, hydro, etc.) in the system, this source must not restrict
the battery voltage from reaching the GFX’s “Absorb” voltage and sustaining it for the “Absorb Time” (1 hour
default).
Capabilities
Currently, the Grid-tie inverters can only be classically stacked. Usually, this means that the system is limited to two
GFX’s, one per hot load leg. In reality, the number of GFX’s are limited to the number of hot load legs in the
power system. Future GFX systems will be capable of stacking up to 10 GFX’s.
A stacked system (two GFX’s) can provide up to 7.2 kW of power to your loads or to sell back to the utility grid.
If the utility grid fails, the GFX seamlessly transfers your loads to the battery bank. When the utility grid reappears,
the GFX automatically recharges your battery bank in case of future power outages.
WARNING: The X-240 transformer cannot be used for stacking with a GFX system at this time.
The X-240 can be used to step-down a generator or step-up the AC output of a single-GFX system, however.
Requirements
SOLAR PANEL (or another renewable energy source)
Your basic energy collecting device. The greater the power, the more you can sell back to the utility grid.
CHARGE CONTROLLER (Outback’s MX-60 is highly recommended)
Converts renewable energy to the proper voltage level in order to maintain healthy batteries, essentially
extending their life. Controllers using MPPT technology and multi-stage charging work best. The MX-60
works in conjunction with the GFX.
BATTERIES
Your batteries should have a capacity of at least 100 amp-hours (four car batteries), but there is not a
maximum limit. OutBack Power Systems recommends sealed AGM batteries because of their low
maintenance and low discharge rate.
OTHER
OutBack Power Systems Mate with a Code Revision of 3.30 or higher is needed if programming of any
kind is needed. OutBack Power Systems Hub is needed for stacking of two GFX’s or communication
between any OutBack products.
Performance
Once the complete system has been configured, it can be powered by connecting the batteries to the GFX’s through
the DC disconnect breakers. The LED’s on the GFX’s will light, showing the state of the batteries and the status of
the GFX’s. The GFX’s will automatically sense if the utility grid is present and connect to it after a 30 second time
delay. After sensing the utility grid, there is a five minute time delay before the GFX is able to start selling power or
charging the batteries. (This five minute period of time is due to UL regulations.) After the 5 minute time delay,
the GFX automatically charges the batteries. It performs this charge to ensure the batteries are full if the grid fails.
The GFX will not sell back to the grid until it performs this charge. After this charge is performed, the GFX will
operate under the constraints listed below. If the battery voltage is below 24.8 volts (for a 24 volt battery bank) or
49.6 volts (for a 48 volt battery bank) or the GFX has just been powered up, the GFX performs a “Bulk” charge,
otherwise it will go directly into “Silent” (no charge or sell) mode. This “Bulk” charge charges the batteries to the
“Absorb” voltage of 28.8 volts (for a 24 volt battery bank) or 57.6 volts (for a 48 volt battery bank). Once it reaches
this “Absorb” voltage level, it sustains this voltage for the “Absorb Time” of one hour. It performs this “Bulk” and
“Absorb” charge to regain 100% of the battery capacity. After this hour of time the GFX will go into “Silent” mode,
essentially doing nothing. At this time, if the batteries are above 25.6 volts (for a 24 volt battery bank) or 51.2 volts
(for a 48 volt battery bank), then the GFX will go into “Sell” mode. As long as the batteries are above the “Sell”
voltage the GFX’s will sell power back to the utility grid. If the batteries fall below the “Sell” voltage then the
inverter will go back into “Silent” mode. If the batteries fall to the “Refloat” voltage of 25.2 volts (for a 24 volt
battery bank) or 50.4 volts (for a 48 volt battery bank) then the GFX’s will perform a “Float” charge. The “Float”
charge charges the batteries to 27.2 volts (for a 24 volt battery bank) or 54.4 volts (for a 48 volt battery bank) for the
“Float Time” of one hour. If the batteries fall to 24.8 volts (for a 24 volt battery bank) or 49.6 volts (for a 48 volt
battery bank) then the GFX’s will do another “Bulk” charge as described above. With the Mate, the above
parameters can be adjusted to your specifications.
Certifications
All OutBack Power Systems GFX’s are listed under ETL following UL 1741 which also encompasses IEEE 929.
The GFX’s are listed on the CEC as 91% efficient for the 24V models and 92% efficient for the 48V models
Models
OutBack Power Systems Grid-Tie inverter/charger comes in the following models.
GTFX2524
Sealed with Turbo Kit, produces 2.5kW continuous, 24 V battery bank
GTFX3048
Sealed with Turbo Kit, produces 3.0kW continuous, 48 V battery bank
GVFX3524
Vented Chassis, produces 3.5kW continuous, 24 V battery bank
GVFX3648
Vented Chassis, produces 3.6kW continuous, 48 V battery bank