AC Coupled Grid-tie with Battery Backup Power Systems
|Grid Tie to Off Grid Backup Power Models||Backup Inverter Max Output||AC Volts||Battery Bank||Power Supply||Part Number||Price|
|American Gridtie Independence 4400
|4,400 watts||240||See Options||Gridtied Solar Array
|American Gridtie Independence 8800
|8,800 watts||240||See Options||Gridtied Solar Array
|American Gridtie Independence 13,200
|13,200 watts||240||See Options||Gridtied Solar Array
A lot of folks believe that a solar power system will protect them from blackouts. While this is true of off-grid systems, grid-tie systems shut off when the grid goes down. Micro-grid AC Coupling allows a grid-tie system to work with a backup battery system that can be charged even during grid blackouts. It's perfect for folks who want to add a battery back-up package to their existing grid-tie solar power system.
In an AC Coupled solar power system, a grid-tied inverter can continue to operate during grid power outages by syncing with the output of a battery-based inverter. In this scenario, both inverters are connected to the "critical loads" sub-panel. A "critical loads" sub panel is a subsidiary breaker panel that's separate from a building's main breaker panel, designated only for appliances backed up during power outages.
Wholesale Solar designs and sells AC Coupled systems using Magnum Energy PAE series inverters, because they are the safest and most versatile inverter for this type of application.They will not backfeed to the grid, and they can be "coupled" with a variety of grid-tie inverters including microinverters.
How do these Micro-grid AC Coupling Systems work?
When the grid is functioning normally, the Magnum Energy inverter will use both the utility grid power and the AC output of the string inverter to maintain charge on the battery bank and to power the critical loads.
During utility blackouts, the Magnum off-grid inverter creates a "local grid" by supplying power to the critical loads in the subpanel. The grid-tie inverter doesn't disconnect because it doesn't know the difference between the utility produced grid and the "local grid" created by the Magnum inverter. When the grid is working, the Magnum inverter allows solar power produced by the gridtie array to feed back to the main utility service breaker panel. The Magnum Inverter is UL 1741 compliant which means it won't backfeed a dead power line.
In its AC-Coupled mode, the Magnum inverter will shift its frequency to 60.6 Hz to un-synchronize with the grid-tie inverter or back to 60.0 Hz to re-synchronize. The battery will re-sync and charge when the voltage falls too low, and unsync when the voltage rises too high to prevent overcharging.
Click image to enlarge diagram
Advantages and Conveniences of Battery-based Inverters that can be AC Coupled into Existing Utility-interactive Inverter Systems
- The connection from the renewable energy source to the utility-interactive inverter doesn’t require any rewiring. (This is typically required with standard back-up inverters to provide the battery charging requirements).
- Connects in parallel with the utility circuit to provide charging to the inverter’s battery bank.
- If there is a utility failure, the inverter’s transfer switch will de-couple from the utility circuit (so not to energize the grid and create a safety hazard).
- Provides the AC voltage and frequency reference needed for the utility-interactive inverter to continue to operate while using the renewable energy to provide power to the home during a power outage.
- Capable of operating as a standalone inverter or Standby mode (battery charging with AC transfer), with automatic transition from one state to the other.
Block Diagram of Utility-interactive Inverter AC Coupled To Backup Inverter - Normal Operation