Good news to off-grid installers: SMA is happy to announce that starting this month, all approved Sunny Boy inverters will be shipped with the Backup Mode parameter installed to the “On_all” setting.
In a grid tied battery backup application, the relationship between a Sunny Boy and a Sunny Island is like nothing else. Each inverter is in tune with the other and responds precisely when the other makes a request. However, advanced communication protocol is only available when a specific parameter is set within the Sunny Boy.
Previously, the default Backup Mode parameter had been set to “off.” Changing this setting at the factory will simplify installations since installers will not need a communication device to change the parameter setting when installing and commissioning AC coupled systems. One less concern for installers and one more step closer to commissioning and making clean, renewable power.
How it works
In a battery backup AC coupled application, the Sunny Island will increase its bus frequency to reduce the output power of the Sunny Boy. The Sunny Island performs this frequency shift to prevent the excess PV from overcharging batteries and only increases the frequency when these three conditions exist:
- The grid is out
- All batteries are fully charged
- There is no demand on the protected loads panel
When the Backup Mode parameter is set to “On_All,” the Sunny Boy will respond to the Sunny Island command to enter into “backup mode” when the grid goes down. Once in Backup Mode, the Sunny Boy will open various voltage and frequency windows that are wider than the limits which the inverter is normally constrained to. However, with the Sunny Island as the gatekeeper to the grid, no PV will back feed when the grid is down—the Sunny Boy can operate in this UL approved mode all it wants!
Communication is the key
It’s important to note that the Sunny Boy will only open these windows when the Sunny Island gives the command and it will return to the original default values when the Sunny Island sends a command to go back to the original values once grid is operational. These commands are sent via RS485 wiring that must be installed with the system.
The communication abilities between the Sunny Island and Sunny Boy via RS485 are crucial to the system’s success. Without it, the Sunny Boy would not be able to switch to Backup Mode when the Sunny Island sent its commands. Since the Sunny Boy wouldn’t open its voltage and frequency windows it’s still restricted to the preset frequency limits of 59.3 to 60.5Hz. When the Sunny Island increases its frequency the Sunny Boy will trip off just like a regular grid tied scenario with a bad grid. This same reaction would occur in a system using a non-SMA inverter in an AC coupled application.
To view a list of approved SMA inverters that can ship with Backup Mode enabled, click here.
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