Using the Sunsynk Inverter as a Battery Charger

If a property has a string inverter installed on site it is possible to keep the current string inverter and use a Sunsynk inverter with batteries to utilise the excess power form the string inverter to charge these batteries.

Method 1: Connecting the String Inverter to the GEN terminals of your Sunsynk Inverter

The GEN terminals on the inverter can be used as an input or as an output, this means it is possible to connect the AC output of your string inverter directly to these terminals.

When using this method the string inverter size must NOT exceed the size of the Sunsynk inverter.

You can also connect a DC input to the MPPTs on the Sunsynk inverter whilst using this method however to do so we would recommend the string inverter connected has a power rating of no more than half of the Sunsynk Inverter.

Method 2: AC Coupling the String Inverter and the Sunsynk Inverter on the GRID/LOAD Side

This method is best if the string inverter has a larger capacity than the Sunsynk inverter as the Sunsynk inverter will not limit any PV produced by the string inverter and will only draw what is needed to charge the battery after the household consumption has been covered.

When installed in this way the string inverter will cover the household consumption first and then the Sunsynk CT will detect any export and reroute this into the battery. 

If the string inverter does not cover the full household consumption the Sunsynk inverter will be able to detect this load and discharge the battery to cover this.

In this set up you will see the battery charge as coming from the GRID and the household consumption will only display if not covered by the string inverter as all connections are on this side.

If you would like to record the values from the string inverter on the Sunsynk system you can use an Eastron Meter to send this data to the inverter. Below are some basic schematics and a link to the correct set up for this.

How to connect Eastron Meter for String Inverter Setup

Micro/String Inverter Input Settings

For these systems to work correctly the settings in the Auxiliary Load must be set accordingly.

Settings -> Aux Load -> For micro inverter input

MI Zero Export – When using the GEN terminals of the inverter when this setting is selected the micro inverter or string inverter will not export excess power to the GRID.

AC Couple OFF Batt -  When the battery SOC exceeds setting value, Micro inverter or the string inverter will shut down.

AC Couple ON Batt - If choosing “Micro inverter input”, as the battery SOC reaches a gradually setting value (OFF), during the process, the microinverter output power will decrease linearly. When the battery SOC equals to the setting value (OFF) the Microinverter will stop working and stop exporting power produced by the microinverter to the grid.

AC Couple on GRID Side – This should be selected if the string inverter is coupled to the distribution board on the GRID side.

AC Couple on LOAD side - This should be selected if the string inverter is coupled to the distribution board on the LOAD side.