AC Coupling Solar to a Sunsynk Hybrid Inverter

Key Takeaways

• AC coupling integrates an existing string or micro-inverter array with a Sunsynk Classic, Acure, or Elite hybrid inverter.
• Connecting to the Sunsynk's GEN terminals allows your AC-coupled array to function during load-shedding.
• The string inverter's size must not exceed the Sunsynk's size, and half that if DC PV is also connected.
• Always ensure all work is performed by a registered person to maintain your Certificate of Compliance (CoC).

Integrating an Existing Solar Array with a Sunsynk Hybrid Inverter

AC coupling allows you to add battery storage and hybrid inverter functionality to an existing grid-tied solar system that uses a string inverter or micro-inverters. This is a common upgrade path in South Africa for homeowners looking to enhance their energy independence and manage load-shedding with their current solar infrastructure. Sunsynk Classic, Acure, and Elite hybrid inverters support two main AC coupling topologies.

How AC Coupling Works with Sunsynk Inverters

AC coupling involves connecting the AC output of your existing string inverter to your Sunsynk hybrid inverter. The Sunsynk inverter then manages the power flow, directing excess solar generation to charge batteries, supply household loads, or, if configured, export to the grid.

There are two primary methods for AC coupling with Sunsynk Classic, Acure, and Elite inverters:

Method 1: Connecting to the GEN Terminals

This method involves connecting the AC output of your string inverter directly to the Sunsynk inverter's GEN terminals.

What happens: The GEN terminals on the inverter can be used as an input. This means it is possible to connect the AC output of your string inverter directly to these terminals. This setup allows the string inverter to contribute power even when the grid is down, providing backup power during load-shedding.

Sizing Rules:

• When using this method, the string inverter size must NOT exceed the size of the Sunsynk inverter.
• If DC input is also connected to the Sunsynk's MPPTs, the string inverter connected should have a power rating of no more than half of the Sunsynk Inverter.

Method 2: Connecting on the GRID/LOAD Side

This method involves AC coupling the string inverter and the Sunsynk inverter on the GRID/LOAD side of your distribution board.

What happens: The string inverter will cover the household consumption first. The Sunsynk CT (Current Transformer) will then detect any export from the string inverter 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 it.

Sizing Implication: This method is best if the string inverter has a larger capacity than the Sunsynk inverter.

Monitoring Considerations: In this setup, you will see the battery charge appearing to come from the GRID on your monitoring interface. The household consumption will only display if it is not fully covered by the string inverter, as all connections are on this side.

Data Integration: 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. This meter would typically be configured as the second meter on address 002. For more details on meter configuration, refer to our guide on /za/guides/systems/sunsynk-eastron-meter-vs-ct-clamp.

Essential Settings for AC-Coupled Systems

Sunsynk Classic, Acure, and Elite inverters offer specific settings to manage AC-coupled systems. These are found within the inverter's menu.

What You Can Change Yourself, and What You Cannot

Owner-facing settings such as AC Couple OFF Batt and AC Couple ON Batt (which determine battery State of Charge thresholds) can typically be adjusted by the homeowner to suit their energy needs.

However, settings related to grid protection, export limits, and the fundamental configuration of the AC coupling topology (e.g., MI Zero Export, AC Couple on GRID Side, AC Couple on LOAD side) are critical for safe operation and compliance with South African grid regulations (NRS 097-2-1). Changing these settings requires a registered person. Any work on the electrical installation, including the connection of inverters and solar arrays, must be performed by a qualified and registered electrician. This ensures compliance and maintains the validity of your Certificate of Compliance (CoC). Unauthorised changes can void warranties, breach connection agreements, and pose safety risks.

What the Published Sources Do Not Tell You

The Sunsynk documentation for AC coupling, while comprehensive for setup, does not explicitly detail the behaviour of grid-side AC-coupled PV generation during a grid outage or load-shedding event. This is a critical consideration for South African users.

Additionally, the documentation does not specify default values for AC Couple ON Batt or AC Couple OFF Batt settings, nor does it provide a list of compatible third-party string or micro-inverters. It also does not state maximum AC-coupled input power limits or GEN-terminal current ratings for specific Sunsynk inverter models.

If you encounter a fault code such as F47 or W04, which can be expected in AC-coupled systems due to frequency shifting, refer to our dedicated guide on /za/guides/fixes/sunsynk-fault-codes-explained for troubleshooting.