VANPOWERCALC

Adding Victron AC Coupling to a SolarEdge + LG Chem Battery Setup

How to add AC coupling with a Victron MultiPlus to a SolarEdge + LG Chem RESU system for backup power during grid outages.

The Problem: No Power During Grid Outages

You have a beautiful 6.3 kW SolarEdge system with S500B optimizers, a SE6000H inverter, and an LG Chem RESU 10H (9.6 kWh) battery. Everything works flawlessly — until the grid goes down. Then your inverter goes into safety mode, the LG Chem shuts off, and you sit in the dark surrounded by thousands of watts of unused solar capacity on your roof. This is by design: grid-tied inverters must disconnect during outages to prevent back-feeding the grid (anti-islanding protection).

The Solution: AC Coupling with Victron MultiPlus

AC coupling allows you to create a micro-grid behind your main panel. A Victron MultiPlus II (3000VA or 5000VA) sits between the grid connection and your SolarEdge inverter. When the grid drops, the MultiPlus creates its own 230V reference signal, allowing the SolarEdge to continue producing solar power. That solar power either feeds your critical loads directly or charges a secondary battery bank (typically Pylontech US3000C or similar).

The Complication: Existing LG Chem Battery

Here's where it gets tricky. The LG Chem RESU is tightly coupled to the SolarEdge inverter via a dedicated StorEdge interface. It's not designed to work simultaneously with a Victron-managed battery like Pylontech. The LG Chem communicates over CAN bus with the SolarEdge and may interfere with the MultiPlus's frequency-shifting algorithm that controls solar production during backup mode.

Recommended Configuration

The cleanest approach: (1) Keep the LG Chem connected to the SolarEdge for daily self-consumption and grid arbitrage. (2) Install the Victron MultiPlus II on a separate sub-panel feeding only critical loads (fridge, router, lights). (3) Add a separate Pylontech battery bank managed exclusively by the Victron. (4) Use a Victron GX device (Cerbo GX) to communicate with SolarEdge via the SolarEdge Modbus interface — this allows the Victron to monitor total solar production and manage battery charging without conflicting with the LG Chem. The key rule: the LG Chem and Pylontech must never be on the same DC bus or CAN bus. Keep them electrically isolated; the Victron handles only the Pylontech, and the SolarEdge handles only the LG Chem.

⚡ Expert tip
During a grid outage with AC coupling, the Victron must use frequency shifting to throttle SolarEdge production when batteries are full. If this isn't configured correctly, excess solar can damage the MultiPlus — set the frequency shift parameters in VEConfigure before commissioning.

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Comparison table

ComponentRoleManaged By
SolarEdge SE6000HGrid-tied solar inverterSolarEdge system
LG Chem RESU 10HDaily self-consumption batterySolarEdge StorEdge
Victron MultiPlus IIBackup inverter + micro-gridVictron GX
Pylontech US3000CBackup battery bankVictron GX
Cerbo GXSystem monitor + frequency shiftingVictron ecosystem

About this tool

Adding a Victron AC-coupled battery backup to an existing SolarEdge + LG Chem system is a project that many homeowners attempt after a grid outage shows the limitation of their current setup: most grid-tied solar systems without battery storage go dark the moment grid power fails, even on a sunny day. AC coupling Victron hardware to a SolarEdge system solves this, but requires careful configuration to work reliably.

How AC coupling works with Victron MultiPlus: the Victron MultiPlus or Quattro creates an "island" grid during a power outage — it became the synthetic grid reference for the PV inverter. The SolarEdge inverter, which is a grid-following device, synchronizes to the Victron frequency and continues producing power. The AC-coupled energy flows to both the loads and the Victron battery bank simultaneously, so consumption and storage happen in real time.

Frequency shifting — the critical control mechanism: Victron uses frequency shift (the Watt-frequency principle) to control power flow from the SolarEdge inverter. When the LG Chem batteries reach 100% SOC, the Victron MultiPlus raises the AC frequency from 50.0 Hz to 51.0-53.0 Hz. SolarEdge inverters, when they detect frequency above 50.2 Hz, automatically reduce output by a ratio defined in the EN 50549 standard (P(f) curve). This is the only way Victron can "dim" the solar production without direct communication with SolarEdge. If the SolarEdge inverter's P(f) curve is not enabled (it's disabled by default in many markets), the battery will overcharge — this is the most common failure in this configuration.

Enabling P(f) on SolarEdge: access the SolarEdge SetApp (requires installer license in some regions) → Advanced → Grid Protection → P(f) Droop Function → Enable. Set: Overfrequency threshold: 50.2 Hz. Maximum droop: 100% (full reduction at 52 Hz). This allows Victron to fully curtail SolarEdge output using frequency — essential for safe AC coupling.

LG Chem RESU compatibility with Victron: if you're adding Victron to control the LG Chem as the battery in this island setup, use the Victron CCGX or CerboGX with the LG Chem CAN-bus communication cable. The LG RESU 10H communicates via CAN at 500kbps and the CCGX supports this natively. Without CAN communication, the Victron does not know the LG Chem's SOC accurately and will rely only on voltage-based estimation.

Frequently asked questions

Can I use Victron with a SolarEdge inverter?▼
Yes, through AC coupling. The Victron MultiPlus creates a micro-grid reference signal that allows the grid-tied SolarEdge to keep producing during outages.
Will the LG Chem battery conflict with Pylontech?▼
Only if they share the same CAN bus or DC bus. Keep them electrically isolated: LG Chem managed by SolarEdge, Pylontech managed by Victron.
Do I need a GX device for AC coupling?▼
Yes, a Victron Cerbo GX or Venus GX is needed to manage frequency shifting and communicate with the SolarEdge via Modbus for production monitoring.
What size Victron MultiPlus do I need?▼
For a 6.3 kW SolarEdge system, a MultiPlus II 5000VA is ideal. A 3000VA works if you limit critical loads to 2.4 kW.
Can SolarEdge SE6000H work in off-grid mode?▼
Not truly off-grid alone, but with AC coupling via a Victron MultiPlus, it can work in island mode as long as the MultiPlus provides the 230V reference signal.

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