Set grid setpoint on multi rs solar duo via home assistant

Been down this rabbit hole myself recently. Got a Multi RS Solar paired with a Cerbo GX and I've been trying to get proper grid setpoint control working through Home Assistant via Modbus TCP.

The idea is straightforward enough — you want HA to dynamically tell the inverter how much to pull from (or push to) the grid depending on battery state, tariff rates, whatever. Dead useful if you're on Octopus Flux or similar and want to charge cheap overnight then export during peak.

My issue is that the grid setpoint register doesn't seem to behave consistently. Sometimes HA writes the value and the Cerbo picks it up instantly, other times it just... ignores it. Wondering if there's a polling conflict or whether the VRM integration and Modbus are stepping on each other.

Few things I'd try (or have tried):

• Make sure you're writing to the correct Modbus unit ID — the Multi RS uses a different one than the Cerbo itself
• Check the ESS assistant is actually installed and active, otherwise grid setpoint does nothing
• Throttle your HA write frequency — hammering it every 5 seconds seems to cause odd behaviour

Anyone else got this working reliably on firmware v1.31? I'm also curious whether the Victron MQTT route is more stable than Modbus for this kind of control. Seems like fewer moving parts potentially.

Would love to see someone's actual HA automation if you've cracked it — happy to share mine in return once I've got it behaving properly.

@MarineGaz the Multi RS Solar is a bit of a special case here — it uses a different internal architecture to the standard Multis, and the grid setpoint via Modbus TCP behaves differently depending on your ESS assistant version.

Key thing to check: on the Cerbo, make sure you're writing to register 2700 (ESS control loop setpoint) rather than the generic inverter registers. The Multi RS also requires ESS mode to be properly enabled with the correct AC input type configured, otherwise the setpoint writes just get silently ignored — no error, it just does nothing.

I had exactly this on my garden office setup. Verified the register was accepting writes via mbpoll on the command line before even touching HA. Saved hours of debugging the HA side when the problem was actually upstream.

What firmware are you running on the Multi RS? There were some ESS-related fixes around v1.08.

@MarineGaz worth knowing the Multi RS Solar doesn't support ESS in the traditional sense — it runs its own internal MPPT logic and the grid setpoint register (2700 on the VE.Bus service) simply doesn't behave the same way as it does on a Multiplus-II setup. I wasted two weekends on this before someone on the Victron community forums pointed out that the RS series uses a completely different charge controller architecture internally.

Your Cerbo GX will expose it via Modbus TCP fine, but writing to that register will either be ignored or cause unpredictable behaviour depending on firmware version.

Check which firmware your Multi RS is actually running first — there were some significant ESS-adjacent changes around the 1.08/1.09 releases. The Victron changelog is poorly documented as usual but it's worth cross-referencing against the VRM portal device info.

Yeah this caught me out too when I was setting up my garden office system. The Multi RS Solar handles grid interaction differently — you can't just chuck a grid setpoint at it the same way you would with a Quattro or standard Multiplus.

What actually works is using the ESS minimum SOC and AC input current limit registers via Modbus rather than direct setpoint control. On my Cerbo I mapped these through HA and got reasonable control that way.

Register 2700 for AC input current limit is your friend here — tweak that dynamically and you're effectively throttling grid draw indirectly.

Also check the VRM portal to confirm your firmware is current — there were some Multi RS specific fixes in recent releases that changed what's exposed over Modbus. Might be worth cross-referencing the Victron Modbus TCP register list PDF, the Multi RS has its own section now.

Good shout from @HeathOllie and @SolarJunkie there. To add a bit of practical detail — the register you're after on the Multi RS Solar is different to what you'd use on a standard Multiplus with ESS. Through the Cerbo GX via Modbus TCP, have a look at register 2700 on the vebus device unit ID, but honestly I'd strongly recommend cross-referencing against the current Victron Modbus TCP register list PDF rather than going off anything you find on older forum posts, as it's changed a fair few times.

Also worth checking whether your firmware is up to date on both the Multi RS Solar and the Cerbo — Victron have been actively developing the Multi RS Solar's grid interaction capabilities and some features simply weren't available on earlier firmware versions. What firmware are you currently running on each?