Pv inverteren on ac out 2

Anyone else running a grid-tie inverter on AC Out 2 of their Multiplus?

Got a similar setup in my shepherd's hut — Victron Multiplus-II 3000 and I've been toying with the idea of hanging a small string inverter off AC Out 2 rather than feeding everything through AC In. The thinking being that on sunny days the PV output helps serve the loads directly before anything touches the batteries.

Main thing I keep coming back to though — AC Out 2 is unswitched when on battery, so if the Multiplus drops to inverter mode overnight and your grid-tie inverter is still connected, does it just see a dead AC supply and shut itself off cleanly? Or does it try to backfeed and cause grief?

I've read a bit about using the Fronius/Victron combo where the Fronius sits on AC Out 1 and does the frequency-shift thing to throttle output — not sure if cheaper inverters like Omnik or even some of the Renogy/Growatt units have that same behaviour.

Couple of things I'd want to nail down before doing it:

• Does AC Out 2 give a clean enough sine wave to keep the string inverter happy?
• Any risk of islanding protection tripping constantly?
• VE.Configure settings needed?

Would be dead useful to hear from anyone who's actually wired it this way rather than just the theory. Feels like there's a lot of conflicting info on the Victron community forums and half of it relates to three-phase setups in mainland Europe which doesn't really translate.

@Gill1983 done exactly this on my narrowboat with a 600W string inverter on AC Out 2 of a Multiplus-II 3000.

The key thing to understand is that AC Out 2 is unswitched — it loses power when the Multiplus goes into inverter mode (i.e., no grid/shore power). So your grid-tie inverter will naturally shut down when shore power drops, which actually satisfies the G83/G98 anti-islanding requirement neatly.

What you'll want to configure in VEConfig:

• AC Out 2 assistant isn't strictly needed, but set your AC In current limits sensibly
• Make sure your grid-tie inverter's input voltage/frequency tolerance matches what the Multiplus presents

The gotcha I hit was the Multiplus's output frequency shifting under PowerAssist — some cheaper string inverters get confused. Fronius handles it beautifully. Generic "MPPT inverter" units from Amazon? Less so.

What string inverter are you considering?

@Gill1983 fellow shepherd's hut dweller here — just make sure your grid-tie inverter's anti-islanding doesn't throw a tantrum and shut itself off every time the Multiplus blinks, because mine spent a fortnight playing dead before I realised it was frequency-shifting it into submission.

@Gill1983 worth knowing that AC Out 2 goes dead the moment the grid drops, so your grid-tie inverter will shut itself off anyway — which is actually the one time you really want solar production. Classic off-grid irony right there.

The Multiplus essentially pulls the rug out from under the very thing you're relying on

Great thread, this. @Gill1983 one thing nobody's mentioned yet — check your Multiplus-II's AC Out 2 load capability against the grid-tie inverter's startup surge. The 3000VA unit can handle it fine in most cases, but if you're also running other loads on AC Out 2 simultaneously, you want to make sure you're not pushing the limits during cloudy spells when the grid-tie inverter is hunting around trying to sync.

Also worth setting a proper AC input current limit in VEConfigure so the Multiplus doesn't end up in a bizarre loop trying to compensate for the grid-tie output. I had a similar arrangement and spent a frustrating afternoon scratching my head before realising the assistant settings were fighting each other. Node-RED on a Cerbo GX can help you manage the logic if you want proper automation around it.

Good points all round here. One thing worth adding — if you're using VE.Configure or VEConfigure 3, make sure you've actually got AC Out 2 enabled in the settings, as it ships disabled by default on some firmware versions. Caught me out once. Also worth considering the frequency shift behaviour — your Multiplus can be set up to nudge the frequency upward when the batteries are full, which will throttle a compatible grid-tie inverter back nicely rather than just cutting it dead. Not all cheap string inverters respond to that properly though, so check the specs on whatever unit you're looking at @Gill1983. Some of the budget ones from the usual Chinese sellers are a bit deaf to frequency signalling and you'll get odd behaviour.