Projet d’amélioration d’une installation solaire

Been mulling over a similar setup for my cabin and wondering if anyone's gone down this route.

Currently looking at pairing rooftop panels with microinverters feeding into a Victron Multiplus II — specifically using the AC-in to harvest grid-tied surplus rather than running everything through a traditional MPPT/battery bank arrangement. The appeal is obvious: you get the panel-level optimisation of something like Enphase IQ8 units, then the Multiplus mops up whatever's left over.

My scepticism kicks in around a few things though:

• Frequency shifting — the Multiplus needs to signal the microinverters to throttle back via frequency. Does this play nicely with Enphase's firmware in a genuine off-grid scenario, or does it get tetchy?
• Sizing — if you're running, say, 3kWp of panels through microinverters, is a 3kVA Multiplus actually sufficient, or does it become a bottleneck on cloudy days when the inverter's also trying to charge a Fogstar Drift LiFePO4 bank?
• Regulatory headaches — G98/G99 compliance gets complicated when you're deliberately designing around grid export. Anyone had grief with DNO sign-off in this kind of hybrid arrangement?

For the boat and cabin I run more conventional Victron MPPT setups, and honestly they're dead simple. But I can see the argument for microinverters if you've got shading issues or an awkward roof.

Anyone actually running this kind of AC-coupled microinverter + Multiplus configuration in a UK off-grid context? Curious whether it's elegant in practice or a faff to commission.

@RelayNomad worth noting that microinverters output AC, so you can't directly charge a battery bank from them without an AC coupling arrangement. The Multiplus II can do AC coupling, but there's a frequency-shifting limitation — Victron's rule of thumb is the 1:1 rule, meaning your AC-coupled inverter capacity shouldn't exceed your battery inverter's capacity.

Also, that thread title's in French — this is an English-language forum 🙂

On my narrowboat I went straight DC-coupled with MPPT controllers (Victron SmartSolar 100/30s). Much simpler, fewer conversion losses. Microinverters make sense for grid-tied but in off-grid they add unnecessary complexity.

What's your battery chemistry? If you're on LiFePO4 the comms integration with Victron kit is worth factoring in.

@OakSpirit has already nailed the core problem, so I won't retread that.

What I will say is I went down a similar rabbit hole with my motorhome before eventually settling the cabin setup properly. The cleaner path — and the one I wish someone had spelled out bluntly for me — is to ditch the microinverters entirely and run standard string panels directly into a Victron SmartSolar MPPT. Your Multiplus II then handles the inverter side. Everything talks to everything via VE.Can or VE.Direct, you get proper Victron ecosystem integration, and the Cerbo GX gives you full visibility.

Fogstar or EVE cells for the battery bank if you're budget-conscious. Pylontech if you want plug-and-play.

Microinverters make sense grid-tied. Off-grid they just introduce an unnecessary conversion layer that costs you efficiency and headaches.

@RelayNomad one workaround I've seen used (and briefly considered for my garden office before going full DC-coupled) is running the microinverter AC output into the Multiplus II's AC-in, letting it charge the batteries via the internal charger. It works, technically, but you're stacking conversion losses — DC→AC from the microinverters, then AC→DC back into the batteries. Victron's own efficiency figures take a hammering.

For anything beyond a basic backup role, a proper MPPT charge controller with DC-coupled panels will serve you far better. I run a Victron SmartSolar on mine and the difference is tangible, especially on those grim grey UK winter days when every watt counts.

If you're already committed to the microinverters for some reason, at least make sure the Multiplus is sized generously enough to handle the charge current without throttling.

AC-coupling via the Multiplus II's grid input works a treat — Victron even has a whole frequency-shift curtailment trick built in so it doesn't explode when your batteries are full, which mine nearly did before I read the manual properly.