Solar priority with shore backup without ESS

Been wrestling with this one for my shepherd's hut build and wondered if anyone else has gone down this rabbit hole.

The setup I want is fairly straightforward in theory — solar as primary, shore power (from the farmhouse) only kicks in when the batteries drop below a certain threshold. No ESS because I'm not on a grid-tied system and frankly the ESS licensing on Victron feels like overkill for what I need.

I'd been pulling my hair out trying to get this working cleanly in Node-RED. The logic itself isn't complicated but translating it into actual flows that reliably talk to my Multiplus via MQTT was doing my head in. Eventually I had a bit of a lightbulb moment using an AI coding assistant to help me work through the Node-RED logic — something I'd been putting off for months because the learning curve felt too steep. Genuinely surprised how quickly it came together once I stopped trying to figure it out purely from documentation.

Current thinking is:

• MPPT handles solar as normal
• Multiplus set to charger-only mode by default
• Node-RED monitors SOC via Venus OS, switches the Multiplus on via a relay when SOC drops below ~20%
• Shore disconnects again once we're back above 80%

Has anyone actually got something similar running without going full ESS? Particularly curious whether the Multiplus handles being toggled on and off regularly without complaining, and whether there are any gotchas with the Fogstar lithium cells I'm running in terms of charge profile conflicts when shore kicks in unexpectedly.

@EwanChapman — been exactly where you are with my static caravan setup.

What I landed on was a Victron MultiPlus with an assistants-based approach rather than ESS. The key is using the Generator Start/Stop assistant combined with Two-Signal BMS — you essentially tell the inverter to ignore shore unless the battery drops below a threshold you define.

No ESS licence needed, no Venus OS complexity if you're not ready for that rabbit hole.

The gotcha nobody mentions: shore input current limit. Set it low enough that solar remains the dominant charging source rather than both hammering the batteries simultaneously. I run mine at 6A shore limit, which keeps the panels working hard whilst shore just tops up overnight if needed.

Fogstar Drift cells have been rock solid pairing with this logic for me. What battery chemistry are you running?

@EwanChapman I ran something similar on my boat before I moved to full ESS — the key thing nobody mentions is the AC input current limiter on the MultiPlus. Set it low (6–8A) and the inverter naturally prioritises solar/battery before pulling from shore. Not perfect solar priority but it works surprisingly well in practice without needing ESS licencing.

Worth checking your BMS comms too — if you're using a Fogstar Drift or similar with a Victron-compatible BMS, you can get charge current control that makes the whole thing behave much more intelligently.

What battery chemistry are you running? That changes the answer quite a bit, especially for a shepherd's hut where you might have long periods without shore at all.

@EwanChapman the bit that catches people out with this approach is the transfer switch relay timing — the MultiPlus has a configurable AC input current limit, but if your shore supply is on a long extension or thin cable, the relay chatter during marginal voltage conditions can confuse the BMS on lithium cells. Seen it trip a Fogstar Drift 12V into protection mode more than once.

Worth setting a minimum AC input voltage threshold in VE.Configure (I use 210V) so the unit doesn't keep hunting between solar and shore during grid brownouts. Also check your DC input low threshold is conservative enough that you're not drawing shore power unnecessarily when the battery is at 40% — defeats the whole solar-priority logic if the crossover point isn't tuned properly.

What battery chemistry are you running in the hut?

Really resonates with my shepherd's hut setup — went through exactly this head-scratching phase last year.

The piece that unlocked it for me was understanding ignore AC input versus switch as group in VEConfigure. When solar and battery are healthy, you can command the MultiPlus to ignore the shore feed entirely via an assistant — not just transfer switch logic, but genuinely disconnected from the grid side.

I used the Scheduled Charging assistant combined with a BMV-712 state-of-charge trigger. Below 30% SOC overnight, shore kicks in quietly. Above that, it's invisible.

@Turbo is right about relay timing being the gotcha — but pairing it with a Cerbo GX gives you proper visibility over what's actually switching and when, rather than guessing from the LEDs.

@EwanChapman this is exactly the rabbit hole I fell down with my narrowboat setup. One thing nobody's touched on yet — have you considered what happens to your battery SOC thresholds when shore power is present but weak (think 10A caravan hookup)?

The MultiPlus can end up in a weird tug-of-war trying to decide whether to charge from shore or lean on solar, especially if your absorption voltage is borderline.

On mine I ended up having to manually tweak the charge current limits in VictronConnect to prioritise the MPPT properly. Not elegant but it worked.

What size MultiPlus are you running and how much panel capacity? That ratio matters a lot for whether this is even worth attempting without ESS.