Opportunity loads - turned on with no solar!

Got me thinking about my own setup at the static van — running a Victron system with a Shelly 1PM on the immersion heater, triggered via Node-RED when the Fogstar Drift hits 90% SOC.

Works an absolute treat until it doesn't.

Had a right head-scratcher last week: woke up to find the immersion had fired up at 2am with zero solar generation and the batteries sitting at 87% (presumably coasted up there slowly from a tiny residual load disappearing). The Shelly had no idea it was the middle of the night — it just saw the SOC threshold get crossed and cracked on regardless.

The core problem is that opportunity loads triggered purely on SOC have no awareness of why the batteries are at that level — surplus solar coming in vs. just quietly sitting there overnight doing nothing.

My workaround now is adding a second condition: battery charge current must also be above a threshold (say 10A+) before the Shelly fires. That way it's genuinely triggering on solar abundance, not just a lucky number.

Anyone else been bitten by this? Curious whether folks are using:

• SOC + charge current (my current bodge)
• Time-of-day windows to fence it off overnight
• Something smarter through VRM or Home Assistant automations?

Would love to know how others are handling it — feels like there's a dozen ways to skin this cat and I've probably tried the worst one first. 🐱

@24VPro nice one — similar vibe here with the shepherd's hut setup. Got a Shelly Plus 1PM on the kettle and a small EV charger, both triggered off Victron MQTT when SOC hits 85%.

The fun bit is stacking the priority — kettle first, then if still above 90% after 10 mins, charger kicks in. Dead simple in Node-RED once you've got your head round the flow logic.

Only gotcha I'd flag: make sure you're pulling SOC from the BMV/SmartShunt rather than the MPPT — learned that one the hard way when the van nearly boiled itself dry on a cloudy November 😅

@24VPro the real opportunity load is realising you've left the immersion on at midnight and your Fogstar's doing its best impression of a hand warmer 🔥

@VanKen 😂 been there — woke up to a BMS low voltage alarm at 2am because I'd manually overridden the Shelly and forgot about it. Lesson learned the hard way.

One thing worth adding — if you're running Node-RED for this, set a time window condition as well as SOC threshold. My immersion only triggers between 10am–3pm and above 85% now. Means you're not accidentally dumping into a load at dusk when the Fogstar's at 90% but dropping fast with no solar coming in.

Stack the conditions, not just the SOC figure. Makes a big difference to whether you're actually using surplus or just eating into your overnight reserve.

Haha @ShortCircuit that 2am alarm is a rite of passage it seems!

I've got a similar Node-RED flow on my setup but added a second condition after a near-miss — it checks the time as well as SOC, so nothing fires up after 8pm regardless. Means on overcast days I'm not accidentally hammering the batteries overnight when I thought I had plenty in reserve.

Also worth looking at @24VPro — I added a rolling average of the solar input watts as a trigger condition alongside SOC. Stops the immersion kicking in during a brief sunny spell that won't last. Mine's been running really reliably since I tweaked that. Took a bit of faffing in Node-RED but there are decent flow examples over on the Victron Community forum if you search for "opportunity load" — saved me a lot of head-scratching.