Tiny house office on wheels — anyone else running pure solar with no grid hookup at all?

Moved my "office" into a converted horsebox six months ago and haven't touched the mains once — Victron SmartSolar 100/30, two Fogstar 100Ah lithium batteries, and a 400W panel on the roof doing all the heavy lifting.

Running a laptop, a small monitor, a desk fan in summer, and a little ceramic heater on the coldest mornings (don't @ me) — typically pulling about 8–12A during a working day, and the system keeps up surprisingly well even through the grim February gloom.

The one thing that's genuinely baffled me: battery state of charge is all over the shop according to the Victron app — sitting at 94% by 10am then somehow 71% by lunch without me doing anything differently. Anyone else find the SOC estimate goes a bit mad on smaller banks?

@CotswoldCruiser solid setup — the 100/30 is a decent controller but at 400W input you're brushing against its limits on a good day. Worth checking your charge current isn't clipping.

Running a similar arrangement at my cabin — Victron SmartSolar 150/45, three Fogstar Drift 100Ah in parallel, and 600W of panels. The 150/45 headroom makes a real difference when you need burst charging before a cloudy stretch.

One thing I'd flag: with two lithiums in parallel, make sure your Victron battery profile is tuned properly — absorption voltage especially. Fogstar publish recommended settings but the defaults can be conservative.

What's your average daily consumption? Knowing whether you're compute-heavy or mostly lighter loads changes the conversation about whether that bank size is genuinely comfortable or just technically sufficient on paper.

MarshPete | Posts: 847

@CotswoldCruiser nice setup! The Victron/Fogstar combo is solid — I ran something similar in a converted horsebox for about eight months before upgrading.

One thing worth checking: how are you getting on through the overcast winter days? That's where most people hit a wall. I ended up adding a small 300W inverter generator as a backup just for the absolute grim February weeks — ran it maybe four times total but the peace of mind was worth it.

Also, what's your actual daily consumption like? I found once I swapped to a 12V laptop charger directly rather than running through the inverter I saved a surprising amount. Little efficiency wins add up enormously when you're battery-limited.

What's the horsebox insulation situation? That affects heating loads massively in my experience.

PU_Sparks | Posts: 312

@CotswoldCruiser great to hear you're making it work year-round — six months is a proper test including some grim weather I'd imagine!

One thing worth keeping an eye on as we head into autumn: with lower sun angles and shorter days, that single 400W panel can really struggle to top the batteries up fully before dusk, especially on overcast days. You might find your state of charge creeping down week on week without noticing.

Chucking a cheap shunt-based battery monitor on there (the Victron BMV-712 pairs brilliantly with your existing SmartSolar via VictronConnect) will give you proper visibility on actual amp-hours rather than just voltage. Saved me from a nasty surprise last November when I thought I had plenty in reserve and absolutely didn't! 😄

What's your typical daily consumption looking like?

My horsebox office runs on fumes and optimism from October to February, so respect to @CotswoldCruiser for actually making it work — what's your winter strategy when the British sun decides to take a four-month holiday?