Went off-grid in my garden office last month — here's what I've learned so far

I finally took the plunge and cut the extension lead from the house. Running a 400W solar setup on the roof of my 4x3m timber office — two 200W panels feeding into a Victron MPPT 75/15, then into a 100Ah lithium (a cheapo LiFePO4 from a UK eBay seller). Inverter is a Victron Phoenix 12/375 for the occasional laptop charge and a desk lamp. Most stuff runs direct 12V where I can manage it.

Honestly it's been fine on the sunny days we've had, but I'm sitting here now in mid-October with two grey days back to back and the battery dropped to about 60% by end of day yesterday. I've got a small fan heater that I've been avoiding using but the damp is starting to get to me. Wondering whether a low-wattage panel heater on a thermostat would be more sensible than trying to run heat from the inverter at all.

The one thing that's caught me out is just how much a monitor draws. I swapped my old Dell 24" for a newer LED one and that alone made a noticeable difference on the Victron app — down from about 35W to 18W just sitting idle. Small wins, I suppose.

Has anyone else gone fully off-grid with a garden office through a UK winter? Curious what your lowest battery state of charge has been and whether you've had to add a backup charging source — I'm eyeing up a small mains hookup just for winter top-ups but it feels like admitting defeat a bit.

@JackieScott really interesting setup — a couple of questions if you don't mind:

1. What battery capacity are you running behind that MPPT? The 75/15 maxes out at around 220W input really, so your two 200W panels are already pushing it depending on your wiring config.
2. How are you handling the darker months? I'm planning something very similar for my own garden office and the November–February period in the UK is what keeps me awake at night — even a south-facing array can struggle badly.

Also worth asking — are you monitoring via the Victron app? The historical data from VictronConnect is genuinely useful for spotting patterns in your consumption vs. generation over the first few weeks.

What's your primary load — lighting and laptop, or are you running anything heavier?

@JackieScott nice one for making the jump! Curious what your winter numbers are looking like — that's where most garden office setups get caught out. Two 200W panels on a 4x3 roof is fine in summer but December/January can be brutal, especially if you're in the north.

I run a similar setup purely as emergency backup so I'm not sweating daily consumption, but if you're relying on it full-time you might want to look at a small Fogstar Drift LiFePO4 to squeeze more usable capacity out of your bank.

What's your main load — laptop, monitor, that sort of thing? Makes a big difference whether you'll need to supplement with a small inverter-charger on grey days.

@JackieScott this takes me right back to when I first unplugged my own garden office — that mix of excitement and mild terror is very real!

One thing nobody warned me about: winter morning voltage sag when you've got a cold battery bank and fire up the laptop simultaneously. My Fogstar lithium cells handled it far better than the lead-acid setup I started with, but it still caught me off guard those first grey November mornings.

Also worth logging your daily consumption properly from the start — I wish I had. When I later added EV charging capability to mine, having baseline data made sizing the extra capacity so much easier rather than just guessing.

What inverter are you running? That'll tell us a lot about how your setup will cope with any spikier loads down the line.