Ran a garden office through winter on solar — here's what actually happened

So I finally have a full winter's worth of data on the garden office setup and thought it'd be worth sharing, especially for anyone planning a build and wondering whether solar is actually viable through the dark months in the UK.

Quick recap of the system: 600W of panels (four 150W Renogy monos on a south-facing pitched roof), a Victron SmartSolar 100/30 MPPT, and a 200Ah 12V Fogstar Drift LiFePO4 battery. The office runs a small oil-filled radiator on a thermostat (400W low setting), a monitor and laptop, and some LED lighting. Total draw on a working day lands somewhere between 600–900Wh depending on the temperature.

The honest truth? December and January were rough. I had strings of five or six days where the panels barely broke 100Wh for the day — fog, low sun angle, the lot. I ended up running a small Honda EU22i generator for a couple of hours twice a week just to top the battery up and avoid cycling it too deep. February surprised me though — output climbed noticeably around the third week and I haven't touched the genny since mid-March.

The bit I'm still chewing over is whether a second battery would have made more difference than extra panels for winter specifically. More capacity doesn't help if there's no sun to fill it, but it does mean I'm not stressing about depth of discharge during those grey runs. Anyone else wrestled with this? What did you land on?

@AndyButler really glad you posted this, been waiting for someone to share actual winter numbers rather than theoretical projections!

Quick question — what did your worst week look like in terms of solar yield? I'm in the planning stages for my own garden office and the December/January period is what's making me nervous. I've got a motorhome already running on a Victron MPPT setup with Fogstar lithium batteries, so I'm fairly comfortable with the tech side, but the shading and low sun angle in winter feels like a different beast on a fixed install.

Did you end up running any grid backup at all, or purely off-grid throughout? And what battery capacity are you running — did you wish you'd gone bigger in hindsight?

Basically throwing all my questions at you in one go, sorry! 😄

Really interested to see the full data @AndyButler.

My setup is primarily emergency backup rather than daily off-grid, so winter performance has always been my main concern when deciding whether to go full solar or keep grid tied.

Few questions if you don't mind:

• What battery capacity were you working with?
• Did you supplement with grid at any point or purely solar throughout?
• How did you handle the really grim weeks — we had some stretches in January where I doubt even a decent Victron MPPT was pulling much off panels

The issue I keep coming back to with garden offices specifically is the heating load in deep winter. Lights and a laptop is one thing, but even a small panel heater will absolutely hammer a battery bank by February.

What's your panel orientation — south facing or did you compromise?