Anyone actually running a garden office purely off-grid year-round in the UK — is it genuinely doable?

After squeezing every watt out of my motorhome setup (200Ah Fogstar lithium, 400W of panels, Victron MPPT), I'm wondering if the same logic scales up to a proper garden office my missus wants built at the bottom of the garden.

Thinking something like 2x 200W panels on a south-facing tilt mount, a decent 100Ah+ lithium bank, and a Victron MultiPlus for the inverter side — running a laptop, monitor, desk lamp, and a small fan heater occasionally. The heater is obviously the scary bit in winter.

Has anyone cracked this without just caving and trenching a cable from the house? Genuinely curious whether UK winters make it a fool's errand or if a bigger battery bank just solves it.

@AlexHobbs the narrowboat life taught me everything I needed to know about this exact question — because a liveaboard through a British winter is essentially a floating garden office stress test.

Short answer: yes, genuinely doable, but winter is the honest reckoning. Your Fogstar/Victron combo is already the right instinct — scale it properly and you're most of the way there.

What tripped me up was underestimating loads in November-February. Heating is the killer. I moved to a small Webasto diesel heater rather than fighting the inverter with electric. Freed up enormous capacity for screens and lighting.

The panels need to be tilted steeper than summer logic suggests — 50-60° captures that low winter sun properly. Roof-mounted flat is basically decorative in January.

Size your battery bank for 3-4 cloudy days minimum, not sunny-day figures.

@AlexHobbs the scaling logic holds, but the UK winter is where garden offices bite harder than motorhomes or boats. You're not moving south.

My shepherds hut setup taught me that south-facing shading matters enormously — a neighbour's roof or mature tree that seems harmless in summer will tank your December generation by 40-60%. Model your worst-case irradiance properly (PVGIS is your friend, use the hourly data not just annual averages).

Key differences from your motorhome rig:

• Static load profile means you can size batteries more precisely
• Heating demand is the killer — resistive heating is a non-starter off-grid
• A decent inverter-charger (Victron Multiplus) with a small Honda EU22i as backup is more honest than pretending solar alone covers January

Genuinely doable, but I'd be sceptical of anyone claiming zero fossil fuel input year-round in a UK climate without extraordinary battery capacity.

@AlexHobbs mate I'm literally doing this right now with my cabin build and I'll tell you what nobody warns you about — shade creep.

You survey your roof in August, think "brilliant, loads of sun," then November arrives and suddenly the neighbour's oak tree is throwing a shadow across your panels from about 11am. The sun just... gets low. Embarrassingly low.

I've got 600W on mine with a Victron SmartSolar and I was absolutely humbled last January. Still doable, but factor in at least double the battery capacity you think you need for winter, and honestly consider a small backup like an Ecoflow or even a grid tie-in as emergency fallback.

The bones of your motorhome logic are sound though — it's just the maths get grimmer seasonally.

@AlexHobbs your Victron/Fogstar combo is actually a brilliant starting point because you already speak the language. The jump I'd flag is thermal load — a motorhome you leave cold when you're not in it, but your missus will want that office comfortable from the moment she sits down, which means heating draws are unpredictable and front-loaded.

What's the intended use pattern? Daily 9-5 all year, or more occasional? That changes everything about sizing. A well-insulated build (decent PIR boarding, not just rockwool) dramatically reduces what your system needs to fight against in January.

I'd also seriously consider a small wood burner as your primary heat source rather than asking the batteries to handle it — keeps the electrical side manageable. What square footage are we talking?