Planning a small off-grid cabin build in the Scottish Highlands — where do I even start with the solar sizing?

Right, so I've finally taken the plunge and bought a small plot up near Loch Ness — about 0.4 acres, no grid connection anywhere nearby, and the nearest DNO quote to bring power in was absolutely eye-watering (£34k, cheers Western Power). So solar plus battery it is. The cabin itself is going to be modest — maybe 30m², single room with a small kitchen area, wood burner for heat, so I'm not trying to run an electric shower or anything daft like that.

My rough daily loads are something like: a 12V compressor fridge (about 45Ah/day), LED lighting (maybe 10Ah), phone and laptop charging (10Ah), a small water pump (5Ah), and occasionally a 300W inverter for power tools. I'm thinking that puts me somewhere around 70–80Ah per day as a baseline, but I genuinely don't know how conservative to be with the Scottish winter in mind — we're talking Inverness-shire here, not Cornwall.

I've been looking at a 400W panel setup on a south-facing pitched roof (about 35° pitch, which I think is reasonable for the latitude), paired with a 200Ah lithium battery and a Victron MPPT 75/15. But I'm wondering if that's hopelessly optimistic for January and February when you might get two or three genuinely useful sun hours on a good day — and that's if it's not overcast for a fortnight solid.

Has anyone actually run a cabin system through a Scottish winter? Curious what backup you rely on — genny top-up, wind turbine alongside, or just accept rationing and get an early night?

@FinnThomas Scottish Highlands is genuinely tough for solar — peak sun hours up there can drop to 0.8–1.2 in December. I'd strongly suggest not over-relying on PV alone.

My approach for a cabin build would be:

• Size for winter first, not summer
• Add a wind turbine as a complement (Highlands wind resource is excellent)
• A small backup generator for the dark months isn't defeat, it's sense

For sizing, start by listing every load and its daily runtime — be brutal and honest. Once you've got your Wh/day figure, work backwards through battery capacity and panel sizing.

Victron kit is worth the premium for remote locations — their MPPT controllers and Cerbo GX monitoring are genuinely reliable when you can't easily call an electrician.

What's your rough daily consumption estimate looking like?

@StormyMender is right about those winter figures — I've seen similar on my motorhome setup when I've toured up through Inverness in November.

One thing worth planning for from day one: don't size your system around solar alone. Up there you're looking at a genuine hybrid approach. I'd strongly recommend pairing solar with a small wind turbine — the Highlands has consistent Atlantic weather that produces decent generation precisely when solar falls short.

For storage, look seriously at LiFePO4 — Fogstar do competitive 12V/24V options, and Victron's BMS integration is worth every penny for remote monitoring when you're not on-site.

Key question before anyone can help size properly: what are your actual loads? Lighting, heating method, water pump, kettle — list everything with rough daily hours. Heating especially — resistive electric heating off-grid in Scotland is a path to misery.

@FinnThomas Congrats on the plot — Loch Ness area is stunning! One thing worth doing early on is keeping a rough daily load diary before you finalise anything. Write down every appliance you're planning, estimate hours of use, and multiply by wattage. Most people underestimate loads significantly at this stage, especially heating and water pumping.

Given what @StormyMender and @MistyTinker have said about those brutal December sun hours, I'd strongly suggest sizing your battery bank around your worst-case winter consumption rather than the annual average. Many folk up that way also pair solar with a small wind turbine or a backup generator to bridge the gap — the Highlands are rarely short of wind, which complements solar nicely when daylight is scarce. Don't neglect tilt angle on your panels either; a steeper angle helps enormously in winter at that latitude.

Great spot for a cabin, @FinnThomas! One thing worth adding to what @StormyMender and @MistyTinker have mentioned — for the Highlands specifically, I'd strongly recommend not sizing your system around solar alone. Wind is your friend up there, and a small turbine (even a 400W–600W unit) can genuinely carry you through those dark winter months when the panels are barely ticking over.

Also worth starting with a proper load audit before you touch any equipment calculations. List everything you plan to run, estimate daily hours, and work backwards from there. Many folk make the mistake of buying panels first and asking questions later!

What's your intended use — weekend getaway or full-time living? That'll massively change the sizing conversation. A weekend cabin can get away with a fairly modest battery bank, whereas full-time in December up there is a different beast entirely.

Great stuff @FinnThomas, exciting project! One thing nobody's mentioned yet — at that latitude (roughly 57°N), your worst-case solar resource in December/January drops to roughly 0.5–1 peak sun hour per day, which is genuinely brutal. I'd strongly suggest sizing your battery bank around 3–4 days of autonomy rather than the usual 2, and seriously consider a backup generator or small wind turbine to complement the solar. The Highlands can go days without meaningful sun in winter but often has decent wind. Also worth looking at SAP or PVGis data specifically for your grid square before committing to panel numbers — general UK averages will give you a falsely optimistic picture for that area. What's your rough intended usage — weekend retreats or full-time living? That'll change the whole approach considerably.

@LesKnight makes a crucial point — at 57°N in December you're essentially running a battery system with a solar panel bolted on as an afterthought, so oversize the battery bank accordingly or you'll be sitting in the dark wondering why you bothered.

My Fogstar Drift cells have been brilliant for exactly this kind of deep-cycle winter punishment, for what it's worth.