Powering a garden office on solar — sizing the system for an always-on setup?

Finally pulling the trigger on a proper garden office build this spring — 4x3m timber frame going in the back garden. It'll be my full-time workspace so I need it to run reliably five days a week, not just on sunny days. I've been lurking here long enough to know that's where most people come unstuck with garden office solar.

My rough daily load works out at around 1.2–1.5 kWh. That's a laptop, a second monitor, a small fan heater on a thermostat (this is the big variable), LED lighting, and a Wi-Fi router running all day. I'm in South Yorkshire so not exactly the sunniest postcode in the country — probably averaging 2.5–3 peak sun hours in winter realistically.

I've been looking at a 2x 200W panel setup on a south-facing pitched roof section, a Victron 100/30 MPPT, and either two 200Ah leisure batteries (AGM) or saving up a bit longer for a 200Ah LiFePO4 like the Fogstar Drift. The LiFePO4 obviously gives me usable capacity that the AGM can't match, but the price jump is significant.

Has anyone actually run a full-time home office setup like this through a UK winter without grid backup? I'm wondering whether the honest answer is just "you need a small grid tie-in or an immersion diverter from the house" rather than going full off-grid. Keen to hear what setups people are actually running day to day.

@KenCrane key thing people miss with "always-on" setups is winter. Your summer solar harvest is basically irrelevant for sizing — design around December/January instead.

For a UK garden office running 5 days/week, I'd be looking at:

• Minimum 400-600W panels (south-facing, no shading tolerance)
• 200Ah+ lithium — Fogstar Drift cells are decent value right now
• Victron MPPT — non-negotiable imo, the data logging alone is worth it

Also worth considering a grid-tie backup feed from the house as a supplementary charge source for those grim cloudy weeks. Running a proper office on solar-only through a UK winter is genuinely hard without either grid backup or a genny.

What's your expected load — monitors, heating, lighting? That changes the numbers significantly.

@OakSpirit is bang on about winter being the killer — I learned this the hard way with my garden office setup before I went hybrid grid-tie.

Worth thinking about battery sizing separately from panel sizing. For always-on 5-days-a-week use, I'd seriously look at a Victron MultiPlus with grid backup. Means solar/battery covers most of your load, but you're not sitting in the dark in December because we've had four grey days in a row.

Also — what's your actual daily load estimate @KenCrane? Monitors, heating, laptop? A small fan heater will absolutely destroy your battery budget. Might be worth considering a dedicated electric panel heater on a separate grid circuit and letting solar handle everything else.

Fogstar Drift LiFePO4 is solid value for the battery side if you're budget-conscious.

@KenCrane worth giving some serious thought to your worst-case scenario: mid-December, heavy overcast for four or five consecutive days. That's what your battery bank needs to be sized against, not your average usage.

One thing I'd add to what @OakSpirit and @SmartSolar_Geek have touched on — a small grid-tie or even just a standard socket run from the house as backup charging input is worth factoring in during the build phase. Running conduit later is a right pain. Doesn't mean you'll use mains often, but having the option there keeps you working when the weather turns truly grim without oversizing the solar array massively to compensate.

What's your expected peak load? Laptop, monitors, heating — that heating element will be the killer if you're running electric.