Powering my new 6x4m garden office - going solar or just a long armoured cable run?

Finally getting round to sorting the electrics for the timber garden office I built last summer. It's about 18 metres from the house and I've been running an extension lead out there which is frankly embarrassing at this point. The office has a laptop, a couple of monitors, a small fan heater I use occasionally, and I'd like to add a small fridge at some point. Rough daily load is probably 1.5–2kWh on a normal working day.

I've had a couple of quotes for running a 6mm² SWA cable from the consumer unit in the house — one came in at £680 fitted, another at £920. Feels like a lot but I appreciate it's a proper job with a Part P cert at the end of it. The upside is obviously unlimited power and no faff.

The alternative I keep coming back to is a modest solar setup — something like a 400W panel on the south-facing office roof, a 100Ah lithium battery, and a decent MPPT controller. Victron kit seems to be the go-to from what I've read on here. Realistically though I'm not sure 400W cuts it through a grey UK winter, and the fan heater alone is 2kW so that's clearly not going solar.

Has anyone been in a similar position and gone one way or the other? I'm also wondering if there's a hybrid approach — run the armoured cable but supplement with solar to keep bills down or add resilience. Curious what people with actual garden office setups think.

@Ben1960 18 metres is absolutely fine for SWA cable — 4mm² twin-and-earth armoured will handle that run without meaningful voltage drop for a typical office load. Get it buried at 500mm minimum under a patio slab or 600mm in open ground with cable tiles and a warning tape above.

That said, if you're even considering solar later, run a separate 25mm² conduit alongside while the trench is open — future-you will be extremely grateful. I did exactly this when I trenched mine and later added a Victron SmartSolar setup feeding a Fogstar Drift lithium battery bank for overnight loads.

The armoured cable route gives you unrestricted grid power immediately, whereas solar-only for an office with monitors, heating and decent lighting gets expensive fast. Hybrid is the sensible middle ground long-term.

What's your anticipated peak load looking like?

@Ben1960 18 metres of armoured cable is basically a Tuesday afternoon job for any half-decent sparky — solar's brilliant but if you're already wiring it up anyway, grid-tied means kettle and monitors without doing the mental arithmetic on whether your Victron's having a strop.

@Ben1960 I went the solar-only route for my van build and learned the hard way that chasing clouds is a proper lifestyle choice, not just a power source. For a garden office where you're actually working — monitors, lighting, maybe a little heater on a grim November morning — the armoured cable run is your foundation. Get that in first.

Then if you fancy bolting a small solar setup on top later (Victron MPPT, a Fogstar Drift LiFePO4 battery), you've got a genuinely resilient system rather than a gamble. I'd never be without my solar experience, but I'd never run my office on it alone either.

Eighteen metres of SWA with a proper consumer unit at the far end means you're building something real, not cobbling it together.

@Ben1960 Worth mentioning that the two options aren't mutually exclusive — plenty of folk on here run SWA from the house for reliable mains power, then add a small solar setup for resilience or to offset running costs. Given you're working in there regularly, having proper mains for heating and any power-hungry tools makes sense, with solar perhaps handling lighting and device charging. Also don't forget to factor in a consumer unit in the office itself with RCD protection — you'll want it done properly rather than just terminating into a socket. What are you actually running in there equipment-wise? That'll help determine whether solar-only is even realistic for your needs.