Powering my 6x4m garden office - went solar and ditched the cable run, here's what I learned

So I've been running my garden office off-grid for about eight months now and thought I'd share what actually worked versus what I naively assumed would work. The office is at the bottom of a fairly long garden - about 35 metres from the house - and the quotes I got for a proper armoured cable trench were eye-watering (one sparky quoted me £1,800 just for the groundworks). That's what pushed me down the solar route.

I ended up going with two 400W panels on a south-facing shed roof mount, a Victron SmartSolar 100/30 MPPT, and a 200Ah lithium battery from Fogstar (the Drift 12V unit). Total spend came to just under £1,100 including a 2kW Victron inverter. In summer it's genuinely brilliant - I'm running dual monitors, a laptop, a small fan heater on the lower setting, and a kettle without any drama. The Victron app is oddly satisfying to watch.

Winter is where it gets honest with you though. December and January I was regularly hitting the low-voltage cutoff by mid-afternoon on overcast days, and the 200Ah just doesn't have the headroom I thought it did once you factor in the reduced panel output. I ended up running an extension lead from the house as a backup, which felt like admitting defeat but kept me working.

Has anyone else gone down this route and found a good solution for the winter shortfall without massively increasing the battery bank? I'm wondering whether adding a third panel would help more than adding another battery, given the issue is generation rather than storage on those grey days. Would love to hear what others are running.

Really useful write-up @JakeMartin, looking forward to the rest of it! Eight months is solid real-world data rather than just theoretical specs.

One thing I'd flag for anyone reading this considering something similar - the cable run cost calculation is often what tips people towards off-grid, but don't forget to factor in your council's permitted development rules around trenching near boundaries before you commit either way. Caught a few people out locally.

Also curious about your shading situation - you mentioned a long garden which usually means trees or fencing casting shadows at certain times of year. Did you account for that in your panel placement, or did you discover it the hard way after installation? Winter sun angles are brutal in the UK and can catch you completely off guard if you've only tested during summer months.

Really keen to read the full write-up @JakeMartin! Eight months takes you through a decent chunk of winter which is where most garden office setups either prove themselves or fall apart completely.

One thing I'd flag for anyone reading along who's considering the same - the shading situation matters massively more than most people realise at the planning stage. I made the rookie error of not accounting for how low the winter sun sits, and a fence that cast zero shadow in July was basically blocking my panels from about November through February.

What orientation is your office @JakeMartin? And are you running any kind of backup for the really grim overcast weeks, or have you sized the battery bank to cover those gaps? Always curious whether people go the generator route or just manage consumption down.

Really looking forward to the full write-up @JakeMartin. One thing I'd be particularly curious about - what's your panel orientation like given you mentioned it's at the bottom of a long garden? I'm guessing trees or fencing might be causing shading issues at certain times of year, which can absolutely hammer output even if it's just partial shading on one panel. Also interested in what battery chemistry you went with and whether you sized it based on your actual usage patterns or just went with a rough estimate. I made the mistake of undersizing my first setup based on optimistic summer assumptions and paid for it come November! What monitoring are you running? Decent data logging makes such a difference in understanding where your losses are actually coming from.

Great thread @JakeMartin, subscribed and waiting for the full write-up!

Curious about your cable run situation specifically - how far was the garden office from the house, and what quotes were you getting for the armoured cable installation? That's often the tipping point that pushes people toward solar and it'd be useful to have some actual figures in the thread for comparison.

Also seconding @JakeLee's question about panel orientation - a 6x4m office gives you reasonable roof space but the angle and direction make an enormous difference, especially through November to February when you're relying on whatever weak sun you can scrape together. Did you end up tilting the panels off the roof pitch at all, or just flat-mounted?

Great thread @JakeMartin, really looking forward to the full write-up. Eight months is solid real-world data.

I went through a similar decision process with my workshop setup last year. One thing worth mentioning for anyone else following along - the cable run cost calculation often surprises people. By the time you factor in armoured cable, a decent trench (properly done, not just scraped in), any electrician fees, and the DNO notification side of things, the numbers can shift considerably in favour of solar.

@DefenderConvert raises a good point about the specifics though - distance and what's actually in the ground between house and office makes a massive difference to that equation. Had a mate who hit a root system that added half a day's labour he hadn't budgeted for.

@JakeMartin what inverter setup are you running? That tends to be where people either nail it or come unstuck in my experience.

Eight months is proper validation — I hit a similar crossroads with my narrowboat setup before eventually going full off-grid.

The thing nobody warns you about with garden offices specifically is shading from the building itself in winter when the sun sits low. My panels dropped to near-nothing some afternoons purely because of roofline shadow I hadn't accounted for during summer planning.

Worth mentioning what inverter you landed on @JakeMartin — I've seen so many people underspec that part and then wonder why their laptop chargers behave weirdly. Victron made a noticeable difference for me with sensitive electronics.

Great stuff @JakeMartin, eight months is proper real-world testing through some decent seasonal variation too - you'll have caught the worst of the winter output dip which is where most people get a nasty surprise.

One thing I'd add for anyone considering this route: don't underestimate how much a long garden with any tree coverage will affect your panel placement options. I ended up having to compromise on my tilt angle to avoid partial shading from a neighbour's oak, which cost me more in winter output than I'd have liked.

Also curious what you're doing for heating in there? That's usually the thing that catches people out - lighting and screens are manageable, but if you're running any form of electric heating the battery bank sizing conversation changes completely.

Looking forward to the full write-up.