Tiny house off-grid power — 18 months in

Right, been living in our 24ft × 8ft timber frame for just over a year and a half now, so thought I'd document what we've settled on rather than what we thought we'd need when we started.

Solar array: 4.8kWp of Renogy 400W panels on the roof, dual-axis tracking. Overkill for winter, but the summers more than compensate. We're in East Anglia, so we get decent solar but it's not Spain.

Battery: 15.36kWh LiFePO₄ (Growatt pack) with a Victron Multiplus II 48/5000 inverter. Honestly, the Victron was non-negotiable — the build quality and firmware updates keep it relevant. Battery cost us £9k but we've not had a single issue.

Charging: Victron MPPT 250/100 and a petrol generator (painful admission) as backup during December/January doldrums. We've averaged 3–4 full cycles per week throughout the year.

Loads: 3.5kW typical daytime draw (induction hob, heat pump, compressor fridge). Radiant heating from the concrete slab with a 40L buffer tank keeps things cosy without hammering the battery.

What surprised us most: we use less energy than predicted because you become genuinely aware of consumption when you're generating it yourself. No phantom loads, no complacency.

The system tracks solar production minute-by-minute via Cerbo GX dashboard. It's satisfying watching the numbers align with cloud cover.

Would happy answer specific questions about sizing, integration, or whether the tracking was worth it (spoiler: mathematically yes, but requires maintenance).

Cheers for putting this together @FenlandSolar.

How's the timber frame holding up in damp? We're looking at a similar setup in a shepherds hut and everyone's warned us about condensation come winter. Are you running any ventilation or dehumidification?

Also curious about your battery setup — did you end up going with LiFePO4 or stick with lead acid? We're torn between cost and the headache of maintenance tbh.

The EV charging bit is what's got me thinking too. How much solar are you dedicating to that vs household use? Reckon the sizing changes drastically when you're not on grid tariffs.

Been following your journey @FenlandSolar — that's properly useful detail. The timber frame question's a good one @GazAllen, though I'd reckon damp's less of a headache than people assume if you've got decent ventilation and your solar setup actually works (which sounds like it does in your case).

I'm running something similar on my van conversion — 24ft space, south-facing panels, Victron controller. The real lesson I've learned is that oversizing isn't waste; it's insurance. You'll have damp days where 2kW nominal becomes 400W actual, so that extra capacity just sits there looking smug when the weather's decent.

@FenlandSolar, are you venting through-wall or relying on natural air exchange? I switched to a small Fogstar unit last winter and the peace of mind alone justified the cost. Condensation stopped being a thing overnight.

What spec solar panels are you running on the roof? I'm sizing up a garden office build (similar footprint to yours) and trying to work out whether I can fit enough capacity without going dual-pitch.

Also — and this might sound daft — have you had to deal with shading from trees at different times of year? I'm surrounded by oaks that'll be full leaf come summer, and I'm worried I'm going to spec for winter generation and then lose half my output when everything greens up.

Are you still happy with whatever battery bank you went with initially, or did you end up upgrading? I'm torn between going larger now versus expanding later.

The damp question's crucial — we underestimated it in year one. Vapour barriers and roof ventilation made the real difference, not just the timber itself. Make sure your gutters are properly sorted or you'll regret it.

@LindaClark90 we're running 400W of Renogy monocrystalline panels facing south-southwest, mounted flush to keep wind loading minimal. Honestly though, the panels aren't the constraint — it's the battery bank. We went 10kWh LiFePO₄ (Victron) and that's where most of our budget went, but it's paid for itself in reliability. People always want bigger solar arrays, but in the UK winter you're not generating enough to matter without proper storage anyway.

Garden office angle's different to living space though — you might get away with smaller capacity if you're only running it daytime. What's your usage profile looking like? Heating, computing, standby loads?

The real insight after 18 months is that "off-grid" requires obsessing over efficiency first. Solar panels are the sexy part but they're not the problem

Brilliant thread this. The damp point @DODQueen mentions is something I'm grappling with in the shepherd's hut — totally different beast to a timber frame obviously, but same headache with a smaller footprint and limited air circulation.

One thing @FenlandSolar might want to stress for anyone sizing up: those first-year figures are gold dust because you're still optimising. We're 18 months into the hut and only now have a proper handle on what our actual winter draw is versus what we guessed. Turns out heated mattress pads and LED worklights add up quicker than you'd think.

On the solar side, if you're genuinely off-grid rather than grid-tied, you need buffer in your battery capacity that most calculators undersell. A Victron MPPT controller's worth its weight — the data logging helped us spot we were undersizing the panel array in autumn.

@LindaClark90 — garden offices are sweet spots for this stuff because you can iterate without living in the build while you're tweaking it. Worth your while getting a humidity meter in there early before you commit to final

Damp is genuinely the villain nobody warns you about until it's too late — my shepherd's hut turned into a condensation factory before I sorted proper ventilation and a decent vapour barrier. The battery bank absolutely hates moisture, so if your Victron kit starts showing weird voltage fluctuations, that's often damp creeping into the electrics rather than an actual fault.

@Spud79 the hut life chose us too, and I'd swear by a small extractor fan on a timer during the cold months — sounds daft but it's saved me from replacing corroded terminals on my Lithium setup. Roof vents are non-negotiable; I learned that the expensive way when I found white crystals all over my positive terminals.

Also worth mentioning — if you're in a similar footprint to @FenlandSolar's build, factor in that your battery bank will need climate control eventually. A simple insulated battery box with a thermostat keeps things running sweetly even when the outside air's doing its best impression of a wet sponge.

Been following this thread and the damp chat's got me thinking about my static caravan setup. I've got a similar footprint to yours — roughly 24ft — and I'm wondering if you've had to deal with the specific issue of thermal bridging through the metal chassis?

That's where I'm getting caught out. The caravan frame creates these cold spots that seem to pull condensation like a magnet, especially around the belly and underneath the window frames. Tried the usual vapour barrier approach but it's a bit different when you've got metal framing conducting heat away.

@DODQueen — did you have to do anything beyond standard roof ventilation? Asking because I'm considering a secondary internal vapour layer but don't want to trap moisture between two barriers.

Also curious whether you sorted heating strategy around this, @FenlandSolar? I'm running a small diesel heater at the moment but wondering if the continuous low-level heating's actually helping or just creating more condensation issues by warming the shell unevenly.

The damp issue is real, but I'd add something from my motorhome years — it's not just about ventilation, it's about understanding where the moisture's actually coming from. Took me two winters to realise my battery box was sweating more than the living space.

What sorted mine was a combination approach: passive vents high and low (heat naturally rises and takes moisture with it), but crucially, a small 12V extractor fan on a humidity sensor running intermittently. Victron's BMV monitors my setup, and I notice the battery performance dips noticeably when humidity climbs above 65% in the cabin.

The other thing — and this sounds daft — is not fighting condensation with aggressive heating. A steady 14-16°C with decent air movement beats trying to maintain 18°C constantly. Saves battery capacity too.

@FenlandSolar, what's your actual battery setup drawing-wise? Curious whether you're running traditional lead-acid or if you've gone lithium. That affects how much the damp genuinely impacts performance versus just being visually grim.

Damp's the silent killer innit. Had it proper bad in my shepherd's hut first winter — woke up to condensation running down the inside of the roof panels, thought I'd made a massive mistake.

What sorted it for me was combining a couple of things: decent cross-ventilation (trickle vents top and bottom) plus a small 12V extraction fan on a humidity sensor. Costs barely anything to run off solar but makes a real difference. Also switched to a wood burner instead of electric heating — the dry heat helps loads and takes pressure off the batteries.

The other thing nobody mentions: your moisture load. If you're cooking, drying clothes inside, doing laundry — that's a lot of water vapour. We moved the washing to happen on sunny days and hang stuff outside or in a separate space now.

@MountainHermit's right about understanding where the damp's coming from. In my case it was thermal bridging through the metal frame plus not enough air changes per hour. Once I got the air moving and the temp differential sorted, it cleared up quick.

What's your setup like @Thingamy

Living on a narrowboat, I've learned damp's basically just part of the deal until you accept you're running a dehumidifier 24/7 like it's a Victron inverter — except this one actually costs money to operate. Proper draught seals and a tiny bit of heating does wonders though.

@PartnerCamper nails it — I've stopped fighting damp on the boat and just embraced the dehumidifier as a permanent fixture. Costs about 40W running, which is nothing compared to replacing rotted timber. Mind you, the real trick is convincing the batteries that moisture management is more important than the kettle. Spoiler: