What size solar panels for my off-grid cabin?

Right, looking for some proper guidance here as I'm planning my setup and want to get it right first time.

I've got a static caravan (about 24ft) that I'm converting to proper off-grid living. Currently running a Victron system with a 48V lithium bank (I know, I should've gone 24V but here we are). The caravan's reasonably well insulated and I'm mostly there weekends plus the odd week in summer.

My main loads are:

• Fridge/freezer (compressor type)
• Heating (fan heater, mainly winter)
• Lighting and misc 12V stuff
• Laptop charging

I'm thinking about panel sizing but I'm genuinely unsure whether I should be looking at 4kW, 6kW or going bigger. I've seen plenty of conflicting info online about the "rule of thumb" stuff.

The caravan's got south-facing roof space (pretty decent angle too) so orientation shouldn't be an issue. I'm in the Midlands so not the sunniest spot in the UK, but not terrible either.

Should I be sizing based on worst-case winter days? And how much headroom do people actually build in for degradation and cloudy spells? I've had a look at Renogy panels and Fogstar kit but keen to hear what's actually working for people in similar situations.

Also, what controller are people running with larger arrays? My current MPPT's a bit modest for expansion.

Any pointers would be genuinely helpful.

Depends massively on your usage profile, mate. The caravan shell helps insulation-wise, which is a bonus.

I'd start by working backwards — how many kWh/day are you actually using? Heating and water heating are the killers. If you're all-electric (no gas backup), you're looking at a serious array. If you've got a gas cooker and heating, the solar load drops considerably.

For a 24ft caravan, I'd be targeting 4-6kW nominal as a starting point, but that assumes decent battery storage behind it (which you'll need).

Few questions: winter only or year-round? What's your latitude roughly? Are you doing water heating? Got a budget in mind?

The underestimating solar is a classic mistake — people always think they'll use less than they actually do. Better to oversize slightly and sell excess to the grid (if you're not fully off-grid) or just enjoy the buffer.

Mate, the "first time right" approach went out the window the moment you bought a caravan — you'll be tweaking this setup until the cows come home.

Real talk though: work backwards from your winter usage (that's the bottleneck), then add 50% because you'll underestimate. Static caravans are notoriously power-hungry with heating, so unless you're planning serious lifestyle changes, you'll want more panels than you think.

Get yourself a Victron MPPT controller and actually monitor what you're pulling — that'll teach you more than any forum advice. A Fogstar monitoring setup's worth its weight in gold for this.

What's your actual kWh per day target? That's the number that matters, not panel wattage.

The caravan advantage is definitely the insulation, but you'll want to nail down your actual consumption first. I'd suggest:

Pull your existing leccy bills if you've got mains data to work from, then ruthlessly cut out what won't work off-grid (immersion heater, tumble dryer, etc.). What's left is your real baseline.

Budget for winter — this catches most people out. A 24ft setup pulling, say, 5-10kWh/day needs roughly 4-5kW of panels minimum if you want December reliability. That's assuming decent battery storage backing it up.

@ExFarmer's right that you'll tweak it, but you can at least avoid the "panels too small, now I'm stuck" scenario if you do the maths properly first.

What's your heating sorted? That changes the numbers massively.

Fair question, but I'd push back slightly on the "first time right" mentality — @ExFarmer's not wrong about the tweaking bit. What actually matters is getting your baseline consumption sorted before you spec the panels.

Have you done a proper audit of what you're actually running? Heating, water heating, fridge, lighting — the loads are different in a caravan versus a cabin because of the thermal mass issue @AngliaOffGrid mentioned.

On my shepherd's hut setup, I started with 4kW and realised I was massively overspecced for winter usage. Now I'm looking at a Victron hybrid system with batteries doing the heavy lifting instead.

What's your heating plan? That's usually the killer for off-grid caravans. And are you aiming for year-round or seasonal use? That changes everything.

Right, before you size anything, you need actual numbers. Stick a kill-a-watt meter on everything for a week and log your usage properly — caravan living's deceptively power-hungry once you factor in heating, water pumping, and fridge cycles.

That said, 24ft gives you decent roof space. Most folk doing this route end up with 4-6kW of panels and 10-15kWh battery storage, but your mileage depends entirely on how much you're actually using.

The caravan shell is your friend for insulation, but the electrics are often dodgy — I'd replace the consumer unit and sort proper DC busbar distribution while you're at it. Victron kit's pricey but bulletproof if you're committing long-term.

What's your average daily consumption looking like? That's the real starting point.

Just count how many times you'll flip the kettle on in winter and multiply by your regrets — that's your actual load right there.

But seriously, @OffGridMax is spot on about logging consumption. For a 24ft static though, you're looking at a sweet spot: most folks end up with 4-6kW of panels and 10-15kWh of battery. The caravan's your friend here — decent insulation means you're not heating the neighbourhood.

Real talk: solar output in UK winter is painful, so you might want a backup (wood burner, gas boiler). I've got a shepherd's hut conversion running on 3.5kW Renogy panels into a Victron MPPT, and even that feels tight November-February without my petrol genny sitting in the corner looking judgmental.

What's your heating plan? That'll make or break your actual requirement.

Been through this twice now — once in the motorhome, once setting up a narrowboat. The honest truth? You'll get it wrong the first time because you won't know your actual usage patterns yet.

That said, @OffGridMax is spot on — get real data before buying anything. I used a cheapo plug-in meter for a fortnight and discovered the fridge was pulling way more than expected in summer.

For a static caravan, I'd size assuming winter worst-case rather than average. You'll have shorter days, lower panel output, and higher heating loads. Better to have surplus capacity than be rationing power in January.

Work backwards: daily watt-hours needed → battery capacity → panel wattage needed to recharge that battery in your local winter peak sun hours. Throw in 30% oversizing for degradation and cloudy stretches.

What's your actual winter heating setup — electric or gas?

Mate, 24ft static is basically a house that happens to have wheels — you'll need properly sized batteries first, then work backwards to panels. I made the mistake of buying panels before understanding winter loads in my van conversion, ended up with a glorified sunroof setup come November.

@MarineGeoff's kettle logic is unironically sound though. Static caravans are energy vampires — heating, water pumps, proper appliances. What's your actual winter usage target? If you're serious about first-time-right, spec out your battery bank (Victron LiFePO4 or similar) for 3-5 days autonomy, then size panels for 60-80% replenishment in worst-case months.

Document everything before you buy anything. Spreadsheets aren't glamorous but they beat buying 10kW of panels you don't need.

@BayTim - you've hit on something nobody's mentioning yet: a static caravan's a fundamentally different proposition to a motorhome or narrowboat. The weight penalty means you can actually run proper solar capacity without chassis concerns.

First thing though — forget panel size for now. You need to answer three questions:

1. What's your actual winter consumption? Not optimistic estimates — measure everything for a fortnight in December. Heating, fridge, lighting, water pump.

2. How many days autonomy do you need? Winter in the UK gives you maybe 1-2 peak sun hours on a poor day. You're not running purely off solar; you're running off batteries charged by solar.

3. Budget for batteries first. This determines everything else. A decent lithium setup (Victron or similar) costs real money, but undersizing here will cripple your whole system.

Once you've got those sorted, we can actually calculate panel capacity. Right now you're asking "what size engine" before knowing how much you need to haul.

@BayTim — right, you've already got three people telling you to sort batteries first, which is correct, but lemme add the practical bit: a static caravan's a thermal nightmare compared to a motorhome. You'll be heating (or cooling) a proper box, not just insulating a van.

I'd honestly start by working backwards from winter consumption.

@BayTim — I went through this exact journey with my cabin, so let me add what the others haven't quite nailed yet: your roof space and orientation matter loads more than you'd think.

Static caravans typically have curved roofs, yeah? That's your real constraint. You might physically fit six 400W panels, but the angle's probably not ideal. I ended up doing a ground-mounted array beside my place instead — sounds faffy but gave me flexibility to angle properly for the season and actually expand later without roof penetration headaches.

Also, 24ft means you've likely got decent roof real estate compared to a van, so you're not fighting for every centimetre like van dwellers are. That's actually your advantage.

Before you commit to panel count, sort out three things in order:

1. Your actual winter consumption (not summer optimism)
2. Battery capacity that won't leave you rationing power
3. Then panels to charge that battery bank reliably

I'm running a Victron setup with Fogstar batteries and two Renogy 400W panels, ground-mounted. Took longer to dial

@BayTim — the lads are spot on about batteries first, but here's what caught me out with my shepherd's hut: solar sizing depends massively on your usage pattern rather than just annual consumption.

Static caravans are brilliant because you're not moving, so you can go bigger on panels without worrying about weight. I'd suggest working backwards from your battery capacity — if you've got 10kWh usable, you want panels pulling in enough on a grey December day to cover your base load plus some charging buffer.

Rule of thumb: aim for 1kW of panels per 5kWh of battery in the UK climate. But honestly, overspec the panels — they're cheap now compared to five years ago. A Victron MPPT controller will squeeze every watt out of them regardless.

What's your daily consumption looking like? That'll tell you whether you need 4kW or 8kW on the roof. And check your caravan's roof loading limits before you go mad — some of the older ones are sketchy.

Mate, everyone's dancing round the real question — what's your winter usage actually look like? Because sizing panels for July is how you end up with a useless array come November.

I've got a van conversion and learned this the hard way: my Victron MPPT controller spends December basically decorating the dash. Started working backwards from "what do I actually need to run in the darkest month" rather than "how many kWh can I theoretically generate," and it changed everything.

Your 24ft caravan's got decent roof space but UK winter angles are brutal. Do yourself a favour — list your essentials (heating, water pump, fridge, lighting), multiply by your actual winter days without sun, then add 40% buffer, and that's your minimum battery size. Only then do you spec panels for charging that battery in the available winter daylight hours.

Otherwise you're just buying expensive roof ornaments that cost you £1k each, mate.

Right, let me add the practical bit nobody's mentioned yet. I've got a garden office setup that taught me this the hard way.

The caravan's your advantage here — proper roof space and decent south-facing aspect usually. But static means you're not optimising angles seasonally like mobile installations do, which matters enormously in winter.

Before touching panel wattage, you must nail your actual consumption. Not estimated — measured. Get a Kill-A-Watt or similar on everything for a fortnight minimum. Your heating load (assuming you've got electric?) will dominate, and winter sun in the UK is genuinely pitiful. I'm talking 1-2 peak sun hours in December depending on your latitude.

For a 24ft caravan with reasonable comfort expectations, I'd ballpark 4-6kW installed capacity, but that's useless without knowing:

• Heating type (immersion, heat pump, gas?)
• Battery capacity (this determines panel oversizing ratio)
• Your tolerance for grid top-ups in November

@JackeryGuy's right about batteries first — they're your real constraint. Size those properly and