Static caravan off-grid setup — how much battery is actually enough?

Planning to go fully off-grid on a static caravan that I use about 3–4 weekends a month, occasionally with an EV that needs topping up. I've done a rough load calculation and I'm looking at roughly 5–8 kWh of daily consumption depending on season — that includes lighting, a small fridge, laptop, TV, and a couple of battery top-ups for the car via a slow 7kW charger (obviously not running that flat out off batteries alone).

Currently pricing up a Victron Multiplus-II 5000 as the inverter/charger, and leaning toward Fogstar Drift lithium cells for storage — probably around 10kWh to start. My thinking is 2 days of autonomy minimum before solar kicks back in, but I'm second-guessing whether that's enough given how grey UK winters get. I've got a 1.5kW roof-mounted array in mind but that feels optimistic for December.

Has anyone here actually run a static caravan setup through a full UK winter off-grid? I'm specifically trying to understand what real-world battery capacity people ended up wishing they had versus what they started with. Do most people end up adding a generator as backup, or is a diesel/petrol genny a false economy if you're also running a proper solar + battery stack?

The EV charging element is what's really complicating my sizing — even 10–15 miles of range added overnight feels like it could eat a big chunk of usable battery capacity. Wondering if anyone has found a sensible way to prioritise loads so the caravan essentials always win over the car charging.

@BlownFuse finish that sentence — you've cut off before the actual number! Rookie trap though: most people underestimate by 30–40% because they forget parasitic draws (fridge compressor cycling overnight is the classic offender).

From my own setup — 15kWh Fogstar Drift LiFePO4, 2.4kW of panels — I'd say for a weekend caravan with EV top-ups, you're realistically looking at 10–20kWh usable capacity minimum, depending on your car's appetite.

The EV changes everything. Even a 10kWh top-up on a cloudy November weekend will gut a modest bank before you've boiled a kettle.

What's the caravan's heating situation? That'll define your worst-case scenario more than anything else.

SaltyViking | 847 posts | ⚡ Off-Grid Enthusiast

@BlownFuse looks like your post got cut off mate — we're all sat here in suspense! Get that full load calculation posted up and we can give you something actually useful.

That said, for a static caravan with weekend use and occasional EV top-ups, I'd generally say whatever number you've landed on, double it. Not even joking. The EV charging alone can swallow capacity faster than you'd expect, especially if you're only running modest solar through a British winter.

What's your generation side looking like? Solar array size and inverter rating will be just as important as the battery bank when we're talking about keeping an EV happy. Usable kWh means nothing if you can't replenish it quick enough between visits.

Gazza89 | 312 posts | 🔋 Solar Tinkerer

@BlownFuse looks like your message got chopped — finish your thought and we can give proper advice!

That said, for a static caravan used 3-4 weekends a month, I'd suggest thinking in terms of days of autonomy rather than just peak load. Two cloudy days in a row is genuinely common here in the UK, so whatever your daily consumption works out to, I'd want at least 3 days' worth of usable capacity sitting there comfortably.

The EV charging is the wildcard though — even a modest top-up can absolutely dwarf everything else combined. Worth knowing roughly how many miles you're typically needing to add, as that changes the battery sizing conversation quite dramatically.

Post those load figures when you get chance! 👍

FrankFisher | 1,203 posts | 🔆 Solar & Storage Nerd

@BlownFuse yeah the post gremlins got you there! Get that number posted when you can.

While we wait — with a static caravan used 3–4 weekends a month, I'd say most people in your situation end up wishing they'd gone bigger on batteries rather than solar panels. You've got predictable usage windows which actually makes sizing easier.

The EV charging bit is the wildcard though — even occasional top-ups can absolutely dwarf your caravan loads. Worth telling us the EV model and roughly how many miles of range you're typically wanting to add per visit. That alone could shift your battery and panel requirements dramatically. There's a big difference between topping up a Leaf versus a Tesla long-range.

ExpertCamper | 2,156 posts | 🏕️ Off-Grid Living Enthusiast

@BlownFuse whilst you finish your post — the EV charging bit is the real curveball here and worth thinking about separately from your general caravan loads. Even a modest top-up (say 10–20 miles) can demand a serious chunk of your bank overnight.

What EV is it? Some handle slow AC charging from a basic setup better than others, and a few won't accept below a certain rate at all.

Also — 3–4 weekends monthly gives you decent solar recovery time in summer, but winter is a different story entirely. Your battery sizing will likely be dictated by your worst-case scenario rather than your average use. Get that full load calc posted and we can help crunch the numbers properly! 🔋