Hybrid inverter for static caravan emergency backup — where do I start?

Looking at setting up a proper emergency backup system for my static caravan. We lose power a few times a year out here and I want something that can keep the essentials running — fridge, a few lights, maybe the router. Not trying to go fully off-grid, just want a seamless switchover when the grid drops.

Been reading about hybrid inverters and the Victron MultiPlus range keeps coming up. The MultiPlus-II 48/3000 seems like it might be overkill, but I don't want to underbuy and regret it. Would something like a 24V 2000W unit be enough for those basics, or is it worth going 48V system from the off?

Planning to pair it with a smallish LiFePO4 bank — maybe 100-200Ah. Fogstar Drift cells look reasonable for the budget, but I'm open to suggestions. Main thing is the inverter needs to handle the UPS-style switching properly so nothing notices when the grid goes down.

Has anyone done something similar in a static or holiday setup rather than a full van build? Curious whether the wiring and planning permission side of things threw up any surprises too.

VanLiam | Posts: 847

@BoxerAdventure good shout on going hybrid rather than a pure generator setup. For a static with modest loads like that, I'd look at the Victron MultiPlus-II 24/3000 as a starting point — solid unit, well supported in the UK, and the VE.Configure software makes setup surprisingly straightforward even if you're not particularly technical.

One thing worth thinking about early on — what's your battery chemistry preference? LiFePO4 will give you more usable capacity for the money long-term, but the upfront cost stings. AGM is cheaper initially but you'll lose a chunk of capacity if you're regularly cycling it.

Also, how long do your outages typically last? That'll really drive your battery sizing. A few hours is very different to wanting overnight coverage.

CraigThompson | Posts: 312

@BoxerAdventure worth thinking carefully about your fridge first — it's likely your biggest continuous draw and the one thing you genuinely can't afford to lose. Check the nameplate for running watts and startup surge, as compressor motors can pull 3-4x their running load on startup, which catches people out when sizing inverters.

For a static caravan backup scenario, I'd also look at what your existing consumer unit setup looks like before buying anything. Some hybrids integrate really cleanly via a transfer switch, others need more work. Brands like Victron or Sofar are popular on here for good reason, but your actual battery capacity needs matching your realistic outage length expectations.

What sort of outage duration are you typically dealing with — hours or occasionally overnight? That'll shape everything else.

MistyTrekker | Posts: 1,203

@BoxerAdventure one thing nobody's mentioned yet — check whether your static is on a 16A or 32A supply, as that'll affect which hybrid inverter you can realistically install. Also worth noting that for a genuine emergency backup scenario, you don't necessarily need massive battery capacity if you're sensible about loads. A 5kWh battery paired with something like a Victron Multiplus or Growatt SPF will see you through a typical overnight outage without breaking the bank.

Also consider whether you want seamless switchover (UPS-style) or if a few seconds' delay is acceptable — most fridges are fine with a brief gap, but if you've got anything sensitive electronically it's worth factoring in. What's your grid connection situation like — single phase I'd assume?

CotswoldExplorer | Posts: 634

@BoxerAdventure hybrid inverter was exactly the route I went for my garden office backup — been solid for two winters now.

One thing worth flagging: transfer time matters for a static. Some cheaper hybrids have 20-30ms switchover which can reset digital thermostats and clocks. Victron's MultiPlus switches in under 20ms which most kit handles fine, but worth checking your specific fridge's tolerance.

Also consider your battery chemistry carefully — if the caravan gets left unheated in winter, LiFePO4 won't charge below freezing without a BMS that handles low-temp cutoff. Fogstar do decent cells but factor that in.

What's your rough daily kWh estimate? That'll drive everything else tbh.

GafferTapeKing | Posts: 847

The part nobody talks about with hybrid inverters in a static is the transfer switching speed. Most grid failures I've dealt with at my place aren't clean — they're spikes and brownouts before the full drop. A Victron MultiPlus will switch to battery in under 20ms, which is fast enough that your fridge compressor won't even notice. Cheaper units can be 40-100ms and some older fridges absolutely hate that.

Also worth knowing: the MultiPlus-II 24/3000 is probably your sweet spot for essentials-only backup. Ran mine through three winters without a drama. Don't let anyone sell you a 48V system for a setup this modest — the added complexity isn't worth it when you're just covering outages.

Size your battery bank for 24 hours minimum. Fogstar Drift cells if you're going lithium and watching the budget.

BigAl31 | Posts: 2,156

Good shout from @GafferTapeKing on transfer switching — worth adding that transfer time matters more than most people realise. Most hybrid inverters quote 20ms or less, which is fine for fridges and lights, but if you've got anything with a sensitive control board (some modern fridge-freezers, certain LED drivers) even that brief gap can cause a reset. Look for units advertising "zero transfer" or pure UPS mode if you want to be belt-and-braces about it.

Also worth thinking about battery sizing early on rather than as an afterthought. Work out how many hours you actually need to bridge — overnight outages are very different from a 30-minute blip. A fridge alone can easily draw 100-150Wh over a night once you factor in compressor cycling.

What's your current setup — mains only, or have you got any solar already on the van?

KeithMartin | Posts: 412

Good points from everyone. One thing I'd add — before you commit to any particular hybrid inverter, get a rough handle on your actual load figures. Fridge compressor startup draws a surprising spike, often 3-4x the running watts. Caught me out first time round. Also worth checking whether your static is wired with an RCD setup that might trip unexpectedly when the inverter kicks in — some older park installations are a bit temperamental with that. What's your rough budget looking like @BoxerAdventure? That'll narrow things down considerably.