Home backup power — where to start?

Been looking at this properly for the first time now our grid's getting dodgier. Currently in a van conversion but planning a tiny house build in the next couple years, so want something that'll work for both scenarios.

Here's my situation:

• Need to cover maybe 3-5 days without sun (UK winter reality)
• Essential loads: fridge, heating (currently gas but might go hybrid), lights, phone/laptop charging
• Would like to run a kettle occasionally without the whole system crying

Got about £4-5k to spend if I'm being realistic.

My questions:

Battery bank size — how do folks actually calculate this? I see people quoting "3 days autonomy" but that seems to vary wildly. Should I be working backwards from my daily consumption?

AC vs DC — loads of threads here contradict each other. For a van setup going hybrid to a house, does it make more sense to go full AC from the start?

Which bits to buy first? Inverter, panels, or batteries? I've seen some folk suggest getting batteries sorted as the limiting factor, others say start with generation.

Brand reality check — keeping hearing Victron's brilliant but pricey. Has anyone actually got a solid Renogy or similar setup that's been reliable?

Cheers for any pointers. Don't want to spend twice by doing this backwards.

Solid thinking to plan ahead. For van-to-tiny-house transition, I'd suggest starting modular rather than buying a full system now.

Get a decent portable power station first (Fogstar or Bluetti range are solid) — works in the van, moves to the house, buys you time to figure out your actual needs. Way cheaper than guessing.

Then when you've got the tiny house plot sorted, you'll know your consumption properly. South-facing roof space? Shading issues? That changes everything for solar placement.

I'm running a Victron setup in my shepherds hut with a garden office extension, and honestly the planning stage was more valuable than the kit itself.

What's your rough power needs currently? That'll help narrow down what makes sense.

Good call planning ahead. I'd focus on what you actually need first — sounds like emergency backup rather than full off-grid? That changes things.

For a van-to-tiny-house move, I'd go battery-first rather than solar panels. Easier to relocate, and you can size panels later once you know your roof situation. A decent 5kWh LiFePO4 setup (Victron or similar) will handle most outages and give you time to think.

What's your current power draw like? That'll tell you if you need 10kWh or 50kWh. Also matters whether you're planning grid-tie eventually or proper off-grid.

Modular makes sense — I've got a garden office setup that started as emergency backup and evolved into semi-permanent. Way cheaper than guessing wrong upfront.

The modular approach @PeakVanLifer mentions is spot on for your situation. Since you're transitioning, I'd actually suggest starting with a decent battery bank and charger now — something like a Victron Smartsolar setup scales brilliantly whether you're powering a van or later integrating into a tiny house.

Key question though: are you looking at mains backup (stays dormant until grid fails) or gradual off-grid transition? Makes a big difference to what you'd spec.

For a garden office or tiny house, a 5-10kWh lithium system sitting between your solar and loads is genuinely future-proof. Costs more upfront but you avoid the false economy of buying twice. Renogy and Fogstar have decent mid-range options in the UK market that don't require you to remortgage.

What's your average daily consumption looking like?

The transition angle is key here — I'd start with a decent battery bank and inverter combo that can handle your van now, then scale it up for the tiny house later. Victron's LiFePO₄ batteries are solid if budget allows, though a quality lead-acid setup like a Fogstar will do the job for less outlay.

Rather than guessing what you'll need, track your actual consumption for a month or two. Most people massively overestimate. Once you know whether you're talking 2kWh or 20kWh daily, the rest becomes obvious.

For the van-to-build transition, a 3-5kW inverter with expandable battery capacity works well. You can run it off leisure batteries initially, then bolt on proper storage when you build. Avoids the nightmare of buying something twice.

What's your typical daily usage look like at the moment?

The beauty of your timeline is you can test everything in the van first—treat it like a proper trial run. I did exactly this when I switched from narrowboat to motorhome, and it saved me making expensive mistakes before the tiny house went up.

Start with a modest Victron setup (MultiPlus inverter/charger combo) and a LiFePO₄ bank you can actually afford—no point going massive if you're still figuring out your real consumption patterns. Solar's a nice-to-have at this stage, honestly. Get your monitoring dialled in with Victron's software so you can see exactly what's happening.

The gear you buy now will either transfer to the permanent build or give you genuine data to spec it properly. Beats guessing at a £10k system based on how you think you'll live, yeah?

What's your current power draw looking like in the van?

Mate, you're in the perfect spot to do this properly. I'd actually grab a decent LiFePO4 setup now for the van — something like a Fogstar or Victron — then you've got two years to figure out what actually works for your usage patterns before committing to the tiny house build.

The van trial run is gold. You'll learn what your real daily draw is, whether you're bothered by charge times, if you need more solar panels than you think. Stuff you can't guess at.

Then when the house build happens, you're not starting blind. You can scale up to a proper battery bank knowing exactly what you need. Plus any kit you buy now will just slot into the new setup anyway.

Definitely don't go full house system while you're still mobile — that's just throwing money at a problem you haven't actually defined yet.

@WonkyMender spot on that you've got the van as a testing ground — honestly, this is how you avoid dropping £8k on something that turns out to be a complete dog in real conditions.

The only thing I'd add to what the lads have said: don't underestimate how much you'll learn about your actual power usage once you're living with it

@WezFisher and @DalesCruiser are spot on about testing in the van first — that's genuinely the smart move. But I'm curious about the practicality side: are you planning to keep the same battery bank when you move to the tiny house, or start fresh?

I'm asking because I've been running a Victron setup in a static caravan for about eighteen months now, and the experience has been brilliant for learning, but I've realised what works in a caravan (compact, mobile-friendly) might not be optimal for a permanent build. The weight considerations are totally different, for instance.

Also — what's your typical daily usage looking like currently? That'll massively influence whether you'd be better with a modest LiFePO4 now or something more scalable. A 5kWh bank works great for a van on a good solar day, but you might find yourself wanting more once you're stationary with proper roof space.

What's your solar situation like at the moment?

Spot on that testing in the van makes sense. I did exactly this — started with a 200Ah LiFePO4 and a 3kW Victron inverter in my boat, now scaling up for a static caravan build.

Real talk though: your power needs in a van vs tiny house will be massively different. Van's probably 2-3kWh daily, house could be 10-15kWh depending on heating. So don't just think "bigger battery of the same thing."

What I'd actually suggest:

• Get a modest 5kWh LiFePO4 setup for the van (Fogstar or Renogy, both solid)
• Learn the bits: charge controller, inverter sizing, loads
• When you build the house, you'll actually know what you need instead of guessing

@DalesCruiser's right that LiFePO4 is the move now — lithium costs have dropped enough it's barely more than lead these days.

What's your rough daily usage look like currently?

The van approach is genuinely your best bet — you'll work out what you actually use versus what you think you'll use, which are two very different things. Most people massively overspec their first build.

What I'd focus on: get a decent battery monitor sorted from day one. Shunt-based systems like Victron's BMV-712 will show you consumption patterns you won't believe. I ran a 100Ah lithium in my van for 18 months before the tiny house — absolutely invaluable data.

One thing worth considering now: if you're planning to upsize to a permanent setup, think about whether you want to migrate components or start fresh. A 5kW Victron Multiplus-II works brilliantly at both scales, but a cheap 3kW inverter you buy for the van might feel limiting when you've got a real kitchen running. That said, don't let tail-wagging-dog syndrome stop you starting small.

Solar sizing matters more than battery size — sounds counterintuitive but undersized panels means you're living off batteries constantly. Van geometry won't work for your tiny house anyway, so

@WonkyMender the van approach is absolutely the way forward, though I'd push back slightly on starting too small. I've got a static caravan setup and the temptation is always to go minimal on battery capacity, then you hit winter or a proper outage and realise you're rationing kettle use.

What you'll learn in the van is your actual consumption patterns — that's the real gold. But don't undersise just to save quid initially. I'd suggest aiming for at least 10kWh usable capacity if budget allows, paired with a decent MPPT (Victron SmartSolar 150/100 for me). The reason: you want enough buffer that you're not constantly topping up daily, especially during grey winters when solar contribution drops to nowt.

The bigger advantage for your future tiny house — once you've run this in the van for 6-12 months, you'll have actual data on your consumption profile. That becomes your spec sheet. You'll know whether you genuinely need 15kW of solar or if 8-10kW handles your actual needs.

One caveat: van elect

Dead right that the van's your prototype workshop — I've been running a static caravan setup for three years now and the difference between what you think you'll need and what actually drains the batteries is hilarious (spoiler: it's the kettle).

One thing I'd add to what @Compo and @SimonKelly mentioned: don't overlook your charging source while you're testing. A decent MPPT controller (Victron SmartSolar if you can stretch, Renogy if you're watching the pennies) paired with expandable solar makes way more sense than a massive battery bank you're constantly topping up from grid. Batteries are expensive; panels are just sitting there being smug.

For the tiny house transition, keep your van system modular — use proper connectors, not solder and hope. You'll want to migrate bits across, and retrofitting a dodgy loom into a building is the sort of joy I wouldn't wish on anyone.

Test your 240V essentials too (immersion heater, cooker elements). DC is lovely until you realise you need actual power for winter heating.

Mate, the van's basically a free A/B test before you drop ten grand on a static setup and realise you've massively overspec'd the battery because you thought you'd run a workshop 24/7 (spoiler: you won't). I've got a Victron setup in mine and it's taught me more about my actual consumption than any spreadsheet ever could — turns out I'm a fairy light person, not a power tools person. When you move to the tiny house, you'll already know if you need three days autonomy or three hours, which makes choosing between Fogstar and Renogy actually worth debating instead of just panic-buying whatever has the shiniest Amazon reviews.

The van's genuinely your best laboratory for this. I learned more in my first six months living aboard than I would've in years of theory.

What nobody mentions though — and this caught me out — is how your actual usage patterns shift once you're properly off-grid. You become aware of energy in a way you're not when the grid's just there. That kettle moment hits different when it's your batteries draining in real time.

Start with a modest battery setup (I'd suggest a single 5kWh LiFePO₄ unit like a Fogstar or similar, nothing fancy) paired with whatever renewable makes sense for your location. In a van you're probably solar-limited anyway. The real win is you'll quickly figure out whether you're someone who obsessively monitors voltage or just wants to forget about it and live normally.

When you build the tiny house, you'll know exactly what size system you actually need rather than guessing. I see people spec'd up to the eyeballs because they're extrapolating from grid living, then they never even get close to their capacity.

Your van's not a stepping stone — it's the prototype run