Tiny house emergency backup on a shoestring — what's the minimum viable system?

After a rough winter with two grid outages lasting 8+ hours each, I've finally decided to stop putting this off. I want a basic emergency backup setup for my tiny house — enough to keep lighting, phone charging, a small 12V fridge, and maybe a 240V pump running when the grid drops. Not looking to go full off-grid, just a sensible fallback that doesn't cost the earth.

Currently eyeing a 200Ah LiFePO4 from Fogstar (the Drift 12V), a Victron SmartSolar MPPT 100/30, and two 200W panels I spotted going secondhand locally. Total budget is trying to stay under £600 for the lot. The Fogstar seems the obvious choice over a cheap AGM given the cycle life, but I'm wondering whether 200Ah is actually enough for an 8-hour overnight outage with the loads I've described — rough calcs put me at around 80–90Ah consumed, so there's margin, but it feels tight once you account for not discharging below 20%.

Has anyone put together something similar at this price point? Specifically wondering whether a Victron Phoenix 375W or 500W inverter is the right call for the 240V pump, or whether I'm overcomplicating it and should just replumb the pump to 12V. Also open to whether the Renogy DC-DC charger route makes sense here as a secondary charge source from the existing consumer unit via a battery charger, rather than relying purely on solar in the depths of a UK December.

XAC_Solar | 847 posts

@CrispyRoamer Decent starting point that won't break the bank: a 100Ah LiFePO4 battery (check Fogstar Drift — genuinely good value), a 40A PWM charge controller, and a single 200W panel. That'll comfortably run LED lighting, phone charging, and a small 12V fan indefinitely during daylight, with several hours of evening use from stored capacity.

Skip inverters initially — run as much as possible at 12V natively. 12V LED strips and USB charging hubs are your friends here.

Total outlay around £350-450 if you shop carefully. Expandable later too, which matters.

What's your roof situation like? Orientation and any shading will affect whether one panel is genuinely sufficient or whether you'd be better served with two smaller ones.