How much solar do I actually need for a full-time van build?

Planning a full-time van conversion and trying to nail down the solar setup before I start cutting holes in the roof. Currently looking at a Renogy 200W panel but not sure if that's going to cut it for living in the van year-round in the UK.

My rough daily loads: a 40L compressor fridge (reckons about 45Ah/day), phone/laptop charging, LED lighting, and maybe a 12V fan in summer. That puts me somewhere around 80-100Ah per day by my maths. Running a 200Ah Fogstar Drift LiFePO4 as the battery bank.

The problem is I keep reading that UK winter solar is basically useless — people talking about only 1-2 peak sun hours in December up north. So even 400W of panels might only give you 40-50Ah on a grim day? Does that mean everyone just relies on alternator charging through winter, or are people actually making solar work year-round?

Has anyone done full-time UK van life and found a panel wattage that actually works across all seasons, or is it just "as much as you can fit on the roof"?

@JH_Power the 200W figure is almost meaningless without knowing your actual consumption first. Work out your daily Ah draw — every load, every hour — then size backwards from that.

Full-time living typically means 100–150Ah/day once you factor in lighting, laptop, fridge compressor cycling, USB charging, water pump, etc. At 12V that's roughly 1,200–1,800Wh daily.

A single 200W panel in the UK realistically yields maybe 60–80Wh per rated watt annually when you factor in our chronic cloud cover, low winter sun angles, and panel shading from roof vents. So 200W might give you 400Wh on a decent day. That's a significant shortfall.

Practically speaking, most serious full-timers run 400–600W minimum, paired with a decent MPPT controller (Victron SmartSolar is worth every penny) and adequate battery capacity — ideally 200Ah+ LiFePO4 like the Fogstar Drift range.

@RustyRoamer is right, and on a boat I learned this the hard way — I thought 200W was loads until I turned the kettle on once.

@JH_Power to build on what @RustyRoamer and @MarineKaren are saying — before you even think about panel wattage, sit down and list every device you plan to run along with roughly how many hours per day. Fridge compressors are usually the biggest culprit in a van, often pulling 30-50Ah daily on their own. Once you've got a realistic daily total, a rough rule of thumb is you want your panel wattage to be at least 3-4x your daily Ah consumption to account for UK weather, shading from trees and buildings, and the frankly miserable winter sun angles we get up here. A 200W panel sounds decent on paper but in January in the UK you might only see 1-2 peak sun hours on a good day. What's your planned battery bank size?

@JH_Power one thing nobody's mentioned yet — location and season matter enormously here in the UK. That 200W panel might give you a decent 6-7 peak sun hours on a clear July day in Scotland, but come November you're realistically looking at 1-2 hours, often less. I'd strongly suggest planning your system around winter usage if you're living in the van full-time, not summer. It's also worth thinking about where you'll actually be parking — a south-facing spot in a rural layby is very different to being squeezed between lorries in a motorway services all night. Once you've done your consumption audit as @RustyRoamer suggests, factor in a 30-40% efficiency buffer on top. Better to overbuild slightly now than be scrambling for hook-ups in January.

@HelenMoore makes a crucial point about seasonality — worth quantifying it properly. In winter at UK latitudes you're realistically looking at 1–2 peak sun hours on a good day, versus 5–6 in June. That 200W panel might yield 400Wh on a decent summer day but drop to 150–200Wh in December. On my narrowboat I run 400W of panels and still needed a B2B charger from the engine alternator to keep me comfortable through November–February.

My practical suggestion: calculate your daily Wh consumption first (as @VanWez says), then size your panel array to cover that figure using winter peak sun hours as your baseline, not summer. Otherwise you'll be perfectly sorted for a festival in August and completely flat by bonfire night. A MPPT controller (Victron SmartSolar is worth every penny) will also squeeze significantly more out of whatever you fit.