Anyone else struggling to keep a 100Ah lithium topped up just on solar during winter trips?

Winter solar is genuinely brutal, isn't it. I don't do much motorhoming myself but the same pain hits my garden office setup every December — even a decent south-facing array can feel almost pointless when you're getting 2-3 hours of usable generation on a grey day.

The maths just don't work in your favour. A 100Ah lithium (say an 80Ah usable chunk from a Fogstar Drift or similar) disappearing overnight on heating, a laptop, and some lighting... you're asking solar alone to recover that by lunchtime with the sun barely clearing the roofline. It won't.

A few things that genuinely helped me stop fighting it:

• Tilt angle matters enormously in winter — panels flat on a roof are leaving a shocking amount on the table. Even a 15° tilt can make a meaningful difference at UK latitudes
• Victron MPPT over PWM is non-negotiable if you haven't already switched
• Realistic consumption auditing — I was horrified when I actually logged mine properly

The honest answer a lot of people don't want to hear is that for UK winter trips, solar alone usually isn't enough. A split-charge relay top-up from driving, or even a small mains hook-up where available, needs to be part of the equation rather than a failure.

What's your panel wattage and controller situation currently? And are you doing mostly static pitches or wild camping? That changes the advice quite a bit.

Would love to hear how others are managing — especially anyone doing Scottish winter trips where the sun seems to exist purely as a rumour.

@48VGal oh tell me about it — I've been fighting this exact battle on the van conversion this winter 😅

Quick question for the thread though: what are people actually getting in terms of usable amp-hours on a typical grey December day? I've got a 200W Renogy panel on the roof (flat mount, not tilted — I know, I know) and a 100Ah Fogstar Drift, and honestly some days I'm pulling in maybe 8-10Ah if I'm lucky?

• Is anyone running a tilt kit worth recommending?
• Or just accepting defeat and using a B2B charger off the engine?

I keep the van as emergency backup too so ideally want the battery maintained without having to drive it round the block every few days like some kind of automotive babysitting service 😂

@48VGal The geometry is the problem more than the irradiance, frankly. A panel that's flat-mounted on a motorhome roof is losing perhaps 60-70% of potential harvest in December compared to a properly angled ground array — you're catching the sun at a pathetically shallow angle while simultaneously accumulating shading losses from any obstruction.

I run a static caravan setup with tiltable frames for exactly this reason, but that's obviously not practical on a moving vehicle.

Realistically, a 100Ah LiFePO4 in a van context during winter needs supplementing. Either a decent B2B charger off the alternator (Victron Orion-Tr Smart is what I'd recommend) or shore power when available. Solar alone through December and January is unlikely to maintain any meaningful state of charge unless consumption is extremely conservative and you're lucky with the weather.

@Compo raises a fair point on the geometry, but I'd add that the real killer combination is short day length plus low angle plus frequent overcast — it's not just one factor.

In practical terms for a 100Ah LiFePO4 (assuming ~1.28kWh usable), you're realistically looking at perhaps 150–200Wh of useful harvest on a grim December day in, say, Scotland. That won't even cover a basic heating/lighting load.

My approach for winter: treat solar as supplementary, not primary. A quality DC-DC charger (Victron Orion-Tr Smart is what I run) pulling from the alternator during any driving becomes absolutely essential. Even 40 minutes of driving makes a meaningful difference when solar is contributing almost nothing.

Tilt mounts help considerably if your setup permits them — even getting from flat to 45° can roughly double effective irradiance at UK winter sun angles.

@SueThompson nailed it really. I run a similar capacity on my static and a shepherd's hut setup — December is genuinely grim regardless of panel quality.

One thing worth adding: state of charge matters more in winter. Lithium doesn't care much about partial charging in summer when you're topping up daily, but if you're repeatedly cycling between say 40–80% because the solar just isn't there, you're not getting the usable capacity you think you are.

A small Victron MPPT with proper absorption settings helps squeeze every last bit out of weak winter sun. Also worth checking your Fogstar or whoever's cells are actually configured for lower charge voltages in the cold — some BMS defaults aren't great out the box.