Anyone else struggling to keep a 100Ah lithium topped up just from solar in winter?

Really common struggle this time of year, and something I dealt with badly in my first winter before getting the setup dialled in.

The core issue is that a 100Ah LiFePO4 sitting at 50% needs roughly 50Ah to recover, and in December/January in the UK you're realistically looking at 2–4 usable hours of decent sun even on a clear day. If your panels are undersized or poorly angled, you might be harvesting 20–30Ah on a good day — which barely covers overnight loads let alone makes inroads on deficit.

A few things that genuinely helped me:

• Panel tilt — flat-mounted roof panels lose a significant percentage of output at low winter sun angles. Even a small tilt bracket made a noticeable difference
• MPPT controller — if you're still running PWM, swap it out. Victron SmartSolar controllers extract considerably more from weak winter light
• Load audit — a Fogstar 100Ah is still a finite resource. Knowing exactly what your fridge, lighting and inverter are pulling overnight changed how I managed things
• Shore power top-ups — I'm not ashamed to admit I'll plug in at a site once a week through winter just to keep the battery healthy above 20%

The bigger question worth asking is whether 100Ah is actually enough for how you're using the van in winter. For mild three-season use it's fine, but serious winter camping often warrants 200Ah minimum.

What's your current panel wattage and controller setup? That would help narrow down where the losses are happening. Others on here have had good results adding a second panel on a tilt mount — worth discussing if that's an option for your roof space.

@VanGill yes, and the panel angle makes a huge difference that people underestimate. I've got a fixed roof mount on the boat and in December I'm sometimes only seeing 10-15% of rated output even on clear days — low sun angle just skims straight over the panels.

A few things that genuinely helped me:

• Tilt your panels if possible, even a cheap adjustable bracket helps enormously
• Don't let the bank drop below 80% if you can help it — topping up 20Ah is far more manageable than recovering 50Ah from winter sun
• A small MPPT (I use Victron SmartSolar) will squeeze every usable watt out of weak winter light far better than PWM

Shore power or a DC-DC charger from your engine are really your safety nets when solar just can't keep up.

Fixed tilt is basically donating your winter generation to the solar gods as a sacrifice.

Running a 200W panel through a Victron MPPT on my garden office and even that struggles on a gloomy January day in the Midlands — and mine isn't bouncing down the M6 at a sub-optimal angle. For a van I'd seriously look at adding a second 100Ah Fogstar Drift before worrying too much about optimising the panel, because doubling your buffer means the same rubbish 2-hour generation window doesn't leave you at 30% by teatime. Alternatively a small shore power hookup overnight at a site whenever possible — even 10A for a few hours transforms winter resilience completely.

@RelayBuild mine's fixed too but I tilted the whole van by parking on a kerb — the neighbours think I've had a stroke but I'm pulling an extra 15% in December so who's laughing now 🏆

@Brummie84 that kerb trick genuinely made me laugh but I've seen worse solutions.

Worth flagging something that often gets missed in winter top-up discussions — your charge controller's absorption voltage matters more than usual when you're only getting a few amps from weak winter sun. If it's set too low the battery never actually reaches full. Check your Victron or whatever you're running and bump absorption up slightly if you're seeing the charger call it done at 97%.

Also, shade paths shift dramatically in winter. My garden office setup taught me this the hard way — a shadow that cleared by 10am in August doesn't shift until nearly midday in December. On a van that's even more variable depending on where you're parked.

A 100Ah LiFePO4 is borderline marginal for full-time winter van life on solar alone unless your consumption is very disciplined.