Anyone else struggling to keep a 100Ah lithium topped up on a cloudy Scottish trip?

Been through similar on my boat up around the west coast — Scottish summers look great on paper but the solar yield is genuinely poor for days at a stretch.

Few things that made a difference for me:

• Panel angle matters more than size up there — a flat roof mount loses a lot at low sun angles. Even propping panels at 45° manually can add 20-30% on overcast days
• Check your actual consumption — a 100Ah LiFePO4 sounds decent but if you're running a compressor fridge + lighting + phone charging it disappears fast
• Shore power top-up when you can — even a campsite hook-up for 2 hours sorts it

What panels are you running and what's your daily draw roughly? Worth knowing if this is a capacity problem or a harvest problem — they need different fixes.

I run a Victron SmartSolar with the app logging so I can see exactly what came in each day. Made diagnosing this kind of thing much easier. Fogstar cells in my bank so I'm not babying them with conservative discharge limits either — using the full usable capacity helps.

Scotland in July I was averaging maybe 150-180Wh/day from 200W of panels on decent-ish days. Cloudy days dropped to 40-60Wh sometimes. If your fridge alone is pulling 30-40Ah that's your answer right there.

Anyone else found a tilt mount solution that works well on a van roof without being a faff to deploy?

@BatteryRay — on my narrowboat I run a Victron SmartSolar MPPT and the thing that genuinely transformed cloudy-day performance was enabling the "BatteryLife" algorithm off and switching to fixed absorption voltage instead. The default adaptive settings were cutting charge cycles short on overcast days precisely when I needed every amp.

Also worth checking your panel wiring configuration — series vs parallel matters enormously in low-irradiance conditions. Partial shading kills parallel strings disproportionately. I rewired mine to series and saw measurable gains on grey days around the Caledonian Canal.

One more point: a 100Ah bank is genuinely undersized if you're running anything substantial. Scottish west coast in summer realistically gives you 2-3 peak sun hours on a good day. Do the maths against your actual daily consumption before assuming the solar is the problem.

@BatteryRay this resonates — I'm in a similar boat (literally). One thing I've not seen mentioned yet: have you looked at your panel orientation? On overcast days you're essentially capturing diffuse light from the whole sky dome rather than direct sun, so tilting panels closer to vertical can actually help in Scottish conditions rather than hurt. I did some experimenting last summer up around Skye and noticed a measurable difference just from adjusting my tilt angle.

Also worth asking — what's your actual daily consumption? I found I was massively overestimating how much solar I needed until I fitted a Victron BMV and properly tracked usage. Sometimes the answer isn't more generation, it's finding where the power's actually going.

Not directly related to boats but I've fought the same battle with my static caravan setup in a similarly grey part of the country.

One thing worth adding to what's been said: panel orientation matters more on overcast days than people realise. Flat-mounted panels lose a significant chunk of diffuse light capture compared to even a modest tilt — around 15-30° makes a measurable difference when you're relying on that flat grey sky luminance rather than direct sun.

Also worth checking your actual consumption figures honestly. A 100Ah lithium sounds generous until you add up EV charging trickle losses, a compressor fridge, and an inverter on standby. I use a Victron BMV-712 to log what's actually happening rather than guessing — the data usually tells a different story than you'd expect.

@BatteryRay yeah Scotland will absolutely humble you. I've done the Caledonian Canal on the narrowboat and had four consecutive days where my 200W panel was producing basically nothing useful — we're talking 10-15W at midday.

Honest advice: stop chasing more solar and just add a DC-DC charger from your alternator. Fogstar do decent lithium-compatible ones and it'll top you up properly every time you run the engine. Way more reliable than hoping for sun.

Also worth checking your panel angle — boats tend to have panels flat on the roof which is terrible for low Scottish sun. Even propping one panel up 30-40° makes a noticeable difference on dull days.

100Ah is also quite tight if you're running a compressor fridge. That's probably where most of it's going.