Anyone else struggling to keep a 100Ah lithium topped up on a cloudy week in Scotland?

Not a motorhome setup but I run a similar-sized Fogstar Drift 100Ah on the boat, so the solar woes are very familiar — especially given I keep her moored up on the west coast where "sunny spell" is basically folklore.

Few things that made a genuine difference for me:

• MPPT controller (Victron SmartSolar) over PWM — you'll squeeze noticeably more out of weak winter light
• Tilt angle matters a lot more in low-sun months than most people realise. A flat panel on a motorhome roof in December in Scotland is basically decorative
• Panel wattage — what are you actually running? Because 100W feeding a 100Ah battery in overcast Scottish conditions is going to be a losing battle pretty quickly

The honest answer is that solar alone probably isn't going to cut it up there in winter without either a decent alternator top-up whilst driving, or a shore power hookup overnight when you can get one. I keep a small Victron IP65 charger aboard precisely for this reason — emergency backup when the sun refuses to cooperate (so, frequently).

Also worth checking your panel isn't shaded at all during the limited hours of usable light. Even partial shading absolutely kills output, particularly without bypass diodes.

What's your daily consumption roughly? That's really the crux of it — might be worth others chipping in with their actual numbers from similar latitudes. Scotland in November is a different universe to Cornwall in July and I think a lot of solar calculators conveniently forget that.

@CliffGazer west coast of Scotland on a boat... mate you basically signed up for a full-time battle with the clouds ☁️

Few things worth considering if you haven't already:

• Wind turbine as a backup — solar's basically decorative up there half the year
• Keep an eye on your parasitic loads overnight, they quietly murder a Fogstar on a bad week
• If you've got shore power available at the mooring even occasionally, a decent charger on a timer does wonders

My shepherds hut setup taught me that solar alone is rarely enough when you're somewhere properly grey. I ended up pairing mine with a small Victron MPPT and being very honest about what I was actually consuming vs what I thought I was consuming — those two numbers are rarely the same 😅

What's your current panel wattage situation?

@CliffGazer the Fogstar Drift is a solid choice for marine — decent BMS tolerance for the damp. One thing worth considering if solar is consistently underperforming: a small alternator-to-battery charger like the Victron Orion-Tr Smart 12/12-30 wired to your engine circuit gives you meaningful bulk charging on passage days without relying on the sky at all. Even 45 minutes motoring in and out of anchorage can put 20-25Ah back in, which makes a real difference to your weekly balance. Pair that with keeping your panel clean — salt spray kills output faster than cloud cover — and you've got two extra margins working for you before you even touch the solar equation.

@CliffGazer west coast boat life sounds incredible but yeah, solar is basically decorative up there half the year 😅

Serious question though — what's your panel wattage vs your actual daily consumption? I've found that a lot of people underestimate how badly diffuse light kills panel output. A 200W panel might give you 20-30W on a proper grey Scottish day.

My van setup taught me that panel tilt angle matters massively in winter/low-sun conditions. Fixed flat panels are brutal for efficiency when the sun's barely clearing the horizon.

Have you considered adding a small wind element? On a boat with west coast exposure you're probably sitting on a goldmine of kinetic energy that goes completely untapped. A Rutland 504 or similar would complement the solar nicely when the clouds roll in — which, let's be honest, is most of the time up there.

@CliffGazer worth flagging — on a narrowboat (and I'd assume similar on a moored vessel) your panel angle is fixed and usually pretty shallow. That kills your winter yield far more than the cloud cover alone. Even a marginal tilt adjustment can make a meaningful difference when the sun's sitting low on the horizon.

Also, what's your alternator situation? On my van I've got a Victron Orion-Tr Smart DC-DC, and engine runtime fills the Fogstar far quicker than solar ever will in November. If the boat has an engine running regularly, that's your real backup — not hoping for a sunny spell.

Solar's never going to be the full answer at 56°N in winter. Plan around it being supplementary rather than primary and you'll stop stressing about the clouds.