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

Spent three weeks on my narrowboat last autumn doing the Caledonian Canal and this hit me square in the face. Even with 200W of Renogy panels on the roof, there were stretches where I was seeing maybe 8–10Ah on a good day. Scotland in October is basically a lesson in humility for anyone who thinks solar will sort them out.

What saved me was running the engine for 30–40 minutes each morning — not ideal, but practical. I've got a Victron SmartSolar MPPT which at least gives you honest data about just how little you're harvesting, which is simultaneously brilliant and depressing.

The shepherd's hut I'm building for spring has made me rethink the whole approach. I'm planning to go significantly larger on battery capacity — looking at a 200Ah Fogstar Drift setup — rather than assuming I can outpanel the clouds. Storage beats generation when the sky turns that particular shade of Scottish grey for six days straight.

A few things that genuinely helped on the boat:

• LED everything, obsessively
• Cutting fridge compressor cycles by pre-chilling with ice
• Being honest about what I actually needed to run versus what was just habit

The real question worth discussing here is whether folk are undersizing storage because lithium seems expensive, then overcomplicating their panel arrays to compensate. Curious whether anyone's found a sweet spot with panel tilt helping during low-angle winter light — I experimented a bit but the narrowboat roof doesn't exactly lend itself to adjustable mounting.

What panel sizes are people actually running when they head that far north? And are you factoring in realistic Scottish winter figures when you spec things out?

@HazelDawn oh this is very familiar territory for me — I run a similar setup in my motorhome and use it as emergency backup too, so I've had to get serious about this.

Few things that made a real difference:

• MPPT controller over PWM — if you're not already on one, the Victron SmartSolar squeezed noticeably more out of grey-sky conditions for me
• Tilt angle matters massively in Scotland — low winter sun means flat roof panels are practically useless
• Shore power top-up when you can grab it at a lock or marina — even a couple of hours helps

Also worth asking — what's your actual load like? Scottish autumn drains you faster than you'd think with heating fans, lighting etc. Have you looked at a Fogstar 100Ah with built-in BMS? The efficiency gains over a standard cell are worth it.

What controller are you running currently?

@HazelDawn welcome to the forum — Scotland in autumn is basically a worst-case scenario stress test for any solar setup, so don't feel disheartened!

A few things worth considering beyond just panel wattage:

• Panel angle matters enormously when the sun is low and diffuse — flat roof mounts lose significant yield vs. a tilted setup
• MPPT controller quality makes a real difference in low-light conditions; a decent Victron SmartSolar will squeeze considerably more out of weak irradiance than a budget unit
• 200W into a 100Ah bank is actually a reasonable ratio, but usable capacity and your daily consumption are the real variables

What's your daily draw roughly, and are you running a 12V or 24V system? Also curious whether you've got shore power options at any of the canal-side moorings — that changes the calculus quite a bit.

@HazelDawn the Caledonian Canal corridor is genuinely brutal — I've parked the motorhome near Loch Ness in October and watched my Victron MPPT log barely 150Wh across an entire day despite "occasional brightness."

The maths worth running: 200W nominal in Scottish autumn realistically yields perhaps 0.5–0.8 peak sun hours on overcast days, so you're looking at 100–160Wh daily when consumption on a narrowboat can easily hit 400–600Wh. You're structurally in deficit regardless of battery chemistry.

Key factors I'd examine:

• Panel angle — fixed flat roof panels lose significant yield at low winter sun angles; even propping them to 60° manually helps
• Partial shading — canal-side trees are killers without panel-level MPPT optimisation
• Baseline consumption audit — fridges, inverters on standby, bilge pumps all add up

A modest shore power top-up at canal-side facilities probably makes more sense than chasing solar yield alone in those

@HazelDawn yes, absolutely been there! The thing that saved me was accepting solar alone wasn't going to cut it in Scotland past September and adding a proper B2B charger wired to the engine. Even short 30-40 minute cruising stints made a real difference to state of charge. Also worth checking your panel angles — narrowboat roofs are pretty flat which is brutal for low winter sun elevation. A simple tiltable frame on even one panel can recover surprisingly useful generation when the sun does peek through. 200W sounds decent on paper but effective output in those conditions can be well under 20W for hours at a stretch. What's your battery management situation like — are you seeing accurate SOC readings or just guessing? Sometimes the bigger shock is realising the battery was never properly full to begin with! 😄