Canal boat solar — winter performance report

We've been running a 400W Fogstar system on our narrowboat for two winters now, and I've got to say the performance drop is... significant. Down to maybe 30-40% of summer output on grey days, which we get plenty of up here.

The real challenge is space constraints. Unlike a cabin where you can sprawl panels across the roof, boat space is precious. We've got four 100W panels mounted on the cabin roof, angled as steeply as we can manage without looking mad, but winter sun angle still hammers us.

What's helped most:

• Battery oversizing (we went 400Ah LiFePO4) to buffer the lean months
• Hybrid inverter (Victron MultiPlus) so we can run a small petrol generator on demand without stress
• Seriously cutting phantom loads — every amp counts
• Positioning over winter in areas that get south-facing exposure

The canal boats I know doing best have either added wind turbines (controversial on the towpath, mind you) or accepted they'll need more generator runtime December-February.

Are others finding the same dip? I'm wondering if anyone's experimented with tiltable mounts or seasonal repositioning. Also curious whether diesel heating changes the equation — we use it for space heating but it frees up battery capacity that would've gone on electric heaters.

Would be interested to hear winter strategies from the marine crew, especially anyone up north where light hours are brutal.

Canal boats and winter sun are like a relationship that needs counselling — technically possible but requiring serious effort and compromise. That 30-40% figure tracks with my static caravan setup; I'm running a similar Fogstar array and December basically means "hope you've got a good battery bank" season. The narrow boat advantage is you can at least rotate position without planning permission, unlike us lot stuck in one spot. Have you considered repositioning the panels seasonally or are they fixed to the roof? Also worth checking if winter canal-side tree cover is doing you dirty — I lose maybe 10% just to overhanging willows in January.

That's bang on with the winter reality. I've been watching my cabin system closely these past months, and the angle thing is crucial that nobody mentions enough. Even a modest 20° tilt makes a noticeable difference when the sun's barely climbing above the treeline.

The Fogstar units are solid — I ran one for a season — but a narrowboat's got the added problem of being flat. You're fighting both reduced daylight and the worst possible panel angle. @PartnerProject, have you considered tilting yours seasonally? I know it's fiddly on a boat, but even temporary brackets for winter can help.

That said, 30-40% output is closer to realistic than pessimistic. You're dealing with cloud cover, atmospheric moisture, the lot. Where I'd push back slightly is expecting anything near summer figures. The actual sun hours in December are roughly a third of July's, so maths-wise you're already down before clouds even enter the conversation.

What's your battery setup? That matters more in winter anyway — you might be generating less but the real question is whether you're storing enough for grey spells.

Winter canal positioning is your real enemy here. Unlike stationary installs, you're constantly shifting angle relative to the sun's low arc. I've noticed this massively in the van — even a 15° difference in panel pitch kills output on those grey December mornings.

400W should theoretically hold better than 30-40% though. Worth checking:

• Panel cleanliness. Narrowboat spray, condensation, bird mess — it all stacks up faster on water
• Wiring losses over longer runs if you've added cable length
• Battery voltage sag in cold. Your charge controller might be throttling earlier than summer

The Fogstar gear is solid, but winter on a boat is brutal. Have you monitored actual DC input versus what the controller's reporting? Sometimes the MPPT isn't the culprit — it's the batteries being reluctant to accept charge below 5°C.

Consider a tilt frame if you're stationary for stretches. Even temporary repositioning can unlock another 10-15% on those rare crisp winter days. Canal boats have decent roof space if you're willing to think creatively.

The angle issue @CoveMick mentions is spot on, but I'd push back slightly on the "constantly shifting" bit — narrowboats do tend to settle in one orientation for weeks at a time, which actually works against you. You end up locked into a suboptimal angle through winter.

What I've noticed with my own setup is that the 30-40% figure assumes you're comparing like-for-like conditions. The real killer isn't just lower sun — it's the consistency of cloud cover this time of year. I'll get three days of useful output, then a week of 15-20% on the best days.

Have you considered a tiltable mount for at least one panel? Even a basic adjustable frame lets you angle toward the winter sun during your peak season. Costs a bit extra but transformed my winter yield by around 15-20 percentage points.

Also worth checking: are your panels actually clean? Narrowboat life means regular dust, pollen, and canal spray. Winter's when people stop bothering with cleaning them — that alone can lose another 5-10% easily.

What's your current battery capacity sitting at

I'm curious about your tilt setup — are you running fixed panels or do you have adjustable brackets? I've been toying with a similar 400W Fogstar system for my static caravan, and I'm wondering if seasonal angle adjustments might actually be worth the faff.

The winter sun is so low in the UK that even a 15-20 degree difference in panel angle could shift your output noticeably. On a boat you've got movement working against you obviously, but on fixed ground I'm starting to think a winter reangle might beat out accepting that 30-40% loss.

Also — are you getting any shading from your boat structure or the canal itself? Winter shadows behave differently, and I've noticed canal-side trees can be brutal in that low-angle sunlight. Might be worth mapping where your panels sit relative to the towpath through the darker months.

What's your battery capacity like? I'm wondering if oversizing winter expectations downward and running a smaller daily cycle actually extends lithium lifespan better than chasing those grey-day outputs with bigger systems.