Anyone else running solar on a narrowboat moored in the Fens — what's your winter output actually like?

Just finished fitting a pair of 200W Renogy panels flat on the cabin roof (no tilt, limited by the low bridges round here). Running into a Victron SmartSolar 100/30 and a 200Ah Fogstar Drift LiFePO4. Summer performance has been decent — hitting 40–50Ah on a good day without much effort.

Now heading into October though and I'm starting to worry. Flat mounting in the Fens means short days AND a low sun angle, so the panels are basically looking straight past the sun rather than at it. Yesterday I got a measly 8Ah by 4pm and that's with no real cloud cover.

Anyone in a similar flat-panel situation on a boat — what kind of minimum daily input are you actually seeing through November to February? Wondering whether to add a small genny as backup or if a third panel would make enough difference to bother.

GaryLewis87 | 📍 Cambridgeshire Fens

@FenlandOffGrid Flat mounting is a real killer in winter up here — you're essentially getting peak sun for maybe 2-3 hours on a clear day, and "clear days" in the Fens between November and February are pretty rare! Realistically I'd budget for 150-300Wh daily on decent days, virtually nothing on overcast ones.

The good news is your Fogstar Drift is a solid choice — LiFePO4 handles those shallow daily cycles much better than AGM would. Your Victron will also give you proper data through the app, so track it for a few weeks rather than guessing.

If you're stationary long-term, even a small tilt frame (30-45°) at your bow or stern could make a surprising difference without causing bridge clearance issues. Worth considering over winter.

FrostyTrekker | 📍 Norfolk Broads

@FenlandOffGrid Cracking setup overall, but just worth flagging — you're posting in the Motorhome & Campervan section rather than the Liveaboards or Solar & Batteries boards. Might get more narrowboat-specific responses if a mod can shift it across!

On your actual question — the Fens are notoriously foggy through November to February, so even a tilted panel would struggle. That said, your Fogstar Drift is an absolute trooper for holding charge through cold snaps, which helps enormously. I'd honestly focus more on reducing consumption than chasing extra generation this time of year. LED lighting, a 12V blanket instead of heating the whole cabin — that sort of thing buys you more headroom than any panel tweak will in December up there.

What's your typical daily consumption looking like at the moment?

LiFePO4_King | 📍 Norfolk Broads

@FenlandOffGrid Lovely setup — Fogstar Drift is a solid choice for a boat install. One thing worth checking: with flat panels in the Fens, you'll get a surprising amount of diffuse light bouncing off the water on overcast days, which partially offsets the poor angle. Don't rely on peak wattage figures though — realistically budget for maybe 15-20% of rated output on a grim December day up there.

Your SmartSolar 100/30 will log daily yield history, so pull that data after a few weeks and you'll have a proper picture rather than guessing. Also worth enabling the absorption/float temps compensation in VictronConnect for the cold — LiFePO4 charging below 5°C needs watching carefully on that Drift battery.

What's your typical daily consumption looking like? That'll tell us whether 400W flat is actually enough for winter.

WillowWalker | 📍 Lincolnshire Fens

@FenlandOffGrid We're in very similar territory — I ran a single 175W flat-mounted panel through last winter on a 58-footer and honestly December and January were grim. On a clear frosty day I'd see maybe 20–30% of rated output, and fog (which is relentless round here as you'll know) would drop that to practically nothing for days at a stretch.

The Victron SmartSolar is your friend though — dig into the history data after a few weeks and you'll get a proper picture of what you're actually harvesting rather than guessing.

My honest advice: budget your consumption around 150–200Wh per decent winter day and treat anything more as a bonus. A small Honda genny kept me sane in the depths of January when the haar sat for a fortnight solid.

SamStevens60 | 📍 Cambridge Fens

@FenlandOffGrid Worth mentioning that on genuinely clear winter days you'll often see a decent spike around solar noon — don't be discouraged by the averages. I'm running 400W flat on my widebeam and December/January I typically scrape 150-300Wh on bright days, near nothing on the heavy overcast days we get rolling off the North Sea. The Victron app's historical data is brilliant for spotting patterns — check your yield graph after a fortnight and you'll get a realistic feel for what your system actually produces rather than going off theoretical figures. Also keep those panels wiped down; bird mess and algae from low Fen mist can knock output noticeably. The moisture here is relentless.

GlenSimon | 📍 Array

Flat panels on a Fen boat in December is basically a very expensive way to power your disappointment.

LiamFox | 📍 Yorkshire

@FenlandOffGrid One thing worth keeping in mind with flat mounting in the Fens specifically — you've got very little horizon elevation to the south, which actually helps compared to hillier areas. You're not losing much to shadowing from landscape. What will hammer you is the infamous Fen mist sitting low all morning in November and December — diffuse light rather than nothing, but your SmartSolar logs will show painfully slow morning ramp-ups. Check your Victron app's yield history after a few weeks, it'll tell you more than any calculator. Your 200Ah Fogstar should handle the overnight loads comfortably enough even on lean days.

MrBodge | 📍 Array

Worth adding: flat panels in winter suffer badly from the low sun angle but the Fens compound this with their notorious haar and freezing fog sitting for days at a time. Your Victron SmartSolar logs will tell the real story — check your daily yield history across December/January rather than chasing peak figures.

On the Fogstar Drift: that 200Ah is going to feel tight once you're below ~15°C and the usable capacity quietly drops. I'd seriously look at a small secondary charging source — diesel Webasto or even a quality inverter-charger on shore power at marinas. Solar alone through a Fen winter is genuinely marginal.