Anyone know if a 200W panel will keep a 12V 100Ah battery topped up over winter?

Running a shepherd's hut in a field in the north of England, so this question is very much on my mind heading into the darker months.

Currently I've got a single 200W Renogy panel on the roof feeding into a 100Ah lithium (Fogstar Drift) via a Victron SmartSolar 100/20. Works brilliantly from March through to October — battery barely drops below 90% most days.

But last November I noticed the battery slowly creeping down over consecutive grey days, ending up around 40% by mid-month before I panicked and ran an extension lead from the farmhouse. Not ideal.

The hut is used mainly at weekends — a few LED lights, a 12V compressor fridge, and occasionally charging a laptop. Nothing extravagant. I've been toying with the idea of adding a second 200W panel, but I'm not sure if that's genuinely necessary or whether I'd be better off just looking at reducing consumption further.

A few specific questions:

• Has anyone actually run numbers on realistic winter yield for a south-facing panel in northern England? I've seen figures as low as 0.5–1 sun hours per day in December/January being quoted.
• Would a second panel make a meaningful difference, or is it diminishing returns when the sky is just permanently overcast?
• Anyone using a small backup charger — like a Victron Blue Smart IP22 — just as a winter safety net rather than primary charging?

The complication is I'm also slowly building toward being able to trickle-charge an EV from the hut eventually, so whatever I spec now needs to have some headroom for that ambition down the line.

Genuinely stumped on whether 200W is just fundamentally undersized for winter up here.

WrongFuse99 | Posts: 847

@Davo49 Honest answer — it'll be marginal at best up north. In December/January you're realistically looking at maybe 1-2 peak sun hours on a good day, so that 200W panel might only push out 200-400Wh on a decent winter day. Factor in cloud cover and you could have several consecutive days producing next to nothing.

The bigger question is what your actual daily consumption looks like. If you're running LED lighting and a small 12V device or two, you might just about scrape through. But if there's anything heavier on the load, you'll be drawing the battery down faster than it's recovering.

Worth considering tilting the panel steeper for winter — closer to 60-70 degrees helps significantly at northern latitudes. Makes a noticeable difference in my experience.

BlownFuse | Posts: 312

Worth thinking about this in terms of actual numbers. Up north in December you're realistically looking at 1–1.5 peak sun hours on a good day. So your 200W panel might yield 200–300Wh daily if you're lucky — and that assumes no shading, correct tilt angle, and clean panels.

The critical question is what your actual daily consumption is. Have you logged it? Even a rough figure from a Victron SmartShunt would tell you immediately whether you're in deficit.

A few things that genuinely help in winter:

• Tilt the panel steeper (closer to 60°) to catch the lower sun angle
• Keep the panel clear of frost
• Consider adding even a second small panel in series

What loads are you running in the hut? That'll determine whether this is a minor tweak or a fundamental sizing problem.

PeakVanLifer | Posts: 1,203

Got a shepherd's hut myself so been through exactly this. Even on a good winter day that 200W panel is doing maybe 20-30Wh if you're lucky — clouds, low sun angle, the lot.

Couple of things that actually helped me:

• Tilt the panel steeper — like 60° ish for winter, makes a noticeable difference
• Keep a close eye on your battery SoC, a Victron SmartShunt is dead cheap and worth every penny
• Honestly? A small secondary panel is cheaper than you'd think, Fogstar and others do decent deals

If your 100Ah is lithium you've got more usable capacity to play with. If it's AGM... yeah you're working with maybe 50Ah realistically.

What's your actual load? That's the bit nobody's mentioned yet and it changes everything.

LiFePO4Fan | Posts: 634

One thing nobody's mentioned yet — panel angle matters a lot in winter. Low sun means a near-vertical tilt gives you significantly more harvest than flat-on-a-roof mounting. If you can adjust it seasonally, do it.

Also worth checking what your actual consumption looks like. 100Ah sounds decent but if you're running heating, lighting, a phone, laptop... it adds up fast. I log mine with a Victron BMV-712 and was genuinely surprised how much I was pulling on grey days.

The LiFePO4 in my setup handles partial state of charge better than lead-acid would, so if you're still on AGM that's another consideration — lead-acid really dislikes sitting at 50% repeatedly over winter.

Might be worth a second panel if roof space allows. Two 200W panels changed things considerably for me.

CarlBaker | Posts: 847

@LiFePO4Fan makes a valid point on tilt angle. To add some concrete numbers: at 54°N latitude, optimal winter panel angle is roughly 65-70° from horizontal. Most hut roof pitches sit around 30-35°, so you're losing a significant chunk of already-limited irradiance.

Worth pulling your actual location into PVGIS (free EU tool) and running the simulation — it'll give you monthly yield estimates rather than guessing. For a north-England location in December, realistically budget 0.5-0.8 peak sun hours on many days.

Your 200W panel might produce 100-160Wh on a reasonable winter day. Against a 100Ah/1.2kWh LiFePO4 that's borderline if you have any meaningful load. A second panel would transform your winter resilience considerably, and they're cheap enough now that it's hard to justify not doing it.