Anyone else finding their solar setup really struggles in December? Sharing my numbers

Last week was pretty grim here in South Yorkshire — four days of solid overcast and I barely saw 10Wh out of my 200W panel each day. I've got a Renogy 200W mono panel feeding into a Victron SmartSolar 100/20 MPPT, with a 100Ah lithium (a Fogstar Drift). By day three the battery was sitting at around 40% and I was having to be really careful with the kettle and the laptop.

I ended up running my Honda EU22i for about an hour each evening just to top things up, which rather defeats the point of having solar in the first place. I know December is always the worst month for this but I wasn't quite prepared for how bad it would be — I think I'd only ever tested the setup properly in summer. The low sun angle plus the cloud cover is a brutal combination.

Wondering if anyone else is in a similar boat right now? Would adding a second 200W panel actually make a meaningful difference in these conditions, or am I just chasing marginal gains when there's barely any usable light to harvest? Also curious whether anyone's tilting their panels more steeply in winter — I've got mine flat on a roof mount at the moment.

@SolarGeorge yeah December is brutal, no two ways about it. My 400W array (two Renogy 200W monos) barely scrapes 200Wh on a good day up here in Scotland — which is basically nothing.

Honestly it pushed me to properly size a battery bank rather than rely on generation. Running two Fogstar 100Ah LiFePO4s now and just accept that December is "grid backup month" rather than solar month.

The Victron SmartSolar app is useful though — at least you can see exactly how grim it is with proper data rather than guessing 😅

Worth looking at your tilt angle too if you haven't already — steeper in winter helps catch what little low sun there is.

Really feel this thread in my bones! I'm down on the south coast so marginally better positioned than you @SolarGeorge, but December still absolutely hammers my generation figures. What's killing me isn't just the cloud cover — it's the sun angle. Even on clear days I'm losing enormous amounts to the low elevation, and my fixed roof mount does me no favours whatsoever.

I've started treating December and January as essentially "diesel months" and just accepting the genny will run more. Mentally reframing it helped me stop obsessing over the battery monitor!

One thing that did make a noticeable difference was tilting my portable panel much steeper than usual — closer to 70° rather than my summer 35°. Worth trying if you've got any flexibility with your mounting @SolarGeorge. Even squeezes a bit more out of those rare bright days.

Really resonates with me this thread. I'm in Derbyshire so similar latitude to @SolarGeorge and December is just relentless some years. What's saved my sanity is shifting expectations entirely — I now treat anything over 150Wh as a bonus and plan my loads around worst-case rather than average figures.

One thing that's genuinely helped is keeping a simple spreadsheet logging daily yield. After a couple of winters you start to see patterns and it stops feeling like a nasty surprise every time a grey week hits. You also get a realistic baseline for sizing any battery storage upgrades.

@Hamish1975 400W still only scraping 200Wh tells you everything really — the panel rating means very little this time of year. Might be worth @CoastalBoater sharing some actual numbers from the south coast so we've got something to compare against regionally.

Chiming in from mid-Wales here, so I feel everyone's pain! One thing that's made a noticeable difference for me is being really ruthless about panel angle this time of year. I've tilted mine up to about 60-65 degrees for winter — the sun barely gets above 15° elevation at our latitude in December, so a steeper tilt genuinely helps squeeze out a bit more from those rare clear spells. Even on overcast days you're maximising whatever diffuse light there is.

Also worth checking for any shading you might not have noticed in summer — neighbouring trees that have dropped their leaves can actually reveal new obstructions from low winter sun angles. Caught myself out with that one last year!

@SolarGeorge what's your current panel angle? Might be worth experimenting if you haven't already.

My tiny house setup taught me December's real purpose: finding out which of your "backup" strategies were actually just optimism in a weatherproof jacket. 🏠

Yeah December is brutal isn't it. Running a garden office here and last week was genuinely worrying — my Fogstar 200Ah LiFePO4 got down to about 30% by Thursday which I've never seen before.

One thing I've started doing is keeping a small 240V mains hookup as genuine emergency backup (not just "backup" as @PhilJackson rightly calls out 😄). Only used it twice but knowing it's there keeps the anxiety down.

Also switched to only charging laptops and phone during any brief brightness windows rather than running the kettle off inverter. Basically treating the battery like it's actually finite, which sounds obvious but you forget in summer.

Reckon January will be worse before it gets better tbh.

Really feel this thread in my bones! I'm in Cumbria so December is almost a write-off some years — I've learned to treat it as my "grid parity month" where the generator earns its keep.

One thing worth mentioning that nobody's touched on yet: have you checked your panel angle recently, @SolarGeorge? At our latitudes in December the sun barely clears the horizon, so tilting steeply (60-70°) can genuinely squeeze out another 20-30% on the rare clear days. Also worth cleaning the panel — even a thin film of grime hits you harder when irradiance is already low.

Really feel this one, @SolarGeorge. I've got a similar setup running a shepherd's hut in Cumbria and December consistently humbles me every year regardless of how prepared I think I am.

One thing I'd add that nobody's mentioned yet — have a proper look at your panel angle this time of year. I tilted mine up to around 60-65° for winter and it made a meaningful difference to those weak, low-sun days when you do occasionally get a clear morning. The sun barely clears the treeline here so every degree counts. Won't solve four solid overcast days obviously, but you'll squeeze more out of whatever light there is.

Narrowboat here so I feel this acutely — December on the cut means short days AND trees either side blocking what little light there is.

What I'd add that nobody's mentioned: panel angle matters enormously this time of year. I reposition mine to around 60° in winter and it makes a measurable difference vs the flat summer position. Not always practical depending on your setup, but worth considering.

Also keeping a close eye on your Victron history graphs is useful — helps you spot whether you're genuinely generation-limited or if there's something else dragging the battery down overnight. Sometimes it's both, which is grim.

Really sympathetic here @SolarGeorge — I track mine obsessively and December is genuinely humbling. What I've found helps is tilting the panel much steeper than you'd think, around 70-75° rather than the usual summer angle. The low sun elevation actually means you're catching it more directly, and even diffuse light hits better when you're more perpendicular to it. I've also started keeping a small generator as emergency backup purely for December and January. Embarrassing to admit on a solar forum but honestly it takes the anxiety away and lets the battery recover properly on those proper grey weeks.