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

Running a 200W panel into a 100Ah AGM on my garden office setup and genuinely not sure what to expect once we get into November/December.

Current situation: panel is south-facing, roughly 35° tilt, no shading. Going through a Victron SmartSolar MPPT 75/15. The battery runs a few LED circuits, a small 12V fan heater occasionally, and keeps a Raspberry Pi ticking over 24/7.

My concern is that even with a decent panel, UK winter irradiance is just awful. I've been poking around on PVGIS and the numbers for my location look pretty grim — we're talking maybe 1-2 peak sun hours on a bad December day.

A few specific questions:

• Is 200W realistically going to maintain a 100Ah battery without it sitting at 60-70% SOC for weeks on end?
• Does anyone have real-world data rather than theoretical calcs? PVGIS is useful but it doesn't account for the weeks of solid cloud we get
• Would tilting steeper (50-55°) actually make a meaningful difference in winter or is it marginal?
• At what point does it make sense to just chuck a small trickle charger on mains as a winter backup rather than flogging the solar?

The Raspberry Pi draw is roughly 5W continuous so that's ~120Wh/day minimum regardless. Fan heater use is irregular but probably adds another 50-100Wh on cold days.

Basically — is this a viable winter setup or am I kidding myself and need to either reduce loads or accept a mains backup?

@BMS_Geek the brutal truth for UK winters: a 200W panel might only deliver 1-2 peak sun hours on a decent December day, so realistically 200-400Wh on good days, potentially near zero during overcast weeks.

For a 100Ah AGM you're looking at roughly 50Ah usable (don't go below 50% SoC on AGM). That's around 600Wh.

The maths isn't kind in December.

Key variables:

• Horizon shading becomes significant when sun stays low (~15° elevation)
• AGM self-discharge increases in cold
• What's actually drawing from it?

Your 35° tilt is reasonable for winter — steeper (50-60°) would help slightly.

Personally I wouldn't rely on solar alone for critical loads November-March without either a backup charger (Victron IP65 on a timer works well) or significantly oversized panels. 200W into 100Ah feels marginal even for standby loads.

What's the actual consumption pattern?

@BMS_Geek 35° tilt is actually sub-optimal for winter — steepen it to 55-60° and you'll claw back meaningful generation when the sun's scraping along the horizon like it's embarrassed to be here.

The real villain isn't panel size, it's AGM self-discharge plus load — if your garden office is drawing anything above ~10-15W average, that 200W panel won't keep pace on a grey Scottish December fortnight.

Practical suggestions:

• A Victron SmartSolar MPPT will squeeze every last milliwatt out of grim skies (genuinely makes a difference vs cheap PWM)
• Log your actual consumption for a week — most people dramatically underestimate their loads
• Consider a Fogstar 100Ah lithium swap; AGMs hate partial state-of-charge cycling through winter and capacity drops badly in the cold

Running similar on my setup — November onwards I treat solar as supplemental, not primary.