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

Running a small garden office setup and trying to work out if I've got enough panel capacity to keep things ticking over through the dark months without the battery going flat.

Currently running a single 200W mono panel (Renogy) on a 20-degree tilt facing roughly south-southwest, feeding into a Victron SmartSolar MPPT and a 100Ah AGM leisure battery. The office draws maybe 150-200Wh a day — just a router, a couple of LED strips, and occasionally a laptop charger.

My concern is December/January. I know the UK is brutal for solar in winter — I'm in the East Midlands and I've seen days where the panel barely registers 20W all day. I've read the rough rule of thumb that you get maybe 0.5-1 peak sun hour on a bad winter's day in the UK, which on a 200W panel is only 100-200Wh best case, and that's before MPPT losses, wiring losses, temperature derating and everything else.

So realistically, is 200W enough to cover 150-200Wh daily consumption and still keep the battery healthy? Or am I going to end up in a situation where the battery is slowly cycling deeper and deeper over a run of overcast days, which would obviously kill an AGM pretty quickly?

A few specific questions:

• Has anyone actually measured real-world winter output from a similarly-sized panel in the UK Midlands?
• Would bumping the tilt angle up to 60-70 degrees for winter actually make a meaningful difference?
• Is there a point where I should just accept I need a small AC charger as a backup?

Any real-world data rather than calculator estimates would be massively appreciated.

@WheresMeWires short answer: probably not, and here's the maths that'll ruin your afternoon ☀️

In December/January you're realistically looking at 1–2 peak sun hours in the UK, so your 200W panel is delivering maybe 200–400Wh on a good day — and that's ignoring the inevitable cloud, panel soiling, and wonky angle losses.

If your office is drawing even 100–150W consistently, you're in deficit before lunch.

My recommendation:

• Add a second panel (Renogy do decent budget 200W units)
• Fit a Victron SmartSolar MPPT if you haven't already — squeezes every last photon out of weak winter light
• Consider a Fogstar Drift LiFePO4 to replace that leisure battery — proper depth of discharge without the sulphation drama

What's your actual daily consumption in Wh? That's the number we actually need to help you properly.

@WheresMeWires worth factoring in that a standard flooded leisure battery will sulphate badly if it sits below 50% for extended periods — which is pretty likely in a UK winter with 200W. If you're not already on LiFePO4, that'd be my first upgrade actually. Can discharge much deeper without damage, so your usable capacity is effectively double.

Also — panel angle matters a lot this time of year. Steep tilt (60°+) makes a meaningful difference in winter sun capture. Easy win if yours is flat-mounted.

What's the actual load? Garden office is vague — if it's just LED lighting and a router that's very different from running monitors all day.

@WheresMeWires one thing nobody's mentioned yet — panel orientation makes a dramatic difference in winter. At UK latitudes you'll squeeze significantly more out of a south-facing panel tilted steeply (think 60–70°) versus the typical shallow summer angle. I've got a 200W Renogy panel on my garden office and tilting it up for winter genuinely recovered maybe 20–30% more generation versus flat-mounted.

Also worth checking your MPPT controller's temperature compensation if you're using a flooded battery — cold electrolyte needs a higher charge voltage to actually reach full state of charge. Victron controllers handle this well with a temperature sensor probe, which is a cheap addition.

Realistically though, for a working garden office in December, 200W into 100Ah is marginal at best. A second panel is the practical fix rather than optimising around an undersized array.

@WheresMeWires to put some numbers on this — a 200W panel in December across most of the UK will realistically generate maybe 0.5–1.0 peak sun hours daily, so you're looking at 100–200Wh on a decent day, often less. If your office load is even 150Wh/day (a modest router, LED lighting, laptop charging), you're borderline at best and underwater on overcast days.

@BaySeeker's point on orientation is critical — tilt that panel steeper for winter, 60–70° will outperform a summer-optimised 35° mount significantly in December.

My shepherd's hut setup runs a similar ratio and I added a second 200W panel specifically for winter — game changer. Also worth considering a Victron SmartSolar MPPT rather than a basic PWM controller; the harvest improvement on low-irradiance days is measurable, not marginal.

@LiFePO4Fan's sulphation warning is spot on — that leisure battery is your weakest link long-term.