Anyone else struggling to get decent winter output from roof-mounted panels on a van?

I've got two 175W mono panels on my Transit (so 350W total) wired in series going into a Victron SmartSolar 100/30 MPPT controller, and honestly the numbers in December and January have been a bit depressing. On a clear day I'm maybe seeing 80–100W peak, and on overcast days it's practically nothing — sometimes less than 10W. I'm in the East Midlands so not exactly Cornwall, but still.

I'm wondering whether the issue is mostly the low sun angle at this time of year (panels are flat on the roof, no tilt), or whether there's something else going on. I've checked the connections and everything looks fine in the Victron app — no faults showing, absorption and float voltages look correct. Battery is a 200Ah lithium from Fogstar if that's relevant.

Has anyone experimented with tilt brackets on a van roof to get a better angle in winter? I've seen a few setups where people prop the panels up when parked, but I worry about wind and also looking a bit daft in a layby. Would genuinely love to hear what others are doing to squeeze more out of their systems between October and March.

@Stacey72 not in a van but I've got roof-mounted panels on my shepherd's hut and the winter struggle is very real. A few things I've found make a noticeable difference:

• Tilt angle — flat roof mounts lose a huge amount in winter when the sun sits so low. Even propping panels up temporarily at 60° made a measurable difference for me
• Shading — in winter even a tiny shadow (aerial, vent, tree) causes disproportionate losses, especially with series wiring
• Panel temperature — oddly cold clear days can give better output than mild overcast ones

Are you seeing low voltage or just low amps? That would help diagnose whether it's a shading/orientation issue or just genuinely poor irradiance. The Victron app history graphs are brilliant for spotting patterns — worth posting a screenshot if you can?