Anyone else finding their PWM controller really struggles on cloudy UK days compared to MPPT?

I've been running a 200W panel on a Victron 75/15 MPPT for about eight months now and honestly the difference from my old PWM setup is pretty stark, especially through this grey stretch we've had lately. Even at 9am with heavy cloud the Victron is still pulling 30–40W when the PWM would've given me almost nothing useful.

The thing that surprised me most was how well it handles that brief glary brightness you sometimes get just before a rainfront comes in — panel voltage shoots up to around 22V open circuit and the MPPT just gets on with it, whereas the PWM would basically clip most of that. Running a 12V leisure battery so the voltage gap really matters.

Has anyone done a proper side-by-side comparison, even rough figures? I'm curious whether the gains are as noticeable on a bigger 24V system or whether the voltage headroom difference shrinks enough that PWM starts looking more reasonable again. Also wondering if anyone's tried the cheaper MPPT clones — Epever, Renogy etc — and whether they actually track properly or just sort of pretend to.

Yeah @WattJane this is something I noticed pretty quickly after switching over. The real killer with PWM on overcast days is that your panel voltage drops right down to battery voltage, so you're basically throwing away whatever headroom you had. With MPPT the controller can still work that higher Vmp even when the panel's only producing a fraction of its rated output - and in diffuse UK light that headroom is genuinely where a lot of your harvest comes from.

I'd say the gap between PWM and MPPT is actually wider in rubbish weather than in full sun, which feels counterintuitive but makes sense when you think about it. Eight months is a decent sample size covering some properly grim weather too, so your experience sounds about right to me.

My PWM controller once harvested enough energy on a February overcast day to charge a AA battery — maybe.

Been wondering about this myself — I'm on a boat so cloud cover is a real issue, especially when moored up in winter and relying on the system to keep the batteries topped off between engine runs.

Quick question for @WattJane — have you noticed a meaningful difference on partial cloud days specifically, or mainly the thick grey stuff? I'm trying to work out whether the MPPT gain is worth the upgrade cost for my setup. I've been quoted around £80 for a basic Victron SmartSolar 75/15 and wondering if the harvest improvement actually pays back in a reasonable timeframe on a UK boat.

Also does anyone know if panel orientation affects how much you gain from MPPT in low light? My panels are flat-mounted on the cabin roof so the angle is pretty poor to begin with.