Anyone else struggling to get decent output from budget MPPT controllers in winter?

I picked up a Renogy Wanderer 30A MPPT last spring and it was brilliant through the summer — hitting around 85–90% of my panel's rated output on good days. But since October it's been really disappointing. I've got two 200W panels wired in series on a south-facing roof, and even on clear days I'm barely seeing 60W going into my 100Ah lithium. The panels themselves check out fine with a multimeter.

I'm wondering if it's purely the low irradiance and angle, or whether cheaper MPPT units genuinely struggle to track properly when the input voltage and current are both low. I've read that some budget controllers have a minimum operating threshold and just don't bother trying below a certain point. Has anyone done any proper comparisons between something like the Renogy and a Victron SmartSolar 75/15 in winter conditions?

My setup is on a static caravan in Derbyshire, so we're talking proper grey British winters here. I'm not expecting miracles but 60W from 400W of panels on a sunny February day feels like I'm leaving a lot on the table. Would upgrading the controller realistically make a noticeable difference, or should I be looking at rewiring the panels differently first?

@EllaDixon71 yeah winter on the water is brutal for this. My setup on the narrowboat dropped off a cliff around October too.

Few things worth checking:

• Panel angle — low sun means you really want them tilted steeper, flat roof mounts are basically useless Dec/Jan
• Temperature compensation — cheaper MPPTs often don't handle it properly, Victron spoils you with proper adaptive charging
• Shading — even partial shadow from a bridge or tree at low sun angles kills output disproportionately

The Wanderer's not a bad bit of kit but it's not in the same league as proper Victron SmartSolar for winter harvesting. Might be worth logging your actual battery voltage vs panel input to see where it's losing efficiency.

Winter solar on a boat is genuinely hard — I run mine alongside a decent alternator setup now just to cope.

@EllaDixon71 Worth checking your panel angle first — I've got fixed mounts on the shepherds hut and adjusting tilt seasonally made a noticeable difference once the sun dropped low. Are you also accounting for cell temperature? Panels actually produce better in cold air, so if you're still getting poor numbers it could be the controller's absorption/float voltage settings being off for winter conditions.

On the boat I switched to a Victron SmartSolar and the difference in low-light harvesting was pretty significant — the MPPT algorithm seems genuinely smarter at finding peak power when irradiance is weak. The Renogy units aren't bad but I do wonder how well their tracking performs under partial cloud conditions. What's your battery chemistry? That affects whether the charge profile is even appropriate for what you're seeing.

@GrumpyHermit replied:

@EllaDixon71 Quick correction first — the Wanderer is actually a PWM controller, not MPPT. Renogy's genuine MPPT units are the Rover series. Worth double-checking your paperwork because it matters quite a bit here.

That said, winter losses are partly just physics regardless of controller type. Lower sun angle, shorter days, more cloud — you're never getting summer figures back until March.

If you do have a PWM unit, the voltage mismatch with your panels in cold weather is likely costing you considerably more than you realise. A proper MPPT controller genuinely earns its money in winter because panels actually run higher Voc in the cold, and MPPT can harvest that properly.

What's your panel wattage and voltage, and what's your battery bank? Might help diagnose whether the controller is actually your bottleneck.

@HollyGraham87 replied:

@EllaDixon71 Just to back up what @GrumpyHermit is saying — worth double-checking which Renogy model you've actually got, as the Wanderer is definitely PWM. The MPPT equivalent is the Rover series. It matters because a genuine MPPT controller will make a noticeable difference in winter, especially on those cold, bright days we occasionally get — panels actually perform better in the cold theoretically, but the lower sun angle and shorter days are what really hurt you.

If you do confirm it's PWM, honestly that's probably a bigger factor in your disappointment than anything else. The gap between PWM and MPPT widens considerably in winter conditions. Might be worth looking at a Rover 20A or 40A depending on your array size — secondhand ones come up fairly regularly on eBay for reasonable money. 🙂

@DaiHughes65 replied:

@GrumpyHermit makes a fair point about the Wanderer being PWM — worth double-checking your model number @EllaDixon71, as that'll affect what you can realistically expect.

That said, even proper MPPT controllers struggle in winter, and it's not always the kit at fault. Low sun angle means your panels are working at a fraction of their rated capacity regardless of what's tracking the voltage. I'm in mid-Wales and between November and February I just budget for roughly 30–40% of summer output on a good day, less when it's overcast.

One thing that genuinely helped me was monitoring panel temperature — cold clear days can actually boost output briefly because panels are more efficient when cold, so if you're seeing decent sunshine but still poor numbers, I'd look at potential shading from low winter sun angles hitting obstacles that weren't an issue in summer.

@EllaDixon71 Once you've confirmed whether it's PWM or MPPT, it's worth knowing that winter performance drops are pretty normal regardless — lower sun angles mean your panels are rarely facing the light optimally, and you're losing a good chunk of potential harvest just from that geometry. Even a genuine MPPT controller can only work with what the panels are actually receiving. A few things that genuinely help: keeping panels clear of any shading (even partial), tilting them steeper than you would in summer (closer to 60–70° in the UK winter gets you closer to perpendicular with the low sun), and making sure connections are clean and tight as cold can affect resistance. What's your panel orientation and tilt currently?

@PW_Sparks replied:

@EllaDixon71 One thing nobody's mentioned yet — have you checked your panel voltage in the cold? Panels actually produce higher VOC in winter, which sounds great, but if it's pushing close to your controller's maximum input voltage you can get protection cutouts, especially on frosty mornings. Worth logging the voltage first thing on a clear cold day. Also, low sun angle means increased shading from things that cast no shadow at all in summer — gutters, aerials, neighbouring trees. Even partial shading hits output disproportionately hard.

Deano13 replied:

@EllaDixon71 One thing nobody's mentioned yet — have you checked your panel voltage under load in cold weather? Panels actually produce higher voltage in winter due to lower cell temperatures, which can sometimes cause issues if your controller's input voltage ceiling is on the tighter side. Worth logging the VOC on a cold clear morning and comparing it against your controller's max input spec. I've seen budget units throttle themselves as a protective measure even when everything else looks fine. Might explain the disappointing output even on bright days.