Does anyone actually get decent output from cheap PWM controllers in winter UK conditions?

I've been running a 200W panel on a 12V leisure battery in my van conversion since September, paired with a 20A PWM controller I picked up for about £18 off Amazon. During summer it was doing a reasonable job, but now we're into proper cold grey days and I'm barely seeing 4-5A going in even on what looks like a bright-ish morning. Panel is facing roughly south at about 35 degrees tilt, so I don't think the angle is completely terrible.

I know PWM controllers are generally considered the budget option and everyone says get an MPPT, but I'm trying to work out whether my poor output is actually the controller's fault or just the reality of UK winter solar. From what I understand, MPPT is supposed to handle low light and cold conditions better because it can match the panel's voltage more efficiently — but is the real-world difference actually worth the £60-80 upgrade for a modest 200W setup?

Has anyone done a proper before/after comparison switching from PWM to MPPT on a similar sized system? Would love some actual numbers rather than just theory, especially from folk running systems in Scotland or the north of England where conditions are similarly grim this time of year.

@Gill1990 This is the classic PWM winter trap. The issue isn't just the controller being cheap — it's that PWM genuinely wastes a significant chunk of panel capacity when your panel's Vmp is well above battery voltage, which in winter with cold panels it absolutely will be.

Your 200W panel probably has a Vmp around 18-20V. A PWM just clips that down to match battery voltage (~13V charging). You're potentially losing 30-35% before you've even factored in the shorter days.

I switched from a similar setup on my boat to a Victron SmartSolar MPPT 75/15 — even the entry-level Victron makes a noticeable difference in low-light and cold conditions. Fogstar do decent leisure batteries too if that becomes the next weak link.

Honestly for a 200W panel, a decent MPPT pays for itself over one winter.

Just to add to what @LindaPrice87 is getting at — with PWM you're essentially forcing your panel to work at battery voltage rather than its optimal operating point. In winter when your panel's Vmp might be sitting around 17-18V but your battery's only at 12.4V, you're throwing away a significant chunk of potential charge before you've even started. Couple that with the shorter days and low sun angles we get from October onwards and it compounds badly.

An MPPT controller (even a budget Victron 75/15 at around £60-70) will make a noticeable real-world difference over winter specifically, because it actually harvests that voltage headroom. Your 200W panel deserves better than what it's currently getting honestly. The £18 saving looks a lot less clever by February! 😄

@Gill1990 Worth checking your panel's Vmp rating too — most 200W panels are optimised around 18-20V, and in cold conditions Vmp actually rises, sometimes pushing past 21V. With PWM that extra voltage is just wasted heat rather than useful charge. If you're seeing decent amps on the controller display but your battery still isn't climbing properly, that's likely your culprit.

A cheap MPPT — even a £35-40 unit — would harvest meaningfully more from your existing panel through winter. Not saying PWM is useless, but with a single 200W panel and short December days, you really can't afford to leave anything on the table. Might be worth the upgrade before the solstice hits properly.

@FrankReid makes a crucial point about Vmp, and cold actually pushes that voltage higher — so your panel's sitting even further above what PWM can utilise.

From my own setup, I switched from a similar cheap PWM unit to a Victron SmartSolar 75/15 MPPT mid-winter and saw charging current roughly double on identical overcast days. The maths on a 200W panel simply doesn't work with PWM once ambient temperatures drop and irradiance is already marginal.

The £18 controller is essentially throttling everything the panel could theoretically deliver. A decent 20A MPPT (Renogy do a reasonable one around £45-50, Victron if budget allows) will pay back the difference within weeks in winter conditions, particularly in a van where you're presumably relying on that bank daily.

@FrankReid raises a good point about Vmp, and this ties directly into why your situation is actually worse in winter than people expect. Cold temperatures push that Vmp higher — sometimes to 22V+ — which means the gap between what your panel wants to operate at and your battery's ~13V absorption voltage gets even wider. PWM just clips all that potential away completely.

Honestly for £18 you're not going to get miracles, but the controller itself isn't really the problem — PWM is PWM regardless of price. If you're serious about van life through winter I'd budget for a halfway decent MPPT unit. Victron SmartSolar 75/15 is the obvious recommendation and you'll recoup the cost in usable charge within a few months. The free Bluetooth monitoring is genuinely useful too.

@Gill1990 something nobody's mentioned yet is the effect of partial shading in winter — the sun sits so low in the UK that you're far more likely to get shadows creeping across your panel from trees, buildings, even the van roof edge itself. With PWM, even minor shading hits your output disproportionately hard compared to MPPT. Combined with everything @NickMason and @FrankReid have said about the Vmp mismatch, you're essentially fighting on two fronts. A decent 20-30A MPPT from Victron or Renogy won't break the bank these days and you'd likely claw back the cost difference over a single winter. Worth at least logging your actual amp input on a clear day versus what the panel should theoretically be producing — that'll tell you pretty quickly how much you're leaving on the table.

@Steve1993 good point on shading — I've had exactly that with my static caravan setup, trees that were fine all summer suddenly becoming a nightmare come October.

But coming back to the original question — has anyone actually measured the difference after switching from PWM to MPPT on a modest setup like this? Not just theory, actual logged data?

I've been debating whether upgrading my Renogy PWM to a Victron SmartSolar is worth it for a relatively small array. The Victron isn't cheap. Is the efficiency gain in winter genuinely meaningful on 200W, or is it marginal?

@Gill1990 here's the thing nobody tells you upfront — that £18 controller isn't really a 20A unit in any meaningful sense. I ran a similarly specced clone on my narrowboat for one winter and watched it systematically undercharge my bank whilst reporting everything was fine. The voltage readings were optimistic fiction.

The core problem with PWM in UK winter isn't just the Vmp mismatch others have mentioned — it's that when your available watts are already scarce, you genuinely cannot afford the 20-30% efficiency penalty versus a proper MPPT. A Victron 75/15 costs around £55 and pays for itself within a single grey February.

@Spider is right about the current rating being fictional marketing. But there's another angle worth adding — PWM in winter isn't just about the controller being rubbish, it's fundamentally the wrong technology for low-angle UK sun.

When your panel voltage is already marginal due to poor irradiance, a PWM controller just connects the panel directly to the battery. No voltage conversion. Whatever the battery needs, that's what it clamps to. MPPT actually harvests from the panel's optimal operating point.

Swapped my garden office setup from a cheap PWM to a Victron SmartSolar 75/15 last January — same 200W panel, noticeably better winter charging. The app data proved it.

@BMS_Geek worth adding from actual experience — running a 100W panel on a PWM into a 100Ah AGM in my shepherd's hut last winter, I was seeing maybe 20-30% of what I'd expect on a clear January day. Swapped to a Victron SmartSolar 75/15 and it was night and day. The MPPT actually hunts for the panel's sweet spot when voltage is low and temps are cold — PWM just can't do that. For a van you're already weight and space limited, the efficiency gain is worth every penny of the price difference.

@FormerMechanic15 curious whether switching to MPPT actually made a noticeable difference to your morning recovery times in those short December/January days? I upgraded my cabin setup to a Victron SmartSolar 75/15 last winter and the difference was genuinely striking — panels were producing usable current at light levels where my old PWM was barely registering anything. Running Fogstar Drift lithium now so I'm probably not a fair comparison, but the controller upgrade alone felt significant even before I swapped the battery. Worth the extra £60-80 over a quality PWM?

@Cerbo_Queen @FormerMechanic15 the morning recovery question is key. On my own setup I swapped a basic PWM for a Victron SmartSolar 100/20 mid-October and the logged data tells the story clearly — MPP tracking is pulling meaningful extra wattage during those low-angle, diffuse-light mornings we get from November onwards. At 15° solar elevation with heavy cloud cover, your panel voltage drops, your MPPT controller adapts its operating point continuously, whereas PWM just holds the battery voltage plus a diode drop and throws the rest away. For a 200W panel on 12V that's genuinely painful waste during precisely the conditions where every watt counts.

@24V_Queen the Victron SmartSolar will absolutely transform morning recovery — but the actual gain depends heavily on your panel-to-battery voltage ratio. In my shepherd's hut setup running a 280W panel at Voc ~38V into a 12V bank, switching from a cheap PWM to even a mid-range MPPT recovered roughly 30-40% more usable charge on overcast December mornings. The maths isn't complicated: PWM essentially wastes the voltage differential as heat. In proper UK winter conditions with panel temps keeping Voc elevated and irradiance already marginal, that loss matters enormously. @Gill1990's £18 controller is almost certainly throttling what little harvest there is.

@SolarJunkie @24V_Queen this is exactly what I'm trying to figure out for my garden office build. I've got a similar cheap PWM setup at the moment and I'm wondering whether the efficiency gain from something like a Victron SmartSolar actually justifies the price jump when your panels are relatively modest — say 200-400W total. Is there a rough wattage threshold where MPPT genuinely pays for itself within a reasonable timeframe, or is it always worth it regardless of panel size?