Why is my MPPT not reaching full power?

Got a Victron SmartSolar 150/60 sat on my shepherd's hut roof, paired with a 6kWp array and a pair of Pylontech US3000C batteries. In theory, I should be pulling around 9kW at peak, but I'm consistently maxing out at about 5.5-6kW even on clear days.

The array's in decent condition — no shading issues, I've checked the panels themselves for dirt and they're clean. Wiring's proper 10mm² cable run, checked the connections at the MPPT and they're tight. Voltage reading at the controller sits around 390-400V on a good day.

Battery side seems normal — they're typically at 50-80% SOC when I'm getting these readings, so it's not a case of them being full and rejecting charge. The SmartSolar's firmware is up to date as of last month.

What's puzzling me is the discrepancy. My solar calculator reckons that array size should easily hit rated wattage in these conditions, but something's clearly limiting it. Could it be:

• The MPPT itself being undersized? (Though 60A seemed adequate)
• Some cable resistance issue I'm missing?
• A battery limit setting I've overlooked?
• Environmental factor I haven't considered?

Anyone else dealt with this? Keen to hear if there's something obvious I'm overlooking before I start swapping gear around.

Have you checked what your actual array voltage is hitting under load? I ask because on my narrowboat setup, I discovered my string wasn't properly balanced—one panel was shaded by the mast at certain times, dragging the whole voltage down.

Also worth confirming: is the 150/60 actually seeing the full array voltage it's designed for? The SmartSolar caps at 150V input, so if you're wiring a 6kWp array, how many strings are you running in parallel? That could be your bottleneck rather than the MPPT itself.

What's your battery voltage reading when the array is running? If the batteries are hitting their charge limit, the controller will throttle back intentionally—completely normal behaviour. Check your Pylontechs' CAN comms are properly configured too.

Worth checking a few things on the Victron kit itself - have you logged into the system via the app to see what the MPPT's actually reporting? Sometimes the issue's voltage-related as @RustySkipper hints, but I've also seen string configuration problems cause similar issues.

With a 6kWp array feeding a single 150/60, you're already maxing out the controller's input current capacity. That unit's rated for 60A, which means you're hitting a hard ceiling around 8-9kW depending on your array voltage. Are your panels configured in series or parallel?

Also worth verifying your DC wiring from array to MPPT isn't undersized - voltage drop there will absolutely tank your efficiency. What gauge cable are you running?

Right, couple of things @RustySkipper and @MelKing83 haven't touched on yet—what's your actual string configuration? A 150/60 maxes out at 6kW input, so if you're expecting 9kW from a 6kWp array, the MPPT itself is the bottleneck, not the batteries.

Also, those Pylontechs will happily throttle charge acceptance once they hit a certain state-of-charge or temperature—check the BMS settings. On my caravan setup with identical batteries, I discovered mine was limiting to 80A instead of the full 120A because the firmware was being overly cautious.

What's your actual measured output versus what the Victron app's showing? That'll tell you if it's a hardware issue or software configuration.

Been wrestling with similar issues on my cabin setup. Few questions worth exploring:

What's your actual DC cable gauge running from array to the MPPT? I discovered mine was undersized—voltage drop was killing efficiency before the charge controller even saw it. Also, are you running a single string or multiple strings into that 150/60? The SmartSolar can struggle with imbalanced strings.

Have you checked the battery voltage under load? If your Pylontechs are sitting at lower state of charge, the MPPT won't push full power—it'll throttle to match what the batteries can accept. That's normal behaviour, not a fault.

One more: what's your actual irradiance where the array's mounted? Cloud cover and panel angle make a massive difference. I assumed my peak figures were conservative until I installed a decent monitoring setup.

Worth logging into the Victron app and checking the real-time voltage, current, and power figures under full sun?

Hey @MarshLover, good shout getting this looked into. A couple of things the lads haven't mentioned yet:

Battery voltage state - those Pylontechs will throttle your MPPT if they're near full charge or in a protection state. Check the battery management system settings in the Victron app to see if there's any current limiting happening.

Temperature coefficients - in British weather, you might not be hitting ideal conditions as often as you'd think. Cold panels actually perform better electrically, but cloud cover and angle make a massive difference.

Also worth confirming: are you seeing the issue across different times of day, or mainly midday? That'll help rule out string configuration problems that @RetiredChef mentioned.

Have you actually measured the DC voltage coming off the array at peak sun? That's a quick way to verify if the issue is generation-side or MPPT-side.

Cheers

Bit of a gap in what's been covered so far—what's your actual array voltage hitting at peak? The 150/60 has a 250V input limit, so if you're undersizing strings to stay safe, you're leaving performance on the table.

Also worth checking: are your batteries actually accepting charge at full rate? Pylontechs can throttle input when they're near full or if BMS is being cautious. What's the state of charge sitting at when you're trying to pull peak power?

One more thing—cable losses compound fast with longer runs to a shepherd's hut. If you've got 50m+ of cable, even 10mm² copper will cost you a fair percentage. What's the actual run length and gauge you're working with?

The 150/60 will throttle itself if your array voltage is sagging under load—have you checked what you're actually seeing at the MPPT terminals during peak generation? Not at the array, but at the controller.

Dodgy connections are the silent killer here. Even a slightly corroded MC4 or loose terminal on the positive rail will cause voltage drop that makes the MPPT think it's getting less power than it actually is. I had this exact problem on my garden office setup last year—turned out one of my connector blocks had worked itself slightly loose.

Also worth verifying: are your Pylontechs actually accepting charge at full current? If they're sat at 95%+ SOC, the MPPT will back off. Battery management systems can be quite conservative about accepting peak power in certain states.

What does the Victron app show for input vs output power? That'll tell you if it's a generation problem or a throttling issue.

@MarshLover Right, so you've got a proper mismatch happening here—6kWp array feeding a 150/60 MPPT is like trying to pour a swimming pool through a garden hose. That controller maxes out at 60A, which means you're throttled to roughly 9kW if everything's perfect, but realistically you're hitting the amperage ceiling well before your array reaches peak output.

@MultiPlusGeek and @BreezySparky are spot on about voltage sag though. With a 6kWp array, what's your string configuration? If you've wired it for low voltage to compensate for winter losses, you're burning through that 60A limit faster and leaving power on the table.

Honestly, for your setup you either need a beefier MPPT (Victron 250/100 would actually utilise that array) or split the array across two controllers. I learned this the hard way with my van conversion—threw too much panel at a modest controller and wondered why I wasn't seeing the numbers on the spec sheet.

@AnneButler's spot on there. Look, I ran into exactly this with my setup—tried feeding a 6kWp array through undersized kit and wondered why I was leaving money on the table.

The 150/60 is rated for 60A output, which at your battery voltage (Pylontech US3000C runs roughly 48V nominal) gives you about 2.88kW actual throughput. Your 6kWp array is massively oversized for that controller—you're throttling yourself before the MPPT even gets a look in.

The real question is: what were you hoping to achieve? If you genuinely need 9kW peak charge, you're looking at either:

• Running dual MPPT controllers (Victron 250/100 or similar) in parallel
• Accepting that one 150/60 will only ever harvest a fraction of that array

I'd check your actual array voltage under load like @BreezySparky mentioned, but honestly, the controller specs are your limiting factor here. What's your typical daily usage pattern looking like? Might be worth right-sizing the whole

@MarshLover - yeah, that's the issue right there. Your 150/60 is maxing out at 9kW input because that's literally its limit—it's a 60A controller, so at whatever voltage your array sits at (probably around 150V nominal?), you're hitting the ceiling.

The 6kWp array is oversized for that controller. You'd need at least a 150/100 or ideally a 250V controller to actually harvest what that array can produce. I've got a similar headache on the boat with a Victron 100/50—keeps me honest about what I can actually use.

What's your actual array voltage under load? And are you seeing the MPPT regularly throttle back, or just sitting at that 9kW mark consistently? That'll tell you whether it's a voltage sag issue like @BreezySparky mentioned, or just pure wattage limitation.

Could also check if your strings are balanced properly—dodgy wiring can make it worse, but honestly you've probably just got a controller that's too modest for the job.

@MarshLover mate, your 150/60 is doing exactly what it's rated to do — it's the MPPT equivalent of trying to fit a garden hose through a drinking straw. Your array's got the potential but the controller's got a 60A ceiling, so that's your ceiling too. You'd need a Victron 250/100 or similar to actually harvest what that 6kWp is throwing at it. Painful but at least you know where the bottleneck is — could be worse, could be watching a perfectly good array just baking in the sun doing sod all.

@MarshLover - hang on, have you actually checked what voltage your array's running at under load? I ask because on my narrowboat setup, I was getting similar ceiling issues and it turned out my strings weren't balanced properly. The MPPT was throttling itself because the voltage was dropping faster than expected.

Also worth confirming: are you certain your 150/60 is the bottleneck here, or could it be the battery side? Those Pylontechs will only accept charge at a certain rate depending on their state of charge and temperature. On cold mornings I see my charge current capped well below what the MPPT could theoretically deliver.

What's the actual amperage you're seeing at peak? If you're consistently at 60A, then yeah, your controller's maxed out. But if you're sitting at, say, 45-50A, it might be something else holding back the array.

@MarshLover - quick question before we go further: what's your array configuration? String voltage matters enormously here.

Your 150/60 is rated for 150V input maximum, so if you've got your 6kWp array strung to hit higher voltages (which is common practice for longer roof runs or to minimise cable losses), the MPPT will simply throttle down. I made exactly this mistake on my narrowboat system years back — thought I was being clever with a 48V string config, didn't realise I'd ballsed the input voltage.

At 150V max input, you're looking at roughly 9kW theoretical ceiling with decent irradiance. That's not a limitation of the unit itself; it's the spec doing its job.

If you genuinely need to harvest more power from that 6kWp array, you'd be looking at either:

• A second MPPT (messy, but workable)
• Stepping up to a Victron 250/100 instead
• Reconfiguring your strings to operate within the 150V envelope

What voltage are you actually seeing on

@MarshLover — think @NotAnElectrician80 and @FenlandSolar have nailed it. Your 150/60 is maxed out at 9kW (150V × 60A), so you're not actually undershooting — that's the ceiling.

The real question is whether your array's even seeing those conditions. I ran into similar on my static caravan setup years back. Check:

String voltage under full sun — if you're not hitting 150V input, your array config's working against you. What's your Voc per string? Most folk underestimate voltage drop in long runs too.

Shading — even partial cloud or a tree edge will tank the whole string if you're in series. Sounds daft but it catches everyone.

Cable sizing — undersized runs between array and controller absolutely hammer efficiency. I've seen 3-4% losses that people miss entirely.

If your array's genuinely capable of higher wattage, you'd need a second MPPT controller really. The 150/60 isn't a bottleneck — it's just