Anyone else running a Victron MPPT alongside cheap Amazon panels — what efficiency are you actually seeing?

Picked up four 200W "Newpowa" panels from Amazon back in spring for about £280 the lot, wired them in two series pairs to get roughly 72V open circuit into a Victron SmartSolar 100/30. Setup is on a static caravan in the Brecon Beacons, feeding a 200Ah lithium (a Fogstar Drift 12V). Been running it since April so I've got a fair few months of data through the Victron app now.

On a decent sunny day in July I was hitting around 340–360W actual harvest at peak, which on paper sounds reasonable but feels like it should be higher. Panels are tilted at about 35° facing pretty much due south, no shading worth mentioning. The Victron is reporting panel voltage and current fine, absorption and float all look correct. I did wonder whether the cheap panels are just significantly underperforming their rated wattage, or whether 100/30 is somehow bottlenecking things.

Has anyone done a proper back-to-back comparison between budget panels and something like Risen or JA Solar on the same controller? I keep seeing people say "you get what you pay for" but I'd love some actual numbers rather than vibes. Also curious whether anyone's noticed a meaningful difference between PWM and MPPT on identical cheap panels — I know MPPT should win but by how much in UK conditions specifically?

TracyRobinson | 📍 Yorkshire | ⚡ Solar since 2019

@UWW_Power Sounds like a solid little setup! I'm running something similar — three 180W panels from a brand I'd never heard of before, paired with a SmartSolar 75/15, and honestly the Victron side of things is doing exactly what it promises.

What I'd say is: don't judge the panels purely on their rated wattage. Check your actual Voc and Vmp against the label on a clear day — mine were about 8% under rated. Not catastrophic, but worth knowing.

The Victron's efficiency itself is genuinely excellent, usually 97-98% as advertised. Any losses are almost certainly the panels underperforming rather than the controller.

Have you connected it up to VictronConnect yet? The yield history graphs are brilliant for spotting patterns.

LeeParker | 247 posts

@UWW_Power nice setup for the price! I'm running something similar — three 180W Renogy panels (picked up refurbished) into a SmartSolar 75/15, and honestly the Victron side of things is rock solid. The controller itself is doing exactly what it should.

What I have noticed is those cheaper panels tend to underperform on cloudy days more than the spec sheets suggest — probably lower quality cells struggling with diffuse light. Bright sunshine they're often surprisingly close to rated output though.

Worth checking your actual Voc on a cold morning with the Victron app — I found one of mine had a noticeably weaker panel dragging the string down. Swapped it to a separate string and instantly saw the difference.

What's your typical peak wattage reading on a decent day currently?

SarahClark75 | 📍 Shropshire | ⚡ Solar since 2021

@UWW_Power I've got a similar pairing here — three 190W panels from a brand I'd never heard of before purchase, running into a Victron SmartSolar 75/15 on a smaller setup. Honestly the Victron controller is doing all the heavy lifting in terms of squeezing efficiency out of them. I use the VictronConnect app to monitor yield and I reckon I'm seeing roughly 80-85% of rated output on a decent clear day, which I'm happy enough with given what I paid. The MPPT tracking seems to compensate nicely for any panel quality inconsistencies. One thing worth checking — are you seeing any shade mismatch issues between the two series pairs? That caught me out initially and rearranging the panel orientation made a noticeable difference to my daily totals.

48VQueen | 📍 Somewhere on the cut | ⚡ Narrowboat/EV nerd

Four Amazon specials into a Victron MPPT — brave, or just skint? 😄 Genuine question: did you actually verify those panels hit anywhere near rated wattage, or just trust the bloke in Shenzhen who printed "200W" on the label? Running Fogstar cells here and even they occasionally test below spec. The SmartSolar 100/30 will do its job regardless, but if your panels are quietly lying about their output you'll never know what efficiency you're actually seeing — you're just measuring how well Victron compensates for mediocrity. Chuck a clamp meter on the strings on a clear solar noon and compare against the theoretical max before you declare victory.