Picked up a cheap 200W panel from Facebook Marketplace – worth it or waste of time?

Depends entirely on what you actually got rather than what the seller claimed you got.

Facebook Marketplace solar panels are a lottery. Half the "200W" panels on there are either degraded to 140W in reality, have microcracks from being chucked in someone's van for three years, or are knock-off specs that never hit rated output to begin with. Had one myself — bloke swore blind it was "barely used." Put it on my roof, measured it properly on a clear day, got 160W peak on a good day. Wasn't worth arguing over at the price I paid, but still.

That said, cheap panels can absolutely be worth it if you test them properly before committing them to a permanent installation. Chuck a proper load on it and measure actual output against rated specs. If you're within 10-15% of rated, that's honestly not terrible for second-hand.

A few things worth checking:

• Visual inspection for yellowing or delamination on the backsheet
• Any physical damage to the frame (warping, cracked junction box)
• Bypass diodes — stick a meter on it and shade individual cells to check they're still working

What brand/model is it? Some budget panels hold up surprisingly well. Even a genuine 160W panel for £40 off Facebook is better value than a shiny new Renogy at full retail if your budget is tight.

What are you planning to use it for? If it's a shed setup or topping up a leisure battery, even a partially degraded panel is probably fine. If you're trying to run anything critical, that's a different conversation.

Anyone else picked up second-hand panels and actually tested them properly? Curious what people found.

@VitoProject slapped a multimeter on mine before handing over the cash and the seller's face was priceless when it read 23V open-circuit instead of the claimed 37V 😂 — turns out it was a 12V nominal panel masquerading as a 24V one, which would've absolutely cooked my Victron MPPT settings.

Key thing nobody mentions: check the label on the back of the panel itself, not just the seller's listing — if that sticker's been scratched off or suspiciously clean, walk away faster than a dodgy van disappears from a lay-by.

@VoltBarry ha, wish I'd thought of that before I bought mine for the narrowboat last spring! 🙈

Genuine question though — even if the panel IS degraded, is it worth running through a proper MPPT controller like a Victron SmartSolar to squeeze everything possible out of it? Or does significant degradation mean the voltage profile is so messed up that even a decent controller can't compensate?

I ask because I picked up two "180W" panels that Victron's app is consistently reporting around 140W peak combined. Fogstar cells inside apparently, but the previous owner had stored them face-down in a barn for two years which can't have helped...

Are there any decent UK testers or solar clinics that'll give you an actual spec sheet reading rather than just marketplace guesswork?

@RustySkipper what was the genuine question? Post got cut off mate!

But I'll jump in anyway — for narrowboat use specifically, degraded panels are extra painful because you're often dealing with partial shading from bridges, trees, locks etc. A panel that's already at 70% capacity before shading losses kicks in is going to frustrate you endlessly.

What I'd actually recommend before buying secondhand: ask for the panel's Voc (open-circuit voltage) reading in full sun. A genuine 200W panel should be hitting around 45-48V Voc depending on cell count. Significantly lower and the cells are either knackered or it was never what they claimed.

Victron's MPPT controllers log this stuff beautifully if you've already got one fitted — dead useful for diagnosing dodgy panels after the fact too.

@VoltBarry the multimeter test is elite behaviour honestly — I once bought a "200W" panel that turned out to be a relabelled 150W with someone's optimistic Sharpie work involved 🖊️

Check the back of the panel for the actual manufacturer sticker underneath any dodgy rebranding — the real specs are usually still there if you scratch around a bit.

Also worth bunging it into a Victron SmartSolar and watching what it actually produces over a clear midday hour; numbers don't lie even if Facebook sellers absolutely do.