Picked up a second hand 200W panel for £30 – worth getting it tested or just chance it?

£30 for 200W is a solid grab if the glass is intact and the junction box isn't cracked or waterlogged. I've taken chances on panels like that before and mostly come out ahead.

That said, I'd at least do a basic sanity check before committing it to your system. Grab a multimeter and measure open-circuit voltage (Voc) in decent sunlight — it should be within about 5–10% of the rated figure on the label. If it's reading significantly lower, you've likely got cell degradation or delamination issues. Short-circuit current (Isc) tells you even more, though you need a decent clamp meter for that.

The bigger concern with second-hand panels isn't always power output — it's microcracks. They don't always show up visually but they kill performance under real-world conditions. A proper EL (electroluminescence) test would catch them, but those are specialist kit and hard to access unless you're near a solar installer willing to help. Some of the Renogy resellers and independent solar shops have offered informal testing locally for me in the past — worth asking around.

My approach with cheap second-hand panels is:

• Visual check (delamination, hotspot burn marks, cracked cells visible through the back sheet)
• Voc test in full sun
• Run it for a week or two with a Victron SmartSolar and check the yield logs against expected output

If it's consistently 20%+ underperforming on yield, shift it on or relegate it to a low-priority circuit like a water pump or trickle charging a leisure battery.

At £30 the risk-reward is still reasonable even if it's degraded. Curious whether anyone else has had panels tested professionally — worth the cost?

@CrafterDream ...run a quick IV curve trace on it if you can borrow a tester.

I picked up three secondhand panels for my garden office build last year — looked immaculate, junction boxes perfect. Two performed brilliantly. The third was producing about 60% of rated output and nobody could tell from a visual inspection. Turned out to be internal delamination, which you only spot when output drops mysteriously on sunny days.

If you can't get hold of a proper tester, at minimum check the Voc with a cheap multimeter in full sun. Should be within 5% of the datasheet figure. Anything significantly under that and something's wrong.

£30 is fine to gamble on for a shed or low-stakes setup, but I'd want to know what I was actually getting before wiring it into a Victron system.

@CrafterDream for £30 I'd just wire it up and see what the Victron SmartSolar makes of it — that's basically a free IV curve trace right there and the bonus prize is either working solar or a very cheap garden ornament.

@ThistleVicky is basically right but I'd add — check the junction box diodes first before you even bother wiring it up. Seen a few cheap second-hand panels where the bypass diodes have cooked and you get weird shading behaviour even on a clear day.

Also worth a quick visual on the backsheet for any yellowing or delamination. Glass intact means nothing if the cells underneath are shot.

£30 though? I'd chance it personally. Worst case you've lost £30. I've got a couple of iffy panels on the cabin roof that underperform but still contribute — every watt counts when you're trying to keep costs down.

@DownsCruiser good shout on the diodes. I'd also give the frame a proper look along the edges where it meets the glass — delamination often starts there and you won't always spot it from the front. Hold it up to bright light if you can and look for any yellowing or bubbling between the cells and the encapsulant.

At £30 it's almost certainly worth the punt either way, but if you do spot delamination it'll degrade faster than you'd like, especially through a UK winter with all the moisture we get. Worth knowing upfront so you can factor it into where you position it in your setup — maybe not your primary panel if it's showing signs.

@Kelly1983 all solid points. One thing nobody's mentioned — check for delamination. Hold it up to daylight or a bright sky and look for any milky/yellowed patches in the cells. Bit of browning round the edges of individual cells is often hotspot damage from a bypassed or dead cell, and that'll drag the whole string down.

Had one from a Facebook Marketplace grab for my shepherd's hut that looked mint externally. Wired it up, Victron reported about 60% of rated output. Delamination throughout when I properly inspected it.

For £30 it's probably still worth a punt tbh, just don't build your whole system around it until you've clocked some real-world numbers over a few days.