solar panel tester

Love Andy's channel too. 

I also test panels using my bench power supply in combo with and multi-meters would be nice to have an all in one solution waiting to see what it actually does.  I don't buy used panels but over the years have had to troubleshoot my own panels.

I think the only shortcoming of this meter is that it doesn't give you an I/V graph that will show any knee points in the panel's output which may point at problems.  The stupidly expensive meters can do that, but the price is simply unjustifiable.

Why people go for 2nd hand? I mean are they really reliable? How can we measure their health

My entire 12kw array is comprised of secondhand panels (more or less).  No issues so far.  First panels (SolarWorld SW245) were from a retired solar farm...they performed above expectations.  Remaining panels were from a solar farm that encountered severe damage during installation (unexpected windstorm), so they're technically pretty new.  No issues there, if you discount bent frames 😉.

As long as you get a significant discount on secondhand "used" panels, I would say "go for it."  Over time, the solar panels' output wattage will slowly decrease, but this will be characterized in the specification sheet for the panels.

Just pay attention to what you are buying.  Signs of tarnishing on the cells / interconnecting wires / busses is usually an indicator that moisture has made its way into the encapsulation.  The panel may last for years more, it might fail, and possibly catch fire, tomorrow.  If the clear encapsulation has crazed / cracked, like broken safety glass panes, edges, it also has moisture problems.  Trina had a lot of panels go crook due to problems with the back sheet and ingress around the edges.  You can buy them by the pallet load cheap in the USA, so be aware of that issue with them.  Panels with moisture ingress go electrically leaky to the frame and that might be enough to trip protection devices and can certainly be a hazard to a person with high voltage strings.

Babk to the original topic, that solar panel tester/meter seems to be a useful tool.  Wish I'd had one a few years ago when I was setting up my arrays.  It would be handy for spot tesing suspected problem panels too.

It seems to be a new tool, but they are for sale on ebay now, so in a month or so the price should come down some.

I have had one for a while and they work ok.  These are great for a spot check when you are buying panels (assuming it is at or near full sun) or as you are grabbing them out of a pile before install.  The only annoying thing is that the designer did not add any sort of active cooling and heatsink to the unit to allow it to measure faster.  The larger the panel you use on it the longer it takes between measurements for it to find the max power point (at least on my unit) so it sometimes takes a minute or 2 for the reading to be stable and take a few measurements for an average.  It would be nice if the unit could track every second or 2 even if active cooling was needed.  It would also be nice if it could store measurements and give you an min, max and average over a short period of time, say 30 seconds.  Not a lot you can expect for such a cheap unit and they are coming down in price somewhat.  I don't have any larger panels to try the tester on.  Most of my panels are the small 315 and 345 watt units and they state that you can measure up to a 400 watt panel with it.  It would be nice to know if that is actually the case or if the tester could be used on some of the newer 500-700watt panels.  Maybe with active cooling.  My guess is that it will be a voltage and current limitation but the unit says 60V and 20A which is 1200watts so it would be interesting to know if it can go above 400watts since 400+ watts is slowly becoming the norm on the second hand market.

Based on the pictures and footage there is no chance of it doing 1200W.  Zip.  The temperature rise would exceed the maximum junction temperature for the transistors before Vmp could be found.  Active cooling would work if there is a temperature sensor involved, but if it's just computed temperature rise values, no chance.

For what it's intended, testing of most common panels to see how they are travelling or before installation, it does the job well enough.  In real terms, just how quickly can you disconnect a single panel from an array, connect the meter, test, reconnect panel to array anyway.  It'd take me at least a minute to fish the wires out from under an installed panel, then another minute to undo the MC4 connectors, and that'd be rushing it.