Micro Short Circuiting on Solar Panels

[FNQGU]

@Cuppa - wow! Thanks mate. That is a great explanation and gives me something to work on.

I haven't yet measured and compared the output of the panels and will have to replace my multi-meter first (cheap nasty one fell apart yesterday). The wiring may also be on the small side and the panel with the 'worming' is the second panel of the two in the string. The cells that are damaged are the ones furthest away from the controller also.

I have no idea what a 'blocking diode' is, but no doubt my local Jaycar guy will.

By the sounds of it, this sort of thing could happen to any and all solar panels without the blocking diodes? eg. an expensive panel might also have the same problem as these eBay ones.

[Cuppa]

A blocking diode as I understand it is an ‘electrical one way valve’ to stop back flow. I’m only guessing that fitting one may help. However heavier cabling is probably the better solution I’d think. Blocking diodes will be cheap, & I don’t think doing both would do any harm.

I would hope that any 12v panels made for mobile use would still have blocking diodes fitted, but who knows? I do recall in my early RV days folk having issues with batteries discharging through the panels at night & blocking diodes being the solution.... before they became standard fitments.

Easiest way to check output of panels, if you can get to the individual positive/negative cables is with a dc clamp meter. They can be had fairly cheaply, or come as a combined multi meter/clamp meter. Need to check they are suitable for dc though. Some are only good for ac.