Solar Diagnosis Help Please


Tail-End Charlie
If one panel is working and the other isn't, then I'd take Haf-E's advice and check the bypass diodes (if they're accessible) on the non-functioning panel. Properly sandwiched solar cells and wiring almost never fails - it's usually something outside the sandwich which fails. I.e., the diodes or connections.

A solar panel with failed diodes can allow power to flow backwards though the cells. That will turn the solar cells into neat little radiant heat units which will consume the power being produced by the other panel.

Also, any shade at all can reduce a panel's output. Say the panel is made with 2 strings of 32 .5v cells in series. That panel will produce 16v, but if even 4 of the cells in one string are shaded, that string will only produce 14v. If the voltage on the string drops enough to get bypassed by the diode, then that panel's rated output just dropped by half.

If that same panel has one bad diode, then the string that is working properly will produce power, which will then be consumed by the other string and that panel's output just dropped to 0.


Anyone have recommendations for a single rigid panel (possibly two depending on wattage) totaling 120-150 watts?
I'm not sure what happened, but I noticed 12V panels (ones rated 17-19 Vmp) much over 120W or so have recently all but disappeared :confused: So for 150 watts I think your only choice is to have two or more separate panels (that, or use a 24V panel with a MPPT controller).
IMO, I think multiple panels is better anyway since it offers some level of redundancy (if one panel becomes shaded or broken, you'll still have some system capacity that is functional).

I have a portable 170W setup for my use (2× 85W that folds up). This allows me to park the vehicle in the shade where it's cooler while also allowing me to face the panels directly at the sun throughout the day, maximizing energy harvest. While traveling I simply keep them stored on the roof which is where they'd be either way.