RV solar power system degrading

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My RV solar system is charging poorly. I bought it from you in 2007 (invoice #4420). It includes two Sunsei SE-8000 8A 130W panels and one SE-CC2500 25A controller. A couple of years later I switched to a Morningstar SunSaver Duo 25A controller and revert to the SE-CC2500 when a Morningstar fails (two have failed so far). It provided plenty of voltage and current for a few years, but has degraded dramatically regardless of which controller I’m using.

Eastern Washington state desert, bright blue skies, clean panels, midday, two new Trojan T-105 golf cart batteries deliberately discharged by 100 Ah, the wiring you provided. Open circuit panel output is > 19V, but all I can get into the system is ~3 amps @ 12.7 volts with a drop between panel output and battery terminals at just 5-15 mv*. I’ve changed batteries and controllers without significant effect. I’m getting my numbers from my OEM Winnebago power monitoring system, my Link 1000 system, and a high-quality digital multimeter. My low charging amperages are reflected in the fact that a whole day in the desert sun adds just 20-30 Ah to my batteries even when I’m not using them (my parasitic loss is < an amp.) My hungry batteries will accept scores of amps from genset or shore power.

What’s going on? Can you point me to a detailed solar panel troubleshooting website Google can’t find? I’m an engineer, but have been stumped by this for a couple of years now, relying mostly on my generator when boondocking.

* Does that combination of high OC voltage and low power output suggest a bad (high resistance) connection between both panels and the controller?

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